HR: 14:25h
AN: V53E-04 INVITED    [Abstracts]
TI: Fluid and Melt Inclusion Evidence for Halogen, Sulfur and Metal Contents in Magmatic Hydrothermal Systems
AU: * Bodnar, R J
EM: rjb@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24061, United States
AU: Cannatelli, C
EM: claudiac@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24061, United States
AU: Cannatelli, C
EM: claudiac@vt.edu
AF: University of California Santa Barbara, Department of Earth Sciences, Santa Barbara, CA 93106, United States
AU: Esposito, R
EM: nonac004@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24061, United States
AU: Fedele, L
EM: lfedele@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24061, United States
AB: Information on halogen, sulfur and metal contents of active volcanic systems is readily available from analyses of volcanic gases and condensates. Similarly, fluid and melt inclusions in phenocrysts and vein material provide a sample of the melt and fluid that existed at depth in the magmatic system and may be used to constrain the geochemistry of the system at depth. Detailed studies of fluid and melt inclusions over the past several decades, combined with gas analyses in active systems, has led to a better understanding of the geochemical evolution and the processes that link the deeper geologic environment with the near surface. White Island, New Zealand, is an active andesitic-dacitic volcano associated with subduction of the Pacific plate beneath the Indian-Australian plate. Current annual fluxes to the atmosphere from this volcano are: 0.078 Mt S; 0.49 Mt CO₂; 0.03 Mt Cl; 110 t Cu; >36 kg. Melt inclusions from White Island show several hundred ppm S, ~1000 ppm Cl and several hundred ppm Cu. The Cl/H₂O ratio of melt inclusions is ~0.15, indicating that the magmatic gas phase can efficiently remove Cu from the melt during volatile separation. Over the 10,000 yr lifetime of the White Island volcano, it is estimated that 1 Mt of Cu has been discharged into the atmosphere. The tectonic and geochemical environment at White Island is analogous to that in which porphyry copper deposits form. Based on Cu contents of melt inclusions, it is estimated that extraction of Cu from about 5 km³ of melt at White Island could generate a porphyry copper deposit containing 250 Mt of 0.75 percent Cu ore. Fluid inclusions in fossil magmatic-hydrothermal systems such as the porphyry copper deposits are characterized by elevated S, Cl and metal contents. Early, magmatic fluids often contain several 10's of weight percent Cl, as well as up to several thousand ppm metals and up to 1 weight percent S. These fluids represent the "residue" that remains in the deeper parts of the magmatic-hydrothermal system after phase separation and loss of volatiles and metals to the atmosphere. Thus, even though large quantities of halogens, sulfur and metals are lost to the near surface environment, the largest proportion of these components remains in the deeper geosphere.
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8409 Atmospheric effects (0370)
DE: 8410 Geochemical modeling (1009, 3610)
DE: 8419 Volcano monitoring (7280)
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting