A MULTIDISCIPLINARY CONSTRUCTION OF THE 3D THERMO-RHEOLOGICAL STRUCTURE IN CALIFORNIA AND NEVADA: IMPLICATIONS ON THE TRANSTENSIONAL DEFORMATION ALONG THE ACTIVE MARGIN

The thermal architecture of the crust exerts a significant control on rheological and deformational behaviors. In active orogens, recognition of the thermal structure variation may provide insights into the pattern of crustal seismicity, mid-lower crustal rheology, crustal dynamics, and geothermal energy exploration. Here, we integrate multiple datasets and proxies to construct a 3D thermal model across the active transtensional orogen in California and Nevada by combining surface heat flow observations and geophysical data to constrain the seismogenic depth (with a temperature of ~350°C for the onset of quartz to feldspar plastic creep) as well as Moho depth and temperature. We generate steady-state conductive thermal profiles with varying thermal properties (e.g., crustal radioactivity, thermal conductivity, mantle heat flow) within each adaptively sized bin, where we subsequently seek for the best-fit thermal profile through statistical comparison with the temperature-depth constraints from the collated geophysical datasets. The crustal rheology, including viscosity and yield strength, are obtained through interpolating the resultant 3D thermal model with the dislocation creep flow law. Our model yields clusters of elevated thermal structure and weak rheology in the Salton Trough, Coso, Clear Lake, and north-central Nevada. In contrast, the Great Valley, Sierra Nevada, Mojave, and eastern Great Basin display a colder thermal architecture and stronger rheology. The steady-state thermal profile in regions with elevated thermal structure are generally inconsistent with the mid-lower crustal constraints, suggesting that advective processes, such as volcanism and hydrothermal fluid circulation, are actively modifying the crustal temperature. We also evaluate the relationship between thermo-rheological structure with the productivity of earthquake sequences to assess how the physical condition of the crust impacts seismicity and its spatial and temporal variations. Our results can also be used to refine existing crustal dynamic models and provide a novel perspective on the stress state across the western United States.