HR: 09:40h
AN: V51F-07    [Abstracts]
TI: Sulfur behavior during magma genesis: constraints from apatite crystallization experiments and natural glass inclusions in apatite
AU: * Parat, F
EM: fparat@min.uni-heidelberg.de
AF: Mineralogisches Institut, Im Neuenheimer Feld 236, Heidelberg, 69120 Germany
AU: * Parat, F
EM: fparat@min.uni-heidelberg.de
AF: Institut fuer Mineralogie, Callinstrasse 3, Hannover, 30167 Germany
AU: Holtz, F
EM: f.holtz@mineralogie.uni-hannover.de
AF: Institut fuer Mineralogie, Callinstrasse 3, Hannover, 30167 Germany
AB: Accurate methods for tracing the evolution of sulfur contents in magmatic system (pre-eruptive concentrations) are scarce and would be useful to understand the transport and/or degassing of sulfur at the scale of a volcano. Since sulfur can be incorporated in apatite at oxidizing condition, the analysis of sulfur (S) content in apatite minerals collected from volcanic rocks is a possible indicator of S concentrations in melts, provided that the partitioning of S between apatite and melt is calibrated experimentally. Experimental and petrological studies have been performed on sulfur behavior and distribution during apatite crystallization at oxidizing conditions. Crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk S contents (0.15 to 2wt.%S) at 900-1100°C, 200MPa and Δlog fO₂=NNO+3.6. The S content in the glass increases with increasing amount of added S. The S content in apatite increases with an increase in S content in the glass under anhydrite-undersaturated conditions. Under anhydrite-saturated conditions, S content in apatite decreases slightly with increasing S content in the glass. The S exchange reaction in apatite is influenced by the bulk composition of the melt (e.g., P content). However, changing melt composition has only little effect on Kd_S^apa/melt for the investigated rhyolitic composition. Kd_S^apa/melt does not depend directly on temperature, decreases from 14.2 to 2.7 with increasing S content in glass from SO₃=0.03 to 0.19wt.%, respectively, and can be predicted from the following equation: lnKd_S^apa/melt=-0.0025*(S in glass in ppm)+2.9178. The determination of Kd_S^apa/melt from the analyses of glass inclusions and host apatites in alkaline gabbros (La Palma, Canary Island) confirms the experimental results. The combination of natural and experimental data reveals that the S partition coefficient tends toward a value of 2 for high S content in the glass (>0.2wt.%SO₃). Using S in apatite as proxy for determining S content in melt is promising but additional experimental data are needed to clarify the individual effects of T, fS₂ , P and Ca content in the melt on S partitioning.
DE: 1043 Fluid and melt inclusion geochemistry
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005