Stable Isotopic Study of Sulfur Degassing During the Climactic and Pre-Climactic Eruptions of Mt. Mazama, Crater Lake, Oregon

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9814559MandevilleOf the volcanic gases, sulfur dioxide (SO2) has the greatest potential for climatic impact due to its direct injection to the stratosphere during explosive eruptions, its slow conversion to submicron H2SO4 aerosol and long residence time in the stratosphere. H2SO4 aerosol loading resulting from the climactic 6845+/- 50 yr. B.P. eruption of Mt. Mazama, Crater Lake, Oregon is estimated at 2 x 10^14 grams, approximately one order of magnitude more than was released during the recent eruption of Mt. Pinatubo, yet there have been no previous studies of the source of sulfur in Mazama magmas. Sulfur isotopic data will be used to delineate the source(s) of dissolved sulfur in Mazama magmas based on the characteristic isotopic signatures of the Earth's sulfur reservoirs (i.e., mantle, crustal, meteoric/hydrothermal) and quantification of isotopic shifts which may have occurred due to extensive degassing. Objectives of the proposed research include: 1) testing the hypothesis that elevated d34S values in Mt. Mazama tephra are the result of open-system degassing; 2) quantifying the amount of sulfur that degassed from the volume of erupted magma; 3) experimental determination of sulfur isotopic fractionation factors at magmatic temperatures; and 4) demonstrating the applicability of sulfur isotopic data to characterize degassing style in ancient tephra. Most importantly, stable isotopic data obtained in this study will delineate the likely source(s) of SO2 released by past explosive volcanism and will contribute towards our understanding of sulfur recycling between the mantle, crust, hydrosphere and atmosphere.