23. SULFUR, CHLORINE, AND FLUORINE IN GLASS INCLUSIONS IN OLIVINE AND CLINOPYROXENE FROM BASALTIC HYALOCLASTITES REPRESENTING THE GRAN CANARIA SHIELD STAGE AT SITES 953 AND 956 ¹

Thor H. Hansteen ² and Andrey A. Gurenko ²

ABSTRACT

Sulfur, chlorine, and fluorine concentrations of primary silicate glass inclusions in olivine and clinopyroxene from basaltic hyaloclastites representing the Gran Canaria shield stage at Sites 953 and 956 were investigated using an electron microprobe. Inclusion compositions corrected for post-entrapment, host-mineral crystallization range from 46.3 to 54.4 wt% SiO₂ , and from 5.7 to 10.3 wt% MgO. Significant spread in S and Cl values (200–2390 ppm S, and 120–870 ppm Cl) and the lack of correlation between S and Cl with MgO and P suggest partial degassing of the magmas prior to eruption. F was not degassed during magma evolution and thus can be used to discuss magma source compositions. The lack of correlation between SiO₂ and F in the calculated parental magmas suggests that pressure is not likely to have exerted the main control on volatile contents. A source with heterogeneous F contents is inferred. The occurrence of S^2- , as the only detectable S species in the glass inclusions, suggests crystallization conditions with fO₂ levels at or below the Ni-NiO (NNO) buffer.

¹ Weaver, P.P.E., Schmincke, H.-U., Firth, J.V., and Duffield, W. (Eds.), 1998. Proc. ODP Sci. Results, 157: College Station, TX (Ocean Drilling Program).
² GEOMAR Forschungszentrum,Wischhofstraße 1-3, D-24148 Kiel, Federal Republic of Germany. thansteen@geomar.de