Melt inclusions in basalts of Ross Island area,Antarctica |
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| Authors: | Mao Dongqing Lu Huanzhang Fang Genbao |
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| Institution: | (1) Institute of Gold Research, Shenyang;(2) Institute of Geochemistry, Academia Sinica, China |
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| Abstract: | There are many melt and fluid inclusions (mainly CO2-rich) in olivine and pyroxene phenocrysts in basalts from the Ross Island area. The melt inclusions can be classified as
follows: (1) crystalline melt inclusions (type I), (2) fluid-melt inclusions (type II) and (3) glass inclusions (type III).
The daughter minerals in type I include olivine, plagioclase, ilmenite, etc. Fluid-melt inclusions are a new type which represent
the immiscibility of magma and fluid at a particular stage of evolution. Three types of fluid-melt inclusions were examined
in this study: a) crystal + liquid + gas, b) inclusions coexisting with glass inclusions and fluid inclusions, and c) crystal
+ daughter mineral (dissolved salt) + gas. Both primary and secondary melt inclusions are recognizable in the samples. The
secondary melt inclusions were formed during healing of fractures in the host minerals in the process of magma rise.
The homogenization temperatures (both Leitz 1350 stage and quench method were used) of melt inclusions in basalts range from
1190 to 135°C at high pressure (about 7 kbars), indicating that the basalts may have come from the upper mantle. Melt-fluid
immiscibility in basaltic magma shows that the CO2-rich fluids may be the main fluid phase in the upper mantle, which are of significance in understanding the evolution of
magma and various processes in the deep levels of the earth.
The homogenization temperatures of melt and aqueous fluid inclusions in granites and metamorphic rocks in this area vary from
980 to 1100°C and 279 to 350°C, respectively. |
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