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Cretaceous plutons in the Sierra Nevada provide a ~35 million year record of magma production in the Cordillera. Some periods of Sierran magmatism were exceptionally productive: the 95-85 Ma Sierra Crest event and the 101-98 Ma period in the axial Sierra Nevada batholith yielded some of the largest plutons; however, the transitions into and out of these intervals of building of big plutons and high net magma flux periods are not well-studied. To better understand the the transitions between high levels of magma flux in the Sierra arc, we have focused on a suite of small, granite to granodiorite plutons in the Kings River and Monarch Divide regions of Kings Canyon National Park. Notable among them are the Tehipite Dome, White Divide, Kennedy Lakes, Dougherty Peak, Cartridge Pass, Arrow, and Pyramid plutons. These plutons lie between the large middle Cretaceous plutonic suites of the axial Sierra Nevada (e.g. Mitchell Suite) and the Mount Whitney and John Muir suites of the Sierra Crest. New U-Pb zircon of ~97-92 million years old among the plutons confirms their transitional placement and era. Geochemically, the granite suites show distinct geochemical arrays from the coeval granodiorite plutons, suggesting that the two are not related by fractionation or degree of magma mixing. Radiogenic and stable isotopes also point to these plutons as distinct from each other. It follows that the mixed bulk chemistry and isotopic character of the Kings River and Monarch intrusions likely reflects a switchover in source during diminished magma flux. Thus, they appear to be recording heterogeneous source and plumbing systems in the transition that may be otherwise erased during more efficient, high-flux magmatism. 

The Sierra Nevada Batholith is a record of copious magmatism caused by subduction of the Farallon oceanic plate under the western margin of North America during much of the Mesozoic Era, between 256 and 80 Ma. The diversity of rocks produced during these sub-surface interactions depends on several variables, including fluid availability, melt source, and mantle partial melt emplacement geometry (Ducea et al., 2015). The analysis of zircon is particularly appealing because zircon is a robust mineral that endures periods weathering and erosion and commonly lingers as detrital crystals in the rock record. It thus has the potential to add value as a lens into global magmatism and planetary evolution given its use as a thermometer (Watson and Ferry, 2007), and measure of magma source composition (Davies et al. 2021). Several researchers suggest that zircon can be a useful tool for constraining depth of crystallization (Tang et al. 2020). Building on thesis work on the utility of europium anomalies in zircon to model depths and, by proxy, crustal thickness for batholithic granitoids, this project provides additional data and insight to understand spatially and temporally varied trends of the arc’s plutonic record. Magma emplacement occurs in pulses and typically exhibits an eastward younging trend during the Mesozoic (Chen and Moore, 1982). Chinen (2022) found that the arc’s Western Margin exhibits both younging and thickening trends towards the east. Recent research exposed the issues associated with traditional cerium anomaly calculation because of a reliance on lanthanum, a poorly analyzed element (Loader et al., 2022). We incorporate these new methods to calculate zircon metrics for our data; this project further constrains the precision of interpretations about geochemical trends using laboratory analysis and zircon because it draws on a large and prolific database of plutonic trace element geochemistry. Because multiple magmatic and environmental processes affect zircon crystallization compositions, we use broad suites of zircon (e.g. rare earth elements, oxygen isotopes) and whole rock (XRF, trace elements, isotopes, additional minerals) geochemical analyses to elucidate aspects of previous research (Brady and Lackey, 2022; Chinen, 2022) and to build upon noted trends of the plutonic Cordilleran record.