Talk:Leon Silver

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Research focus[edit]

I found a useful "old" bio page on a Caltech webpage of the division of Geological and Planetary Sciences at http://web.gps.caltech.edu/faculty/silver/. It's hard to know how much if any of this detail should be worked into the WP bio.~Mack2~ (talk) 03:26, 20 January 2011 (UTC)[reply]

"Leon T. Silver Ph.D., California Institute of Technology W. M. Keck Foundation Professor for Resource Geology, Emeritus Petrologic, Tectonic and Geochemical Evolution of Continental Lithosphere

Professor Silver pursues research in several areas of geology and geochemistry including the petrology and history of the continental lithosphere, the origin and evolution of granitic batholiths, geochemistry and geochronology of uranium, thorium and lead systems and the application of radiogenic isotopes to studies of crustal and planetary evolution.

Regional Tectonics. Professor Silver, together with Professor Jason Saleeby and students, have continued mapping basement structures in the southernmost Sierra Nevada. An extended tectonic history is emerging in keeping with the region's Mesozoic and Cenozoic positions near the active western margin of the American plate. Several major Mesozoic magmatic arcs have invaded the crust which show evidence of pre- and inter-batholithic juxtapositions of contrasting lithospheres sources as far back as the early Mesozoic. This has been noted by Professor Silver and other workers mapping variations in geochemical signatures including lead, strontium and neodymium initial ratios and oxygen isotopic ratios in the youngest arc, the Cretaceous batholith. Professor Silver's recent mapping of the base of the southernmost Sierra Nevada along the Garlock fault zone has revealed that the Cretaceous generation of plutons is detached. They rest in fault contact on intensely deformed orthogneisses, paragneisses and marbles. These gneisses rest, in turn, in low angle fault contact on the distinctive lithologies of the Rand schist, a low temperature-high pressure assemblage of metamorphosed deep water sedimentary and volcanic lithologies. Close tectonostratigraphic correlations of the several plates can be made with a similar structural situation recognized by Professor Silver and students in the Rand mountains, some 60 km to the northeast in the Mojave desert. Graduate student David Wood is extending the known distribution of the low-angle structures to the southwest into the northeastern Tehachapi mountains as part of his dissertational work.

Petrology. The systematic petrologic and geochemical zonation of the Cordilleran batholiths has been the subject of a long-term investigation by Professor Silver, his colleagues and students. With Dr. Catherine Manduca and Professor H.P. Taylor, field, petrographic and isotopic studies have illuminated the petrogenetic consequences of a major lithospheric discontinuity within the western border zone of the Idaho batholith, near McCall, Idaho. A portion of the regionally well-known initial 87Sr/ 86Sr discontinuity has been investigated in detail. Four Cretaceous plutons define a north-trending, steeply-dipping lithosphere boundary between contrasting lithospheric blocks: an accreted oceanic-arc terrane to the west and a Precambrian continental block to the east. The Hazard Creek plutonic complex to the west is alkali depleted and has initial 87Sr/ 86Sr < 0.745, delta 18O 7.6-8.4, and high Sr concentrations, 630-1400 pm. The Little Goose Creek complex contains the major discontinuity with initial Sr and delta 18O values similar to the Hazard Creek complex in the western part rising abruptly from less than Sri, 0.7045, and delta 18O 8.0-9.0 to Srivalues of 0.7080+ and delta 18O, 9.0-10.5 on the east. The adjacent Payette River plutonic complex sustains and supplements the highter values to the west with evidence for a primitive basaltic component. Representative eastern granites of the main body of the Idaho batholith appear to contain a component of cratonal granitic basement. The major transistion takes place in a zone about 6-7 km in width. The Little Goose Creek complex suffered syn-plutonic and post-plutonic Cretaceous deformation oriented along the geochemical discontinuity, suggesting that such a terrane boundary may form a long lasting site for tectonic reactivation.

U-Th-Pb Isotope Geochronology and Geochemistry. Professor Silver continues his long-standing studies of U-Th-Pb behavior in continental crustal rocks and minerals. Utilizing electron microprobe studies of individual zircon crystals, as well as population studies, he has found that zircons which undergo isotopic disturbance appear to contain internally redistributed lead as well as lead loss. This phenomenon must be understood because it limits the geochronological accuracy and precision which can be inferred from measurements in parts of a crystal or groups of parts of crystals. This applies to the highly regarded analyses obtained on parts of crystals by ion microprobe or by conventional analysis of abraded crystals. Primary zonation of uranium and thorium is general in zircons. With geological time, these variations lead to zonation in radiogenic lead accumulations and radiation damage. In many disturbance events, lead diffuses along internal concentration gradients in individual crystals through radiation damaged regions to enhance lower concentration regions (or out of the grains) as the higher Pb sites are depleted. The cumulative isotopic ratios in parts of crystals when augmented by post-disturbance increments of radiogenic lead are dispersed about the mean values for the whole crystals, and, in general, do not satisfy the assumptions involved in various methods of age calculation. In contrast, whole crystals reflect true net lead loss and can be treated by conventional use of "Concordia" calculations. Ion microprobe observations can be powerful approaches to developing improved understanding of these phenomena."

Thanks for the info, it's more than I had to work with when I started this article a few years ago. Abebenjoe (talk) 22:53, 9 September 2011 (UTC)[reply]


Please include one of these pictures from his times at nasa apollo program in the article http://astronautfashions.tumblr.com/post/26867041470/can-you-handle-this-epic-contribution-from

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Reportedly passed on...[edit]

Noted space history author Andrew Chaikin reports on FB, "Another giant of Apollo has passed: Caltech geologist Lee Silver, who helped train the astronauts to explore the moon. He was a fabulous teacher and made an enormous contribution to Apollo. ..."

Condolences to those that knew him personally. 142.167.142.230 (talk) 16:25, 2 February 2022 (UTC)[reply]

Founding editor of this article[edit]

As the person that started this article, after watching HBO's mini-series on DVD back in in 2008 or so, I was shocked that Lee Silver didn't have a Wikipedia page. From the little I knew of him, I created this article as a stub. It has grown substantially ever since. I'm grateful that other editors have filled in the holes of the knowledge of such a great scientist. It's always shocking when writing about someone, even when one doesn't know them personally like me, that eventually they die. I think Lee Silver is one of the more underrated people associated with Project Apollo, and I'm glad this article brings his accomplishments to light. May Lee Silver's memory be a blessing.--Abebenjoe (talk) 04:12, 28 May 2022 (UTC)[reply]

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