摘要
帕米尔构造结位于特提斯构造域中部,它记录了完整的特提斯演化过程。然而,对于该区原特提斯洋俯冲极性、过程及原特提斯到古特提斯的转换,还存在很大争议。在北东帕米尔地区,我们识别出晚奥陶世辉石闪长岩,顺层侵入于布伦阔勒岩群石榴黑云片麻岩中。笔者等对岩体的岩相学、锆石U-Pb年龄、全岩地球化学、矿物学、全岩Sr—Nd及锆石Lu—Hf同位素组成进行测试分析。分析结果显示,塔什库尔干辉石闪长岩主要由角闪石(40%~45%)、斜长石(35%~40%)、黑云母(6%~10%)、未交代完全的单斜辉石(15%~20%)组成。锆石U-Pb谐和年龄为457.6±2.6 Ma。岩石的Al_(2)O_(3)(13.17%~18.79%),SiO_(2)(49.85%~55.85%)、MgO(3.52%~9.12%)和全碱含量(Na_(2)O+K_(2)O=2.93%~4.92%)变化大,显示拉斑系列特征。在微量元素方面,岩石富集大离子亲石元素和轻稀土元素(La_(N)/Yb_(N)=2.47~5.87),亏损高场强元素,(Nb/La=0.31~0.81),显示岛弧玄武岩特征。岩石具有不均一且解耦的Nd—Hf同位素组成,(ε_(Nd)(t)=-8.79~-2.24,ε_(Hf)(t)=-2.1~+4.5),表明其原始岩浆来源于主要受到俯冲流体交代的富集地幔楔的部分熔融,并有亏损的软流圈物质加入。其原始岩浆具有高的氧逸度lgfO_(2)(-15.71~-11.98)和含水量(4.35%~5.24%)。结合前人研究,表明帕米尔地区原特提斯洋为南向俯冲,从寒武纪早期持续到奥陶纪晚期。
Objectives:The Pamir syntax at the central part of the Tethys tectonic domain records the whole Tethys evolution process.However,some key issues such as the subduction orientation and process of the Proto-Tethys Ocean,and the transition from the Proto-Tethys to Paleo-Tethys transition in the region,are still hotlly debated.This study attempts to address the genesis and tectonic background of Ordovician pyroxene diorites in Tashkorgan,and to shed new light for our better understanding the Early Paleozoic tectonic evolution in the Proto-Tethys Ocean.Methods:In this paper,we present field observations,petrography,new zircon U-Pb ages,whole-rock as well as mineral geochemistry,bulk-rock SrNd isotopic and zircon Hf isotopic data of the Early Paleozoic Tashkorgan pyroxene diorites in the Pamir syntax.Results:The Ordovician Tashkorgan pyroxene diorites were emplaced at the southern part of the Bulukuole Group as sheets and extended several kilometers in length.They are mainly composed of hornblende(40%~45%),plagioclase(35%~40%),biotite(6%~10%),and altered pyroxene(15%~20%).The LA-MC-ICPMS zircon U-Pb dating yields concordant age of 457.6±2.6 Ma(MSWD=0.68,n=20).The rocks have variable Al_(2)O_(3)(13.17%~18.79%),SiO_(2)(49.85%~55.85%),MgO(3.52%~9.12%),and alkali(Na_(2)O+K_(2)O=2.93%~4.92%)contents,and they are enriched in large ion philanthropists elements(LILEs)and LREE(La_(N)/Yb_(N)=2.47~5.87),and are depleted in high-field-strength elements(HFSEs)(Nb/La=0.31~0.81),sharing the features of island arc basalts.The samples exhibit decoupled Nd—Hf isotopic compositions,with enriched bulk-rock Nd isotopic compositions(ε_(Nd)(t)=-8.79~-2.46,)but depleted zircon Lu—Hf composition(ε_(Hf)(t)=-2.1~+4.5).All these characteristics demonstrated that the Tashkorgan pyroxene diorites most likely originated from partial melting of the enriched lithospheric mantle metasomatized by subduction slab fluids but with variable involvement of melts from depleted asenthospheric mantle.Conclusions:The data presented in this contribution,in combination with previous works,unambiguously argue for the southward subduction of the Proto-Tethys oceanic slab.
作者
王泓然
张传林
Masumeh SARGAZI
宋志豪
景妍
叶现韬
刘晓强
WANG Hongran;ZHANG Chuanlin;Masumeh SARGAZI;SONG Zhihao;JING Yan;YE Xiantao;LIU Xiaoqiang(College of Oceanography,Hohai University,Nanjing,210098;School of Geology and Mining Engineering,Xinjiang University,Urumqi,830017)
出处
《地质论评》
CAS
CSCD
北大核心
2024年第6期2142-2160,共19页
Geological Review
基金
科技部重点研发项目子课题(编号:2021YFC2901904-1)的成果。
