XENOLITH CONSTRAINTS ON LITHOSPHERIC ARCHITECTURE BENEATH THE MOJAVE AND SIERRA NEVADA AND IMPLICATIONS FOR INTRAPLATE VOLCANISM

Xenoliths of the Western US have been studied for over three decades and have been instrumental in revealing the composition of the deep crust and upper mantle across the diverse terranes of North America. Yet, fundamental questions remain unanswered concerning the nature and origin of the volcanics that erupt xenoliths, particularly their depth of origin, geochemical composition of their source region, and rheological properties of the lithosphere through which these magmas erupt. Here, I review the current state of knowledge on xenoliths from the Sierra Nevada, Owens Valley, and Mojave Desert, and the information they bear on lithospheric architecture and composition beneath these regions, which influenced subsequent regional tectonic events and govern the style and composition of Late Cenozoic intraplate volcanism. A key point of discussion is the dichotomy between the Sierran and Mojave blocks as constrained from deep crustal and upper mantle xenoliths, and the contrasts in Late Cenozoic magmatism and tectonic evolution between these two regions. In addition, I discuss results of recent and ongoing research on the rheological properties (constrained using electron backscatter diffraction mapping) of Sierran vs. Mojave xenoliths and how such properties may influence deep crustal magmatic processes, as well as models of lithospheric strength as a function of depth. I show that even within the relatively narrow confines of the eastern Sierra Nevada to the Mojave Desert, significant lithological and rheological variation exists within the deep crust and upper mantle, and that such heterogeneity is key to understanding the temporal and spatial distribution of continental intraplate volcanism.