GSW: 1994 MEETING MINUTES

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1246th Meeting, 12 January 1994

     President Rosalind Helz called the meeting to order at 8:01 p.m. The minutes of the 1245th meeting, prepared by John Slack, were read and approved. Five new members were announced: Connie Bertka, Yingwei Fie, Reto Giere, Geophysical Lab, David Bruce, Planet Productions, Ltd.; Kevin Crowley, National Research Council;.

     Four (?) guests were introduced: Duncan Hurt, Goddard; Mike Walter and Tom Duffy, Geophysical Lab; Doug Brown.

E-an Zen made two announcements: First, Fairfax County is in the process of changing their earth science curriculum from a compulsory 9th grade course to an elective, under conditions that make earth sciences less likely to be elected than the alternatives. Second. Virginia State University at Petersburg, one of the few historically black colleges with a geology department, is considering abolishing the department. E-an urged you to write immediately, if your actions are to do any good. The contact persons are Nancy Sprague, Assistant Superintendent for Instruction, Lacey Center, 8101 Lorton Road, Lorton, Virginia 22079. and Dr. Martha E. Dawson, Provost and Vice President for Academic Affairs, P.O. Box 9404, Petersburg, Virginia.

     There were no informal communications.

     The scheduled first speaker was Karen Prestegaard, scheduled to talk on the 1993 Iowa floods, but Karen underwent surgery shortly before the meeting and was unable to appear.  Sorena Sorensen from the Mineral Sciences Division of the Natural History Museum filled in for Karen at the last moment. Ol' Sorena was given a charming introduction by our President.

     Sorena talked on "The Tales of Two Meta Tuffs". Her collaborators include Mark Barton, Brooks Hanson, and Dick Fiske. The two meta tuffs strike approximately NW-SE through the largest roof pendent in the Sierra Nevada Batholith, the pendent being a metamorphosed, west- facing section which ranges in age from 210 to 140 million years (Triassic to mid-Cretaceous). 

     Sorena subjected 30-plus samples from these tuffs to a battery of technology-intensive analyses aimed at deducing their geologic history. The δ18O ratio of the tuffs was about +12. There was pervasive potassium alteration of the tuffs, as indicated by the lush blues of rather pretty photomicrographs, so that the tuffs are now K-feldspar quartz rocks with a little plagioclase. Whole rock analysis, X-ray fluorescence and neutron activation for trace elements indicated stratigraphic controls within the two tuffs on an assortment of elements, including Ti, Al, Sc, Si, and Th. Sodium is anomalously low in the whole section.

     Rare earth abundance patterns of the two tuffs are virtually identical, except that near a pluton, there was evidence of rare earth mobility in the upper tuff. When normalized to a factor depending on concentrations in the Bishop tuff and Al2O3, the two tuffs are congruent with each other and with the Bishop tuff. The significance of the Bishop tuff is that it is unaltered, and being fight next door, it presumably passed through the same crust as Sorena's meta tuffs did.

     Sorena interprets the tuffs to have formed as part of a volcanic arc; subaerial deposits originally, later submerged and altered by seawater under relatively low temperature (<250°C), and then subjected to contact metamorphism of about 500°, producing recrystallization, with especially significant effects within 50m of the pluton. In her words, "although the rocks appear hopelessly screwed up geochemically, they still remember who they once were," although, as a question brought out, memory of the parent magma chamber is rather dim.

In opening her talk Sorena had pointed out that her title, "The Tales of Two Meta Tuffs" was loaded with literary allusions, including, among others, Dickens' A Tale of Two Cities Because she chose her title and pointed to its analogy with Dickens, one wonders if she meant for us to recall at the end of her talk, Dickens' sentence at the end of A Tale of Two Cities Dickens gave his main character the final sentence, which includes these words: "It is a far, far better thing that I do, than I have ever done."

     Questions by John Price, Dallas Peck and Bevin French.

     Charles Meade of the Geophysical Laboratory gave the second talk on "Ultra High Pressure and Temperature X-ray Diffraction of Mantle Minerals". Charles continues the tradition of the Geophysical Laboratory in investigating the state of selected minerals under conditions appropriate to the depths of the earth. In this case, the mineral is silicate perovskite (pyroxene composition with perovskite structure), which has a density and elemental composition that fits seismic constraints on minerals possible in the lower mantle. If deductions based on these constraints are correct, some form of silicate perovskite is the most abundant mineral in the earth.

     Charles used the diamond anvil to achieve high pressures, in this case 38GPa and 65Gpa, and a CO2 laser to obtain the heat, in this case up to 1800°K for sure, and in excess of 2300°K implied. These pressures are typical of those in the upper half of the lower mantle, and this temperature is that estimated for a cool mantle. The diamond anvil and laser heating are techniques well known from prior Geophysical Lab investigations. The principal technological advance in this investigation has been to connect the pressure-temperature apparatus to a source of very bright, highly-polarized radiation now available from synchrotrons. In these experiments, the laser heats a spot approximately 100 microns in diameter, and the X-ray looks at a spot approximately 20 microns in diameter within that 100 micron heated area.

     Charles found that perovskite at 38GPa and 1800°K preserves its orthorhombic structure. When raised to 65GPa and higher temperature, he found reversible changes in diffraction lines, which he concluded were driven by temperature.

     To explain them, Charles looks at three hypotheses:

anisotropic thermal expansion;

texturing of the sample;

transition to a higher-symmetry phase.

The data suggest that (1) is not very likely, and that (2) and (3) are more probable, but not yet distinguishable. Charles concluded on a general level that he had demonstrated techniques that could be used for a new class of structural studies at high pressure and temperature for a wide range of proposed mantle minerals, and on a more specific level, that silicate perovskite could undergo important structural changes in the mantle.

     Questions by Mike Ryan, Motoaki Sato, Alperr (?), E-an Zen, and Brooks Hanson.

     Lindrith Cordell, USGS, gave the final talk of the evening, coauthored with Stanislaw Wybraniec of the Geological Survey of Poland, on "High Resolution Geophysical Mapping of the Buried Alkalic-Ultramafic Tajno Massif in North Poland." This structure had been located by geophysical reconnaissance during the mid-1960's and shown to be a carbonatite-bearing alkalic pyroxenite at 600m depth when drilled. Rock types cored in and near the structure included gneiss, syenite, jacupirangite, a chimney breccia, and tuff. The gneiss is considered to be pre-Cambrian country rock.

     Lindrith emphasized the geophysical potential fields in his presentation, relying on his Polish colleagues for the geological constraints. The very dense network of observations supplied by the Poles enabled extreme downward continuation of the surface data.

     The two geophysical fields of interest are the gravity and magnetic fields. The form of the plotted magnetic field is counter-intuitive for the person trying to visualize the shape of the rock mass generating the field, but the form of the plotted gravitational field resembles the rock mass.  Therefore, it is of interest to transform the observed magnetic field into an equivalent pseudo-gravity field for better understanding. You can do this because the magnetic and gravity fields are related to each other by the ratio of their respective Green's functions, each Green's function describing how its respective field falls off with distance from the rock mass.

     When transformed, mapped, and projected down to 600m depth, the geophysical fields sharply defined an annular rock mass that was consistent with geologic expectation. The magnitude of the resulting Bouguer anomaly was about six milligal and the magnetic anomaly was about 1500 gammas, both relatively small anomalies on a regional scale, but for this feature 3 km in diameter at 0.6 km depth, they stand out.

     Questions by Dallas Peck, Mike Ryan, Pat Taylor, Bevin French, Fred Keer, E-an Zen, Carter Hearn, Vasile Rusu, Gene Robertson, and Pat Taylor (again).

     President Helz adjourned the meeting at 9:36 p.m. Attendance approximately 71 (67 - 75).

     Respectfully submitted (26 Jan 94)

     Cyril Galvin

     Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1247th Meeting, 26 January 1994

     President Rosalind Helz called the meeting to order at 8:01 p.m. The minutes of the 1246th meeting were read and approved. One new member was announced: Richard B. Carfin, USGS.

     Seven guests were introduced: Edna Gallegher, USGS; Elsa McFarland, George Mason University; Martitia Tuttle, University of Maryland; Keith Harper, University of Maryland (already a member but not previously introduced); Reginald Spiller, US Department of Energy; Azouni Ouiza, Algeria; Grant Pearson OTM).

     John Jens, Public Service Committee, Science Fairs Division, presented a schedule of science fairs in the coming months and asked for volunteer judges. President Helz endorsed this request. There were no informal communications.

     Bruce Lipin, USGS, gave the first talk of the scheduled program: "Rising and Expanding CO2 Bubbles, the Cause of Pressure Increases and Chromite Deposits in the Stillwater Complex, Montana." The Stillwater Complex in south-central Montana is an elongate Precambrian igneous rock, approximately 40 km long and 6 km at its thickest, much studied both because it is a potential source of chromium and because it is thought to be an example of cyclic fractional crystallization.

     In vertical section, the Stillwater consists of 20 to 25 cyclic units, with each unit representing a new influx into the chamber. It is reported that some units can be correlated horizontally for 10 km or more. The 'ideal' unit consists of olivine cumulate at the bottom (1 to 2% chromite), overlain by olivine bronzite (somewhat less than 1% chromite), overlain by a bronzite cumulate at the top. Many cycles are incomplete. The ratio of Mg to (Mg + Fe) is reasonably constant through the unit.

     There are three major hypotheses to explain the origin of the Stillwater Complex: (1) Magma mixing. (The most widely held opinion.)  (2) Increase in oxygen fugacity, causing chromium to crystallize out.  (3) Increase in total pressure. (The minority opinion which Bruce favors.)

     Bruce began his analysis by critically examining inconsistencies in the fluid mechanics needed for early magma mixing. Using data on the liquid properties of magma, he concluded that Kilauea and Krafla lava flows must be well on the laminar side of any critical Reynolds number separating laminar from turbulent flow. By extension to the Stillwater, its magma must have oozed rather than fountained into the depositional chamber, so early mixing was not very likely in the formation of the Stillwater complex.

     As evidence in favor of his third hypothesis, Bruce examined the system olivine- plagioclase-silica, where the order of crystallization appears to follow the cyclic unit in the Stillwater, without the chromite. The phase relations of a system olivine-chromite-bronzite-anorthite will crystallize out the chromite, if shifted to higher pressure. The trigger that initiates the increase in pressure is the introduction of CO2 in the magma. Bubbles form and expand dramatically, at least 4 to 6 times, as the magma rises from about 10 km to 2 km depth. This increase in volume increases the pressure in the Stillwater crystallization chamber enough to cause chromite to come out.

     Questions or comments by: Motoaki Sato, Mike Ryan, Bevin French, Gene Robertson, Dave Stewart, Roz Helz, Mike Ryan (again), Mark McBride, Roz Helz (again), Pete Stifel, and Kevin Crowley.

     Carol Simpson of Johns Hopkins and NSF presented the second talk on "Structural Analysis of Rocks in Shear Zones that are Neither Pure nor Simple." The Shear Zone of the title is a mass of rock contained between a pair of rigid parallel rock surfaces; for example, a mylonite between the opposite wails of a fault. The mylonite undergoes Pure Shear if the fault walls move perpendicular to the fault, compressing or stretching the mylonite. The mylonite undergoes Simple Shear if the fault wails maintain a constant spacing while moving parallel to the fault, dragging the mylonite in the direction that the nearest fault wail moves.

     It is desired to use the sense of rotation of objects embedded in the mylonite to determine the direction of shear. However, when the shear is a composite of Pure Shear and Simple Shear, it may happen that adjacent objects apparently indicate opposite directions of shear.

     These ambiguities may be clarified by considering the exact motion of randomly-distributed elongate objects in the Shear Zone, when subject to a combination of Pure Shear and Simple Shear. In such cases, a minority of objects having particular orientations will indicate a retro- grade sense of shear as shear planes are compressed into near parallelism with the foliation.

     For crystals embedded in the Shear Zone, rotation is often accompanied by recrystallization and the development of tails. Carol indicates that the tails shed by rotating crystals have a geometry determined by the ratio of recrystallization rate (R) to strain rate (gamma). When R/ gamma is high, wedge-shaped tails result (sigma tails) and the direction of shear is given by looking for the direction in which pairs of tails shed from the same crystal "step up" across the Shear Zone. When R/gamma is low, stringy tails result (delta tails) which require more careful study to determine the shear direction.

     Questions by Mike Ryan, Bruce Hansen, Chris Talbert, Dave Stewart, and Gene Robertson.

     Boyce Rensberger of The Washington Post gave the final paper of the evening on "What Makes Science News?". In the 1930's, Albert Einstein's opinions on everything, scientific and non-scientific, were worth reporting. Jonas Salk was given somewhat similar treatment when Salk began nationwide testing of his polio vaccine in 1953. Even 20 years ago, science had unquestioned authority, and "breakthroughs" were common. But now science is treated more realistically. Boyce attributed the present more realistic consideration of science by the public to education by science reporters like him. Scientists must read the science news articles as well as non-scientists, because the citation rate for a science paper soars after it is mentioned in the Post or New York Times.

     Boyce then fulfilled the promise in his title by giving us five criteria for determining what makes science news. These five criteria are:

1.      Inherent fascination. Dinosaurs, earthquakes and volcanoes have greater star quality than algae and soil erosion. A complicated story usually lacks sufficient fascination.

2.      The size of the natural audience. Diseases have a large natural audience because sickness affects us all. Earthquakes have a large natural audience in southern California.

3.      Importance of topic. How much difference will the subject make in the lives of readers? Boyce said that the spread of AIDS is more important than proof that significant climate change will take 1000 years.

4.      Reliability of results. Reliability is indicated by publication in a peer-reviewed journal (not necessarily the top journal). A controversial story usually has lower reliability in Boyce's sense. Asked about the reliability of government scientists, Boyce endorsed USGS geologists, who were the majority in the audience before him, and scientists at NIH, where his wife works.  Scientists with commercial interests have lower reliability.

5.      Timeliness. The newer the better.

     His leads for stories come largely from Science and Nature. Ideas for stories also come from his own mental science citation index, personal curiosity, and a sense of when the time is ripe. He receives perhaps 40 press releases per day from University public relations offices touting new findings at the University, but he does not pay much attention to them. He does not attend many national science meetings.

     The science reporter competes for space and position in the paper by selling the editor on the story, which involves a temptation to hype a story. The copy editor writes the headline, and the reporter must go out of his way to have any influence on its wording. (As if to illustrate this point, the printed GSW announcement of Boyce's talk miss-spelled "Washington" in describing his affiliation). There was some discussion about whether a science reporter may over-glamorize science by leaving out the boring parts. Boyce said he went into journalism to avoid boredom.

     The unusually extended discussion of this talk included questions by: Moto Sato (who effectively gave the speaker an open-ended opportunity to go beyond the 20-minute limit to finish his talk), Margaret Chauncey, Mike Ryan, Jeff Williams, Pete Toulmin, Louis Pribyl, Lindrith Cordell, Bob Ilchik, Tom Dutro, Murray Hitzman, Hendrick van Oss, Reginald Spiller, Alan Linde.

     President Helz adjourned the meeting at 10:17 p.m. Attendance approximately 81.

     Respectfully submitted (23 Feb 94)

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1248th Meeting, 23 February 1994

     President Rosalind Helz called the meeting to order at 8:13 p.m. The minutes of the 1247th meeting were read and approved. There were no new members to announce.

     Fourteen guests were introduced: Jaquidon Gallego and Margaret Lewis from Defense Mapping Agency; Genyong Peng, Diane Loy, Adrian Abraham, Joe Dyer, Bill Logan, Sean Ben- Safed -- all from George Washington University; Scott Ator, Scott Daly, Judy Tegler, Mee Lim, Sarah Leiker-- all from the University of Maryland; and Jeff Eppink of ICF Resources.

     Jeff Williams invited the listeners to attend the 20th Annual Assateague Shelf and Shore Workshop which will meet in Ocean City, Maryland, for technical discussion on 15 April and tour the Delmarva shore on 16 April.

     John Jens, Chairman of the Public Service Committee, introduced Ellen Houseknecht, a high school junior, who won the 1993 GSW Science Fair Grand Prize for her project on "The Effect of Sediment Size of Sand and Gravel on Permeability". President Helz awarded a book and $50.00 check to Ellen. John then lobbied for more Science Fair judges, the next pressing need being two fairs on 12 March -- the Prince William - Manassas Fair in Nokesville and the Fairfax County Fair at Robinson Secondary School.

     There were no informal communications.

     Dan Hayba, USGS, gave the first scheduled talk, "Petroleum Migration in the Los Angeles Basin". Dan presented the results of a numerical investigation of fluid flow along a cross-section from Long Beach on the west to Brea Olinda on the east, a distance of about 30 km. This cross- section is floored by a granitoid intrusive and includes up to 8 km of sands, silts and clays ranging in age from mid Miocene to Pleistocene and Recent. The numerical model was a version of BASIN 2, developed by Craig Bethke, which considers subsidence, sedimentation, compaction, and thermal evolution to track the migration of groundwater in a basin accumulating sediment.

     For boundary conditions, Dan selected no water or heat flow across the sides, continental heat flux from below, constant 1 atm pressure at the surface, surface temperature which depended on the presence or absence of free-surface water, and a string of wells to control the section. As brought up in the questions, the boundary conditions seem to assume no significant faults to interrupt the path of the water flow.

     The outputs were time slices of water flow at 3.2, 1.8, 0.5, and 0.0 million years. Water was driven in the earlier times by compaction at velocities of 25 to 50 km/my to the east, but a slight uplift along the east edge of basin about 0.5my ago abruptly reversed the direction and speeded up the flow.

     BASIN 2 computes water, but not oil, flow. To estimate oil flow, Dan took the ratio of the equation for the flow of oil to the same equation for water. This ratio indicates that oil moved primarily because of its buoyancy in relatively steep strata. The oil now being pumped at the West Coyote Field on the east edge of the basin probably left source beds in the center of the basin 2.5 to 0.7 my ago, flowing as a separate phase and in thin layers, at velocities nearly an order of magnitude faster than the water.

     Questions by Nick Woodward, George Helz, Lin Cordell, E-an Zen, Moro Sato, and Gene Robertson.

     Paul Lowman, NASA Goddard Space Flight Center, spoke on the "Size and Shape of the Sudbury Structure, Ontario". The Sudbury Structure includes and surrounds the Sudbury Igneous Complex. The Complex is a 60 km by 30 km, basin-shaped body of norites and granophyres, with an age of 1.85 billion years. Paul acknowledged Dietz and Bevan French as pioneers in this study, and urged us to believe that he is not mad at Grieve et al (JGR, 1991), whose reasons for enlarging the Sudbury Structure formed the outline against which Paul's talk argued. Grieve's primary conclusion is that the Sudbury Structure was originally a much larger and approximately circular structure that attained its present ENE elliptical shape from post-impact Proterozoic orogeny.

     Paul criticized six supposed lines of evidence supporting Grieve's primary conclusion: Airborne radar indicates reasonably conclusively that the supposed Outer Ring Fracture of Grieve is a misinterpretation of two independent sets of fractures in the bedrock. Field studies show that there are no downfaulted outliers attributable to impact. The Levach Gneiss is not impact-related, as per Grieve, but Archean rock, deformed in early Proterozoic, and definitely pre-impact. Much of the supposed Sudbury Breccia has a tectonic origin, and not an impact origin. Shatter cones from an extended area north of the more narrowly defined Sudbury Structure are poorly developed or not present, based on Paul's field work, and at any rate, shatter cones are highly dependent on the rock lithology, not well developed in coarsely crystalline rock, and not a quantitative measure of impact. Finally, Paul attributes the anomalously large volume of suspected impact melt to the 1.85by age of the structure, at which time, Paul believes, heat flow from the earth was considerably higher than at present, so that the geometric relations developed from Phanerozoic impact craters are not applicable to Sudbury. Paul concluded (1) that the Sudbury Structure was never more than 5km wider on the North than it is now, and (2) that the crater was originally elliptical and that the ellipticity was only increased, not initiated by, the Penokean Orogeny.

     Questions by Mary Hill French, Bevan French, Doug Rankin, Gene Robertson, Grant Pearson and Bevan French (again).

     David Bell, Geophysical Laboratory, presented the third talk, "the Global Geochemical Cycle of Water in the Mantle".  Rubey is credited with the classical idea for the source of earth's water: the degassing of the mantle, basically a one-way, outward flow. What David calls the Recent View is the hypothesis implied in the title of his talk, namely that processes analogous to the hydrologic cycle operate at a number of depth scales, including a cycle in which water resides part of the time in the mantle. The historical pedigree of this hypothesis includes studies of water producing hydrolyric weakening in quartz, development of solid state solutions involving structural OH motivated by the possibility of hydrogarnet in the mantle, and the discovery of OH peaks in almost any nominally anhydrous mineral you look closely at.

     We now know that there is hydrogen in the mantle in fluids and melts, in the essential structure of relatively common crystalline minerals such as amphibole, mica, humite; in hydrous silicate minerals at high pressure; and, the mechanism David investigated, as a trace substituent in common anhydrous minerals.

     Although the trace substituents are present as OH, David's study reports concentrations in ppm by weight of 1-120, consistent with other geochemical work. In these units, pyroxenes of suspected mantle origin are the most hydrous minerals, ranging from 100 to 1000 ppm. Garnet and olivine have relatively little OH. In terms of whole rock, in water units, source regions of N MORBs have 100 to 200 ppm, sources of E MORBs have 300 to 400 ppm, and sources of Hawaii basalts have 250 to 550 ppm. These results show that there can be water in the mantle, which is expected to influence rheology and diffusivity in the mantle.

     In an attempt to balance the books on the hydrologic cycle in the mantle, David provided a five-box flow diagram, identifying sources and sinks. The principle source of water from the mantle is through the ocean ridge basalts. These basalts interact with the ocean, increasing their water content. By hypothesis, this water can be stored as OH in the subducted slabs returning to the mantle, and eventually reside in the eclogite and peridotite of the mantle.

     Questions from Steve Shirey, J. K. Bohlke, Moto Sato, and Craig Schiffries.

     President Helz adjourned the meeting at 10:13. Attendance approximately 85.

     Respectively submitted (9 Mar 94)

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1249th Meeting, 9 March 1994

     President Rosalind Helz called the meeting to order at 8:05 p.m. The minutes of the 1248th meeting were read and approved. Three new members were announced: Jaquidon Gallego and Margaret Lewis, both of Defense Mapping Agency, and Jeff Eppink of ICF Resources.

     Ten guests were introduced: Cliff Oss (?), USGS; Bob Swinton, EPA; Eleanor Ingraham, future AGI Intern; Rod Feldmann, Kent State University; Art Snoke, VPI; Sean Kennedy, DOE; Cathleen Dyer Williams, (?); and three post-docs from DTM: Lanbo Liu, Ingi Bjarnason, and John Vandecar.

     Bill Burton announced that Randall Orndorff and Jack Epstein will lead the GSW Spring Field Trip on "A Structural and Stratigraphic Excursion through the Shenandoah Valley of Virginia", Saturday, 7 May 1994, leaving 8:30 a.m. from USGS Visitor's Parking Lot.

     President Helz requested volunteers to judge upcoming science fairs. There is an acute need for judges from GSW.

     There were no informal communications.

     Steve Obermeier, USGS, began the scheduled program with a talk on "Liquefaction Evidence for a Large Earthquake 300 Years Ago Along the Cascadia Subduction Zone". A significant earthquake causes loosely consolidated sediments to shake. The shaking can liquefy sands between depths of 2 and 20 meters. When this happens, the weight of the overlying muds presses down on the liquefied sand, forcing sand up cracks in the mud and on to the surface.  When the flow stops, a marker sand bed is left on the surface, and the cracks through which the sand escaped become sand dikes.

     Steve identified sand sheets and dikes in the eroding banks of marsh islands in the Columbia River. About half the sand sheets were found to have sand dikes, but the dikes, in Steve's classification, were dinky (max of 30 cm thick), and their thickness decreased going inland.

     The age of these sand dikes is constrained by the absence of large earthquakes during historic times, the ages of trees (up to 230 years) growing on the sand sheets, 14C ages of 500 to 800 years from material cut by the dikes, and a 1480 AD tephra layer underlying most dikes.

     Based on comparison of sand dike features and on analysis of blow counts needed to penetrate the source sands, Steve concluded that his earthquake had a magnitude well below the 9.2 magnitude of the great 1964 Alaska earthquake, but above magnitude 7. His best guess is about magnitude 8. Based on the fact that he found only one significant interval of sand sheets with dikes in a section going back over 1000 years, the area appears to have been relatively quiet, seismically. In discussion, points were raised on the logic behind the blow-count curve, and on the possibility of long duration, low frequency earthquakes escaping detection.

     Questions by George Helz, Dallas Peck, Meyer Rubin, John Price, Kurt Dodd, Bob Ilchik, and Alan Linde.

     Walter Hayes, USGS, Reston, presented the second scheduled talk on "Lessons of the January 17, 1994 Northridge, California Earthquake". The Northridge earthquake, of revised magnitude 6.8, struck 18 miles from downtown Los Angeles, at 4:31 a.m. on a holiday, thereby considerably lessoning injuries and fatalities, but it still managed to cause damage now estimated at $30 billion, possibly the most expensive disaster to strike the US. The "big one" of magnitude 8.25, which has, by definition, more than 31 times the energy of the Northridge earthquake, is still to come. The most significant scientific issue raised by the Northridge earthquake, in Walter's opinion, concerns missing earthquakes: why aren't there more magnitude 6 to 7 earthquakes in the historic record? These are needed to account for the accumulated slip on more than 300 active faults in the region.

     The Northridge earthquake occurred on a little known "blind" thrust fault, about 20 miles from the epicenter of the 1971 magnitude 6.5 San Fernando earthquake. After the San Fernando earthquake, building codes were improved, older structures were retrofitted, and instrumentation installed more widely in southern California. The Northridge earthquake tests these improvements, with potential for even greater improvements.

     Measured accelerations exceeded 0.5g in many places, and reached 2g in some places. An unexpected feature of this earthquake was the relative strength of the vertical accelerations, possibly a consequence of the earthquake originating on a thrust fault. (Vertical accelerations were not previously a specific element in seismic design.) This earthquake had a focal depth of 19 km, slightly deeper than the norm of 16 km, a factor Walter considers significant in warning of future large quakes. There was evidence of a large stress drop (150 to 200 bars), but no evidence of aseismic slip, and no fault breaks at the surface. There have been over 3000 after-shocks, but no evidence of precursor events in the nodal area. Maximum vertical and horizontal displacements appear to be 30 to 70 cm uplift, 30+ cm shortening. Drought may have reduced liquefaction.

     Questions by: Moto Sato, Dallas Peck (twice), Martitia Tuttle, Gene Robertson, and Margo Kingston(OSTP)

     Chris Talbott, Hans Ramberg Tectonic Laboratory, Uppsala University, gave the final talk on "Fountains of Salt". Although not evident from his title, Chris stated that his talk continued the theme of the previous two talks, the first having dealt with the deformation of unconsolidated sediments, the second with stick-slip motion in elastic solids, and his with the ductile flow of a crystalline fluid, namely rock salt.

     The density of rock salt changes little, but the density of fine grained sediments increases significantly, with depth of burial. As a result, buried salt is usually buoyant. Whether it rises to the surface depends on the local density contrast, relative strain rate, and rate of sedimentation.  If the salt does reach the surface, its subsequent history depends on the rate at which it is dissolved.

     Chris quoted evidence that Louanne salt upslope from the Sigsbee Deep in Gulf of Mexico extruded onto the surface and spread downslope as an overturned nappe. The cross-sections of the salt from drilling and seismic work matched the shapes obtained from subaerial extrusion in the laboratory, and in numerical models.

     In the Zagros Mountains of Iran, Precambrian salt extrudes under the weight of the overlying country rocks and domes upward with a cross-section matching the shape of viscous fountains obtained in the laboratory. This salt flows downhill under its own weight, forming large recumbent folds. Field observation indicates that in dry weather, the salt expands and contracts elastically due to daytime heating and nighttime cooling. But only a slight rain converts the elastic salt to a plastic fluid which flows downhill as fast as ice glaciers of the same size.

     Chris identified applications of his findings, including the potential hazard of trying to drill production wells through mobile salt to reach oil in the Gulf of Mexico; the poor prospects for storing rad waste in salt; and academic models of orogen spreading.

     Questions by Bill Burton, George Helz, Moto Sato, Dallas Peck, Dan Milton, Gene Roberts, E-an Zen, Bill Burton (again), Moto Sato (again).

     President Helz adjourned the meeting at 9:58. Attendance approximately 91.

     Respectively submitted (13 April 1994)

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1250th Meeting, 3 March 1994

     President Rosalind Helz called the meeting to order at 8:04 p.m. The minutes of the 1249th meeting were read and approved. One new member was announced, Scott Daly, University of Maryland and Apex Environmental.

     Only three guests were introduced at the start of the meeting, an apparent minimum for the year so far: Professor Sahil Alsinawi, University of Sana'a, Yemen, and Gene and Carolyn Shoemaker, USGS.

     Jane Hammarstrom announced that she was helping Andy Tisinger, Centreville High School, to prepare a geology course for high school juniors and seniors. This is part of the GSA Partnering in Excellence program. Jane sought input on appropriate text books and other assistance. President Helz, acting for John Jens who arrived later, asked for volunteer science fair judges in three remaining fairs. Bill Burton said that announcements for the GSW Spring Fieldtrip (7 May to Shenandoah Valley) were on the table in back of the room.

     President Helz showed a proposed revision of the bylaws dealing with approving new members of the GSW. This proposal was, in itself, a major revision of a proposed revision discussed last year. She said that actual practice has departed significantly from the literal meaning of the existing bylaw. The proposed revision is intended to bring the bylaw more nearly in line with practice, while reserving for the GSW Council a measure of control. Discussion by Steve Huebner and E-an Zen. In accordance with the procedure for amending bylaws, the proposed revision will be brought up again, discussed, and voted on at the next meeting.

     There were no informal communications.

     Co-authors Peter Warwick and Bruce Wardlaw jointly presented the first scheduled talk on "Paleocene/Eocene Stratigraphy of Pakistan and Tectonic Implications".  Bruce spoke first, proving to be about 60% more equal than Peter, measured in speaking time.

     There are two primary lithologic units at the surface: the Ghazij (mostly early Eocene), which is a pile of shales locally containing coal, overlain by the Kirthar (middle Eocene), which is a less thick limestone. Bruce and Peter had to interpret the relation between these units and their relations to the underlying Lockhart, a foraminiferal limestone. Peter indicates that the lower and middle Ghazij is a coarsening-upward sequence that ends below the upper Ghazij.

     Their field work was motivated by the potential for economic coal deposits within the Ghazij. Bruce asserted, in answer to anonymous reviewers, that they actually had been to the field sites under discussion. At the time, the area was subject to political unrest, so a platoon of armed guards accompanied Bruce and Peter to the field, and an unknown party fired a rocket at them during their travels.

     Bruce proposes the following geologic history, based on their field work and available literature: The Paleocene and Eocene strata of northern Pakistan accumulated in a northeast- trending backarc basin between the Indian plate and offshore volcanic arcs. Uplift in the north end of this basin allowed red bed deposition by late Paleocene, and shut off marine access from the north. Bruce believes that this uplift records the collision and accretion of the Kohistan volcanic arc complex to the Indian plate. The basin was further fragmented by a large delta that prograded from the northwest by early Eocene. The delta separated the remaining basin into an evaporitic northern segment, and a southern segment where normal marine carbonate and shale deposition continued into the Lower Oligocene. Bruce believes that the plate-tectonic collision caused the uplift that shed the sediments that built the delta.

     Questions by Moto Sato, Blair Jones, Hal Gluskoter, Gene Robertson (a planted question), Fred Simon, and E-an Zen.

     Pat Taylor, NASA Goddard, gave the second scheduled talk on the "Origin of the Bangui (C.A.R.) Magnetic Anomaly: A Satellite View".

     The largest negative magnetic anomaly in Africa (possibly the largest in the world) includes an area around Bangui, Central African Republic. Pat believes this anomaly outlines the remnants of a large impact structure produced early in Earth history.  Four lines of evidence suggest the impact origin. Ranked by Pat in order of importance, these four are the carbonado deposits, the gravity anomaly, topography, and the magnetic anomaly. Shaded digital topo data hint at the existence of concentric rings, 810 and 490 km in diameter. A negative Bouguer anomaly occupies this bullseye, which is consistent with negative gravity anomalies at all craters.

     Carbonados are placers consisting of polycrystalline diamonds, used as industrial diamonds. Carbonados have a crustal, not mantle origin, and no kimberlites have been found in the C. A. R., despite much prospecting. The C.A.R. is the world's principal source of carbonados, primarily from two mines located on the concentric circles surrounding the anomaly. Earlier geologic mapping had identified charnockites with a 2 - 3 billion year age. Subsequent field work by Bruce Marsh, Bob Regan and A1 Chichester had collected rocks, but the whereabouts of these rocks is currently unknown. Pat suggests that shattercone striations would look similar to the foliation striations in granite gneiss, shown on slides of these lost samples. He mentioned the peculiar fact that, worldwide, many geologists working in the areas of supposed impact craters do not believe they are impacts.

     His new theory: the impact raised the temperature of lower crustal rocks (the charnockites) above the Curie Point, so they remagnetized with a TRM without going into a melt phase.

     Questions by Lin Cordell, Doug Rankin, Bob Ilchik, Gene Shoemaker, Moto Sato, Lin Cordell (again), E-an Zen, Gene Robertson, Tom Armstrong, Gene Shoemaker (again).

     Karen Prestegaard, University of Maryland, gave the final talk of the evening on "Did Land-use Influence the Magnitude of the 1993 Iowa Floods".

     Karen has personal interest and experience in her subject because her family has a farm in southern Wisconsin. For the July 1993 floods, her study area was in the lower Raccoon River above Des Moines. The 1993 summer rainfall patterns cut across the drainage basins locally, and successive storm tracks moved southward regionally. As a result, the upper reaches of many basins did not suffer record floods. In addition, about 50 years ago, the upper reaches of the drainage basins had been ditched, eliminating meanders, so that water now drains rapidly from these areas. For a given discharge, the flood flow had significantly less width, more depth and higher velocities in the channelized streams than in the meandering streams. Using channel slope and depth, Karen concludes that there was more shear in the ditched channels. Although questions in the discussion period were unable to clarify how the computed shears were used.

     Local bank erosion damaged bridges over the straightened channels. The net result of rapid drainage in the headwaters and southward shifting storm tracks was to bring a lot of water at one time to the lower reaches of the drainage basins.

     Questions by Curt Linsey, E-an Zen, Bruce Hansen, Raymond Rye, Curt Linsey (again), Dennis Krohn, Rick Wonderman, Mary Hill French, Bob Schneider, Gene Robertson, and Mar), Hill French (again).  During the discussion, Karen introduced three of her coworkers and students: Brendan Shane, Nancy Cato, and Kevin Houghton, thereby eliminating the apparent year-to-date minimum for guests set at the start of the meeting.

     President Helz adjourned the meeting at 9:52. Attendance approximately 79.

     Respectively submitted (13 April 1994)

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1251st Meeting, 13 April 1994

     President Rosalind Helz called the meeting to order at 8:05 p.m. The minutes of the 1250th meeting were read and approved with one correction. One new member was announced, Gordon P. Eaton, USGS.

     Three guests were introduced: James Joyce, University of Maryland; Jorge Aranda, Instituto de Geologia, UNAM; and Howard Evans, USGS.

     President Helz announced the recent death of Clyde Wahrhaftig. The members stood for a moment of silence in his memory. Bill Burton said that announcements for the GSW Spring Fieldtrip (7 May to Shenandoah Valley) were on the table in back of the room. He encouraged teachers to attend.

     President Helz introduced the proposed revision of the bylaws dealing with approving new members of the GSW. This revision had been explained and discussed at the previous meeting. There was further discussion by E-an Zen and Dallas Peck, and further explanation by the President. The question was moved by Phil Bethke and seconded by (?). The proposed revision was adopted.

     Pete Stifel gave the first informal communication of the year on problems of slope stability caused by construction on and near the University of Maryland Campus, College Park.

     The University is at the boundary between the Coastal Plain and the Piedmont where the Coastal Plain sediments have had a long history of problems. Pete pointed to a dual failure to study the past: the geologic past which produced the unstable sediments and the historic past which witnessed man-made problems with the sediment. Pete's slides showed classic and anomalous landslips, scarps, and hummocky topography on newly steepened slopes in the Cretaceous Patuxent formation. The steepening was caused by widening roads and parking lots. The convenient location made for excellent teaching opportunities.

     Questions by Bill Hauser, Murray Hitzman, Moto Sato, and Brace Doe.

     Paula L. Gori, USGS, gave the first scheduled talk on "The Social Dynamics of a False Earthquake Prediction and the Response by the Public Sector."

     In October 1989, the late Iben Browning predicted that there existed a 50% chance for a magnitude 6.5 to 7.5 earthquake in the New Madrid area in early December 1990. Browning held a PhD in zoology, but was a self-identified climatologist. Eventually over 300 news articles in 45 publications dealt with Browning's prediction. David Stewart of Southeast Missouri State College, a PhD geologist with a past history of supporting a false prediction, gave early support to Browning's prediction, but it was not until a year later (October 1990) that the National Earthquake Prediction Evaluation Council denounced the prediction.

     In addition to the lack of strong government response, Paula identified other factors that enabled this prediction to be considered seriously: the extremely severe 1811, 1812 earthquakes in the area; the heavy media coverage of the 1989 Loma Prieta earthquake; an unlucky, new USGS Circular that said a magnitude 8+ earthquake was within the realm of possibility; the recent death of three earthquake experts; and other factors.

     Paula believes the prediction was costly both in monetary terms and in government credibility, because local and state agencies had begun to react to public interest as if the predicted earthquake was imminent. She recommends that government agencies prepare in advance to evaluate unofficial predictions, and vigorously denounce them if they are unjustified.

     Questions by Moto Sato (two), Karen Prestegaard, Dallas Peck, Bill Burton, Sorena Sorensen, and Bob Ilchik. President Helz deferred further questions till after the formal meeting.

     Jim McDougall, Department of Geography and Earth Systems Science, George Mason University, gave the second talk of the evening, switching places on the program with the scheduled second speaker. He spoke on "Cenozoic Tectonics of West-Central New Zealand."

     Jim's field area was a zone across the northern part of South Island, the southern part of North Island, and adjacent marine areas. His field problem was the interpretation of surface and seismic evidence for major faults in the vicinity of the Alpine strike-slip fault, but not the Alpine fault itself.

     Two major faults, the Waimea and the Flaxmore, merge northward into the subsea Manaia fault, known from seismic data. Another group of faults branch westward off the Alpine fault.

     Surface outcrop and two east-west seismic lines going down 20 km suggest that the faults are reverse faults. They tend to be en echelon, east over west, with displacements ranging from 3 to 6 km. The submarine Manaia fault has a 3 to 4 km offset with Miocene in the footwall. Plio-Pleistocene strata are thinner and relatively complete on either side of the faults.

     The evidence does not admit of significant strike-slip motion during the Cenozoic on those faults which branch off the Alpine fault, and seems to restrict the amount of right lateral motion on the Alpine fault itself.

     After cutting off questions on the first talk, President Helz sought questions on the second talk. Gene Robertson and Murray Hitzman responded.

     Betsy Moll-Stalcup, USGS, the scheduled second speaker, gave the third talk of the evening on "Redoubt Volcano, Alaska: A Progress Report on Arc Magma Genesis".

     Redoubt is a stratovolcano that threatens air traffic and a petroleum tank farm in the area, but Betsy's principal interest in it is as an example of arc magmagenesis. The cone-building magmas at Redoubt are generally more mafic than the ash. Most of the lavas are low-Mg, high-A1 basaltic andesite and andesite.  Petrologists believe the magmas originate in a subduction zone, and the accepted cross-section has Redoubt about 100 km above the Benioff zone. The fundamental question is, What melts? The slab, the mantle, or both? The magmas have negative Nb and Ta anomalies (less Nb and Ta than Alkali and Rare Earth abundances in the magma suggest), but none of the proposed magma sources have this anomaly. Betsy thinks the proper explanation is given in high-pressure experiments by Tasumi. He found that the alkali elements are highly soluble in water and that the LREE are at least soluble in water, but that Nb and Ta are highly insoluble. The implication is that the magma gets the alkalis and LREE, but the Nb and Ta remain behind in the slab.

     These arc magmas are believed to incorporate some oceanic sediment because they usually have higher concentrations of beryllium 10 than magmas from other environments, and beryllium 10 is strongly enriched in ocean sediments. The implied sediment source is supported by lead isotope studies. Previous plots of 207Pb against 206Pb have produced separate clusters for MORB and for pelagic sediments, but the data from Redoubt and the Aleutians scatter along a trend joining the MORB and pelagic clusters, suggesting a mixture.

     Betsy then examined what happens in the magma chamber, including crystal fractionation, magma mixing, and the interaction of the mantle magma with crustal melts or country rock. She interpreted two photomicrographs, one as showing feldspar from two distinct magmas in the same thin section, and the other as a cumulate cluster of clinopyroxene breaking up.

     Questions by Moto Sato, Bruce Doe, Dallas Peck, Phil Bethke, Steve Shirey, Eirik Krogstad; R. Helz (comment) and Carter Hearn.

     President Helz adjourned the meeting at 10:09. Attendance approximately 81.

     Respectively submitted (27 April 1994)

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1252nd Meeting, 27 April 1994

     President Rosalind Helz called the meeting to order at 8:02 p.m. The minutes of the 1251st meeting were read and approved. One new member was announced, Karen Bryant, USGS.

     Two guests were introduced: Morris Aizenman, NSF, and Don Hull, State Geologist, Oregon.

     President Helz reminded members of the GSW Spring Fieldtrip (7 May to Shenandoah Valley). There were no informal communications.

     Tom Wright, USGS, gave the first scheduled talk on "Understanding Kilauea Volcano: A Historical Perspective."

     Tom's talk summarized materials to be used in a book on Kilauea by Tom and Dick Fiske.  The general impression from the talk is that a more-or-less constant magma supply from depth produces complex responses near the surface including earthquakes, magma intrusion, eruptions, caldera formation, spreading, rifts, and failed rifts. The terms were not only plate-tectonic, but anthropomorphic.

     Early missionaries recorded that around 1790, the entire caldera was active and filling; there was a significant decline in eruptive activity during the 19th century; the rift zone reopened around 1840, a unique event since the arrival of Europeans. In 1969, a continuous rift eruption first occurred; and in 1975, a magnitude 7.2 earthquake marked an abrupt downslope movement of the south flank of the volcano. Tom interprets these observations to show a progressive shift from summit to rift eruptions in the past two centuries. The potential exists for runaway spreading, leading to sector collapse, a once-in-a-volcano lifetime event.

     In the general case, magma intrusion and extrusion eventually construct a mass that is gravitationally unstable. This instability is perturbed by the continuous addition of magma from below, producing rifting. Rifting spreads the base and allows the escape of magma at lower elevations, temporarily increasing the structural stability of the volcano, whereupon the summit eruptions may resume.

     Questions from Doug Rankin, Glen Brown, Frank Jacoby (?), Dallas Peck, Murray Hitzman, and Gene Robertson.

     Gene Shoemaker, USGS, Flagstaff and Lowell Observatory, gave the scheduled second talk on "The Crash of P/Shoemaker-Levy 9 on Jupiter." These minutes are being written in early May 1994, shortly after Gene's talk on 27 April, so they reflect the anticipation in Gene's talk, but not whatever will have been learned from the actual impact by the time these minutes are read.

     The observing team at the Lowell Observatory scans the entire sky with the 18-inch telescope during one year of observing. It is basically a fishing expedition to see if anything new is happening in their field area. Something new is found by spotting the motion of bright objects against the background of more-or-less stationary stars. Carolyn Shoemaker picks out this motion from the photographs, and she found a squashed comet, P/Shoemaker-Levy 1993e, on 27 March 1993. This finding was immediately confirmed by astronomers at other observatories, and shortly afterwards Harold Marsden computed the orbit which indicated that the comet probably had begun to break up on 7 July 1992, following capture sometime within the past century, and that the comet will impact Jupiter in July 1994.

     Pieces from the broken comet are strong out in a line, giving it the squashed appearance noted by Carolyn. Initial observations identified at least five pieces, which became 10 or 11 nuclei on further inspection. Assuming the same albedo as Halley, these nuclei have estimated (upper bound) diameters of 2.5 to 4.3 km. The original, unbroken comet was probably about 10 km in diameter. Empirical observation suggests a conservation of nuclei law for the comet, with new nuclei being formed as old ones disintegrate. No OH has yet been found; we see only dust now.

     The expected impacts on Jupiter will be just out of sight, around the rim of Jupiter from earth observatories, but the impact sites will quickly rotate into view of earth. Considerable effort is being made to sense the impacts from Galileo, which will have the best view, and indirectly from earth by measuring the disturbance in Jupiter's cloud patterns and gravity waves at Jupiter's cloud top.

     Gene is happy to have this July impact to show that comets do indeed collide with planetary bodies.

     Questions from Mike Ryan, Steve Shirey, Pat Taylor, Gene Robertson, Moto Sato, Dallas Peck, An McBride, and Bill Hauser.

     Mike Walter, Geophysical Laboratory, Carnegie Institution of Washington, gave the third scheduled talk of the evening on "Experimental Constraints on Segregation of the Earth's Core."

     The earth's metallic core consists of iron, nickel, and the light elements of your choice, surrounded by a silicate mantle with much lower concentrations of iron and nickel. Mike presented experimental results on partitioning of nickel, cobalt, and tungsten between silicate and metallic phases as a means of understanding the segregation of the earth's core. Some elements are chemically suited to go with metal - these are the siderophile elements, including, among others, Ni, Co, and W. The distribution of elements in the C1 Chondrite is taken as the standard, against which the distribution of the siderophile elements may be compared. Moderately and highly siderophile elements are depleted relative to the C1 Chondrite. Analyses indicate that siderophile elements are included in upper mantle above the level expected using 1 arm distribution coefficients. Many explanations have been advanced, but recent work suggests that siderophile elements show greater lithophile behavior as pressure and temperature increases.

     Mike ran experiments using apparatus with pressure capability up to 25GPa, temperatures in the range 2100 - 3000°K known to + 50°K, durations of 3 to 10 minutes, liquid quenched.  Many elements show a significant dependence on oxygen fugacity when treated in isolation, but two-component distribution coefficients show relative independence of fO2.

     Ni, Co, and W show decreased siderophile tendency (increased lithophile tendency) with increased pressure, and to a lesser extent with increased temperature. Within the (P, T) range investigated, the observed partition coefficients still cannot account for the observed upper mantle abundances of siderophile elements. Within the magma ocean, pressure is an order of magnitude more important than temperature.

     Questions from Moto Sato and Gene Shoemaker.

     President Helz adjourned the meeting at 9:57. Attendance approximately 90.

     Respectively submitted (14 September 1994)

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1253rd Meeting, September 14, 1994

     President Helz opened the meeting at 8:05 p.m.   Eleven new members were announced: Sean Kennedy, Timothy Merrill, Allison MacFarlane, Michael Fleming, Harold Williams, Judy Hannah, Daniel Patronik, Jeffrey Hightower, Judith Tegeler, Cathleen Tenace, and Gary Solar.  Seven guests were introduced,  including Yasutaka Terakado, Thomas Meisel, Edward Bolton, Munir Humayun, Cecile Wolf, David Applegate, and Judy Hannah.   President Helz announced the deaths of five members-- or former members--of the Society: Betsy Pebbles,  Cornelia Cameron,  Frank Flanagan, James Balsley, and Irving May.   John Price of NSF announced that the American Chemical society is sponsoring a "kids in chemistry project" and looking for volunteers to go to area schools to give children hands-on activity in the classroom.   President Helz also announced  that she had received from AAPG a copy of a color magazine entitled "Kids Discover" that talks about the uses and benefits of oil, which can be ordered for distribution to grade-school children. There were no informal communications.

     The first formal talk of the evening was by George Stephens of George Washington University, and coauthors Francisco Nullo and Paul Baldauf of CONICET in Argentina, who spoke on "Tertiary Tectonic Evolution of the Central Argentinian Andes."   George described the results of recent field studies in western Argentina that focus on the uplift history of a Mesozoic fold-and-thrust belt, through detailed stratigraphic and structural analysis of an adjacent Tertiary and Quaternary sedimentary sequence derived from it.   Basement in the study area consists of Carboniferous schists and Permian to Triassic granites.   Overlying this basement is the fold-and-thrust belt, which comprises two fining-upward sequences of Early Jurassic to Late Cretaceous age, consisting of nonmarine arkosic sandstone and conglomerate at the base, marine shale and limestone in the middle of the cycles, and evaporitic gypsum deposits at the top.   Andesitic plugs and other intrusions, which are common within the fold-and-thrust belt, yield Ar-Ar ages of 10.6 to 5.3 Ma, which are believed to approximate emplacement ages since the andesite bodies probably cooled relatively quickly.

     The Tertiary and Quaternary basin to the east, which was deposited as a series of coalesced alluvial fans, formed in part by the erosion of the adjacent fold-and-thrust belt.   Clast lithology and other features such as deformation permit the basin to be divided into five subdivisions, which are used to understand the uplift and erosion history of the fold-and-thrust belt.   The nature and structure of the Tertiary and Quaternary sediments also record the tectonic history of the fold-and-thrust belt.   Based on these and other relations, George suggested that 1) horizontal shortening in the fold-and-thrust belt ended prior to the emplacement of the Molles suite of andesitic plugs, 2) vertical uplift began at the beginning of the Tertiary, and 3) significant vertical uplift continues to the present.

     Questions by Murray Hitzman, Dave Stewart, Gene Robertson, Nick Woodward, and Charles Druit.   (19.5 minutes)

     The second talk, by Elisabeth Widom of the Mass Spectrometry Group at the National Institute of Standards and Technology, was on "Os Isotopic Systematics of the Azores and Canary Islands."  Elisabeth reported on osmium and other radiogenic isotope data for Holocene basalts from the Azores and Canary Islands, as a mechanism for evaluating the degree of crustal contamination in the basalts. Osmium isotope studies are well suited to this task, because rhenium is incompatible while osmium is compatible during partial melting of the mantle, whereas the parent and daughter isotopes of strontium and lead are all incompatible during partial melting.   Osmium isotopes thus can be used to identify recycled crustal material in the deep mantle.

     The osmium contents of the basalts are extremely low,  reaching a maximum of less than 150 picograms per gram (one picogram per gram is one part per trillion).  Higher 187Os/186Os ratios and low osmium abundances are interpreted to reflect contamination of the basalts by manganese oxides, whereas the opposite trend suggests control by a mantle lithosphere component.   Attempts to decipher the degree of crustal contamination through strontium isotopes were unsuccessful, because although the strontium isotope range is large, the osmium isotope range is small, thus precluding a distinction between recycled terrigenous sediments and subcontinental lithosphere.   However, thorium isotope data were helpful in distinguishing largely mantle sources (lower 230Th/232Th) from sources influenced significantly by crustal contamination (higher 230Th/232Th); lower crustal contamination is indicated for basalt samples from the Canary Islands that are believed to have come from a mantle plume.   Elisabeth concluded by suggesting that 1) osmium isotope ratios in ocean island basalts are affected by lithospheric mantle and not by crustal contamination, 2) radiogenic osmium isotope ratios may be produced by contamination from manganese oxides and perhaps from carbonatites, and 3) unradiogenic osmium isotope ratios are produced by contamination with lithospheric mantle.

     Questions by Ken Towe, Craig Schiffries, Murray Mitzman, Roz Helz, and Charles Druit.  (19.0 minutes).

     The last talk of the evening was by Marilyn Fogel of the Geophysical Laboratory, who spoke on "Isotopic Records of Global Change."  Marilyn used data on nitrogen abundance and nitrogen isotopes to evaluate the role of humans on the global cycling of nitrogen.   Major sources of nitrogen to the atmosphere are industry, agriculture, auto emissions, lightening, and coastal waters.   In general, rainfall in oceanic areas has low nitrogen contents, whereas continental storms produce relatively high nitrogen rain; the nitrogen in the rain is present as ammonia and as nitrate.   Marilyn described her study area in coastal North Carolina, where rain has been systematically collected for the past 4 years.   Measurements have been made of amount of rainfall, pH, amount of ammonia, and amount of nitrate.  Seasonal variations exist,  including increased pH during winter and fall, which is associated with increased ammonia and nitrate contents of the rain.   Stable nitrogen isotope data, reported as d15N values, decrease with increasing rainfall, although the observed variation is only from +2 to +5 permil.

     Marilyn then described her "Mesocosm" Experiments in which nitrate and ammonia were artificially added to rainwater and coastal waters, and monitored for d15N values and parameters such as chlorophyll.   Significantly, adding small quantities of ammonia resulted in a major decrease in phytoplankton productivity.  Detailed monitoring by the hour, however, shows a lag of approximately one day in chlorophyll production, in response to adding the ammonia.   The presence of ammonia in rainwater thus affects the biosphere, since an estimated 35-80% of the nitrogen in coastal waters is derived from atmospheric deposition.

     Questions by George Helz,  Brooks Hanson, Ken Towe,  Bob Ilchik,  and Moto Sato.  (22.0 minutes).

     President Helz adjourned the meeting at 9:35 p.m.   Attendance was 91.

     Respectfully submitted,

     John F. Slack (for Cy Galvin)

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1254th Meeting, September 28, 1994

     President Helz opened the meeting at 8:05 p.m.  Minutes of the 1253rd meeting were read and approved following minor corrections.   Five new members were announced: Holly Stein, Gene La Porta, Barbara Fowler, Sharon Givens, and James Joyce.   Pour guests were introduced, including Victor Press, Lori Keith, Jackie Mann, and Mark Frank.  President Helz announced that the GSW Council had lowered student dues to $11, and did not approve Ellis Yochelson as a corresponding member.  There were no informal communications.

     The first talk of the evening was by Philip Candela of the University of Maryland, who spoke on "Tertiary Magmatic Phase Permeability in Granites, Theory and Field Observations.,,  Phil described the results of studies aimed at developing models of magmatic phase evolution, specifically with regard to the mechanisms of volatile egress from crystallizing plutons.  Recent field studies have included work on several high-level plutons in the Hodgkinson, New England, and Lachland fold belts of eastern Australia, where the common presence of miarolitic cavities in the plutons indicates that the magmas were saturated with respect to a volatile phase.  Phil showed hand-specimen photographs of granites that contain miarolitic cavities interconnnected by miarolitic textures, and crudely concentric bands of miarolitic cavities within an aplitic matrix.  The externally nucleated micropegmatitic textures are considered evidence of an interconnected magmatic volatile phase during crystallization, which is enhanced by low pressures and wet magmas.  Fractal experiments were shown that may have relevance to modeling the evolution of volatiles in high-level granites.  There are additional implications for trace element distributions in granites, in terms of batch devolatiltzation versus finite reservoir fractionation.  With respect to mineralization, high-level granites with textural variability and miarolitic cavities are commonly associated with magmatic and hydrothermal deposits of tin, molybdenum, gold, and tungsten.

     Questions by Moro Sato, Bob Ilchik, Sorena Sorensen, Bruce Doe, and Mike Brown.   (20.0 minutes).

     The second talk, by Erik Hauri of the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, was on "Chromatographic Effects of Melt Migration: A Case Study from Kilauea Volcano, Hawaii."    Erik presented various chemical, isotopic, and phase equilibria data bearing on the nature of volcanism at Kilauea Volcano.  Major unanswered questions are: 1) what is the composition of the primary Kilauea magma?; 2) What is the depth of generation of primary Kilauea magma?; 3) What is the depth of last equilibration of the primary Kilauea magma?; and 4) What is the role of the lithosphere in shield building of Hawaiian volcanoes?  A significant paradox exists between experimentally- and chemically-based models for the primary Kilauea magma.  Experimental melting of Hawaiian picrites are inconsistent with equilibration with garnet lherzolite, yet rare earthy element data on these picrites are similar to data produced by melting of garnet lherzolite, and residual garnet is apparently required to buffer the heavy REE contents of the picrites.

     Erik presented a model that separates elements like a chromatographic column, as a function of different partition coefficients of elements between liquid and solid phases.   Lead,  for example, has a very low partition coefficient of about 0.001, which is thus preferentially fractionated into the liquid phase; osmium,  in contrast, has a very high coefficient of about 10, and thus stays behind in the solid phases.   Osmium isotope data- shown as 187Os/186Os, plotted against lead isotope data, shown as 206Pb/204Pb, suggest that Kilauea magmas have not significantly interacted with the lithosphere or asthenosphere.   The Kilauea magmas thus must move through the lithosphere quickly to avoid contamination during ascent.

     Questions by George Helz, Mike Ryan, Bruce Doe, Bevin French, Sorena Sorensen, and Hat Yoder.   (18.5 minutes).

     The last talk of the evening was by Brooks Hanson of Science Magazine, who spoke on "Making Room for Granites Slowly: Bringing Ocean Ridges on Land."   Brooks started by reviewing the three principal means proposed for granite intrusion in the crust,  including stoping, diapirism or forceful emplacement, and extension, all of which have major mechanistic problems.   A plot of over a thousand granitoids in the western United States that are believed to have been emplaced at greater than or equal to 6 kilometers depth are mainly less than 20 kilometers in diameter.   Examples were shown from the White Mountains and the southern Sierra Nevada, the latter containing granites commonly spaced 40-50 kilometers apart.   Are these features consistent with extension as a means for providing room for granite intrusion in the crust?  The problem with an extensional model, according to Brooks, is that extension is too slow by several orders of magnitude, based on the recurrence interval of modern earthquakes in regions undergoing active extension.   What extension rate, therefore,  is necessary?  Scaling Norm Sleep's theoretical data from ocean-ridges to continents and use of temperature-time plots of half-extension rates shows that slow spreading--like that typical of continents--can maintain small magma chambers.   At a minimum extension rate of 2 centimeters per year, a stable magma chamber can form in relatively cool crust; only 1 centimeter per year extension is necessary to maintain the chamber once it has been created.   Brooks also suggested that zoned mafic to felsic magma chambers are very stable thermally, and that the actual size of magma chambers may be much smaller than the size of the preserved granitoids.

     Questions by Bevin French, Mike Ryan, E-an Zen, and Phil Candela.  (19.0 minutes).

     President Helz adjourned the meeting at 9:50 p.m.   Attendance was 74.

     Respectfully submitted,

     John F. Slack (for Cy Galvin)

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1255th Meeting, 12 October 1994

     President Rosalind Helz called the 1255th meeting to order at 8:03 p.m. This was a joint meeting with the Paleontologic Society of Washington. The minutes of the 1254th meeting were read and approved with one correction. No new members were announced.

     Three guests were introduced: Brett Lesley, EPA (?); Leonid Popov, VSEGEI; and Dr. Tong Jinnan, Associate Professor, China University of Geosciences.

     President Rosalind Helz announced that Professor George Helz heads the 1995 slate of GSW officers proposed by Doug Rumble, Chair of the Nominating Committee.

     Ellis Yochelson showed two slides of a portrait of Charles Doolittle Walcott [1850-1927], in an informal communication, appropriate for this joint meeting because Walcott had been both the first president of GSW and a noted paleontologist. Ellis said that the portrait probably represents Walcott around age 75, but was finished posthumously in 1928 by Walcott's daughter [Helen Younger], and recently given to the National Portrait Gallery by Walcott's great granddaughter.  These slides were the first public showing of the painting. Although it is not evident on the portrait, Ellis said that Walcott once had red hair.

     Bruce Molnia, USGS, gave the first scheduled talk on the "1993-1994 Surge in Bering Glacier." The Bering glacier in Alaska is the largest glacier on continental North America and the largest surging glacier on earth. By definition, glacial surges are accelerated movements, for durations up to about 2 years, during which glaciers may move at speeds up to 100 times their long-term average speed. The onset of the surge was identified from satellite SAR images, which showed large pressure ridges moving 90 m/day down the glacier, disturbing the normally flat surface of the ice. In the period from October 1993 to July 1994, the surge involved over 4000 km2 of ice, and parts of the glacier terminus advanced 9 km. However, over the longer term, the glacier shows a net loss of 120 km2 during the 20th Century.

     Seaward of the terminus of the present glacier, there is a large submarine trough. There is a landward extension of this trough well under the glacier. In the future, Bruce expects retreat to dominate, and salt water to intrude along this trough far into the mountains. Twentieth century glacial retreat has produced Lake Vitus along the axis of this trough, and the present surge reoccupies part of that lake.

     The surging ice volume at the terminus is only partially replaced from upslope so at intermediate positions the ice surface of the glacier drops vertically. Bruce showed slides of the glacier margin where the snow line of a prior winter hung on valley walls, 30m above the present ice level.

     Glacial surges recur intermittently, 3 to 5 years on short term, 100 years on long term, the surge periods being specific to the glacier. For the Bering glacier, the period is about 20 to 30 years. Surges are believed to be caused by water pressure building up at the base of the glacier which may suddenly overcome bottom friction so that the glacier 'hydro-planes' down the valley as a slab, in Bruce's terms. The glacier eventually stops surging when the water pressure is released. Release of subglacial water is often catastrophic. As of 7 September 1994, the surge appears to have nearly stopped.

     This is the best documented glacial surge yet, and involved unusually high ice volumes and speeds.

     Questions by Dallas Peck, E-an Zen, Moto Sato, Steve Shirey, Gene Robertson, Alan Linde, Charles Druit, and Blair Jones.

     Debra Willard, USGS, gave the second scheduled talk on "Response of Terrestrial Marine Ecosystems to Changes in Pliocene Climate: An Example from the South Atlantic Ocean."  Debra's study area is in the south Atlantic, adjacent to southwestern Africa. The land area contains the Namib Desert, and the adjacent ocean has the Benguela Current, and the Walvis Ridge. The talk described Debra's part of the PRISM project to which she was contributing pollen analyses. Her personal work was the pollen analysis of DSDP core 532, which she correlated with vegetation changes described by others onshore. She is looking for evidence of climate change during part of the Pliocene, and between Pliocene and the present, a 3 million- year difference.

     On a worldwide basis, Pliocene sea level was considerably higher, there was much less land and sea ice, and the vegetation differed.

     In her South African study area, the critical driving phenomenon is the strength of the Antarctic Intermediate Water, a tongue of water 600 to 1000m deep that spreads northward from Antarctica, and upwells on the South African coast, or at Walvis Ridge. The Benguela Current is a shallow north-flowing current. This current is important in distributing Antarctic Intermediate water which is rich in nutrients and has a low temperature that promotes aridity.

     Prior studies suggest that the Oligocene and most of the Miocene was relatively wet and cool. The late Miocene and Pliocene was colder and dryer, with rainfall less than 50 mm/yr in the Namib. This Desert persisted almost without change in the Pliocene interval under study.

     Three classes of vegetation occur on the mainland: grasses, chenopod, and asters; all represent desert assemblages. Prior work has established that from early Pliocene to the present, grass pollen dominates the Namib Desert region, with chenopod and aster pollen subdominant.

     Debra concludes that vegetation and marine life change synchronously in response to changes in the Benguela Current, and that the pollen and planktic forams are good proxies for climate change.

     Question by Dan Milton.

     Scott Ishman gave the final scheduled talk of the evening "Paleoceanographic Evolution of the Western Arctic Ocean." Sediments in the Arctic Ocean have been deposited so slowly that cores typically show sedimentation rates of only 1 mm/1000 yrs, but in the Canada Basin near the Northwind Ridge, rates get up to 4 mm/1000 yrs. Scott studied three cores, 2 to 6m in length, that exploited this expanded scale. These cores came, in order of approximate depth, from 1000 m, 1500 m, and 2000 m.

     These cores are from the Western Arctic Basin, of which the Canada Basin is part. In the present, this Basin has three water masses to note: shallow water, intermediate water, and deep water. The deep water now is formed from supercooled shelf water that flows down the slope to become deep water. Under these modem Arctic conditions, the three water masses are associated with three benthic foraminiferal biofacies. The uppermost of these three biofacies was above the three cores, but two cores did sample the intermediate (C) biofacies and all three cores sampled the deep water (O-E) biofacies. The present boundary between C and O-E biofacies is about 1200 to 1500 m depth. The C biofacies is so called because it is characterized by Cassidulina, and the O-E biofacies is so called because it is characterized by Oridorsalis and Eponides.

     There are still other relevant forams, but they are not now found in the Western Arctic Basin, although their fossils do occur in the cores. These are the agglutinated forams which have tests consisting of quartz grains glued together by an iron-organic cement. Because of their tests and their occurrence elsewhere, these agglutinated forams are interpreted to thrive where more acid water keeps out forams with calcite tests.

     The core from 1000 m depth has a good paleomagnetic record indicating the Brunhes-Matuyama Boundary (780,000 yrs BP). This date was correlated to the other cores by lithology and to some extent by the forams.

     Scott concluded from these data that two major oceanographic events affected the Western Arctic Basin over the last one million years: first, about the time of the Brunhes-Matuyama Boundary, 780,000 years BP, there was an influx of North Atlantic water which replaced corrosive bottom water almost down to 2000 m depth; second, at about 300,000 yrs BP, modern conditions began where deepwater was generated on the shelf, producing the modem deepwater foram assemblage.

     Questions or comments by Jane Hammarstrom, E-an Zen, Ellis Yochelson.

     President Rosalind Helz adjourned the meeting at 9:38p.m. Attendance approximately 65.

     Respectfully submitted

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1256th Meeting, 2 November 1994

     President Rosalind Helz called the 1256th meeting to order at 8:05 p.m. The minutes of the 1255th meeting were read and approved. There were many announcements before the scheduled talks.

     Five guests were introduced: DeVeerle Hams, University of Arizona; Carolyn Harris, Teacher, McGogney Elementary School; Karen Griffen, Assistant Principal, Hall Junior High School; John Boroughs Parsons Engineering Science; Adele Conover, Smithsonian Magazine.

     Pete Stifel announced that E-an Zen had received an award from AGI for furthering public understanding of geology and for his work on science education in the United States.

     President Helz announced that there will be no GSW fall field trip.

     Three new members of GSW were announced: Thomas Duffy, Geophysical Laboratory; Anne Ledbetter, University of Maryland; and Matt McMillan, University of Maryland. Dave Berry transferred from student to regular membership.

     Bob Ilchik announced that he was returning to the University of Arizona from his temporary position at the Geophysical Laboratory),, and stated his appreciation and thanks for opportunities afforded by these GSW meetings.

     E-an Zen gave an informal communication on the origin of certain boulders at Great Falls.  The boulders in question are up to 2.25 m in diameter, and they rest on the fresh bedrock surface of Glade Hill, which formerly was the river channel. The boulders appear to be early Paleozoic Weaverton whose closest probable source is 40 km distant by river. The fresh surface of the boulders suggest a Late Pleistocene or later origin. The fact that they are unmixed with boulders from other sources suggests to Wan that they all arrived at their present resting places in one fell swoop. By an analysis of historic floods, and the hydraulic requirements to move these boulders, E-an thinks that 4 to 5 m/s velocities are needed within the channel. A reasonable channel configuration that would provide such velocities has a 300m width, a depth of 10 to 15 m, and a slope of 0.001 to 0.0015. Probably the river was not like the modern Potomac when these boulders were deposited.

     Questions by Tom Dutro and Ray Rye.

     J. K. Bohlke, USGS, Reston, gave the first scheduled talk on "Ground water dating and the progress of agricultural chemicals through aquifers." J. K. was primarily concerned with nitrogen introduced as fertilizer. He studied three agricultural sites: near Princeton, Minnesota, at Locust Grove, Maryland, and near the South Platte, north of Denver, where he plotted the progress of nitrogen through aquifers.  To date, he used the peaks or first appearances of tritium, and the variation in three specific freon compounds whose concentrations in the atmosphere are historically known. 

     In the Minnesota cornfield, nitrogen applied on the surface permeates vertically down and flows horizontally to terminate in a wetland. Age contours appear to be horizontal under the field and turn up vertically at the wetlands.

     J. K. presented three graphs to illustrate his Minnesota results. The lust graph plotted Argon against Nitrogen gas to estimate the amount of denitrification that occurred. This plot assumes that some nitrogen entered the groundwater as a gas from the atmosphere, which should be correlated with argon. Other nitrogen originally entered as nitrate fertilizer, which should not be well correlated with argon.

     The second plot dealt with fractionation of nitrogen isotopes, which was consistent with J.K.'s assumptions about the denitrification of fertilizer nitrates. Finally, a third plot isolates clusters of data points identified with non-agricultural use, pre-1980 agriculture, alfalfa cropping during the 1980's, and corn in 1990. This indicates that the groundwater preserves a record of past land use and that J.K. can calculate the initial nitrate in the water before it was reacted away.

     At the Locust Grove site on the Eastern Shore, he investigated two adjacent watersheds whose streams had very different nitrogen content. This difference J.K. attributed to the elevation of the streams above a Tertiary greensand which dipped southward under the area. N in the recharging water in this area has exceeded the safe drinking water standard since 1970%, and because the residence time of the water is on the order of 20 years, a radical change in nitrogen use on the surface will not show up in surface water discharge for quite a while.

     At the South Platte locality, manure from local feedlots is spread on corn fields, to become a major source of introduced nitrogen. For the past 20 to 25 years, groundwater in this area has had nitrate concentrations at twice the drinking water standard.   The river itself has high dissolved organic carbon which permeates into the bed and denitrifies the water adjacent to the channel.

     J.K. has two primary conclusions: (1) nitrified water moves through near-surface aquifers on a time scale measured in decades, and (2) there is a need to know more about the distribution of reactive compounds in the aquifers, which is work for geologists to do.

     Questions by Dave Stewart, Murray Hitzman, Bruce Hanson, Craig Schiffries, Will Logan, Mark McBride, and Ken Towe.

     Norrie Robbins, USGS, Reston, gave the second scheduled talk, after some starting slide difficulties, on "Giant biogeochemical anomalies on the bottom of the sea -- the bacteria recycling the SS Central America and the RMS Titanic."  The SS Central America went down with three tons of gold on board in September 1857, 200 miles east of Savannah on the Blake Plateau.

     Norrie discussed two types of bacteria, one producing 'rusticles' which are linear bacterial deposits of iron, some of them leaning in the direction of the mean current. The bacteria precipitate bright orange iron oxide. The second type of bacteria is the oil film bacteria which precipitate a ferrohydrate on its way to being hematite.

     'Rusticles' grow at rates up to 7 cm/yr on the Central America. Rust flow structures, whose bacterial origin is less well known, grow at rates up to 25 cm/yr on the Titanic. Sheaths with bacteria in them form filaments get coated with Fe. Microscope slides placed near the Central America on the ocean floor were colonized as hard ground.

     Norrie experimented with these bacteria in sterile sea water. She used pig iron in this water for a control and got "green rust." She used pig iron with rusticles from the Central America, and pig iron with rust from the Titanic for the experiments, and vials got coated with oil film bacteria. There remains a question about the possible effect of light on the experiments.

     Pat Stoffyn and Dale Buckley of the Canadian Geological Survey found lepidocrosite outside the rusticles and goethite within, indicating very local changes in the chemical environment. From work elsewhere, it is known that bacteria are catalysts accelerating iron oxidizing reactions by 100 to 1000 times.

     Norrie's primary conclusion is that bacteria have a significant role in what are often assumed to be abiotic reactions.

     Questions and comments from George Helz, Dave Stewart, Murray Hitzman, Mark McBride, Moro Sato, Ken Towe.

     Roger Haskins gave the final scheduled talk of the evening on "The road to mining law reform: a study in perpetual motion." Roger reviewed the history of the subject, beginning with 1872 General Mining Law, passed while Grant was president, at a time when a laissez faire philosophy of government prevailed The 1872 law was intended to distinguish mining from agriculture laws. Subsequent laws include the 1920 law to separate out oil, coal, and phosphate resources for leasing, and the 1955 law which did the same for construction aggregates.

     In 1964, Congress set up the Public Land Review Commission which was supposed to review the public land law system, including 150 separate laws, and to suggest a replacement for the 1872 law.

     The period from 1986 to the present has seen a series of attempts to change the basic law but these attempts have, to date, not achieved their objective. These efforts were prodded by Senator Bumpers and Representative Rahall, and excited by Interior's settlement of oil shale claims at $2.50/acre. Issues include: abolishing patenting, the fight of the government to say 'No' after exploration is done, royalties and whether they should be on net or gross, reclamation, SMACRA, and annual fees. (SMACRA is the Surface Mining and Coal Reclamation Act.) Senators Diconcini and Craig have been involved in recent efforts, as well as Senator Johnson and Rep. Miller. Western senators have generally held a veto over Administration proposals.

     Roger said that he believes prospects look good when the issue comes up again in January 1995. At least that is what he said at the meeting on 2 November. When I reviewed these minutes with him on 10 November, Roger now said that he believes that prospects are guarded, if the issue comes up in January.

     Questions by Phil Bethke, Todd Loomis, Bob Ilchik, George Helz, Gene Robertson, E-an Zen, John Price, Ann Dorr. Roger strongly maintained before doubting questioners that  explorationists have gone south because of uncertainties in the mining law, EPA enforcement, and length of permitting process, rather than because of the exhaustion of prospects within the US.

     Both Norrie Robbins and Roger Haskins finished their talks in under 18 minutes, a unique paired occurrence in this society year.

     President Rosalind Helz adjourned the meeting at 10:00 p.m.  Attendance was 79.

     Respectfully submitted,

     Cyril Galvin

     Meeting Secretary.

 

MINUTES OF THE GEOLOGICAL SOCIETY OF WASHINGTON

1257th Meeting, 30 November 1994

     President Rosalind Helz called the 1257th meeting to order at 8:04 p.m.

     Five guests were introduced: Pat Southerland, University of Oklahoma; Dr. T. Matsuzawa, Tohoku University, Japan; Fred Rissberger, John Ackerly, and Norbert N'dorfor, University of Maryland.

     Four new members: Jeff Woodward, Chris J. Murly, Keven Hopson and Fred Rissberger, three of them with Groundwater & Environmental Services..

     President Helz then made five announcements: (1) She asked all GSW officers and committee chairmen to bring their 'grey books' to the Annual Meeting on 14 December.  (2) She drew attention to the McKelvey Symposium which will be held on 13-16 Feb 1995.  (3) Six GSW members received Meritorious Service Awards from the Department of Interior, including John Keith, Bonnie McGregor, Dave Root, John Slack, Tom Wright, and Bruce Wardlaw.  (4) The dues announcement recently sent out is for 1995. President Helz advised members who are in arrears for their 1994 dues that they cannot coast on the float and that they are not forgiven the 1994 debt by merely paying their 1995 dues.  (5) New officers proposed for the coming society year include Pete Stifel, President; George Helz, First Vice President, Steve Shirey, Second Vice President; Margo Kingston, Treasurer; Jeff Grossman, Meetings Secretary; Cy Galvin, Council Secretary; and I. K. Bohlke, Holly Stein, and Rich Walker as new Councilors. Hold-over councilors include Bill Burton, Marcus Millins, and Mike Ryan.

     Natalie Valette-Silver, AAAS Science and Diplomacy fellow at Agency for International Development, gave the first talk on "Contamination in the Coastal United States"

     NOAA has a contamination sampling program, including two main projects: The National Benthic Surveillance Project, initiated in 1984, that analyzes sediments and bottom fishes at about 80 coastal sites, and the Mussel Watch Project, initiated in 1986, that analyzes sediments and bivalves from about 240 coastal sites. There is also the Sediment Core Project, initiated in 1989, intended to get the contamination chronology of ten US estuaries. These projects look at indications of contamination in benthic fish, bivalves (oysters and mussels), the top 2 cm of sediment, and cores. Fish and bivalves retain contaminants differently; for example, the fish keep Zn and Cu permanently, whereas oyster and mussels quickly gain or lose Zn and Cu as ambient concentrations change.

     The continuing projects analyze for up to 16 trace elements, five families of organic compounds, and an array of manmade and natural radioisotopes. Up to six labs were contributing data, but now that is down to two, which is a worry when documenting trends. By definition, contamination occurs when three or more chemicals have concentrations greater than one standard deviation above the national mean.

     High contamination usually occurs near large population centers, particularly at ports. However, the contamination indicators differ among sources from the same site; for example, at the same site, oysters may absorb more Zn, Cu, and Ag than mussels, but the mussels may absorb more Cr, Pb, and As. Contaminants may differ systematically within one region, as shown by oysters in Chesapeake Bay.

     The locations of some hot spots are initially counter-intuitive. For example, 241Am  typically has concentrations an order of magnitude higher along the Pacific coast than along the Atlantic coast, apparently due to upwelling of water contaminated by Pacific atom bomb tests.  Arsenic reaches peaks in relatively unpopulated areas along the southeast Atlantic coast and along the northeast Gulf coast, apparently because of heavy use of herbicides and fungicides, and because of natural phosphate deposits in the region.

     Short-term trends from the top two cm of sediment show a general decrease in organics and Cd from 1986 to 1993, with a possible uptick at the end of this period. At Palos Verdes, PCB decreases from about 3600 units in 1971 to less than 100 units in 1990.

     Long-term trends can be deduced from cores, provided the cores sampled an area where sediment is accumulating without subsequent physical or biological mixing. Nathalie showed a series of slides giving the time distributions of Cu, Pb, Zn, and Cr from cores dating back more than a century. In general, these elements increase in concentration up till the 1970's and then decrease. Over the same period, TOC tended to increase, and organics are somewhat erratic.

     Nathalie concludes that contaminant maxima occur mostly near urban centers, but some have natural causes. The contaminants occur in sediments, fish, and bivalves. Bivalves are good indicators of the level of contamination in their contemporary environment.

     Trends show that contaminant concentrations usually peaked in the mid 1970's. Nathalie thinks that the subsequent decrease was prompted by legislation and increased awareness. There are some data showing a slight rebound in contamination during recent years.

     Questions by Doug Rankin, Kevin Crowley, Raymond Rye, Un Zen, Margaret Chauncey, Mike Ryan, Charlie Prewitt, Craig Schiffries, George Sellers, Margaret Chauncey (again), and Roz Helz.

     Allison MacFarlane, George Mason University, gave the second talk on "Tectonic Evolution of the Nepalese Himalaya"

     Allison's field area is Nepal, where the Himalayas provide the geologist with a full scale tectonic laboratory. She had two primary questions to answer in this talk: (1) What was the timing of the Main Central Thrust? and (2) How do you explain the inverted metamorphic gradient of the thrust rocks? By way of an abstract, she answered both questions at the start: The thrust is both syn and post tectonic, and the inverted gradient is apparent rather than real.

     The core of the Himalayas consists of three major units, defined both tectonically and stratigraphically. In north to south order, they are the Tibetan Sedimentary series, the Greater Himalayan Sequence, and the Lesser Himalayan Sequence. To the south of all three units is the undifferentiated Subhimalayan Sequence.

     The boundaries between these four units are three faults which dip north at low angles.  From north to south, they are: The South Tibetan Detachment System, the Main Central Thrust, and the Main Boundary Thrust. The South Tibetan is between the Tibetan Sedimentary and the Greater Himalayan; the Main Central Thrust is between the Greater Himalayan and Lesser Himalayan; and the Main Boundary Thrust is between the Lesser Himalayan and the Subhimalayan.

     Allison's study emphasized the middle of these three faults, the Main Central Thrust, on which 100km of shortening has been reported. In particular, she studied in detail the Langtang National Park region of central Nepal where there are excellent exposures in roadcuts and along ridge tops.

     She found by Argon dating of micas that movement on the Main Central Thrust was post metamorphic in two areas and synmetamorphic in other areas. The hanging wall (which is the Greater Himalayan Sequence) is amphibolite to upper amphibolite grade. The foot wall (which is the Lesser Himalayan) is greenschist facies.

     There was ductile strain about 16-21 my ago, and brittle deformation at 2.3my. She interpreted the petrology and dates to indicate a lithostatic gradient of 27 MPa/km increasing northward and a virtually constant temperature, all measured across 16km, north to south. A change in pressure, rather than temperature can explain the observed metamorphism, with the temperature locked in from an earlier time.

     Comparison with areas along strike suggests that history of burial and faulting resulted in different time histories of pressure and temperature. This along strike difference in history produced different rocks and structure in areas that initially would be assumed similar.

     Questions by Sorena Sorensen and Bruce Hanson.

     Reto Gieré, Geophysical Laboratory and University of Basel, gave the final talk on "Use of Natural Minerals as Analogs in Radioactive Waste Disposal"

     Reto's work was based on the observation that there are geologically old, naturally occurring minerals that contain relatively high levels of uranium and thorium without significant damage. Three organizations contributed to the work: his University of Basel, the British Natural History Museum, and the Australian Nuclear Science and Technology Organization. The Australian connection stems from Ringwood's suggestion in the late 1970's to copy nature by storing radioactive elements in crystals.

     If ocean dumping is eliminated, disposal options for high level radioactive waste are limited to borosilicate glass or crystalline waste forms. The problem with glass is that it has relatively low resistance to leaching, and that it can absorb only about 10% waste, compared with 20% in the crystalline waste forms. Furthermore, the crystalline forms bind the radioactive elements into the structure, but these elements float around in a glass.

     The major host mineral is zirconolite (CaZrTi2O7), but also hollandite and (real) perovskite. Natural occurrences of these minerals have ages in the million to billion year range; include uranium and thorium in trace to major amounts; and have had potential exposure to hydrothermal fluids.

     Damage to the zirconolite structure is done by alpha particles. Above the critical dose, the crystals transition to a metamict. Reto gave examples of samples with different doses and ages.  A high dose sample from Phalaborwa, South Africa, at 2.5 billion years, is completely metamict.  Samples from Stavenger, Norway, have islands of crystalline material in a sea of metamict.  From Bergell, Switzerland, there is completely crystalline zirconolite, 30 million years old.

     The major concern is microfractures caused by the volume increase in the transition from crystalline to metamict. This is more of a potential problem in the coarser crystals. A vein sample from Adamello subject to 600°C and highly corrosive fluids during its geologic history shows corrosion of the zirconolite along a fracture with release of uranium and thorium. Yellow haloes indicate radiation damage around the zirconolite. A South African sample, which appears to have had little exposure to heat or corrosive fluids, has uranium and thorium not affected by cracks. The transition from crystalline to metamict structure takes a dose on the order of 1015 to 1016 alpha particles per milligram of sample. Only two of 44 natural samples show visible alteration.

     Reto thinks that the development of fine grained zirconolite ceramics with grain size less than one micron is the way to go.

     Questions by Sorena Sorensen, E-an Zen, George Helz, Craig Schiffries, J. K. Bohlke, Moro Sato, and Dave Applegate.

     President Rosalind Helz announced that the next meeting on 14 December would include the President's address at 8:00 p.m. and the Annual Meeting at 9:00 p.m.

     Meeting was adjourned at 9:51 p.m.; attendance approximately 93.

     Respectfully submitted

     Cyril Galvin

     Meetings Secretary

 

MINUTES OF THE GEOLOGICAL SOCIEIY OF WASHINGTON

1258th Meeting, 14 December 1994

     President Rosalind Helz called the 1258th meeting to order at 8:12 p.m. Minutes of the 1257th Meeting were read and approved. Nine new members were announced:

David Applegate AGU fellow, Senate Energy and Natural Resources Committee

Jennifer Blank      Geophysical Lab, Carnegie Institute

Scott Borg          NSF Polar Programs

Adele Conover    Science journalist

Alice Daly           Holy Redeemer School

Martin Fisk         National Science Foundation

John Ackerly       University of Maryland

Dina Lambros     University of Maryland

Norbert Ndofor  University of Maryland

     Five visitors and guests were introduced, including Jack Thompson, College, Alaska; Bryan Howe (?) and Karen Howe, Namibia; Professor A. Paoni, University of Naples; and Peter Buseck University of Arizona and National Science Foundation. 

     Pete Stifel, University of Maryland, President Elect, introduced President Helz, USGS who gave her Presidential Address on "Detectability and Stability of Mature Magma Chambers: Lessons from the Kilauea Iki Lava Lake."

     President Helz showed a sequence of slides illustrating the evolution of Kilauea Ike Lava Lake from its initial molten fountaining stage in 1959 to its present relatively mature condition.  Data included initial visual observations, seismic transmission, and coring results. Based on this study, it is surprisingly difficult to prove by geophysical means that there is a magma reservoir within the lake.

     The 1959 Kilauea Iki lake was initially 135m thick and began cooling immediately. President Helz relied on seismic data taken in 1976, drilling done under contract for Sandia Labs in 1979, and further drilling and seismic in 1981. She also acknowledged Ginger Barth for her reinterpretation of seismic results.

     Initial interpretation of the seismic results by Aki and Chouet in 1976 suggested that the melt could not be more than 10m thick because of shear wave transmission. Vp was measured at less than 2 m/s, even less than 1 m/s much of the time. Ginger's reinterpretation was that melt in vesicles in the 1976 rock retarded Vp.

     Bulk MgO content was fixed in the 1960's. Settling of big olivine phenocrysts was probably finished by mid 1960's. The crystal framework transmits shear so there is no distinctive seismic signature, especially because of a very low velocity material on the surface and cracked dry rock underlying the surface material.

     The 1979 drilling showed unusual and enlightening results. The original hole did not collapse overnight, and took 16 days to back fill. But the mush came back faster on subsequent drilling, and on multiple reentry, the mush rebounded a distance somewhat less than 10 m above the bottom of the hole. Roz believes the drilling acted to unload static pressure, and the mush reacted by becoming more fluid. Roz interprets thin sections to indicate that the hole is not stable for melt contents above 25%, which was at 178 ft. below the surface in 1979, but melt fraction went as high as 41%.

     Examination of titanite vs MgO indicates that all of the ooze from later reentries had higher TiO2 than the original core, which is interpreted to mean melt entering the hole from the mush. No single melt fraction determined rheology.

     The solidus occurred at 1000° and about 180 ft. in 1979. The melt fraction leveled out at 30 to 41%, with variations probably due to olivine concentration.

     Thin sections from cores showed random looking distribution of minerals, with rounded and probably resorbed crystals.

Roz used her findings to highlight potential volcanic hazards. Reintrusion of magma might make a direct hit on the partial melt, or it could perturb the older chamber even if not a direct hit.

     Roz believes 25% melt fraction is the real edge of magma chamber. There is probably an awful lot of melt stashed under volcanoes with no historic eruptions. These magma chambers can be easily destabilized. Magma chambers must be presumed to exist under young volcanoes everywhere, whether or not they have been in recent eruption.

     Meeting was adjourned at 9:14 p.m. Attendance approximately 70.

     Respectfully submitted

     Cyril Galvin

     Meetings Secretary

 

102nd Annual Meeting Minutes:

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