大别-苏鲁超高压榴辉岩中高钛石榴子石的成分特征及其与金红石包裹体的成因联系  

Characterization of high-Ti eclogitic garnets in the Dabie-Sulu ultrahigh-pressure metamorphic belt ( China):Compositional heterogeneity and possible relations to rutile needles in garnet

作　　者：王汝成[1] 王硕[1] 邱检生[1] 倪培[1] 

机构地区：[1]南京大学地球科学与工程学院,南京大学内生金属成矿机制研究国家重点实验室,南京210093

出　　处：《岩石学报》2009年第7期1603-1611,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划973项目(2003CB716507);国家自然科学基金委员会优秀创新群体项目(40221301)资助

摘　　要：石榴子石是榴辉岩中的基本造岩矿物。本文对苏鲁地体中的毛北榴辉岩和大别地体中的双河榴辉岩中的石榴子石进行了研究。结果显示,石榴子石都表现出中心"富"钛特征,即石榴子石颗粒的中心部位的TiO_2含量(0.10%～0.50%)明显高于正常榴辉岩中石榴子石的钛含量(TiO_2一般<0.1%)。另外,在石榴子石中心部位含有大量金红石及其它钛矿物包裹体,其定向分布特征揭示其出溶成因模式。计算结果显示,出溶金红石的原始石榴子石大约含1.7%TiO_2,揭示其超深源特征。此外,在石榴子石中发现了一颗TiO_2含量达8%～9%的钙铝榴石,具超深源成因特征。因此,本文认为超钛钙铝榴石也是超高压变质作用的标志矿物。Garnet is one of the principle rock-forming minerals in eclogites. This mineral, in this paper, was studied to characterize distribution features of titanium in garnet from the Maobei eclogite in the Sulu terrane and the Shuanghe eclogite in the Dabie terrane. Results demonstrated that garnet grains display generally high-Ti cores which are characetrized by the high TiO(2) (0.10% similar to 0.50%). This value is higher than that in classic garnets from eclogitic rocks (generally TiO(2) <0.1%), abundant rutile inclusions also occurred in the core. Crystallgraphic relationship favors an exsolution origin of rutile inclusions from the host garnet. The original composition of garnet host + rutile inclusion was estimated to be ca. 1.70%, which was converted to a depth of formation more than 200km according to published experimental data. Moreover, Ti-rich grossular (ca. 8% similar to 9% TiO(2)), rarely reported in literature, was also identified as inclusion in garnet from the Maobei eclogite. Such a type of garnet reveals a deep subduction process. Therefore, supertitanic grossular maybe also a potential indicator of ultrahigh-pressure metamorphism.

关 键 词：高钛石榴子石 金红石包裹体 出溶 毛北 双河 榴辉岩 

分 类 号：P578.47[天文地球—矿物学] P575.1[天文地球—地质学] P588.348P595