Linking Sierra Nevada, California, uplift to subsidence of the Tulare basin using a seismically derived density model

Abstract

Seismic tomography has previously imaged the high-velocity “Isabella anomaly” southwest of the Sierra Nevada beneath the Tulare basin, a region of ~1 km of anomalous Pliocene subsidence. Additionally, it has been proposed that the eastern Sierra has risen 1–2 km since the Miocene in response to removal of dense lithospheric material. The Isabella anomaly has been variably interpreted as either this lithospheric material or a neutrally buoyant stalled fragment of the Farallon slab. To discriminate between these two, we estimate upper mantle density variations from seismic velocities and show that the estimated mass anomaly accords with 60 km of cold lithospheric material removed from beneath the southern Sierra, sufficient for 1.3 km of range uplift. A flexural model of the surface response to mantle loads predicts 1.3–1.7 km of anomalous subsidence of the Tulare basin, several hundred meters more than is observed. Nevertheless, beam-formed receiver functions show up to 10 km of crustal thickening beneath the basin, which we attribute to viscous response of the crust to mantle loading. This anomalous crustal thickness, the post-Miocene subsidence of the Tulare basin, and the uplift of the Sierra can all be explained by redistribution of cold continental mantle lithosphere; therefore, the Isabella anomaly is more plausibly such continental material than a stalled Farallon slab fragment.