Paper No. 24
Presentation Time: 9:00 AM-6:30 PM


HOLK, Gregory J., Department of Geological Sciences and IIRMES, California State Univ Long Beach, 1250 Bellflower Blvd, Long Beach, CA 90840 and KELLY, Jennifer, Paleo Solutions Inc, 911 S. Primrose, Unit J, Monrovia, CA 91016,

Stable isotope analyses of quartz, schorl tourmaline, and muscovite from the Carboniferous Mount Mica Pegmatite document closed-system crystallization of an anatectic melt. High δ18O values of quartz (+15.5 ± 0.2‰, n = 8), tourmaline (+13.5 ± 0.3‰, n = 15), and muscovite (+12.5 ± 0.3‰, n = 11) similar to those from the host rock suggest anatexis of a local, metasedimentary source for pegmatite magma instead of a cogenetic origin with the Sebago Batholith (δ18O ~ +9‰, Dorais and Paige, 2000). Quartz-tourmaline 18O/16O geothermometry indicates cooling from 760°C to 363°C. Material-balance 18O/16O exchange modeling (Criss et al., 1986) that takes into account modal mineralogy demonstrates closed-system conditions during crystallization. A large range of δD values from tourmaline (–128 to –72‰, n = 17) and muscovite (–132 to –65‰; n = 14) initially suggest open-system infiltration of meteoric-hydrothermal fluids (Dyar et al., 1999), but Rayleigh modeling indicates that these minerals could have just as likely crystallized in the presence of late-stage water liberated from the nearby Sebago Batholith (also a source for boron). Tourmaline and muscovite H2O contents are within stoichoimetric values, indicating primary δD values. These data reveal a fluid history involving an internal magmatic fluid that evolved from δD = –115‰ and δ18O = +14.5‰ to δD = –70‰ and δ18O = +11.5‰ as the wall, intermediate, and core zones of the pegmatite cooled over a 400°C temperature range under closed system conditions. In contrast, variable δ18O (+10.0 to +13.7‰, n = 5) and δD (–135 to –58‰, n = 7) values from pocket zone gem-quality elbaite tourmaline indicate a complex fluid history involving both low- and high-D/H fluids, potentially of external origin that infiltrated these zones of high permeability after pegmatite crystallization. The high-D/H fluids (δD ~ –20‰) were likely meteoric as paleomagnetic data (Torsvick et al., 2012) indicate New England was at low latitude during the Carboniferous.