LATE MIOCENE EXTENSION AND PLIOCENE SINISTRAL SLIP IN THE MINA DEFLECTION: FIELD STUDIES IN THE HUNTOON MOUNTAINS, CALIFORNIA-NEVADA

The HM consist of Miocene andesitic-dacitic lava flows, debris flows, and lahars overlain by the 11.4 ± 0.3 Ma (K/Ar, Gilbert et al., 1968) Tuff of Jack Spring (Mtjs) in the north and a 11.399 ± 0.041 Ma (Ar/Ar, Nagorsen-Rinke et al., 2013) latite ignimbrite (Mlt) in the south. These units are overlain in buttress and angular unconformity by 4.08 ± 0.10 (Ar/Ar, Tincher and Stockli, 2009) to 2.996 ± 0.063 Ma (Ar/Ar, Delano et al., in review) basalt lavas, volcanic centers, and scoria deposits (Pb).

The oldest faults in the HM are NE striking, NW dipping normal faults that cut Miocene lahars and Mtjs but do not cut Pb. Palinspastic reconstruction of Mtjs yields a NW extension magnitude of ~0.7 km between ~11.4 and ~4.1-3.0 Ma, yielding a late Miocene to middle Pliocene NW extension rate of ~0.1 mm/yr. The youngest faults in the HM are set of NE striking sinistral faults and associated left-stepping releasing bend normal-dextral faults that cut all units in the HM and offset buttress and angular unconformities. An offset buttress unconformity between Mlt and Pb records 1.4 ± 0.2 km NE sinistral offset yielding a Pliocene sinistral slip rate of ~0.4 mm/yr.

Our studies in the HM area define two main fault styles, late Miocene NW extension and Pliocene NE sinistral slip. The former provides the first clear field evidence for pre-Pliocene deformation and tilting which created paleo-relief in Mtjs and Mlt as suggested by previous field-based studies in the western MD. Summing our NE sinistral slip rate of ~0.4 mm/yr with sinistral slip rates of 0.4-0.5 mm/yr and 0.7-0.9 mm/yr in the Adobe Hills and River Springs areas, respectively (Nagorsen-Rinke et al., 2013; Delano et al., in review), yields a minimum total geologic sinistral slip rate of 1.8-2.2 mm/yr which approaches the GPS sinistral shear rate of ~2.4 mm/yr (Bormann et al., 2016).