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Petrologic and Geochemical Characterization of Two Cenozoic Felsic Lava Flows, the Jarbidge Rhyolite and Boies Dacite, in NW Knoll Basin, NE Nevada

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Ashlyn Clark

Authors:

Clark, Ashlyn Nicole¹, Jenkins, Travis², Robinson, Sophia³, Cannan, Stefanie⁴, Deibert, Jack E.⁵, Camilleri, Phyllis A.⁶

(1) Earth and Environmental Sciences, Austin Peay State Univ, Clarksville, TN, USA, (2) Earth and Environmental Sciences, Austin Peay State University, Clarksville, Tennessee, USA, (3) Earth and Environmental Sciences, Austin Peay State University, Clarksville, TN, USA, (4) Earth and Environmental Sciences, Austin Peay State University, Clarksville, Tennessee, USA, (5) Department of Earth and Environmental Sciences, Austin Peay State Univ., Clarksville, TN, USA, (6) Earth and Environmental Sciences, Austin Peay State University, Clarksville, TN, USA,

Abstract:

New mapping along the NW margin of Knoll Basin, NE Nevada, reveals two stratigraphically distinct Cenozoic felsic lava flows. The upper unit is tentatively correlated with the 16–14 Ma Jarbidge Rhyolite. The lower unit was previously unrecognized and is informally named the Boies dacite. To assess lateral variation and viability of correlation with volcanic rocks elsewhere in Nevada, we characterized three samples from each unit using petrography and whole-rock XRF geochemistry. Geochemically, the Jarbidge Rhyolite samples are high-silica rhyolites. Thin-section analyses indicate they contain phenocrysts of quartz, sanidine, plagioclase, and minor pyroxene within a microcrystalline groundmass. Major and trace element (Rb, Y, Nb vs. SiO₂) chemistry of our samples closely matches published chemical data from the Jarbidge Rhyolite to the west and east of the study area. However, Rb/Nb ratios in our samples have values between that of the Jarbidge Rhyolite to the west and east of the study area. This suggests a regional continuum of decreasing Rb/Nb values from west to east, possibly related to changes in depth of crustal melting and or the addition of a mafic component to the magma. Analyses of the Boies dacite indicate that it is distinctly different than the Jarbidge Rhyolite. In comparison to the Jarbidge Rhyolite, the Boies dacite has lower silica content, higher alkali content, higher amounts of Rb, Y, and Nb, and contains hornblende and biotite instead of pyroxene. These data refine the volcanic stratigraphy of Knoll Basin and serve to establish a petrogenetic distinction between the Jarbidge Rhyolite and Boies dacite. To assess temporal relationships between these units, our future research will include radiometric dating of samples.