HIGH-RESOLUTION ANIMATED TECTONIC RECONSTRUCTION OF THE DEATH VALLEY REGION

We have developed a new Miocene-Holocene tectonic reconstruction of the Death Valley region. A comprehensive database of offset features and fault slip-rates constrains the kinematic model. Map-view deformation is interpolated in 0.1-Myr time-steps. Two major tectonic transitions emerge: at ca. 12 Ma, rapid extension (~14-15 mm/yr), accommodated on regional detachment faults, began between the Sierra Nevada and Spring Mountains; at ca. 6 Ma, Sierran motion relative to stable North America slowed by ~10 mm/yr, coincident with the southern San Andreas fault relocating onto the Gulf Extensional Province. From ca. 6-3.5 Ma, slip rates on western fault systems of the region accelerated as intraplate strain localized in a zone ~100 km wide east of the Sierra Nevada. From ca. 3.5-0 Ma, Sierra Nevada-North American relative velocity approached modern values of ~11.5 mm/yr.

Mechanical coupling between brittle crust and continental mantle lithosphere appears to have strengthened at ca. 6-3.5 Ma, coincident with an intraplate rheological feedback. Thermo-kinematic modeling and crustal thickness reconstructions suggest that the upper crust was decoupled from lower crust/mantle lithosphere by weak middle crust prior to ca. 6 Ma. Subsequent exhumation, thinning, cooling, and embrittlement of the weak middle crust enhanced crust-mantle coupling via juxtaposition of gabbroic lower crust beneath exhumed/embrittled middle crust. This enabled mantle flow to drive upper-crustal strain, focusing dextral shear into the ~100 km-wide zone east of the Sierra Nevada.

Enhanced crust-mantle coupling following mid-crustal exhumation/embrittlement coincided with the northward propagation of dextral shear into the Walker Lane belt. A NW-oriented, dextral deflection in lithosphere-asthenosphere boundary slope, with magnitude and azimuth similar to post-6-3.5 Ma Sierra Nevada motion, suggests penetrative dextral shear of the entire lithosphere.