Paper No. 6
Presentation Time: 11:00 AM
TEMPORAL EVOLUTION OF EXTENSIONAL STRUCTURES IN THE CENTRAL WALKER LANE DISPLACEMENT TRANSFER SYSTEM, NEVADA
The Lone Mountain-Silver Peak extensional complex represents a stepover that accommodated transfer of Miocene to Pliocene dextral displacement along the Furnace Creek fault system to transcurrent faults of the Walker Lane. Displacement in the extensional complex is recorded by brittle extensional and transcurrent faults developed in the upper-plate that overlies a shallowly northwest-dipping detachment surface. Below the low angle extensional fault, the lower plate includes penetratively deformed Precambrian metasedimentary rocks and multiple plutonic phases that record progressive deformation. Early phases of deformation recorded by isoclinal folds defined by compositional layering and attendant axial planar cleavage are demonstrably Late Cretaceous in age. TIMS and SHRIMP U/Pb zircon ages of pre- and syntectonic igneous rocks suggest that this early deformation initiated prior to 92 Ma and continued through at least 85 Ma. The older amphibolite facies fabrics are cut by: (1) a NW- to ENE-striking spaced cleavage associated with open to closed folds defined by older foliation and compositional layering; (2) N-NE-striking spaced cleavage, conjugate cleavage most commonly observed in intrusive rocks, and N- to NE-trending folds; and (3) a NW-striking spaced cleavage that is axial planar to NW-trending broad to open folds. Dioritic intrusive rocks crosscut the oldest structures and record persistence of amphibolite facies conditions to younger deformation. A sample that demonstrably cuts all younger fabrics yielded a SHRIMP U/Pb zircon age (weighted mean 206Pb/238U) of 23.5 ± 0.5 Ma. Late stage exhumation of metamorphic rocks in the extensional complex is recorded by zircon and apatite fission track ages of 11 and 5 Ma, respectively. The progressive deformation observed in the Silver Peak-Lone Mountain transtensional stepover system records regional Late Cretaceous deformation of uncertain affinity followed by late Cenozoic exhumation.