Landels-Hill Big Creek Reserve

14 Aug, 01 AM - 18 Aug, 01 AM

The Salinian block, principally underlain by Late Cretaceous granitoids of eastern Sierra Nevada batholith (SNB) affinity, and the Nacimiento block, consisting mainly of Mesozoic Franciscan Complex, are separated by the Nacimiento fault, which has long been, and remains, one of the most puzzling features of California geology. By comparison with the Franciscan-Great Valley-Sierran triad east of the San Andreas fault, the juxtaposition of the Salinian and Nacimiento blocks along the Nacimiento fault implies the removal of a width of 150 km or greater of formerly intervening western arc and inner to central forearc basin. While there is general agreement that major displacements along this structure took place between 75 and 56 Ma, with Neogene to Holocene strike-slip remobilization linked to the San Andreas fault system, there is no consensus on the nature of Late Cretaceous to early Tertiary slip along the fault. Existing hypotheses include: 1) the Nacimiento fault is a sinistral fault with ~ 500 to 900 km offset and 2) the Nacimiento fault is a reverse fault with ~ 150 km offset that placed the Salinian block above the Franciscan m?lange. Alternatively, the Salinian block is younger and, in general (with the notable exception of Coast Ridge belt), represents higher structural levels than the Nacimento block, implying that the missing western arc and portions of the forearc may have been removed by normal faulting. In this model, passive rotation of the fault during rolling hinge-style detachment faulting makes it resemble a thrust. In this work I seek to discern between these hypotheses using geologic mapping and kinematic analysis, U-Pb detrital zircon geochronology, and (U-Th)/He thermochronometry.

Visit #28406 @Landels-Hill Big Creek Reserve

Approved

Under Project # 25204 | Research

Constraining the long-term kinematics of the Nacimiento fault with U-Pb geochronology and (U-Th)/He thermochronometry

faculty - University of Arizona

Reservation Members(s)

Alan Chapman Aug 14 - 18, 2012 (5 days)

Reserve Resources(s) | Create Invoice