Showing papers by "William K. Hart published in 2018"

Temporal and geochemical signatures in granitoids of northwestern Nevada: Evidence for the continuity of the Mesozoic magmatic arc through the western Great Basin

Abstract: Granitoid magmatism in the Basin and Range Province of northwestern Nevada remains an important gap in our understanding of the along-strike variability of Mesozoic Cordilleran arc systems. We present a comprehensive investigation on a suite of intrusions within the Santa Rosa Range (SRR) and Bloody Run Hills (BRH) of northwestern Nevada. Petrography, whole-rock geochemistry, and zircon U-Pb geochronology indicate two distinct magmatic systems in the SRR: an older, mafic, and metaluminous pulse (Santa Rosa/Andorno [SRA] group—ca. 102–100 Ma) and a younger, felsic, and peraluminous pulse (Granite Peak/Sawtooth [GPS] group—ca. 94–92 Ma). Within the BRH to the south, the Flynn (ca. 105 Ma) and Bloody Run stocks (ca. 96 Ma) are compositionally similar to the SRA group. New Al-in-hornblende thermobarometry reveals emplacement paleodepths of ~5–10 km for the SRA group. Slightly deeper emplacement levels (~10.5–12 km) are inferred for the GPS group from structural relationships and metamorphic contact aureole assemblages. Elemental characteristics are correlated with whole-rock Sr and Nd isotope ratios, revealing higher εNd(t) (+0.8 to +2.5) and lower initial 87Sr/86Sr (0.7040–0.7054) in the older SRA group than the younger GPS group (εNd(t) = −3.2 to −1.5; Sr/Sr(i) 0.7056–0.7061). New zircon εHf isotope analyses reveal that with the exception of the Bloody Run stock (−0.4 ± 2.1), the SRA group has more primitive zircon εHf(t) values (+2.9 to +5.3) than the GPS group (+0.4 to −3.7). The systematic shift in whole-rock Sr and Nd isotope and zircon εHf(t) values with time suggests fundamental changes in the relative contributions of mantle and crustal sources. A comparison of published geochronology and geochemistry from regional intrusive suites confirms that SRR-BRH magmatism was coeval and geochemically similar to the larger Cordilleran batholiths, providing evidence for the continuity of the Mesozoic magmatic arc through northwestern Nevada. LITHOSPHERE; v. 10; no. 2; p. 327–350; GSA Data Repository Item 2018123 | Published online 1 March 2018 https://doi.org/10.1130/L694.1