马里亚纳海槽玄武岩K-Ar地质年代学及地球化学研究

STUDIES ON K-Ar GEOCHRONOLOGY AND GEOCHEMISTRY OF MARIANA TROUGH BASALTS

对马里亚纳海槽弧后扩张脊上所采集的玄武岩样品进行了系统的 K- Ar定年和微量元素及稀土元素地球化学特征研究。指出马里亚纳海槽的张开及其与之相伴的玄武岩浆活动至今仍在进行 ,海槽的半扩张速率可能为 2 .0～ 2 .5 cm/ a。同时 ,海槽玄武岩年龄在空间上具有从南到北逐渐变新的演化规律。地球化学特征指示 ,地幔岩的部分熔融程度是控制海槽区玄武岩地球化学性质差异的主要机制。岩石学和微量元素地球化学特征及其随纬度的规律性变化 ,指示海槽区玄武岩的岩浆是由具有 N- MORB源区性质的热区地幔物质由南到北在不同深度经不同程度的部分熔融而形成的。同时 ,由南到北其岩浆源区受到了来自俯冲板块富含水及 L IL 流体的不断加深的交代作用影响。据此 。

Basalts collected from the spreading ridge of Mariana Trough between 14°49′14″ and 18°15′14″ are dated by conventional K Ar method,together with the studies on petrology and geochemistry of trace elements,and then reasons of opening and development history in Mariana Trough are discussed.The opening and related basaltic magmation are still active up to now.At the same time,the ages of basalts become older and older from south to north.The half spreading rate of the trough derived from the age results is about 2 0 2 5 cm/a.All the geochemical characteristics suggest that source region of basalt in the trough similar to N MORB come from partial melting of upper mantle.However,magma of basalt in the trough was mostly from partial melting and affected by fluid rich in H 2O and LIL.Regular changes with latitude in the ages and geochemistry of Mariana Trough basalts indicate that the opening and evolution of the trough may be controlled by the hot region in this area.