Tectonics of Pliocene removal of lithosphere of the Sierra Nevada, California

Abstract

Pliocene (ca. 3.5 Ma) removal of dense eclogitic material under the Sierra Nevada has been proposed from variations in the petrology and geochemistry of Neogene volcanic rocks and their entrained xenoliths from the southern Sierra. The replacement of eclogite by buoyant, warm asthenosphere is consistent with present-day seismologic and magnetotelluric observations made in the southern Sierra. A necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase. An increase in potential energy should increase extensional strain rates in the area. If these forces are insuffi cient to signifi cantly alter Pacifi c-North American plate motion, then increased extensional strain rates in the vicinity of the Sierra must be accompanied by changes in the rate and style of deformation elsewhere. Changes in deformation in California and westernmost Nevada agree well with these predictions. Existing geologic evidence indicates that a period of rapid uplift along the Sierran crest of more than ~1 km occurred between 8 and 3 Ma, most likely as a consequence of removal of lower lithosphere. About this same time, extensional deformation was initiated within ~50 km of the eastern side of the Sierra (5-3 Ma), and regional shortening began to produce the California Coast Ranges (5-3 Ma). We suggest that these events were induced by the >1.2 × 10 12 N/m increase of gravitational potential energy generated by the Sierran uplift. Evidence for Pliocene uplift, adjoining crustal extension, and shortening in directly opposing parts of the Coast Ranges is found along nearly the entire length of the Sierra Nevada and implies that lithosphere was removed beneath all of the presentday mountain range. The uplifted area lies between two large, upper-mantle, high-Pwave-velocity bodies under the south end of the San Joaquin Valley and the north end of the Sacramento Valley. These high-velocity bodies plausibly represent the present position of material removed from the base of the crust. Lithospheric removal may also be responsible for shifting of the distribution of transform slip from the San Andreas Table 1) where estimates have been made of the timing of initial extension, the western edge of extension at ca. 5 Ma (thick purple line) and ca. 3 Ma (thick red line), the location of fl oras showing possible uplift (blue dots: T-Table Mountain and W-Webber Lake localities of Wolfe et al. [1998, 1997]), and the extent of tilted Miocene sedimentary rocks along the Sierra/ Great Valley margin (hatched area). The geology in the Sierra is shown in B (after Wakabayashi and Sawyer, 2000) along with the location of the ancestral Yuba River channel plotted in Figure 3 (thin red line) and the positions (bold letters) of other paleochannels plotted in Figure 3: M-Mokelumne River; S-Stanislaus River; and T-Tuolumne River. The position of the Gorda plate's southern edge relative to the Sierra at different times in the past lies along the green lines (from Atwater and Stock, 1998) assum...

Acceleration and evolution of faults: An example from the Hunter Mountain–Panamint Valley fault zone, Eastern California

“…America plate boundary, or due to post-3.5 Ma crustal delamination that led to Sierra Nevada uplift (Jones et al, 2004). In this case, the Hunter Mountain-Panamint Valley fault may have accommodated most of the acceleration.…”

“…However, significant rate differences for different time intervals are possible for individual ECSZ faults. Faults within the ECSZ are constantly evolving, perhaps in response to westward migration of the shear zone (Dokka and Travis, 1990a;Dokka and Travis, 1990b;Stockli et al, 2003;Dixon et al, 1995;Calzia and Ramo, 2000;Jones et al, 2004;McQuarrie and Wernicke, 2005). Figure 1).…”

Crustal redistribution, crust–mantle recycling and Phanerozoic evolution of the continental crust

“…Other sites of proposed lower crustal delamination events include the Sierra Nevada in the western USA Jones et al, 2004;Zandt et al, 2004), the Alboran Sea of the western Mediterranean (Lonergan and White, 1997;Platt et al, 2003;BoothRea et al, 2007) and the Altiplano and Puna Plateaus of the Andes (Kay et al, 1994;McQuarrie et al, 2005). In the latter case extreme crustal thickening over the dipping slab resulted in instabilities in the eclogitic lower crust that led to Pliocene continental lithospheric delamination ( Fig.…”

Influence of climate change and uplift on Colorado Plateau paleotemperatures from carbonate clumped isotope thermometry

“…upper mantle, or the introduction of volatiles to the upper mantle [e.g., Bird, 1979;McQuarrie and Chase, 2000;Humphreys et al, 2003]; (2) mid-Tertiary uplift related to the demise of a Laramide flat slab, where buoyancy is added to the upper mantle by mechanical thinning or chemical modification of the lithosphere [Spencer, 1996;Roy et al, 2005]; and (3) late Tertiary "epeirogenic" uplift associated with regional extensional tectonism, either by convective removal of lithosphere or heating from below [e.g., Bird, 1979;Thompson and Zoback, 1979;Humphreys, 1995;Parsons and McCarthy, 1995;Jones et al, 2004;Zandt et al, 2004]. Quantitative constraints on the timing of uplift therefore have the potential to falsify one or more of these hypotheses.…”