Depths and temperatures of %26lt; 10.5Ma mantle melting and the lithosphere-asthenosphere boundary below southern Oregon and northern California

作者：Till Christy B^*; Grove Timothy L; Carlson Richard W; Fouch Matthew J; Donnelly Nolan Julie M; Wagner Lara S; Hart William K

来源：Geochemistry Geophysics Geosystems, 2013, 14(4): 864-879.

DOI：10.1002/ggge.20070

• High Lava Plains
• Cascades arc
• Modoc Plateau
• lithosphere-asthenosphere boundary
• thermometry
• depth of melting
• high alumina olivine tholeiite

Plagioclase and spinel lherzolite thermometry and barometry are applied to an extensive geochemical dataset of young (%26lt;10.5Ma) primitive basaltic lavas from across Oregon%26apos;s High Lava Plains, California%26apos;s Modoc Plateau, and the central-southern Cascades volcanic arc to calculate the depths and temperatures of mantle melting. This study focuses on basalts with low pre-eruptive H2O contents that are little fractionated near-primary melts of mantle peridotite (i.e., basalts thought to be products of anhydrous decompression mantle melting). Calculated minimum depths of nominally anhydrous melt extraction are 4058km below Oregon%26apos;s High Lava Plains, 4151km below the Modoc Plateau, and 3760km below the central and southern Cascades arc. The calculated depths are very close to Moho depths as determined from a number of regional geophysical studies and suggest that the geophysical Moho and lithosphere-asthenosphere boundary in this region are located in very close proximity to one another (within 510km). The basalts originated at 11851383 degrees C and point to a generally warm mantle beneath this area but not one hot enough to obviously require a plume contribution. Our results, combined with a range of other geologic, geophysical, and geochemical constraints, are consistent with a regional model whereby anhydrous mantle melting over the last 10.5Ma in a modern convergent margin and back arc was driven by subduction-induced corner flow in the mantle wedge, and to a lesser extent, toroidal flow around the southern edge of the subducting Juan de Fuca and Gorda plates, and crustal extension-related upwelling of the shallow mantle.

• 出版日期2013-4