南海新生代玄武岩中单斜辉石矿物化学及成因意义  

Mineral chemistry and its genetic significance of olivine in Cenozoic basalts from the South China Sea.

作　　者：鄢全树[1] 石学法[1] 王昆山[1] 卜文瑞[1] 

机构地区：[1]海洋沉积与环境地质国家海洋局重点实验室国家海洋局第一海洋研究所

出　　处：《岩石学报》2007年第11期2981-2989,共9页Acta Petrologica Sinica

基　　金：科技基础性工作和社会公益研究专项项目(2003DIB3J114);青岛市科技将才专项计划项目(05-2-JC-79)资助成果.

摘　　要：从南海南大陆坡底至北大陆坡底采集的玄武岩样品,基本可以代表南海新生代岩浆活动的代表性样品。本文中对这些玄武岩中单斜辉石的矿物化学成分进行了研究,研究的单斜辉石以顽透辉石为主(占3/4),还有少量普通辉石及次透辉石等,也出现少量较为罕见的富钙辉石,位于深绿辉石区域内。基质微晶辉石比辉石斑晶更富钙、钛、铁,可能反映了岩浆演化向着富钙、钛、铁方向发展,且碱度逐渐降低。与碱性系列的演化趋势基本一致。由单斜辉石-熔体平衡温压计计算的岩浆房深度分别为:碱玄岩岩浆房约49km左右,粗面玄武岩岩浆房约25km;玄武岩岩浆房约15km。由碱玄岩→粗面玄武岩→玄武岩,平衡温度(K)依次降低:从1535～1498→1429→1369。南海新生代玄武岩为板内碱性玄武岩。碱性玄武岩系列可能是地幔柱在上升过程中在不同深度处发生部分熔融并伴随有分离结晶作用等物理化学过程的连续演变的产物。We dredged lots of Cenozoic basalts from areas covered from the northern sub-slope to the southern sub- slope of the South China Sea. Based on the study on mineral chemistry of clinopyroxenes in these Cenozoic hasalts, this paper indicates that pyroxenes are mostly enstatite and a few of augite, sahlite and Ca-rich pyroxene. Pyroxene microlite has higher content in, Ca, Ti and Fe than pyroxene phenocryst, it may reflect that the evolution trend of host magma of pyroxene is coincidence with that of alkali rock series. The depth of magma chambers which calculated from equilibrium temperatures and pressures between clinopyroxene and melt are as follows, that of magma of tephrite is about 49km, that of magma of trachybasalt is about 25km, and that of magma of basalt is about 15km. Correspondingly, Equilibrium temperatures( K) of three types rocks mentioned above gradually decrease from 1535 1498 to 1429 to 1369. By using discriminant plot which developed from pyroxene and alkali discriminant diagram of host rock, Cenozoic basalt from the South China Sea belongs to intraplate alkali basalt. The results suggest that alkali basalt series in the study area may be the products of continuous evolution of mantle plume, which result from some physical and chemistry process including partial melting and fractional crystallization of mantle plume during the course of its ascent to the surface.

关 键 词：单斜辉石 矿物化学 成因意义 新生代玄武岩 南海 

分 类 号：P588.145[天文地球—岩石学] P578.954[天文地球—地质学]