A sulfur isotope study of granitic plutons in the Great Basin, Western United States: Implications for magma-crust interaction and crustal architecture

Sulfur isotope data from Jurassic, Cretaceous, and Tertiary plutons provide important information about the crustal architecture of the Great Basin, which complements interpretations developed using other isotopic systems (i.e., Sr, Pb, Nd, O). Major-element geochemical analyses and whole-rock sulfur isotope analyses were conducted for 283 granitoid samples collected in the Great Basin. Rock geochemistry data indicate that the samples are dominantly metaluminous, I-type granitoids. Values of Aluminum Saturation Index [ASI = molar Al 2O3/(CaO + Na2O + K2O)] are predominantly very close to the metaluminous/peraluminous boundary, and the distribution of values is fundamentally the same for each age group. 8345 values range from -3.2 to +20.7‰, with a mean value of +6.4‰. There is little difference in the 6345 ranges and mean values among each of the three age categories. In addition to sulfur, oxygen isotope data were obtained on quartz from a subset of the pluton samples, and these data combined with the data of King et al. (2004) range from +4.8‰ to +13.5‰, with a mean value of +10.0‰.; Kriged maps of ASI, delta34S, and delta 18O values show very similar patterns in which the highest isotope and ASI values occurs in eastern Nevada, forming a circular high with lower values on all sides. The similarity in kriged patterns suggests that plutons in east central Nevada, and likely throughout the Great Basin, were generated as the result of crustal anatexis rather than through contamination of an ascending mantle melt. These patterns further indicate that the Great Basin can be separated into four distinct crustal domains, thus clarifying the crustal architecture of the region.