Publication
Zircon petrochronology of Cretaceous Cordilleran interior granites of the Snake Range and Kern Mountains, Nevada, USA
Publisher:
Geological Society of America
Date:
03-05-2022
DOI:
10.1130/2022.2555(02)
Abstract: We addressed fundamental questions about the lithology, age, structure, and thermal evolution of the deep crust of the retroarc hinterland of the North American Cordilleran orogen through systematic investigation of zircons from Cretaceous plutons in the Snake Range and Kern Mountains of east-central Nevada. Geochronological (U-Pb) and geochemical (trace element, O and Hf isotopes) characterization of pre- and synmagmatic growth domains of zircons, coupled with traditional petrologic methods (petrography, field relationships, and whole-rock major-element, trace-element, and Sr-Nd and Pb isotope geochemistry), fingerprinted temporal variations in crustal contributions to magmatism. The s les are typical felsic, peraluminous Cordilleran interior granitoids that formed between 102 ± 2 Ma and 71 ± 1 Ma (95% confidence). Over the entire time span of magmatism, 87Sr/86Srinitial, εNd(t), 208Pb/204Pb, and εHf(t) exhibit incrementally more “crustal” ratios. The oldest and youngest s les, respectively, predate and postdate all published timing constraints of Cretaceous peak metamorphism in the region and exhibit the least and most radiogenic whole-rock isotopic results in the study (87Sr/86Srinitial = 0.7071 vs. 0.7222 εNd(t) = −3.4 vs. −18.8 208Pb/204Pb = 38.8 vs. 40.1). Accordingly, the least intras le variability of εHf(t), δ18OZrc, and trace-element ratios in magmatic zircon domains is also observed in these oldest and youngest s les, whereas greater intras le variability is observed in intermediate-age s les that intruded during peak metamorphism. The geochemistry of zircon growth in the intermediate-age s les suggests assimilation of partially molten metasedimentary crust led to increased heterogeneity in their magma chemistry. Interaction of magmas with distinctive crust types is indicated by contrasts between four categories of inherited zircon observed in the studied intrusions: (1) detrital zircon with typical magmatic trace-element ratios (2) zircon derived from high-grade 1.8–1.6 Ga basement (3) zircon with anomalously low δ18O of uncertain origin, derived from 1.7/2.45 Ga basement (or detritus derived thereof) and (4) zircon from variably evolved Jurassic–Early Cretaceous deep-seated intrusions. The progression of zircon inheritance patterns, correlated with evolving geochemical signatures, in Late Cretaceous granitic plutons is best explained by early, relatively primitive intrusions and their penecontemporaneously metamorphosed country rock having been tectonically transported cratonward and superposed on older basement, from which the later, more-evolved Tungstonia pluton was generated. This juxtaposition consequentially implies tectonic transport of synorogenic plutonic rocks occurred in the Cordilleran hinterland during the Sevier orogeny as a result of the interplay of retroarc magmatism and convergent margin tectonism.