大陆科学钻探CCSD-PP3钻孔超镁铁岩岩石学和矿物学特征及其意义  

Petrology and mineralogy of PP3 ultramafic rocks in Sulu UHP belt and its significance.

作　　者：陈世忠[1] 杨经绥[1] 许志琴[1] 李天福[1] 陈方远[1] 张仲明[1] 张文兰[2] 

机构地区：[1]中国地质科学院地质研究所国土资源部大陆动力学实验室 [2]南京大学内生金属矿床成矿机制研究国家重点实验室,南京210093

出　　处：《岩石学报》2005年第2期369-380,共12页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划973项目(2003CB716503)国家自然科学基金重大项目(40399143)中国地质调查局地质大调查项目(编号121201056606)博士后基金的联合资助成果之一

摘　　要：PP3超镁铁岩在钻孔中出露厚度达480米,包括纯橄岩、石榴橄榄岩和闪石化金云母橄榄岩等岩石类型。岩石主要组成矿物橄榄石、铬尖晶石、石榴子石、单斜辉石和斜方辉石等。橄榄石为镁橄榄石(Fo在88.7-93.1之间),SiO2含量在38.8wt.%-42.4wt.%;石榴子石为钙饱和的镁铝榴石(Py65.945Alm18.095Uv7.518Gr4.695And3.605Sp0.142),MgO含量在16.77wt.%-20.04wt.%,CaO含量在5.4到6.4wt.%之间,Cr2O3含量在0.3到3.3wt.%,FeO含量在2.48wt.%-11.78wt.%,TiO2含量小于0.04wt.%,代表早期矿物组合;两类斜方辉石的成分都为顽火辉石(OpxⅠ:En91.86Fs7.80Wo0.34,OpxⅡ:En91.83Fs7.91Wo0.21Ac0.06)。斜方辉石Mg#(Mg/(Mg+Fe)×100)在91.7-92.5间,Cr2O3含量低于0.32wt.%,CaO含量在0.102-0.199wt.%间,Al2O3含量为0.32-1.06wt.%,均值在0.72wt.%;单斜辉石可分为早期透辉石(Wo45.98En47.89Fs2.73Ac3.39)和晚期顽透辉石(Wo27.61En68.78Fs2.27Ac1.34)两种。铬尖晶石的Cr#(Cr/(Cr+Mg)×100)从51到89变化,TiO2和MnO2含量分别低于0.26wt%和0.46wt%。橄榄石、铬尖晶石和单斜辉石等矿物组合表现为3-4期次的特点。Ultramafic rocks about 480 metres sandwiching eclogite are revealed, which include garnet peridotile, dunite, serpentinite and few hargzburgite and amphibole phlogopite peridotite, contain olivine, chromium spinel, diopside, endiopside, or/and garnet, orthopyroxene, amphibole and phlogopite. Olivines have forsterite contents ranging from 88.7 to 93.1, SiO2 ranging from 38.8wt. % to 42.4wt. %. All garnets (Py(65.945)Alm(18.095) Uv(7.518) Gr(4.695) And(3.605) Sp(0.142)) are pyropic, with CaO between 5.4 to 6.4 wt. %, and Cr2O3 from 0.3 to 3.3 wt. %, represent early stage of mineral assemblage. Orthopyroxenes (En(91.8) Fs(7.9) Wo(0.25)) are Unzoned, Cr2O3 ranges from 0 to 0.32wt. %, and CaO ranges from near detection limit to 0.20wt. %. Most of the orthopyroxenes (the average is 0.72wt. %) have Al2O3 < 1.1 wt. %. Composition of clinopyroxenes in PP3 ultramafic rocks is attributed to two generations. the early generation is called diopside (Wo(45.98) En(47.11) FS2.73 Ac-3.39) and the later is endiopside (Wo(27.61) En(68.78) Fs(2.27) Ac-1.34) with higher MgO. Chromite in PP3 ultramafic rocks is compositionally variable, Cr-# ( molar100Cr/(Cr + Al)) varies from 51 to 89, and TiO2 and MnO2 are lower than 0.26wt. % and 0.46wt. % respectively. Olivines, chromites, and clinopyroxenes show multistage, which were associated with partial melting, subduction and exhumation.

关 键 词：石榴橄榄岩 榴辉岩 透辉石 铬尖晶石 

分 类 号：P588.125[天文地球—岩石学]