LITHOSPHERIC STRENGTHENING AND INDIRECT TECTONOMAGMATIC LINKS DURING MID-CRETACEOUS OROGENESIS IN THE CENTRAL SIERRA NEVADA
This new synthesis contradicts previous models invoking direct tectonomagmatic links in arcs: magmatism did not control the location, intensity, or kinematics of intra-arc deformation, nor did shear zones control the spatiotemporal patterns of magmatism. Arc and orogenic processes instead interact indirectly by driving the evolution of lithospheric architecture (e.g. thickening; compositional stratification), modifying these same processes in turn. The waning of intra-arc deformation coeval with continued contraction in the Cordilleran foreland indicates that arc lithosphere strengthened as flare-up magmatism proceeded. Potential causes include: lithospheric thickening; increasing additions of competent intrusions that crystallized quickly relative to strain accumulation; disruption of through going, crustal-scale shear zones; and mafic residue accumulation in the deep lithosphere. In addition to changing plate-scale boundary conditions, lithospheric evolution likely played a significant role in the shifting of Late Cretaceous deformation observed within the arc and across-strike of the SW US Cordillera. We highlight the need for a whole-orogen perspective, incorporating the impacts of arc activity and evolving lithospheric architecture, in interpreting paleo-dynamics from continental deformation in convergent margins.