Abstract

Geological studies of mantle xenoliths entrained in late Neogene–Quaternary lavas from the southern Sierra Nevada region and regional geophysical studies suggest that the high-density mantle lithosphere that formed beneath the Sierra Nevada batholith in conjunction with arc magmatism is being convectively removed as a “drip” structure. This structure, as imaged seismically, is roughly cylindrical in shape with a diameter of ∼100 km, and extends to ∼225 km depth. Centered above this structure is a region ∼120 km in diameter that is undergoing active subsidence relative to adjacent regions. Such subsidence is seen in the active fluvial-alluvial sediment flooding of mountainous topography of the southwestern Sierra and in the development of the adjacent Tulare Lake basin of the San Joaquin Valley. Dynamic modeling of such upper-mantle drip structures predicts a phase of overlying surface subsidence during the most vigorous phase of drip formation. The southern Sierra upper mantle drip and the overlying crust appear to be in this phase of their dynamically coupled evolution.

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