Dating topography of the sierra nevada

(2004) attribute ~1 km of late Cenozoic uplift to removal of a dense, eclogitic root to the Sierra Nevada batholith.Studies of xenoliths in late Cenozoic igneous rocks support removal of the eclogitic root (Farmer et al., 2002), and coeval, rapid increase in river incision support uplift at that time (Stock et al., 2004).Ash-flow tuffs like those investigated by Cassel et al.are found across the Great Basin, so similar paleoaltimetry could be done across possibly the entire Great Basin.However, a rain shadow should have formed as soon as the Sierra Nevada became a topographic high, so analysis of the older (pre-middle Miocene) isotopic record in the Great Basin is worthwhile.For example, a study of ~40 Ma old mineral deposits in northeastern Nevada (Hofstra et al., 1999) indicates ∂D of meteoric water at that time overlapped with that found by Cassel et al.Analysis of stable isotopes in material that incorporated ancient meteoric water is an important tool for determining paleoelevation.In the western United States, the underlying premise is that precipitation depletes O and D from air moving eastward off the Pacific Ocean and rising over the Sierra Nevada.

In one proposed mechanism, Ducea and Saleeby (1996) and Jones et al.

Continuity of paleodrainages from central Nevada across the Sierra Nevada to the Pacific Ocean demonstrates that the Sierra Nevada was the flank of the Nevadaplano, but does not resolve the absolute elevation of either.

Following Lindgren (1911), consensus until recently was that Sierran uplift occurred in the last 10 Ma, predominantly by westward block tilting of the entire range (e.g., Unruh, 1991; Wakabayashi and Sawyer, 2001).

Conversely, many recent studies argue that the Sierra Nevada was uplifted in the late Mesozoic, and remained high or even subsided in the late Cenozoic (Small and Anderson, 1995; Wernicke et al., 1996).

In this case, late Miocene faulting on its eastern flank represents subsidence of the Basin and Range, rather than uplift of the Sierra Nevada.

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