Age, geochemical composition, and distribution of Oligocene ignimbrites in the northern Sierra Nevada, California: implications for landscape morphology, elevation, and drainage divide geography of the Nevadaplano

Eocene-Early Miocene paleotopography of the Sierra Nevada-Great Basin-Nevadaplano based on widespread ash-flow tuffs and paleovalleys

“…Total Zr concentration ranges from 136 to 83 ppm (mostly ≥98 ppm) in whole-rock samples and is as low as 76 ppm in glass shards (analyzed by Cassel et al, 2009a). This range probably results from crystallization and separation of zircon and allows use of Zr as an indicator of magma evolution.…”

“…This range probably results from crystallization and separation of zircon and allows use of Zr as an indicator of magma evolution. Samples with high Zr concentrations (H07-230 and H01-61) are least evolved, whereas samples with the lowest Zr concentrations (H08-35 and the shard samples of Cassel et al, 2009a) Intracaldera (H00-101, H08-33, H08-35, H10-101) White Rock Canyon (H08-58)…”

“…It is now well established that the Great Basin (western United States) was an erosional highland in the middle Cenozoic, following crustal thickening during Mesozoic-early Cenozoic shortening, batholith emplacement, and shallow slab subduction (e.g., Dilek and Moores, 1999;Humphreys et al, 2003;DeCelles, 2004;Geosphere, February 2012Dickinson, 2006Best et al, 2009;Cassel et al, 2009aCassel et al, , 2009bColgan and Henry, 2009;Ernst, 2010;Henry and Faulds, 2010). Major river systems drained this highland both west to the Pacifi c Ocean and east to the Uinta Basin ( Fig.…”

“…Based on stable isotope and organic molecule paleothermometry and altimetry, together with detrital zircon geochronology, the Eocene-Oligocene Sierra Nevada is interpreted to have been at approximately the same elevation (~2.5-3 km at the latitude of Lake Tahoe) as it is today (Horton et al, 2004;Mulch et al, 2006Mulch et al, , 2008Cassel et al, 2009aCassel et al, , 2009bCecil et al, 2010;Hren et al, 2010). In contrast, Huber (1981), Unruh (1991), Wakabayashi and Sawyer (2001), Jones et al (2004), Stock et al (2004Stock et al ( , 2005, and Clark et al (2005) concluded from dated stream incision and gradients that the Sierra Nevada was much lower in the Eocene (≤1 km) and attained its present elevation following 1.5-2.5 km of uplift during the Late Miocene and Pliocene.…”

“…Major river systems drained this highland both west to the Pacifi c Ocean and east to the Uinta Basin ( Fig. 1; Henry, 2008;Cassel et al, 2009aCassel et al, , 2009bHenry and Faulds, 2010). The absolute elevation and structural-topographic evolution of this highland in the mid-Cenozoic remain highly controversial, however, particularly the paleoelevation of what is now the Sierra Nevada (Wakabayashi and Sawyer, 2001;Mulch et al, 2006Mulch et al, , 2008Cassel et al, 2009aCassel et al, , 2009bMolnar, 2010) and the timing of extension in northeastern Nevada, especially around the Ruby Mountains-East Humboldt Range metamorphic core complex (McGrew and Snee, 1994;Snoke et al, 1997;McGrew et al, 2000;Howard, 2003;Colgan and Henry, 2009;Druschke et al, 2009;Colgan et al, 2010;Henry et al, 2011;Mix et al, 2011).…”