Northeastern Geology and Environmental Sciences
v. 24, no. 2, 2002, June
abstracts
Special Issue: Lamont and Plate Tectonics: Geological Society of America (GSA) History of Geology Millenium Symposium: Lamont 1949-1999, Pardee Keynote Symposium for the year 2000
[please note that not all papers in this symposium contained abstracts]
EARTHQUAKE SEISMOLOGY AND PLATE TECTONICS
Jack Oliver
Snell Hall, Cornell University, Ithaca, NY 14853; [email protected]
ABSTRACT: When Maurice Ewing's research group moved, in 1950, from Columbia's Manhattan campus to Palisades, NY to initiate the Lamont Geological Observatory, one justification for the move was the need for a quiet site for operation of a first-class seismograph station. Early installation there of such a station was quickly followed by deployment of a ten-station global network of seismographs and of specialized instruments in a mine, on the sea floor, on the moon, and in various regional arrays of limited duration. The data resulting from this seismological and inductive style of approach to study of the earth, coupled with a steady stream of fine students and research scientists, brought new understanding of Earth and its earthquakes in topics such as crustal and mantle surface waves, microseisms, seismic waves from nuclear explosions, focal mechanisms, seismicity, microearthquakes, and various kinds of seismic wave guide propagation. The wealth of data, the related expertise in analysis, and convenient communication with Lamont geomagneticians as they contributed to the development of the sea-floor spreading hypothesis, put Lamont seismologists in a position to produce many of the important contributions that seismology would make to the early development of plate tectonics during the great paradigm shift of the 1960s, and thereafter. Those of us caught up in that effort were privileged to experience that thrill of discovery and that opportunity to make major contributions to science that scientists commonly seek.
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MARINE MAGNETIC ANOMALIES AND THE RECONSTRUCTION OF THE WORLD
J.R. Heirtzler
NASA Goddard Space Flight Center, Greenbelt, MD 20771
ABSTRACT: The main contribution of the Lamont magnetics program to the development of plate tectonics theory was three fold: (1) It showed that magnetic anomalies in the oceans are linear and symmetric about the ridge axis. (2) It developed a geomagnetic reversal of time scale for the last 76 million years. (3) It used the above two results to show that seafloor spreading has occurred in all the major oceans and can be used to reconstruct the positions of tectonic plates through 76 million years. If this motion is extrapolated to earlier times, one sees how the oceans developed and most of the tectonic plates and landmasses of the Earth originally fit together.
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LAMONT HISTORY TALK: RADIOGENIC ISOTOPE TRACERS AND PLATE TECTONICS
Karl K. Turekian
Department of Geology & Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109
ABSTRACT: When I came as a new graduate student to Columbia in 1949, Lamont Geological Observatory was being established. My recruiter and mentor, Larry Kulp, had determined to make a major commitment of Lamont to the field of geochronometry. My assigned thesis topic was to use the presumed monotonic growth of radiogenic 87Sr in the crust over time and its record in the oceans as seen in limestones over the ages as a chronometric tool. As I worked on determining which limestones I would analyze and their Sr concentrations, Paul Gast, who had arrived as a graduate student and was at the Department of Terrestrial Magnetism learning thermal ionization mass spectrometry techniques to bring to Lamont, showed that the three limestones of markedly different ages that he analyzed showed no monotonic increase with time and the chronometric premise of my thesis was destroyed. So I figured that I'd better find out more about the geochemistry of Sr. I had to wait for subsequent developments to understand what went wrong. The 87Sr/86Sr in limestones over time proved to be a complex pattern and Garry Brass, one of my students at Yale, demonstrated that, at least for the Cenozoic, the 87Sr/86Sr curve could be explained as a mix of strontium from the continents and from a mantle source such as basalt. Subsequent work in mid-ocean ridge basalts and hydrothermal vents identified the way the mantle source was imprinted on the oceans and directly implicated plate tectonics. One component of the plate tectonic controlled signature was the spreading centers, and the other the continental crust as seen in convergence regions such as the Himalayas. The 87Sr/86Sr curve then was an index of plate tectonic variations and the riddle was solved. Subsequent work in my laboratory at Yale on radiogenic 187Os showed another face of the plate tectonic control on the isotopic signatures of the oceans.
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