Geology and geochronology of the Pine Forest Range, northwest Nevada: Stratigraphic, structural and magmatic history, and regional implications

The Pine Forest Range, northwest Nevada, exposes a section of Paleozoic and Mesozoic rocks that were multiply deformed and metamorphosed and widely intruded by plutons in Mesozoic time. Paleozoic strata comprise early(?) Paleozoic to Upper Mississippian clastic sedimentary rocks, mafic to silicic volcanic and volcaniclastic rocks and limestone, overlain unconformably by Permian and Permian(?) limestone, clastic sedimentary rocks and chert. Mesozoic strata are late Middle or early Late Triassic to latest Triassic and consist of arc-derived basaltic to andesitic lavas and volcaniclastic rocks, limestone and siliciclastic sedimentary rocks. Facies analysis indicates that Triassic strata were deposited in a deep marine environment and suggests that the area was characterized by active subsidence during early Mesozoic time. Paleozoic and Mesozoic rocks are separated by an unconformity that reflects uplift, tilting and weak folding during the latest(?) Permian to Middle or Late Triassic.; Paleozoic strata exhibit lithologic similarities to those in other volcanic arc sequences of the western U.S. Cordillera, supporting an interpretation of Paleozoic paleogeographic ties between these sequences. The presence of a Permo-Triassic unconformity in the Pine Forest Range represents new evidence that these arc sequences experienced uplift and erosion during the Late Permian-Early Triassic Sonoma orogeny, consistent with an arc-continent accretion model for this orogenic event. Early Mesozoic subsidence in the range is inferred to reflect arc development in an extensional to neutral tectonic regime, possibly in response to changes in plate motion following the Sonoma orogeny.; Two main periods of deformation and metamorphism affected the Pine Forest Range. The first was regional in extent, produced a strain and metamorphic gradient that increases with stratigraphic depth, and appears to have occurred in the hanging wall of a top-to-the-NW bedding-parallel shear zone. {dollar}sp{lcub}40{rcub}{dollar}Ar/{dollar}sp{lcub}39{rcub}{dollar}Ar and U/Pb dating indicate that this deformation was broadly synchronous with intrusion of Middle Jurassic ({dollar}sim{dollar}190-180 Ma) plutons. A second deformation is spatially restricted, affecting rocks only in the aureoles of Cretaceous plutons and increasing in strain and metamorphic grade towards the pluton margins, and represents a combined response to regional NE-SW shortening and forceful pluton emplacement. {dollar}sp{lcub}40{rcub}{dollar}Ar/{dollar}sp{lcub}39{rcub}{dollar}Ar and U/Pb dating confirm that deformation and metamorphism were synchronous with pluton emplacement at {dollar}sim{dollar}108-100 Ma.