DOCUMENTING SPATIAL AND TEMPORAL CHANGES IN THE GROWTH OF THE SIERRA NEVADA BATHOLITH, AS RECORDED IN ZIRCON TRACE ELEMENT SIGNATURES

The Sierra Nevada batholith (California, USA) is often considered an excellent natural laboratory for understanding continental arc systems. Many geochemical and isotopic studies have been performed in the Sierra Nevada that reveal interesting changes in magmatism through both space and time. In particular, range-perpendicular trends have been well-documented (e.g. eastward decrease in age and increase in radiogenic Sr), whereas along-strike changes have received less attention. We present a new, range-wide zircon U-Pb + trace element study of the Sierra Nevada batholith (SNB) that examines changes in zircon geochemistry as a function of both magmatic tempo (time) and basement domains (space). The goals of this study are to better understand spatial and temporal differences in magmatic processes and document distinctive SNB domains that could be useful for detrital provenance analysis. We present 505 new zircon analyses, collected from 29 plutonic samples, and compile those with an additional 48 grain analyses from 5 plutonic samples from the published literature. In addition to U-Pb isotope data, a suite of 19 elements were measured, which include all rare earth elements plus Ti, Hf, Th, U, and Y. Zircon geochemical discriminators such as U/Yb, Ce/Yb, Gd/Yb, Th/U, Eu anomaly, Hf concentration, and Ti temperature were used to identify magmatic trends. Our results reveal complexity in all geochemical indicators in Jurassic to early Cretaceous time. During the mid-to, Late Cretaceous flare-up (from ca. 110 – 85 Ma), Hf, U/Yb, and Gd/Yb increase steadily, while Ti-in-zircon temperatures decrease. These patterns indicate greater fractionation, increasing involvement of crustal materials in melts, and crustal thickening through time. Spatially, we observe significant differences between similarly aged plutons intruded into different basement terranes. For example, Jurassic plutons emplaced into different metamorphic belts in the western foothills yield markedly different Th/U and Gd/Yb ratios. These results suggest that: 1) zircon geochemistry is sensitive to processes also recorded in whole rock data, and 2) igneous zircons inherit geochemical markers from the basement rocks they were emplaced into, possibly allowing for discrimination of basement domains in detrital datasets.