Document Type


Date of Degree Completion

Summer 2019

Degree Name

Master of Science (MS)


Geological Sciences

Committee Chair

Jeffrey Lee

Second Committee Member

Wendy A. Bohrson

Third Committee Member

Chris Mattinson


New geologic mapping and structural studies in the Huntoon Mountain area (HMA), California-Nevada document the volcanic and deformation histories across the south-central Mina Deflection (MD). Our work allows us to (a) test whether present-day GPS predicted sinistral slip rates are the same as geologic slip rates in the southern MD, and (b) determine the kinematics of fault slip is transfer through the MD. The HMA exposes primarily Miocene andesitic-dacitic volcanic rocks overlain by the 12.114 ± 0.006 Ma (40Ar/39Ar sanidine, Petronis et al., 2019) Tuff of Jack Spring and the 11.399 ± 0.041 Ma (40Ar/39Ar plagioclase, Nagorsen-Rinke et al., 2013) latite ignimbrite. These units are overlain in buttress and angular unconformity by basalt lavas and mafic volcanic centers that range in age from 4.08 ± 0.10 (40Ar/39Ar groundmass plagioclase, Tincher and Stockli, 2009) to 2.996 ± 0.063 Ma (40Ar/39Ar groundmass plagioclase, DeLano et al., 2019). The oldest faults in the HMA are NE-striking, NW-dipping normal faults that cut Miocene volcanic rocks, but not Pliocene basalt lavas. The youngest faults in the HMA are ENE-striking sinistral faults and associated left-stepping releasing bend NW-striking normal-dextral faults that cut all units in the HMA and offset unconformities between Miocene volcanic rocks and Pliocene basalt lavas. Offset unconformities record a minimum total Pliocene ENE sinistral and NW dextral slip rates of 0.8 ± 0.4 mm/yr and 0.3 ± 0.1 mm/yr, respectively. Summing our new ENE sinistral slip rate of 0.8 ± 0.4 mm/yr with Pliocene sinistral slip rates from other studies in the southern MD (Tincher and Stockli, 2009; Nagorsen-Rinke et al., 2013; DeLano et al., 2019), yields a minimum ENE sinistral slip rate of 1.9-3.0 mm/yr. Our new net minimum ENE sinistral slip rate of 1.9-3.0 mm/yr is within error of both GPS data constrained elastic block model sinistral shear rate of ~2.4 mm/yr (Bormann et al., 2016) and transrotational modeled rate of 2.1-3.2 mm/yr (DeLano et al., 2019). Our studies have determined that geologic and geodetic ENE sinistral slip rates are the same and the kinematics of fault slip transfer through the southwestern MD are characterized by vertical axis clockwise rotating blocks bounded by ENE sinistral faults.

HM_Plate-1.pdf (67555 kB)
Plate 1 showing geologic map of HMA.

HM_Plate-2.pdf (1529 kB)
Plate 2 showing interpretive cross sections from the HMA.

HM_Plate-3.pdf (681 kB)
Plate 3 showing stratigraphic column from the HMA.