Composition of modern sand and Cretaceous sandstone derived from the Sierra Nevada, California, USA, with implications for Cenozoic and Mesozoic uplift and dissection

Abstract

The California Sierra Nevada represents the roots of a primarily Cretaceous magmatic arc that is presently being dissected extensively in the south and to a lesser degree in the north, where it is covered by Cenozoic volcanic rocks. The Cenozoic magmatic arc built on top of the Cretaceous arc has been dissected concurrently with northward migration of the Mendocino triple junction, south of which the magmatic arc is inactive. A north-to-south transect from the modern Cascade arc along the Sierra Nevada, therefore, acts as a proxy for evolution from an active undissected magmatic arc to a transitional arc to a dissected arc to intensely uplifted basement.Discriminant analysis of Cascade and Sierra Nevada modern alluvial sand defines four compositional groups and clearly distinguishes volcaniclastic undissected-arc and plutoniclastic uplifted-basement end members. Two intermediate compositional groups are primarily volcaniplutoniclastic and metamorphiplutoniclastic. The former group represents Dickinson's (1985) “transitional arc;” the latter represents “dissected arc.” Sand composition in the southern Sierra Nevada reflects significant uplift, resulting from a combination of latest Cretaceous–Paleogene uplift and late Cenozoic Basin and Range extension (footwall uplift of the western rift shoulder), possibly enhanced by mantle–lithosphere delamination. High concentrations of quartz and feldspar, and near absence of aphanitic lithic fragments are typical of the southern Sierra Nevada and are characteristic of Dickinson's “basement uplift.”Cretaceous sandstone petrofacies of the Great Valley Group (GVG) of western California document dissection of the Cretaceous magmatic arc, as well as erosion of residual orogenic highlands (analogous to modern Taiwan) formed during latest Jurassic arc–continent collision (Nevadan orogeny). When Cretaceous petrofacies data are entered into the modern-sand discriminant analysis as unknowns, they are classified into the modern Cascade/Sierra Nevada groups and a group from Taiwan. The results confirm that the lowest GVG petrofacies represent erosion of the Nevadan suture belt and the undissected post-Nevadan arc. Increasing dissection of the arc occurred during the Cretaceous, but most samples represent “transitional arc,” indicating that even by the latest Cretaceous (Laramide) cessation of arc activity in California, dissection of the magmatic arc was less than what we see today in the central and southern Sierra Nevada. No Cretaceous samples have compositions equivalent to the “basement uplift” of the southern Sierra Nevada.The application of actualistic sand(stone) petrofacies in this study provides important constraints on models for the Cretaceous to modern history of the Sierra Nevada, as well as implications for arc evolution in general.