@Article{Schmitt:2004, author = {A.K. Schmitt and J.I. Simon}, title={Boron isotopic variations in rhyolites from {L}ong {V}alley, {C}alifornia: recycling of hydrothermally altered intrusive margins}, journal={Contrib. Mineral. Petrol.}, year={2004}, volume={146}, number={}, month={Jan}, pages={590--605}, note={}, annote={}, keywords={}, url={http://sims.ess.ucla.edu/PDF/Schmitt_Simon_CMP_2004.pdf}, doi={10.1007/s00410-003-0514-6}, abstract={In this paper, we present boron isotope analyses of variably degassed rhyolitic glasses from Long Valley, California. The following results indicate that pre-eruptive boron isotopic signatures were preserved in degassed glasses: (1) averaged secondary ionization mass spectrometry (SIMS) measurements of H$_{2}$O-rich ($\sim$3 wt\%) melt inclusions from late erupted Bishop Tuff pumice are indistinguishable from positive thermal ionization mass spectrometry (PTIMS) analysis of vesiculated groundmass glass ($\delta$$^{11}$B=+5.0$\pm$0.9$\permil$ and +5.4$\pm$5$\permil$, respectively); (2) SIMS spot-analyses on H$_{2}$O-poor obsidian ($\sim$0.15 wt\% H$_{2}$O) from younger Glass Mountain Dome YA (average $\delta$$^{11}$B=+5.2$\pm$1.0$\permil$) overlap with compositionally similar late Bishop Tuff melt inclusions; and (3) four variably degassed obsidian samples from the 0.6 ka Mono Craters (H$_{2}$O between 0.74 and 0.10 wt\%) are homogeneous with regard to boron (average $\delta$$^{11}$B=+3.2$\pm$0.8$\permil$, MSWD=0.4). Insignificant variations in $\delta$$^{11}$B between early and late Bishop Tuff melt inclusion glasses agree with published experimental data that predict minor $^{11}$B depletion in hydrous melts undergoing gas-saturated fractional crystallization. Melt inclusions from two crystal-rich post-caldera lavas (Deer Mountain and South Deadman Dome) are comparatively boron-rich (max. 90 ppm B) and have lower $\delta$$^{11}$B values (average $\delta$$^{11}$B=+2.2$\pm$0.8$\permil$ and -0.4$\pm$1.0$\permil$) that are in strong contrast to the boron isotopic composition of post-caldera crystal-poor rhyolites (27 ppm B; $\delta$$^{11}$B=+5.7$\pm$0.8$\permil$). These variations in $\delta$$^{11}$B are too large to be caused by pre-eruptive degassing. Instead, we favor assimilation of $^{11}$B depleted low-temperature hydrothermally altered intrusive rocks subsequent to fresh rhyolite recharge.} }