Miocene evolution of the western edge of the Nevadaplano in the central and northern Sierra Nevada: palaeocanyons, magmatism, and structure

Abstract

The Sierra Nevada of California is the longest and tallest mountain range in the co-terminus USA, and has long been regarded as topographically very young (, 6 Ma); however, recent work has provided evidence that the range is very old (.80 Ma), and represents the western shoulder of a Tibetan-like plateau (the Nevadaplano) that was centred over Nevada. A great deal of effort has been invested in applying modern laboratory and geophysical techniques to understanding the Sierra Nevada, yet some of the most unambiguous constraints on the Sierran landscape evolution are derived from field studies of dated strata preserved in the palaeochannels/palaeocanyons that crossed the range in Cenozoic time. Our work in the Sierra Nevada suggests that neither endmember model is correct for the debate regarding youth vs. antiquity of the range. Many features of the Cenozoic palaeocanyons and palaeochannels reflect the shape of the Cretaceous orogen, but they were also affected by Miocene tectonic and magmatic events. In the central Sierra Nevada, we infer that the inherited Cretaceous landscape was modified by three Miocene tectonic events, each followed by ,2 -5 Myr of subductioninduced magmatism and sedimentation during a period of relative tectonic quiescence. The first event, at about 16 Ma, corresponds to the westward sweep of the Ancestral Cascades arc front into the Sierra Nevada and adjacent western Nevada. We suggest that this caused thermal uplift and extension. The second event, at about 11 -10 Ma, records the birth of the 'future plate boundary' by transtensional faulting and voluminous high-K volcanism at the western edge of the Walker Lane belt. The third event, at about 8 -7 Ma, is associated with renewed range-front faulting in the central Sierra, and rejuvenation and beheading of the palaeocanyons. Volcanic pulses closely followed all three events, and we tentatively infer that footwall uplift of the Sierra Nevada occurred during all three events. By analogy with the , 11 Ma event, we speculate that high-K volcanic rocks in the southern part of the range mark the inception of yet a fourth pulse of range-front faulting at 3 -3.5 Ma, which resulted in a fourth tilting and crestal uplift event. Cenozoic rocks along the western edge of the Nevadaplano record the following variation, from the central to the northern Sierra: decrease in crustal thickness (and presumably palaeoelevation), decrease in palaeorelief and attendant decrease in coarse-grained fluvial-and mass-wasting deposits, and greater degree of encroachment by Walker Lanerelated faults beginning at 10 -11 Ma. By mapping and dating Cenozoic strata in detail, we show that what is now the Sierra Nevada was, at least in part, shaped by the Miocene structural and magmatic events.

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).…”

“…Slab fallback was completed by 16 Ma, when the arc front reached the position of the eastern Sierra Nevada, and arc extension between 16 and 11 Ma was likely controlled by development of the San Andreas Fault system (south of the triple junction), and direct interaction between the North America and Pacific plates (Dickinson, 2006). The $16 Ma flood basalts were mainly erupted in a backarc position, except for the Lovejoy basalt of California, which erupted within or immediately in front of the arc front (Garrison et al, 2008;Busby and Putirka, 2009). The sea-floor reconstruction is shown at 15 Ma (Dickinson, 1997), showing positions of the triple junction at 15 Ma and 10 Ma (see also Atwater and Stock, 1998).…”

“…Following the widely used Figure 19.1 of Unruh et al (2003), the perspective shown is an oblique projection of the western Cordillera about the preferred Sierra Nevada-North American Euler pole. The Sierran microplate lies between the San Andreas fault and the Walker Lane belt, which currently accommodates 20-25% of the plate motion between the North American and Pacific plates, and may represent the future plate boundary (see references in Busby and Putirka, 2009). Plate-tectonic reconstructions show a change from more westerly motion to more northerly motion of both the Pacific plate and the Sierra Nevada microplate, relative to the Colorado Plateau, at 10-12 Ma (see references in McQuarrie and Wernicke, 2005).…”

“…Other models have been proposed to explain this volcanism (e.g. Humphries, 2009) but I consider extensional basins that formed within these volcanic belts to be intra-arc basins (see summary in Busby and Putirka, 2009). Plate-tectonic reconstructions of McQuarrie and Wernicke (2005) show that this extension was E-W ( Figure 19.2A).…”

A tale of two Walker Lane pull-apart basins in the ancestral Cascades arc, central Sierra Nevada, California

“…2) and located by global positioning system (GPS; see Supplemental Table S1 1 ). Although abundant field photographs and descriptions have been previously published (Slemmons, 1953(Slemmons, , 1966Noble et al, 1974;Busby et al, 2008a;Busby and Putirka, 2009;Gorny et al, 2009;Busby et al, 2013aBusby et al, , 2013bBusby et al, , 2016, this is the first paper to link outcrop photos (Figs. 6 and 10) with photomicrographs (Figs.…”