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Origin and significance of clay-coated fractures in mudrock fragments of the SAFOD borehole (Parkfield, California)

Geophysical Research Letters

By:
, , ,
DOI: 10.1029/2006GL026505

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Abstract

The clay mineralogy and texture of rock fragments from the SAFOD borehole at 3067 m and 3436 m measured depth (MD) was investigated by electron microscopy (SEM, TEM) and X-ray-diffraction (XRD). The washed and ultrasonically cleaned samples show slickenfiber striations and thin films of Ca-K bearing smectite that are formed on polished fault surfaces, along freshly opened fractures and within adjacent mineralized veins. The cation composition and hydration behavior of these films differ from the Namontmorillonite of the fresh bentonite drilling mud, although there is more similarity with circulated mud recovered from 3479 m MD. We propose that these thin film smectite precipitates formed by natural nucleation and crystal growth during fault creep, probably associated with the shallow circulation of low temperature aqueous fluids along this shallow portion of the San Andreas Fault. Copyright 2006 by the American Geophysical Union.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Origin and significance of clay-coated fractures in mudrock fragments of the SAFOD borehole (Parkfield, California)
Series title:
Geophysical Research Letters
DOI:
10.1029/2006GL026505
Volume
33
Issue:
16
Year Published:
2006
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geophysical Research Letters