Study Of The Inclusions And The Isotopic Compositions Of Volatile Components In Volcanic Rocks In The Okinawa Trough

The inclusions hosted in the phenocrysts of basalt and pumice in the Okinawa Trough was systematically studied in this thesis for the first time. The homogeneous temperature, decrepitation temperature, major element compositions and volatile components of the inclusions were determined. Meanwhile, the content of volatile components in whole-rock and their carbon, hydrogen, helium and neon isotopic compositions of the same samples were also analyzed. Based on the obtained data, the magma genesis, magma evolution process, relations in the petrogenesis of different kinds of volcanic rocks, and effects of magmatism on the hydrothermal activity were discussed. (1) The inclusions hosted in plagioclase were trapped at two periods at least, which respectively corresponded to the two stages of crystallization of plagioclase. Plagioclase was the mineral crystallized throughout the whole magmatic process. So, the inclusions hosted in plagioclase have recorded the information of magma source and magma evolution. (2) The major element compositions of inclusions hosted in basalt and pumice samples were correlated and inheritance in the same evolution series. The presents of the components N2 and CO generally originated from the mantle and the mantle-sourced characteristics of carbon, hydrogen isotopic compositions suggest that basalt and pumice were cognate and respectively represented the products at early stage of magmatism and at the late stage of crystal fractionation. / (3) The magma in the trough was rich in H20 and other volatile components. The carbon, hydrogen and helium isotopic compositions of volatile components displayed the characteristics of the fluid dehydrated from subducting slab. Therefore, the fluid dehydrated from subducting slab should have been added to magma at its forming stage or play an important role in the melting of mantle. (4) The volatile component was not only the 揷atalyzer?of melting of the mantle to form initial magma but also one of the main factors to control the trend of magma evolution and the formation of zoned magma chamber under the trough. (5) The magmatism in the Okinawa Trough contributed a lot to the hydrothermal activity not only as heat source but also as material source.