LATE CRETACEOUS AND LATE TERTIARY STRUCTURAL EVOLUTION OF TURTLEBACK STRUCTURES WITHIN THE CENTRAL WALKER LANE DISPLACEMENT TRANSFER SYSTEM, WESTERN GREAT BASIN

Miocene to Pliocene dextral displacement along the Furnace Creek fault system and transcurrent faults of the Walker Lane were kinematically linked via the Silver Peak-Lone Mountain transtensional stepover. Displacement transfer was accommodated by extensional and transcurrent faults in a brittle upper-plate underlain by a shallow northwest-dipping decollement. Displacement along the basal decollement exhumed a lower plate assemblage of greenschist to amphibolite metamorphic tectonites exposed in the cores of northwest-trending turtleback structures of the Silver Peak-Lone Mountain extensional complex. The lower-plate is composed of deformed Precambrian metasedimentary rocks and several generations of igneous plutons that record a history of progressive deformation that was initiated in the Late Cretaceous and renewed during late Cenozoic extension and exhumation. First generation structures include synmetamorphic centimeter-scale tight to isoclinal folds of compositional layering(S1a) with an associated axial planar cleavage(S1b). Second generation structures include open to close folds with a NW- to ENE-striking spaced cleavage(S2). Third generation structures are defined by a N- to NE-striking spaced cleavage(S3) within metasedimentary rocks, a conjugate cleavage set within intrusive rocks(S3a and S3b), and N to NE-trending folds. Fourth generation structures include a NW-striking spaced cleavage(S4) axial planar to NW-trending broad to open folds. Conventional and SHRIMP U/Pb zircon ages of pre- and syntectonic igneous rocks establish initiation of D1 structures in the Late Cretaceous (92 Ma) with continued deformation after 85 Ma. Younger intrusive rocks cross-cut D1 structures and record amphibolite conditions during subsequent deformation. SHRIMP U/Pb zircon ages indicate that D2, D3, and D4 structures formed after 24 Ma. Final cooling and exhumation of the metamorphic rocks is recorded by zircon and apatite fission track ages of 11 and 5 Ma, respectively. Late stage penetrative structures formed during late Cenozoic exhumation in the Silver Peak-Lone Mountain transtensional stepover. In contrast, first-generation structures have an unclear tectonic significance but are part of a widespread belt of Late Cretaceous metamorphic tectonites in the western Great Basin.