REGIONAL DISPLACEMENT ANALYSIS AND PALINSPASTIC RESTORATION OF DISPERSED CRUSTAL FRAGMENTS IN THE SOUTHERN SIERRA NEVADA, CALIFORNIA

The Sierra Nevada batholith (SNB) is a predominantly NNW-trending feature with distinct transverse zonation in structural, petrologic, geochronologic, and isotopic patterns. This zonation is expressed in terms of bulk composition as a west to east variation from mainly mafic to felsic plutonic assemblages. South of 35.5 °N latitude, the depth of exposure increases markedly and aforementioned trends are disrupted in the following ways: 1) the primary zonation of the SNB takes on an east-west trend; 2) western zone rocks are truncated by eastern zone rocks along the proto-Kern Canyon fault; and 3) fragments of shallow-level eastern SNB affinity rocks overlie deep-level western zone rocks and subjacent subduction accretion assemblages (the Rand and Sierra de Salinas schists) along a major Late Cretaceous detachment system. The magnitude of displacement along this detachment system is constrained here by palinspastic reconstruction of vertical piercing points provided by primary batholithic and metamorphic pendant structure and stratigraphy. We present new field, petrologic, thermobarometric, and U-Pb zircon geochronologic data from plutonic and metamorphic framework assemblages in the southern SNB that reveal four potential correlations between dispersed crustal fragments and the SNB autochthon. These correlations include: 1) the Long Valley and Bean Canyon/Tylerhorse Canyon pendants; 2) the Monolith and Quinn Ranch pendants; 3) the Erskine Canyon sequence and metavolcanics preserved in the Tehachapi Valley area; and 4) the Pastoria plate, eastern SNB affinity granitoids and metamorphic pendant rocks preserved in the San Emigdio Mountains, and similar assemblages in the southern Tehachapi Mountains across the restored Garlock fault. Each correlation suggests at least ~50 km of SW-directed transport and excision of at least ~5 km of crust along the Late Cretaceous detachment structure. The timing and pattern of regional dispersion of crustal fragments in the southern SNB is most consistent with Cretaceous extensional collapse above the underplated schists. This interpretation is at odds with models linking disruption of the southern SNB to post-Cretaceous dextral transpression, Miocene transtension, and Cretaceous west-directed thrusting.