柴北缘锡铁山两类榴辉岩的退变质过程及其对俯冲带折返机制的制约  

The retrograde process of two types of eclogite in the Xitieshan terrane,North Qaidam and its constraint of the exhumation mechanism in the subduction zone

作　　者：张聪[1,2] 田作林[2] 张立飞[2] 黄杰[1,3] 陈梅[1,3] 

机构地区：[1]中国地质科学院地质研究所/大陆构造与动力学国家重点实验室,北京100037 [2]造山带与地壳演化教育部重点实验室/北京大学地球与空间科学学院,北京100871 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地质通报》2013年第12期2044-2054,共11页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41202034、41310104002和41172196);中国博士后特别基金(批准号:2013T60030)

摘　　要：榴辉岩作为俯冲带中重要的岩石类型保存有丰富的地球动力学信息。对榴辉岩及其退变质岩石的研究有助于建立俯冲带演化的p-T轨迹，了解俯冲岩石在折返过程中温压条件及矿物相的变化，从而对俯冲带折返的动力学机制进行限定。对柴北缘锡铁山双矿物榴辉岩及含多硅白云母榴辉岩进行了详细的岩石学研究。在NC（K）FMASH体系中对两类榴辉岩进行变质相平衡模拟，得到双矿物榴辉岩的峰期温压条件为745～790℃，大于2．8～3．0GPa（M1），后经历等温降压过程达到角闪石榴辉岩岩相（670～770℃，1．6～2．2GPa，M2），与含多硅白云母榴辉岩经历了相同的折返过程。锡铁山双矿物榴辉岩的原岩具有N-MORB的地球化学特征，而含多硅白云母榴辉岩则显示E-MORB或者OIB特征，二者原岩成分存在明显差异。两类榴辉岩的p-T演化过程和地球化学特征表明．锡铁山双矿物榴辉岩与含多硅白云母榴辉岩矿物学特征的差异是其原岩的多源性造成的，而与俯冲后折返过程中的退变质作用无必然联系。Eclogite, as an important rock type in the subduction zone, contains abundant geodynamic information of the earth. Studying the petrology of the eclogite and its retrogress equivalent helps building the p-T paths of the subduction zone and understanding the changes of the mineral facies and compositions of the subducted rocks and further constraining the exhumation mechanism in the subduction zone. This paper mainly focuses on the petrological studies of the bimineralic and phengite-bearing eclogite in the Xitieshan terrane, North Qaidam UHP metamorphic belt. We have calculated the p -T pseudosection of the eclgites under NC （K） FMASH system. It shows that the peak stage of the Bi-Ec preserved p-T conditions of 745-790℃, 〉2.8-3.0GPa （M1 stage） and experienced isothermal decompression to amphibole-eclogite facies p-T conditions （670-770℃, 1.6-2.2GPa,M2 stage）, which shows similar p-T path with the Phn-Ec. The Bi-Ec in the Xitieshan terrane has N-MORB geochemical characteristics, whereas the PhnEc shows E-MORB or OIB characters. It demonstrates that the protoliths of the Bim-Ec and Phn-Ec are different. Considering the p-T path and geochemical characters of the eclogite, it infers that the difference of the mineral assemblage between Bi-Ec and PhnEc are caused by the multiple origins of the eclogite protolith but not retrogression in the Xitieshan terrane.

关 键 词：榴辉岩 退变质作用 相平衡计算 构造演化 锡铁山 柴北缘超高压变质带 

分 类 号：P542.4[天文地球—构造地质学]