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; 87Sr/86Sr(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.
Temporal and geochemical signatures in granitoids of northwestern Nevada: Evidence for the continuity of the Mesozoic magmatic arc through the western Great Basin
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Kenneth L. Brown, William K. Hart, Richard J. Stuck; Temporal and geochemical signatures in granitoids of northwestern Nevada: Evidence for the continuity of the Mesozoic magmatic arc through the western Great Basin. Lithosphere doi: https://doi.org/10.1130/L694.1
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