冲绳海槽中部和南部玄武岩的区域性差异及其成因研究

本文从岩石学和岩石化学角度出发 ,对冲绳海槽中部和南部玄武岩样品进行了对比研究。结果表明中部和南部玄武岩均系亚碱性玄武岩 ,其中前者兼具钙碱性系列和拉斑玄武岩系列两种性质 ,后者则主要属拉斑玄武岩系列。根据岩石化学特征命名 ,中部样品主体为石英拉斑玄武岩 ,南部样品则为橄榄拉斑玄武岩。两区海槽玄武岩岩浆均由下伏地幔岩部分熔融而成 ,但源区地幔性质不均一 ,岩浆演化程度各异。中部样品源区地幔性质为过渡型 ,结晶分异程度较高 ;南部样品源于近亏损或富集型的地幔 ,结晶分异程度较弱 ;另外两区玄武岩样品均受到了不同程度的陆壳物质混染。中、南部海槽玄武岩在岩石学、岩石化学方面的差异与源区地幔性质不均一和岩浆演化程度各异有直接关系。海槽玄武岩构造环境属于过渡洋中脊玄武岩 (张性 )与岛弧玄武岩 (压性 )之间 ,代表的仍是海槽早期的岩浆活动。

Areal Difference of Middle and Southern Basalts from the Okinawa Trough and Its Genesis Study

After contrasting the features in petrology and petrochemistry between middle and southern basalt samples from the Okinawa Trough, we find both middle and southern basalts belong to subalkalic series, and the former vest in tholeiitic and calc-alkalic series, the latter mainly calc-alkalic series. According to petrochemistry characteristics, middle basalts are named quartz tholeiite primarily and southern ones olivine tholeiite. The magma of the middle and southern Okinawa Trough basalts are both originated from partial melting of the mantle rock underground, while the source mantle are uneven and magma evolution degree are different. Middle samples' source are close to transitional mantle and crystallization & differentiation have a higher degree; however, southern ones normal or prosperous mantle, and a lower degree crystallization & differentiation. Two area basalts have also experienced assimilation & contamination of different degrees. The differences between middle and southern basalts from the Okinawa Trough in petrology and petrochemistry are directly relative to their uneven source mantle and magma evolution at different degree. The tectonic settings of the basalts are transitional between MORB (tensile) and IAB (compressive), still representing the earlier stage of magma activities in the Okinawa Trough.