Geochemistry of the volcanic rocks of the Saline Range, California; implications for mantle composition and involvement in extension beneath the Basin and Range.

Abstract

Actively upwelling asthenospheric melts dominate the sources of Plio - Pleistocene volcanic rocks epsilon sub Nd nearly equal +1 and super 87 Sr/ super 86 Sr sub i nearly equal 0.7048 exposed in the Saline Range of southeast California. Petrographic, geochemical and isotopic data indicate secondary input from sources within the lithospheric mantle epsilon sub Nd NE-8.0 and super 87 Sr/ super 86 Sr sub i nearly equal 0.7070 and silicic continental crust epsilon sub Nd nearly equal -15.0 and super 87 Sr/ super 86 Sr sub i nearly equal 0.7200. The oldest volcanic rocks involved with extension in the Saline Range show petrographic evidence sieved plagioclase and resorbed quartz xenocrysts of mixing between a mafic source and a silicic source. Isotopic data indicates the mafic source is asthenospheric mantle. These data support the hypothesis that Saline Valley is undergoing active rifting. Isotopic data indicates Mesozoic Sierra Nevada crust, emplaced beneath Panamint Valley through west-dipping, low-angle detachment faults, is not present beneath Saline Valley. North of the Hunter Mountain Fault, the Death Valley-Furnace Creek Detachment Fault must reach the base of the crust prior to intersecting the Sierra Nevada Batholith. This can be accomplished if the Death Valley-Furnace Creek Detachment Fault passes through the ernst at nearly equal 15 degrees dip. Isotopic data from this study combined with data from others indicates undepleted asthenospheric mantle is present from the Death Valley area to the Lake Mead, Nevada area. These data show that recognizable heterogeneities within the mantle exist on the order of at least several 100 km super 2 .

48 samples from this reference