Preliminary studies on melt inclusions and volatile analysis in basalts recovered from Australian-Antarctic Ridge

초록

Antarctic KR1 (62° 51.279S, 158° 36.948E) Mid-Ocean Ridge (MOR) is located in a triple junction of the Pacific, the Antarctic, and the Indian plates. Expedition with ice-breaking research vessel Araon in January 2013, we dredged basaltic rocks from in-axis MOR and adjacent off-axis seamounts. Collected rocks contain fine subhedral or anhedral olivine, and plagioclase, and pyroxene phenocrysts. Relatively oOff-axis seamount basalts contain more olivine indicates more phenocrysts compared to in-axis MOR basaltsso it looks like alkali-olivine basalt. Olivine phenocryst in the DG03 basalt recovered from the seamount b asalt is bigger than in-axis MOR basalt, especially the DG03 seamount olivine-rich basalt contains numerous melt inclusions. While some of the olivine contains “homogeneous” glassy melt inclusions, most of the melt inclusions were observed to be internally crystallized. We picked olivine grains containing glassy melt inclusions, and analyzed major elements. The qualitative EPMA spectrum of the melt inclusions show Al, Mg, Si, Ti, Cr, Fe, Ni element peaks. High Mg/Fe ratio of the host olivine suggests high crystallization temperature of the olivine phenocrystin the basaltic magma. Quantitative understanding of sulfur and halogen elements in igneous rocks in MOR might give a better insight into the volatile circulation in the Earth’s mantle. Qualitative SIMS (Secondary Ion Mass Spectrometry) transient signals demonstrateWe found that the Antarctic KR1 basalts contain sufficient sulfur and halogen elements to be determined. We synthesized homogeneous and halogen-rich basaltic glasses for external Standard Reference Material (SRM) for SIMS microanalysis. Basalt powder was mixed with compounds of halogen and sulfur elements such as KI, NaI, CaCl2, KCl, FeS2, CaF2, Fe3O4, LiBr to produce the halogen and sulfur-rich glass beads. Double polished glass beads were checked for its halogen and sulphur sulfur contents, and its homogeneity.