Incremental Emplacement of the Sierra Nevada Batholith Constrained by U-Pb Ages and Potential Field Data

Abstract

How voluminous granite magmas are emplaced in congested convergent regimes is still debated. The space problem is significant for voluminous batholiths, such as Cordilleran batholiths, because granite magmas cannot create their own way into the crust, and the regional tectonic circumstances are contractional. Both regional and local models have been suggested to solve this problem, but these awkward models are limited in space-time framework without any possibility for generalization to repeated pulses within large Mesozoic batholiths. To investigate the Sierra Nevada batholith (SNB) incremental emplacement at different levels, potential field data were integrated with the age database. Three pulses emplaced incrementally during the Mesozoic era contemporaneously with regional events, suggesting a synkinematic origin and implying the same structural framework. The potential field data reveal that the presence of a synorogenic fault zone accommodates the westward migration of the feeder zone. These feeder zones passed underneath the main batholithic body obliquely from northwest to southeast in the Triassic and Jurassic, before the cessation of magmatism within the SNB underneath the Sierra crest shear zone and Kern Canyon fault zone in the Cretaceous. The structurally controlled feeder zones accommodate the spatiotemporal distribution of the SNB Mesozoic flare-ups magmatism, which is disturbed by small feeder dikes underneath the rising plutons. The rising plutons dissected the western part of the Sierra Nevada during the Mesozoic and extended to the Salinas Valley region to the west of the SNB. In conclusion, bends on thrusts are proposed as an alternative model for the space problem; the higher the orogenic stress, the greater the space available for granite magma.