马里亚纳海槽玄武岩岩石学  

BASALT PETROLOGY IN THE MARIANA TROUGH

作　　者：陈穗田[1] 张德玉[1] 

机构地区：[1]国家海洋局第一海洋研究所

出　　处：《海洋地质与第四纪地质》1991年第3期93-104,共12页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金资助项目

摘　　要：马里亚纳海槽岩石学的研究表明本区岩石属基性的玄武岩,又细分为洋底玄武岩(OFB)和钙碱玄武岩(CAB)。微量元素相对球粒陨石标准化数值特征:除了Sc、Ti,V外,其它过渡元素都有亏损,Cr、Ni出现了明显负异常,Ti相对较富集,稀土元素(REE)表现富集型的型式;同位素测试结果,εNd(0)=6.9。可以认为这些玄武岩是上幔岩的局部熔融形成的岩浆沿着扩张中心喷溢到海底,而形成的新生洋壳。Pillow and slaty lavas are widely distributed in the Mariana Trough. Pet-rological and petrochemical studies, and also analysis of major, trace and rare-earth elements and isotopes, indicate that all the rocks are basalts. Two types of basalts are recognized on the basis of major element analysis. One is ocean-floor basalt (OFB) which belongs to tholeiitic series (calcic). The other is calc-alkalic basalt (CAB) which belongs to Al-rich series (calc-alkalic). Trace element analysis indicates that, according to chondrite, Ti shows a positive anomaly, and Cr and Ni show negative ones. Except for Sc, Ti and V, other transition elements are deficient, indicating a Ti-type basalt. The analysis of rare-earth elements shows an enrichment in light rare-earth elements (LREE), relative to chondrite. Basaltic glass on the surface of basalt contains more LREE than the basalt itself. Determinations of Sm and Nd indicate that the basaltic magma is from the mantle, probably a result of fractional melting of the overlying olivine rocks. Eruption of basalt in the Mariana Trough is related to tectonic environment. Tensile cracks were formed in the trough because the subduction of the Pacific plate forced the overlying plate to move toward the ocean. The meltedmentle magma rose and ejected along these tension faults, forming new oceanic crust. Basalts with two different properties show little changes in their chemical compositions, reflecting the differences in depth of melting fractionation, in ranges of mantle melting and in degree of crystal differentiation of magma. The distributions of the two types show a certain regularity in time and space. The OFB is mainly distributed on the central ridge of the Mariana Trough, and is the youngest in age. The calcic-alkalic basalt is mainly distributed on both sides of the ridge, and is relatively older in age. Therefore, the changes in time and space of the rocks and the lithological natures can provide powerful evidences for the continuous spr

关 键 词：海槽 玄武岩 岩石学 马里亚纳 

分 类 号：P736.13[天文地球—海洋地质]