【摘 要】
：
The Okinawa Trough is an initial back-arc basin that is influenced by the subduction of the Philippine Sea Plate and deve-lops on the continental crust.The Okinawa Trough is a natural laboratory for the study of basin evolution,magmatism,and crust-mantle
【机 构】
：
Key Laboratory of Submarine Geosciences and Prospection of Ministry of Education,Ocean University of
【出 处】
：
中国海洋大学学报（自然科学英文版）
论文部分内容阅读
The Okinawa Trough is an initial back-arc basin that is influenced by the subduction of the Philippine Sea Plate and deve-lops on the continental crust.The Okinawa Trough is a natural laboratory for the study of basin evolution,magmatism,and crust-mantle processes in the early stage of back-arc spreading.Melt inclusions are small droplets of magma that are captured during the mineral crystallization process and can record the geochemical composition changes during magma evolution.In this study,the geo-chemical compositions of melt inclusions in host plagioclases of two volcanic rock samples at Station nos.9-1 and 9-2 from the southern Okinawa Trough are systematically analyzed.Based on previous studies,the origin and evolution of magma and the intro-duction of subducting materials in the study area are discussed.Results show that melt inclusions are characterized by the relative enrichment of large-ion lithophile elements,depletion of high-field-strength elements,and slight enrichment of rare earth elements.Indeed,the subduction of the Philippine Sea Plate introduced sediment-derived melts and fluids into the magma source area of the southern Okinawa Trough.Subsequently,4％ to 5％ partial melting of the hydrated mantle produces basaltic magma.The melt inclu-sions of andesite and dacite investigated in this study were formed by fractional crystallization of basaltic magma.Finally,the crys-tallization of plagioclase,pyroxene,and magnetite occurred during the late stage of magma evolution.The temperature-pressure data show that the melt inclusions in plagioclase have two capture periods:one is at temperatures above 1250℃ and the other is at tem-peratures between 1180℃ and 1200℃.The capture pressure of the inclusions at temperatures between 1180℃ and 1200℃ is be-tween 5.6 kPa and 6.1 kPa,corresponding to the depth of 15-17 km below the seafloor.The geochemical characteristics of major and trace elements in inclusions show that the samples from two stations (i.e.,9-1 and 9-2) have similar or identical magma source areas.However,the crystallization differentiation reflected by inclusions in sample 9-1 is more obvious than that in sample 9-2.The inclu-sions were captured during magma evolution and were not contaminated by crustal materials.
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