Reinterpretation of the Mesozoic thrust complex of the southern Spring Mountains, Nevada

Warren Harding Allen, University of Texas at El Paso


The east verging Keystone thrust fault in the southern Spring Mountains west of Goodsprings, Nevada, is mapped with a sharp bend in its trace near Keystone Wash. This bend was previously explained in the context of out-of-sequence thrusting and a salient-recess relationship along the thrust system; a simple redirection of the Keystone thrust to a north verging thrust. Recent geochronological studies indicate that the east verging Keystone thrust to the north of Keystone Wash formed between 83-103Ma. Approximately 5 kilometers to the east a north verging branch of the fault system overlies rocks as young as 99Ma. At the location of the bend is a dextral strike slip fault system; the Ironside fault zone. This study combines these published data with remapping and structural analysis of the bend to conclude that the ~EW trending, north verging branch of the “Keystone thrust” is a distinct, younger structure, referred to here as the Key-Monster thrust. The Key-Monster system is interpreted as a complication, possibly reactivation, of older thrusts during a change in regional kinematics from ~EW contraction to ~NS contraction. The Ironside fault zone interpreted as a scissoring accommodation zone for the Keystone thrust bend. The Keystone east of the Ironside fault zone is reinterpreted here as a distinct, younger N directed thrust, the Key-Monster. The Green Monster thrust complex, to the west of the Keystone system, is truncated on west and east ends. The western extension of the Green Monster thrust is truncated by the Neogene Stateline Fault and the Green Monster thrust may be the remnants of a longer thrust now displaced by that fault. Restoration of the State Line fault lines up the Green Monster with the Nopah-Gerstley thrust in California suggesting a possible relationship. Previous to this interpretation the thrust complex at Goodsprings was considered an out-of-sequence thrust complex.

Subject Area


Recommended Citation

Allen, Warren Harding, "Reinterpretation of the Mesozoic thrust complex of the southern Spring Mountains, Nevada" (2015). ETD Collection for University of Texas, El Paso. AAI10000770.