Mantle instability beneath the Sierra Nevada Mountains in California and Death Valley extension

The Southern Sierra Nevada mountain range rapidly uplifted at ≈3.5 Ma simultaneously with a pulse of basaltic volcanism. Xenoliths recovered from volcanics indicate that the range lost a dense crustal root after the Miocene. The vertical motions and removal of the root have been linked to a fast seismic velocity anomaly that extends ≈200 km into the mantle but is offset to the west of the range. With visco-elasto-plastic thermo-mechanical numerical models, we have tested the influence of crustal strength on the kinematics of removal and on the amount of associated uplift. We find that delamination of the dense root is the most likely mechanism for gravitational instability to occur. The model satisfies the Plio-Quaternary vertical motions, the shift of the mantle anomaly to the west of the range, and intense Miocene extension to the east. Based on those results, we propose the existence of a dynamic link between the Sierra Nevada mantle instability and Death Valley rifting. © 2006 Elsevier B.V. All rights reserved.