摘要
粤西云开地块高州钙硅酸盐麻粒岩保留了早古生代云开造山带构造热演化的重要信息,对其进行研究可以更好地了解该造山带的变质历史。详细的岩相学研究表明钙硅酸盐麻粒岩仅保留了峰期麻粒岩相和峰期后角闪岩相两个变质阶段的矿物组合(M1-M2)。峰期矿物组合(M1)由基质中平衡共生的石榴石+透辉石+斜长石+钾长石±方柱石构成,峰期后退变质矿物组合(M2)为蠕虫状透辉石+钙长石+石英后成合晶和钙铝榴石+石英冠状体及方解石+榍石+磁铁矿退变质矿物。由传统地质温压计和平均温压法计算获得钙硅酸盐麻粒岩峰期变质条件约为803℃/0.84 GPa,峰期后退变质条件约为660℃/0.63 GPa,指示钙硅酸盐麻粒岩经历了峰期中压高温麻粒岩相变质及晚期角闪岩相退变质过程。CL图像显示该样品中的锆石具有清晰的核‒边结构,LA-ICP-MS锆石U-Pb定年结果表明,锆石核部年龄为~970 Ma,代表钙硅酸盐麻粒岩的原岩形成于早新元古代,锆石边部206Pb/238U加权平均年龄为435±4 Ma,指示麻粒岩相变质作用发生在早古生代(加里东期)。结合变质反应结构、温压估算以及年代学研究结果,获得一条峰期后减压降温型顺时针P-T-t轨迹,指示钙硅酸盐岩麻粒岩形成于华南早古生代碰撞造山的构造环境,记录了扬子陆块与华夏陆块加里东期陆‒陆碰撞及碰撞后抬升的演化过程。
Calc-silicate granulites in the Yunkai massif of Western Guangdong contain important information of thermo-tectonic evolution of the early Paleozoic Yunkai orogen,and study of which may help to better understand the metamorphic history of the Yunkai orogenic belt.Detailed petrographic studies indicated that the samples preserved peak granulite-facies and post-peak amphibolite-facies mineral assemblages formed at two metamorphic stages(M1-M2).The peak metamorphic mineral equilibrium assemblages(M1)are identified as garnet+diopside+plagioclase+K-feldspar±scapolite in the matrix.The retrograde assemblages(M2)are characterized by vermicular diopside+anorthite+quartz symplectites and garnet+quartz coronas and retrograde mineral assemblage calcite+sphene+magnetite.Conventional thermobarometers and average P-T calculation result in the following P-T condition:803℃/0.84 GPa for peak metamorphism(M1)and 660℃/0.63 GPa for post-peak retrograde metamorphism(M2),respectively,indicating relatively high temperature and medium pressure peak granulite-facies metamorphism and post-peak amphibolite facies retrograde metamorphism.CL images of zircon grains from the calc-silicate granulites show a clear core-rim internal texture,LA-ICP-MS zircon U-Pb dating gives an early Neoproterozoic age(ca.970 Ma)for the formation of the protolith and a weighted average 206Pb/238U age is 435±4 Ma for the peak metamorphism.Based on the metamorphic reaction textures and P-T estimates,the post-peak decompressional cooling along a clockwise P-T trajectory was defined,which is consistent with the occurrence of an orogenic event.Combining with the early Paleozoic metamorphic age,we thus concluded that the calc-silicate granulites recoeded the continental collision between Yangtze and Cathaysia blocks and post-collisional uplift processes during the Caledonian orogenic event in South China.
作者
李超
仝来喜
黄小龙
刘兆
仲正
LI Chao;TONG Laixi;HUANG Xiaolong;LIU Zhao;ZHONG Zheng(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,Shaanxi,China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2020年第6期1172-1189,共18页
Geotectonica et Metallogenia
基金
国家重点研发计划“深地资源勘查开采专项”课题(2016YFC0600204)
中国地质调查局地质调查项目(DD2016343)联合资助
