Imaging Sierra Nevada lithospheric sinking | CU Experts

The sinking of dense mantle lithosphere farther into the mantle is an often invoked but still poorly understood process in continental development. Such events have been inferred to cause uplift and extensional deformation in areas around the world and back billions of years. Samples of garnet‐rich mantle lithosphere from under the Sierra Nevada were brought up in basaltic eruptions from before 80 million years ago to approximately 8 million years ago but are absent from volcanics after about 3.5 million years ago [Ducea and Saleeby, 1998]. Granitic batholiths like the Sierra Nevada evolve from more quartz poor melts and thus have roots of mafic (quartz‐poor) residuum that remain under the batholith. This residuum, metamorphosed to a dense garnet‐rich rock, apparently sinks together with part of the mantle lithosphere below it at one or more locations beneath the Great Valley.

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