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Geologic setting and lithologic column of the Cajon Pass Deep Drillhole
Author(s) -
Silver Leon T.,
James Eric W.
Publication year - 1988
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl015i009p00941
Subject(s) - geology , gneiss , geochemistry , epidote , metamorphic rock , petrology , chlorite , quartz , paleontology
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.