ARE DEFORMATION AND MAGMATISM LINKED IN ARC OROGENS? MULTI-SCALE TECTONOMAGMATIC RELATIONSHIPS AND OROGENIC EVOLUTION DURING ARC FLARE-UPS

Arc orogens such as the central Sierra Nevada of California display multi-scale heterogeneous structural development coeval with high-volume magmatism. Numerous tectonomagmatic links during the mid-Cretaceous central Sierra arc flare-up have been proposed ranging from rheological weakening of arc crust and return flow of host rocks in response to voluminous magmatism, to deformation migration following migrating arc magmatic and thermal axes, to shear zones creating space for pluton emplacement. Spatially and temporally heterogeneous deformation, revealed by a new synthesis of map, field, and age data, indicate more indirect and nuanced links between evolving deformation partitioning and coeval arc activity.

Fabric and structural development are consistent with a protracted transition, rather than abrupt change, from widespread contraction to localized dextral transpression. Rather than following arc magmatic and thermal axis migration, deformation was partitioned across the active and dynamic region of arc crust. There is no clear spatial or temporal relationship between pluton emplacement and shear zone location, timing, or kinematics. Solid state fabrics in mid-Cretaceous plutons are limited to localized shear zones, indicating that these intrusions represent inclusions that are more competent than surrounding wall rocks at orogenic strain rates. Synmagmatic shear zones and fabric development reflect partitioned far-field stresses modulated by the structural impacts of arc and orogenic crustal processes.

Arc and orogenic activity extensively rework the lithosphere from the surface to the mantle wedge, driving processes which modify the magmatic and tectonic expression of subduction. Detailed reconstructions of magmatic and tectonic histories interpreted within more realistic conceptual frameworks of the potential multi-scale interactions between deformation, arc activity, and subduction dynamics are needed to unravel the physical evolution of convergent margins.