摘要
康滇地轴北缘下元古界河口群记录的众多岩浆活动和沉积信息能被用来反演区域变质特征与变质条件,是扬子西缘古元古代至新元古代地质演化过程研究的重要窗口。本研究开展了河口群新桥组石榴黑云片岩的岩相学和矿物化学测试,结果表明该变质岩系中变质石榴石化学通式为Alm71~79Gro12~20Sps5~13Pyr1~3,属铁铝榴石-钙铝榴石固溶体系列。黑云母富Si、Al、Fe和Mg,贫K、Na、Mn、Ca和Ti,属变质重结晶镁铁质黑云母。石榴石具有较明显的核-幔-边成分环带,反映其可能经历了三个变质阶段(Ⅰ、Ⅱ和Ⅲ),利用GB-G温压计估算出三个变质阶段温压条件:t为484~497℃和p为0.53~0.58 GPa、t为496~538℃和p为0.56~0.72 GPa、t为500~571℃和p为0.62~0.74 GPa,核部至边部为进变质特征。新桥组石榴黑云片岩整体经历了绿帘角闪岩-低角闪岩的中级变质作用,显示了一个较完整的顺时针p-t变质轨迹。综合研究显示河口群可能经历了洋壳向陆缘缓俯冲的过程,俯冲深度>22 km。扬子西缘河口群变质岩在1000~850 Ma应处于挤压背景下的活动大陆边缘或陆缘火山弧环境,为格林威尔造山期的产物。
The abundant evidences of magmatic activities and sedimentary information preserved in the Paleoproterozoic Hekou Group on the northern margin of the Kangdian axis can be used to invert regional metamorphic characteristics and conditions.The Paleoproterozoic Hekou Group serves as an important window for studying the geological evolution process of the western margin of the Yangtze block from the Palaeoproterozoic to the Neoproterozoic.In this study,the petrography and mineral chemistry of the garnet-biotite schist of the Hekou Group were studied.The results show that the general compositional formula of metamorphic garnets in the metamorphic rock series is Alm71-79Gro12-20Sps5-13Pyr1-3,which belongs to the almandine-grossular solid solution series.The biotite is rich in Si,Al,Fe and Mg and depleted in K,Na,Mn,Ca and Ti,and belongs to the metamorphic recrystallized mafic biotite.The garnet has obvious core-mantle-rim compositional zones,reflecting that it could have experienced three metamorphic stages(I,II and III).Using the garnet-biotite thermometer and the garnet pressure formula(GB-G),the estimated temperatures and pressures of the three metamorphic stages are 484-497°C and 0.53-0.58 GPa,496-538°C and 0.56-0.72 GPa,and 500-571°C and 0.62-0.74 GPa,respectively,showing a prograde metamorphic characteristics from the core to the rim of garnet.The garnet-biotite schist of the Xinqiao Formation had generally experienced the medium grade metamorphism(epidote-amphibolite facies to low amphibolite facies),showing a relatively complete clockwise p-t metamorphic path.The comprehensive study shows that the Hekou Group could have experienced a slow subduction process of the oceanic crust toward the continental margin,with the subduction depth of over 22 km.The metamorphic rocks of the Hekou Group on the western margin of the Yangtze Block should have been formed in an active continental margin or continental margin volcanic arc environment under a compressional background from 1000 Ma to 850 Ma and was product of the Greenwell Orogeny event.
作者
陆相吉
任涛
LU Xiangji;REN Tao(Faculty of Land and Resources Engineering,Kunming University of Science and Technology,Kunming Yunnan 650093,China)
出处
《矿物学报》
北大核心
2025年第5期873-885,共13页
Acta Mineralogica Sinica
基金
云南省重大科技专项计划项目(批准号:202202AG050014)。
关键词
元古代
变质岩
河口群
P-T轨迹
扬子西缘
Proterozoic
Metamorphic rocks
Hekou Group
p-t path
Western Yangtze Block
