Timing of volcanism in the Sierra Nevada of California: Evidence for Pliocene delamination of the batholithic root?

Recent seismic experiments across the southern Sierra Nevada, California, s how that the range lacks a thick crustal root. Xenolith studies indicate th at delamination and loss of much of the lower crust may have occurred betwe en 10 and 3 Ma. We estimate that delamination occurred ca. 3.5 Ma on the ba sis of a sudden pulse of mafic potassic magmatism within and just east of t he Sierra Nevada from 4 to 3 Ma. This pulse interrupted the low level of vo lcanism that had prevailed regionally since 13 Ma. Delamination could have promoted magmatism via decompression melting, heating of the shallow lithos phere by upwelling asthenosphere, and foundering of crustal rocks into the mantle, and could have provided dynamic support to the range. Foundering of the lower crust may have occurred spontaneously, owing to negative buoyanc y, or may have been triggered by extension between the Sierra Nevada and De ath Valley.