Paper No. 7
Presentation Time: 11:20 AM
STRUCTURAL INHERITANCE AND STRAIN PARTITIONING IN THE CENTRAL WALKER LANE, WESTERN GREAT BASIN
The northwest-trending Walker Lane separates and accommodates differential motion between the Sierra Nevada and the central Great Basin. Motion of the Sierra Nevada block to the northwest is oblique to the Walker Lane and results in transtensional deformation. Incremental extensional strain axes recorded by earthquake focal mechanisms and fault-slip inversion vary from east to west across the Walker Lane and show anticlockwise rotation of 50° from WNW to ENE. In contrast, the regional GPS velocity field increases from 2-3 mm/yr in the central Great Basin to ~14 mm/yr in the Sierra Nevada and is accompanied by clockwise rotation from WNW to NW. The divergence between velocity and strain field trajectories indicate nonplane strain (constriction) deformation in the Walker Lane induced by the obliquity of the velocity field with pre-existing structures. Strain accumulation within the Walker Lane is heterogeneous and defines western and eastern structural domains. The western Walker Lane experiences extension-dominated transtension accommodated by NNW trending structures, and in the eastern Walker Lane deformation is wrench-dominated transtension on NW-trending structures. The strain boundary within the Walker Lane is localized on a long-lived NNW trending structure marking the eastern flank of the Wassuk Range. The structure delimits the eastern margin of the mid-Miocene Yerington extensional complex and fault blocks to the west experienced profound westerly tilts whereas exposures less than 15 km to the east underwent no significant tilting. Westerly tilt of the Wassuk Range by ~60° exposes paleodepths up to ~8.5 km and exhumes a late Mesozoic crustal boundary that had a protracted history of deformation. The boundary now dips ~20° to the east, but with removal of extensional tilt, reconstructs to near vertical. The boundary separates metamorphic tectonites deformed in the mid-Jurassic and in the mid-Cretaceous on the west from semi-brittlely deformed metaclastic and metavolcanic rocks deformed during Late Jurassic and Early Cretaceous to the east. The structure was reactivated in the Late Cretaceous as a brittle shear zone with the timing of deformation constrained by plutons that pre- and post-date deformation yielding U-Pb zircon ages of 91and 88 Ma, respectively.