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Geologic setting and lithologic column of the Cajon Pass Deep Drillhole

Silver, Leon T. and James, Eric W. (1988) Geologic setting and lithologic column of the Cajon Pass Deep Drillhole. Geophysical Research Letters, 15 (9). pp. 941-944. ISSN 0094-8276. doi:10.1029/GL015i009p00941.

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The Cajon Pass Deep Drillhole penetrates a late Tertiary basin developed on crystalline basement in the SW Mojave Desert, 4 km from the San Andreas fault. Cores, continuous cuttings and geophysical logs from phase I show great diversity in rock types, structure, and alteration. The hole encountered Cajon formation arkoses; granodiorite/tonalite; unusual megacrystic granite and augen gneiss; granitic and pelitic gneisses with quartzite; quartzofeldspathic orthogneiss cut by sheets of hornblende gabbro; and interlayered mafic and quartzofeldspathic orthogneisses with rare calcsilicate intervals. Foliation and compositional layering have low dips throughout the column and layered gneisses contain 10-cm-scale recumbent folds. Faults and alteration zones bound several rock units with low apparent dips. Basement cores are typically cut by steep fractures, <1 mm wide, that contain zeolites±calcite or chlorite-epidote. Fractures and faults decrease in abundance with depth.

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Additional Information:© 1988 by the American Geophysical Union. Received April 6, 1988; revised July 14, 1988; accepted July 14, 1988. Synthesis of the column involved major Contributions from Epoch, Inc, especially D. Milham and R. Behl. Assistance by the U.S.G.S. curatorial facility staff, especially W. Campbell, F. Raup, D. Volturno, and W. Linenburger was invaluable. Meticulous reviews by K. Meisling and R. Weldon are appreciated. This work supported by the National Science Foundation and DOSECC. Contribution No. 4635 of the Division of Geological and Planetary Sciences, California Institute of Technology.
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Subject Keywords:Exploration Geophysics: Downhole methods; Information Related to Geographic Region: North America; Mineralogy, Petrology, and Rock Chemistry: Composition of the crust
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Caltech Division of Geological and Planetary Sciences4635
Issue or Number:9
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Official Citation:Silver, L. T. and E. W. James (1988). "Geologic setting and lithologic column of the Cajon Pass Deep Drillhole." Geophysical Research Letters 15(9): 941-944.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39281
Deposited By: Tony Diaz
Deposited On:10 Jul 2013 17:59
Last Modified:09 Nov 2021 23:43

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