Miocene‐Pliocene exhumation along the west Salton detachment fault, southern California, from (U‐Th)/He thermochronometry of apatite and zircon

Abstract

The Salton Trough is the northernmost segment of the active Gulf of California oblique rift system. The main rift‐related structure in the western Salton Trough is the low‐angle west Salton detachment fault (WSDF). Footwall and hanging wall apatite and zircon (U‐Th)/He ages record a significant contrast in thermal history across the WSDF, confirming Pliocene normal slip along the fault. Apatite (U‐Th)/He ages record rapid exhumational cooling from ∼5 to ∼2 Ma, consistent with the timing of accelerated tectonic subsidence recorded in WSDF hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern San Andreas fault in the Salton Trough. Our results indicate that the WSDF caused at least 2.3–4 km of exhumation and >8–10 km of approximately E directed horizontal extension since ∼5 Ma. Slip rate of the WSDF at Yaqui Ridge was likely in the range of ∼2.3–5 km/Ma from ∼7 to ∼2 Ma. The WSDF may have been active well before ∼5 Ma. Middle Miocene apatite (U‐Th)/He ages from samples at high elevations have steep age‐elevation gradients and suggest that exhumation may have initiated by ∼12 Ma, about when subduction ceased along a large segment of the Baja California margin and consistent with the age of onset of extension in northeastern Baja California.