Geology and Geochemistry of the 25 Ma Underdown Caldera Tuffs and the Tuff of Clipper Gap, Western Nevada Volcanic Field, North-Central Nevada

The Stone Cabin Formation, Nevada, USA: Geochemical and Isotopic Indicators of Magma Sources and Crustal Influence in an Eocene Caldera System

“…The two main zones with distinct isotopic signatures across Nevada are the Phanerozoic basement rock to the west and the Precambrian basement rock to the east, with a transition zone between them commonly defined by the 87 Sr/ 86 Sr 0.706 and 0.708 lines (Farmer & DePaolo, 1983;Tosdal et al, 2000). Samples from the Fish Creek Mountains (FCM) were reported by Cousens et al (2019) (Cousens et al, 2019), Underdown Caldera (Little, 2019), and Emigrant Pass volcanic field (Chan, 2020). The red dashed line depicts the change in isotopic signature from group 1 to group 2 of this study, corresponding with the red dashed line on the map in Figure 85.…”

“…The red dashed line depicts the change in isotopic signature from group 1 to group 2 of this study, corresponding with the red dashed line on the map in Figure 85. Additional sample data from Fish Creek Mountains (Cousens et al, 2019), Underdown Caldera (Little, 2019), and Emigrant Pass volcanic field (Chan, 2020). The red dashed line depicts the change in isotopic signature from group 1 to group 2 of this study, corresponding to the red dashed line on the map in Figure 85.…”

“…The topographic high generally prevented the spread of ignimbrite deposition to the west and resulted in north, south, and eastward deposition of the ignimbrites, leading them toward the Indian Peak-Caliente Caldera Complex (Best, et al, 2013b). However, the Nine Hill Tuff and the Tuff of Clipper Gap are found from the Sierra Nevada to the northern edge of the White Pine Range, both of which cross the topographic high (Henry & Faulds, 2010;Little, 2019). Horizontal distances are not to scale, but vertical dimensions are significant.…”

“…Table 3 -Composition of mantle and crustal contaminant endmembers in Figure 80 with Harrison Pass pluton data from Wright and Wooden (1991). Emigrant Pass Volcanics (Chan, 2020) nderdown Caldera (Little, 2019) Fish Creek Mountains (Cousens et al, 2019) Kalamazoo Tuff Kalamazoo Tuff (Gans et al ., 1989) Tuff of Cooper s Summit Butte Mountains…”

“…To better define the boundaries of the Transition Zone, the results from this study of the SCF will be used for direct isotopic comparison with other well-studied Eocene to Oligocene caldera and lava complexes found within or on the margins of the Transition Zone. These igneous complexes include the Fish Creek Mountains (Cousens et al, 2019), the Underdown Caldera system (Little, 2019;Tennant, 2018), and the Emigrant Pass Volcanic field (Chan, 2020). (Watts et al, 2019).…”