A detailed study of the structural evolution and thermal history of the Kern Mountains/Deep Creek Range in east-central Nevada has illustrated for the first time how carefully designed thermochronologic transects in concert with geologic mapping and structural studies can be used to reconstruct the geometry and rates of fault slip on extensional fault systems. Continued work on the "detachment faults" in the metamorphic core complexes of east-central Nevada has led to significant revisions to our understanding of how these enigmatic low angle normal faults form and evolve. We now have unequivocal evidence that movement on these regionally extensive faults was distinctly episodic (from Eocene to mid-Miocene) and that the final "detachment fault" is a composite surface that includes several distinct segments that were active at different times. These exciting discoveries have gone a long way towards solving the mechanical paradox posed by detachment faulting. An entirely new extensional structural style has been documented in the Eldorado Mts. region of southern Nevada - one I believe may be widespread, but overlooked. This style involves closely spaced normal faults that begin as near vertical tensile fractures and then rotate very rapidly "domino-style" to low angles during progressive extension. This structural style suggests a runaway phenomena, wherein elevated pore-fluid pressures and low differential stresses of a thin brittle crust results in localized extension fracturing and then rapid fault block rotation - a sort of large scale strain softening. A review of other areas that display this type of geology suggest it may be due to the presence of shallow magma chambers in an extensional environment.
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