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P‐wave image of the upper mantle structure of central California and southern Nevada
Author(s) -
Biasi Glenn P.,
Humphreys Eugene D.
Publication year - 1992
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/92gl00439
Subject(s) - geology , lithosphere , mantle (geology) , subduction , transition zone , volcano , seismology , mantle convection , foothills , cenozoic , mantle wedge , geophysics , tectonics , paleontology , structural basin , ecology , biology
We image the upper mantle velocity structure of central California and southern Nevada by inverting teleseismic P ‐wave residuals. Beneath the southern Great Valley and adjacent Sierran foothills 4% high velocities extend to a depth of 200–240 km. The magnitude and the depth extent of this anomaly suggest that it is sinking lithosphere. Possible sources of lithospheric material include fragments of slab from Laramide or post‐Laramide time or perhaps North American mantle lithosphere removed from neighboring regions. A west to east contrast from high to low velocities in the shallow mantle beneath the Sierra Nevada correlates with crustal contrasts from low to high heat flow and low to high seismicity, suggesting that the high velocities beneath the western foothills correspond to mantle lithosphere relatively chilled and strengthened by sub‐horizontal Cenozoic subduction. In southern Nevada, low velocity mantle is imaged along the SW extension of the St. George Volcanic lineament, and high velocity mantle is found to the NW beneath most of the Miocene SW Nevada Volcanic Field. Variations in partial melt content most simply explain upper mantle velocity contrasts observed there.