Links between Mountain Building and Non-Steady State, Heterogeneous Orogenic Crustal Development at Multiple Scales: Insights from the Cretaceous Central Sierra Nevada Arc Flare Up and Bench Canyon Shear Zone

The central Sierra Nevada (CSN) preserves a dextral transpressive orogen coincident with a Cretaceous arc flare up, which resulted in extensive crustal reworking and thickening accompanying mountain building. We propose that crustal development due to tectonomagmatic processes, heterogeneous at spatial scales ranging from entire arcs to single outcrops and temporal scales of 1-100 Ma, exerts significant control on mountain building in orogenic systems. New and existing work on the mid-Cretaceous Bench Canyon shear zone (BCSZ) indicates that it accommodated contraction from >101 to 96 Ma, coincident with voluminous magmatic activity, and represents an intra-batholithic boundary marked by isotopic and barometric breaks. Jurassic-Cretaceous metamorphic strata and syn-tectonic intrusions preserve a history of partitioned ductile to brittle deformation. The BCSZ exemplifies the relationship between tectonomagmatic processes and the surface development of arc and orogenic systems.

Orogenic and arc activity are episodic on 10s to 100 Ma timescales and vary along-strike at scales of 100s to 1000 km. Intra-orogenic processes led to crustal reworking during the Cretaceous CSN flare-up, demonstrated by crustal thickening from 30 to 70 km between 125-85 Ma driven by high magmatic addition (>100 km³/Myr) and volcanic eruption rates and tectonic shortening. Mantle input, ascent of magmas, arc root formation/loss, and downward transfer of host rocks associated with tectonism and magmatism likely resulted in changes to lithospheric thermal, rheology, and density profiles. At 1 to 10s Ma timescales spatial scales of meters and 10s of kilometers, the BCSZ demonstrates: (a) 2 km of differential exhumation, shown by barometric differences between plutons across the shear zone; (b) magmatic crustal reworking, evidenced by the change from distinct isotopic signatures to homogenized magma sources at 95 Ma; and (c) heterogeneous structural development, shown by partitioning of deformation from map to outcrop scales.

The heterogeneity of the CSN, as described above, provides a framework for a conceptual model relating intra-arc processes to mountain building due to variability of isostasy, rheology and thermal structure of the lithosphere at multiple spatiotemporal scales.