LITTLE PLUTONS BETWEEN BIG PLUTONS: PROBING TRANSITIONS OF MAGMA FLUX IN THE SIERRA NEVADA BATHOLITH

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.