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Sand injectite architecture and petrographic characteristics of the Panoche Giant Injection Complex (PGIC), Panoche Hills, CA
The Panoche Giant Injection Complex (PGIC), Panoche Hills, CA is one of the best exposed sand injectite complexes in the world with all of the constituent units observable over a 300-400 km2 area. The PGIC offers unparalleled access to a regionally developed kilometer-scale sand injectite complex making it an invaluable outcrop analogue for similar large sand injectite complexes in the subsurface. Previous studies have suggested two potential sources for the PGIC’s intrusions within Upper Cretaceous sedimentary strata; 1) the Upper Panoche Formation and 2) the Dosados Member of the Moreno Formation. In this study, geologic mapping, sedimentary logging, petrographic analyses, and grain-size analyses were utilized to constrain the parent unit involvement in the emplacement of the PGIC in South Dosados Canyon, Panoche Hills, CA. These methods develop the framework and architecture of the sand injectite complex in the study area and characterize the mineralogy and grain size distribution of the architectural elements of the PGIC. In the study area, the Dosados Member is interpreted as the source of most sand injectites observed within the PGIC and is interpreted as the primary parent unit that provided sand to the PGIC. This interpretation is supported by field-based observations of source and injectite stratigraphic relationships in South Dosados Canyon as well as petrographic identification of framework mineral compositions. Grain-size analysis was found to be unsuitable for identifying source and injectite relationships. The Upper Panoche Formation is likely to have acted as a regional pressure cell for the PGIC by supplying high pressure fluids to the stratigraphically higher Dosados Member. This study also compares and contrasts meso- and micro-scale features of parent units and sand intrusions found throughout the course of investigation to better understand the sand injection process.
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