Two phases of granulite-facies metamorphism superimposied on retrograde eclogite:Constraints on the early Paleozoic tectonic evolution of the Qinling Orogenic Belt,central China  

作　　者：Bowen Bai Danling Chen Yunfei Ren Xiaohui Zhu Yunpeng Dong Yuan Tang Haijie 

机构地区：[1]Wang State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,PR China [2]Collaborative Innovation Centre of Continental Tectonics,Northwest University,Xi’an 710069,PR China [3]School of Petroleum Engineering and Environmental Engineering,Yan’an University,Yan’an 716000,PR China

出　　处：《Geoscience Frontiers》2025年第1期1-18,共18页地学前缘(英文版)

基　　金：supported by the National Natural Science Foundation of China(Grants Nos.42372074,42030307,41972058 and 41802056);Natural Science Basic Research Program of Shaanxi(Program Nos.2023-JC-QN-0366 and 2023-JC-YB-254);the MOST Special Fund from the State Key Laboratory of Continental Dynamics.

摘　　要：Existing studies provide adequate petrological evidences on ca.500 Ma ultra-high pressure(UHP)metamorphism in the North Qinling Orogenic Belt(NQOB)in central China,but the genesis of 470-420 Ma multi-phase granulite-facies metamorphism in the NQOB and their relationship with the ca.500 Ma UHP metamorphism remain controversial,resulting in the early Paleozoic evolution of the Qinling Orogenic Belt(QOB)highly debatable.In this study,we present mafic granulites and host felsic gneisses with a“red-eye socket”texture from the Shuanglong area,eastern NQOB,which recorded two phases of granulite-facies metamorphism superimposing on former eclogite-facies metamorphism.The former eclogite-facies metamorphism is indicated by eclogite-facies zircon trace element patterns and 496-495 Ma zircon ages,which are the same with those of the HP-UHP eclogite-facies metamorphic rocks in NQOB.The first granulite-facies metamorphism occurred at 460-448 Ma is characterized by coarse-grained minerals in matrix.Compositions and zonings of these minerals define an anticlockwise P-T path involving a prograde stage(751-763℃),a high-temperature peak stage(9.2 kbar and 864℃),and a near-isobaric cooling retrograde stage(8.3 kbar and 818℃).The second granulite-facies metamorphism occurred at 422-421 Ma is represented by coronal garnet and coexisting fine-grained mineral aggregates.Coronal garnet compositional zonings suggest a clockwise P-T path consisting of a high-pressure peak stage(9.5-11.2 kbar and 748-783℃)and a decompressing and heating retrograde stage(9.2-9.5 kbar and 789-800℃).Combining dating results of leucosomes in these rocks and existing data,we proposed a new model for early Paleozoic tectonic evolution of the NQOB.The North Qinling Terrane(NQT),probably separated from the South China Block(SCB)during the breakup of Rodinia,drifted northwards and underwent UHP metamorphism at 500 Ma and then rapidly exhumed to crust level.Later,the Shangdan Ocean subducted northwards beneath the exhumed NQT at 470-440 Ma,resulting in

关 键 词：“Red-eye socket”texture Granulite-facies metamorphism Multi-cycle collisional orogen North Qinling Orogenic Belt 

分 类 号：P58[天文地球—岩石学]