| Popis: |
Oxygen isotope ratios were measured in zircon by laser fluorination and by SIMS from in over 50 silicic (dacite–rhyolite) volcanic rocks of Triassic to Cretaceous (230-98 Ma) age from the Sierra Nevada batholith, White-Inyo Mountains, and Mojave Desert. These data give broad geographic and temporal context of volcanism in the Mesozoic California arcs system that was previously unobtainable because of secondary hydrothermal exchange that routinely alters original magmatic δ18O values in these rocks (c.f., Sorensen et al. GSAB 1998). SIMS analysis of δ18O using 10 µm spot size, augmented by U-Pb dating by LA-ICP-MS, further allows appraisal of variability within zircon grains and grain populations as potential evidence of assimilation or magma mixing within caldera systems, including mixing during eruptions. Values of δ18O(zircon) in most rocks studied are 5.0–7.5‰, and overlap with values of δ18O in plutonic rocks (6.80±1.85‰, S.D., Lackey et al. 2005,2006,2008,2012). A subset of Late Jurassic (152-148 Ma) tuffs distributed from the Mojave Desert to Mt. Goddard pendant that contain zircons whose δ18O values commonly are |
