An approximately eighteen square kilometer dolomite breccia mapped by Dibblee and Ehrenspeck in 1988 outcrops at or near the base of the Monterey formation in the southern margin of the SMB. Although not recognized as such by the original mappers, it marks the location of an extensive detachment surface, along which large amounts of fluids flowed that dolomitized and cemented an undulating fault zone. This surface is key to allowing excess folding of Monterey strata relative to older strata.
The dolomite breccia exposed in the old Grefco Quarry road cut is analyzed in detail using outcrop description, macro- and micro- rock fabric description, thin section petrography, X-ray diffraction data, carbon and oxygen isotopes, and trace element geochemistry. Deformation, mineralogy, and isotope signatures are consistent with hydrothermal dolomite (HTD) emplacement from evolved, Monterey-sourced connate fluids that ranged in temperature from 36.6 to 99.5oC. Clasts of dolomite, Monterey siliceous rocks and sandstone from underlying formations are locally supported by >35% micritic dolomite and microcrystalline quartz cement in a dilation breccia. A minimum of 128,000-231,000 cm3 of fluid per cm3 of breccia volume were required to deposit the dolomite cements.
|Advisor:||Behl, Richard J.|
|Commitee:||Loyd, Sean J., Stevens, Lora R.|
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 57/05M(E), Masters Abstracts International|
|Keywords:||Breccia, Detachment, Dolomite, Geology, Isotope, Surface|
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