The Snake Range Décollement interpreted as a major extensional shear zone

Abstract

Geological and geophysical constraints suggest that the Snake Range décollement of east‐central Nevada is a major Tertiary low‐angle normal fault zone. This interpretation is consistent with all existing data, and alleviates problems that result if large displacement across the décollement is excluded [Miller et al., 1983]. Based on published surface geology and COCORP seismic reflection profiling, we have constructed cross sections that suggest approximately 60 km of normal displacement on the décollement. Advantages of this interpretation over models that exclude large displacement are that it provides for overburden consistent with kyanite‐grade metamorphism of footwall rocks, predicts reasonable crustal thicknesses before and after extension without invoking unexposed mantle‐derived Tertiary intrusions at depth, and explains contrasting metamorphism and structural styles of hanging wall and footwall without requiring an extreme geothermal gradient during regional metamorphism and extensional strain. The present domal shape of the décollement is interpreted to result at least partly from reverse drag above an underlying, younger detachment related to much of the extension in ranges to the west of the Snake Range.