27-7 Kinematic and Erosional Response to the Passage of the Shatsky Rise Conjugate in the Eastern Mojave Desert

Session: Evolution of Cordilleran-type orogenic systems

Presenting Author:

Authors:

Abstract:

The upper plate response to flat-slab subduction is not well understood, especially in cases where slab-flattening is related to subduction of aseismic ridges or oceanic plateaus. This is particularly relevant in the Mojave Desert region of southeastern California where ­– based on observations supporting removal of mantle lithosphere and lowermost crust, underplating of trench-derived accretionary sediments far inboard of the trench, fluid-fluxed melting to produce peraluminous granites, and hydration (further east) of mantle lithosphere – the hypothesis of flat-slab subduction seems well supported.  Laramide flat-slab tectonics is widely attributed to acceleration in relative convergent velocity coupled with increased slab buoyancy due to subduction of two oceanic plateaus, the Shatsky Rise conjugate (SRC) in the northern Mojave (90-75) and the conjugate Hess Rise (70-60 Ma) in the south-central Mojave. Upper-plate deformation kinematics in the Mojave, during the purported flat-slab subduction, are variable along orogenic strike with both widespread Late Cretaceous extension and local shortening deformation. Widespread cooling of Mojave crust evident in moderate- to low-temperature thermochronometry has been interpreted to record extensional and erosional exhumation, and subduction refrigeration.  Published geodynamical models to address the evolution of elevation of the Mojave associated with flat-slab subduction do not adequately honor the geologic constraints; the underplated yet mobile Farallon plate expelled asthenosphere, and was isostatically coupled to North American lithosphere.  Accounting for the (variable) thickness of plateau basalt and partial-melt-depleted underlying peridotite of the SRC would predict a topographic wave supported by flexural isostasy to propagate through the upper plate, with a shoulder on the NW margin.  Evidence to support localized uplift along the hypothesized SRC trajectory include the Kingman Arch, a regional basement high wherein Miocene sedimentary and volcanic rocks lie nonconformably on Mojave Province basement; Late Cretaceous cooling ages below the sub-Miocene unconformity; and a change from dominant NE-SW Late Cretaceous extension directions to top-NW Late Cretaceous extension in the Death Valley region. We present evidence for a complex kinematic landscape consistent with variable gravitational potential energy gradients influenced by the geometry of the SRC and thermochronology studies that support a Late Cretaceous age for erosional exhumation.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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