Geochemical evidence for water‐rock interaction along the San Andreas and Garlock Faults of California

Journal of Geophysical Research
By:  and 

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Abstract

Mesozoic granitoid rocks adjacent to the San Andreas fault in central California have retained their radiogenic Ar for the last 70 m.y. but have, generally, the highest 18O and H2O+ contents and the lowest D contents of all the granitoid rocks in California. The geographical coincidence of the D, 18O, and H2O+ patterns with the present trace of the San Andreas fault leave little doubt that some kind of groundwater circulation system has operated in the vicinity of the fault in central California. Similar isotopic patterns exist in rocks along the Garlock fault. These water‐rock interactions probably took place at temperatures <200°C, although depth, extent, and timing are not resolved. Stable isotope compositions of rocks from many localities of the earth have provided unambiguous proof that meteoric waters have descended to depths at least as great as 8 to 10 km when a heat source such as a cooling pluton was present. Massive circulation of groundwater is common in the upper crust of tectonically active areas and may affect the frictional stress state along major faults. The geochemical evidence for extensive deep circulation of groundwater and the relatively high permeabilities for most rocks of the upper crust recently compiled by Brace (1980) argues against nearly lithostatic fluid pressures as an ambient condition of the upper crust. Groundwater circulation along the San Andreas provides an efficient mechanism for diffusing the heat flow anomaly that arises in heat transport calculations that are based on thermal conduction alone.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Geochemical evidence for water‐rock interaction along the San Andreas and Garlock Faults of California
Series title Journal of Geophysical Research
DOI 10.1029/JB085iB11p06286
Volume 85
Issue B11
Year Published 1980
Language English
Publisher American Geophysical Union
Contributing office(s) California Water Science Center
Description 7 p.
First page 6286
Last page 6292
Country United States
State California
Other Geospatial San Andreas Fault, Garlock Fault