HR: 0800h
AN: T51D-1378    [Abstracts]
TI: Kinematic Model for the Sierra Nevada Frontal Fault Zone, California: Paleomagnetism of the Eureka Valley Tuff
AU: * Rood, D H
EM: dylan@crustal.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, CA 93106 United States
AU: Burbank, D W
EM: burbank@crustal.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, CA 93106 United States
AU: Luyendyk, B P
EM: luyendyk@geol.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, CA 93106 United States
AB: We document the geometry, timing, rates, and kinematic style of Late Tertiary deformation between Sonora Pass and Mono Basin, central Sierra Nevada, California. Observed mismatches between geodetic and geologic deformation rates in the western Great Basin may be primarily due to underestimates of true geologic deformation. Relatively little attention has been paid to the role of permanent deformation between faults, i.e. folding or crustal block rotation. Current slip discrepancies may be accounted for if a significant component of off-fault transrotational deformation is present. We use geologic and paleomagnetic data to address the kinematic development of the Sierra Nevada frontal fault zone (SNFFZ), and to quantify both the elastic and inelastic strain accumulated across the Sierra Nevada-Basin and Range transition since ~9 Ma. The complex structure of this transition, between the regions of Sonora Pass and Mono Basin, may be a result of three distinct modes of dextral shear accommodation (transtensional, transpressional, and crustal thinning). The study area is characterized by four important structural elements that lie between the SNFFZ and Walker Lane Belt: (1) N- to NNW-striking normal and oblique faults, dominantly E-dipping, and associated W-tilted fault blocks; (2) NW-striking dextral faults; (3) ENE- to NE-striking left-lateral oblique faults that may accommodate overall dextral shear through clockwise vertical axis rotations of fault blocks; (4) E- to NE-trending folds, which may accommodate N-S shortening at large-scale left steps in the dextral transtensional fault system. Between Bridgeport and Mono Basins, a regional E- to NE-trending fold is present that affects both the Tertiary volcanic strata and a Quaternary glacial outwash surface. To the west, normal faulting rates on the SNFFZ are 1-2 mm/yr (Bursik and Sieh, 1989). This slip decreases to the north, into the folded region of the Bodie Hills. This kinematic relationship suggests that the region may be an accommodation zone between two linking faults, possibly an active fold that accommodates N-S shortening at a large-scale left step in the range front fault system. We collected ~200 paleomagnetic samples from the Late Miocene Eureka Valley Tuff of the Stanislaus Group at 21 sites over a 125-km-long, E-W transect (from the Sierra Nevada foothills to east of Mono Basin). Stepwise AF demagnetization reveals a stable characteristic remnant magnetization. Our preliminary data suggest 20-40 degrees of clockwise rotation adjacent to faults of the SNFFZ. An expanded dataset aims to identify specific structural domains, quantify differential vertical axis block rotations, and test geometric models of transrotation (i.e. block-specific versus gradational) during transtensional lithospheric deformation.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8109 Continental tectonics: extensional (0905)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: Fall Meeting 2005