Geology, geochronology, and geochemistry of the Miocene–Pliocene Ancestral Cascades arc, northern Sierra Nevada, California and Nevada: The roles of the upper mantle, subducting slab, and the Sierra Nevada lithosphere

Abstract

The assemblage of ca. 28-3 Ma volcanic rocks exposed in the Lake Tahoe-Reno region of the northern Sierra Nevada, United States, is interpreted to be part of the Ancestral Cascades volcanic arc. The volcanic rocks are commonly highly porphyritic, including abundant plagioclase with clinopyroxene, amphibole, and rare biotite, and range from basaltic andesite to dacite in composition. Less common are poorly phyric, olivine-and clinopyroxene-bearing basalts and basaltic andesites. Porphyritic lavas dominate composite volcanic centers, whereas the poorly phyric lavas form isolated cinder cone and lava fl ow complexes. Tahoe-Reno arc lavas are calc-alkaline, enriched in the large ion lithophile elements but depleted in Nb and Ta relative to the light rare earth elements, and have highly variable radiogenic isotopic compositions. Compared to the modern south Cascade arc, Tahoe-Reno region basalts are enriched in the light rare earth and large ion lithophile elements and have higher 87 Sr/ 86 Sr and lower 143 Nd/ 144 Nd that are consistent with an old, subduction-modifi ed lithospheric mantle source, such as that proposed for lavas of the Western Great Basin. Melting of the lithospheric mantle may be enhanced by fl uid fl ux from the subducting slab if the Juan de Fuca slab dip is shallow. Andesites and dacites evolved from basaltic magmas by a combination of fractional crystallization and assimilation of lower crustal melts. Available geochronological data indicate that the westward sweep of Cenozoic volcanism through Nevada was associated with steepening of the slab dip, but the dip angle was lower during Miocene-Pliocene arc volcanism than it is today beneath the modern south Cascades.

Geology and geochemistry of volcanic centers within the eastern half of the Sonoma volcanic field, northern San Francisco Bay region, California

“…In general, the migratory volcanic centers of north central California with clear northwardyoung ing trends follow the northward progression of the Mendocino Triple Junction and are in some way associated with thermal perturbations asso ciated with the transition from subduction set ting to a strikeslip setting and the development of a slab window tectonic environment (Fox et al, 1985a;Furlong, 1984;Liu and Furlong, 1992;Furlong and Schwartz, 2004;Dickinson, 1997). Neogene volcanic rocks in northcentral California are roughly coeval with the inactive subductionrelated ancestral Cascade magmatic arc in the BodieLake Tahoe area (Cousens et al, 2008) (Fig. 16B), however, volcanic rocks of the Sonoma and other volcanic fields erupted considerably to the west of the magmatic arc and therefore are unlikely to be related to arc magmatism.…”

“…The north ward younging of volcanism has been attrib uted to the transition from subduction and asso ciated arc volcanism to a slab window tectonic environment (or "slabless window," using the terminology of Liu and Furlong, 1992) along the western margin of the North American plate (Dickinson and Snyder, 1979;Johnson and O'Neil, 1984;Fox et al, 1985a). Recent work (Cousens et al, 2008) has defined a MiocenePliocene Ancestral Cascades arc that was active at about the same time and roughly the same latitude as the volcanic centers of the Sonoma volcanic field. In this paper, we discuss the geo chemical and tectonic setting of volcanic rocks of the Sonoma volcanic field in the context of the northward migration of the Mendocino Triple Junction (Johnson and O'Neil, 1984;Dickinson, 1997) and also compare these rocks to the generally contemporaneous rocks of the Ancestral Cascades volcanic arc (Cousens et al, 2008).…”

“…Recent work (Cousens et al, 2008) has defined a MiocenePliocene Ancestral Cascades arc that was active at about the same time and roughly the same latitude as the volcanic centers of the Sonoma volcanic field. In this paper, we discuss the geo chemical and tectonic setting of volcanic rocks of the Sonoma volcanic field in the context of the northward migration of the Mendocino Triple Junction (Johnson and O'Neil, 1984;Dickinson, 1997) and also compare these rocks to the generally contemporaneous rocks of the Ancestral Cascades volcanic arc (Cousens et al, 2008).…”

Extensional and Transtensional Continental ARC Basins: Case Studies from the Southwestern United States

“…(B) The Late Jurassic arc records sinistral oblique convergence along sinistral strike-slip faults related to rifting along the Gulf of Mexico (Silver and Anderson, 1974). The curvature of the continental margin relative to these faults resulted in transpression in the north and transtension in the south (Saleeby and Busby-Spera, 1992 (Dickinson, 2006;Cousens et al, 2008;Busby and Putirka, 2009). This extension was superimposed across a high, broad plain produced by low-angle subduction time under a contractional strain regime during Late Mesozoic to Paleocene time, termed the "Nevadaplano" (DeCelles, 2004).…”

“…This produced a high plateau, referred to as the "Nevadaplano" by DeCelles (2004) because of its similarity to the modern Altiplano of the Andean arc ( Figure 19.2A). Then, in Eocene to Miocene time, volcanism in the SW US and northern Mexico migrated westward (Figure 19.2A); this has been interpreted to record arc magmatism during slab steepening (Coney and Reynolds, 1977;Dickinson, 2006;Cousens et al, 2008). Other models have been proposed to explain this volcanism (e.g.…”