地质学报2026，Vol.100Issue(8)：2789-2808,20.DOI:10.19762/j.cnki.dizhixuebao.2025291
柴北缘乌北地体早古生代变质岩年代学、地球化学及其构造意义
Geochronology and geochemistry of Early Paleozoic metamorphic rocks in the North Wulan Terrane of the North Qaidam Orogen,and its geological significance
摘要
Abstract
The North Wulan Terrane,which represents the overriding plate of the Early Paleozoic subduction-collision system in the North Qaidam Orogen,is key to understanding the composition of the lower crust beneath the arc-back-arc system and the tectonic evolution associated with the subduction of the South Qilian Proto-Tethyan oceanic crust.In this paper,we present detailed petrological,geochronological,and geochemical data,together with metamorphic P-T conditions,for representative mafic to felsic metamorphic rocks from the North Wulan Terrane.The results reveal that the protolith ages and tectonic settings of the three studied metamorphic rock types differ significantly.The amphibolites exhibit compositional characteristics similar to E-MORB,but they do not preserve protolith age information,which limits further discussion of their geodynamic significance.The biotite-amphibole gneisses display geochemical signatures of a continental arc,with protoliths formed at 471±3 Ma,representing magmatic records of a continental marginal arc during subduction of the Proto-Tethyan oceanic crust.The granitic mylonites exhibit geochemical features resembling arc granites and formed at 965±6 Ma,indicating that they represent arc magmatism in an active continental margin setting related to the assembly of the Neoproterozoic Rodinia supercontinent.Combined with previous studies,it is proposed that the lower part of the crust beneath the arc-back-arc system,represented by the North Wulan Terrane,is primarily composed of Precambrian basement(including various types and ages of metasedimentary and meta-igneous rocks)and Early Paleozoic continental arc magmatic rocks.These rocks underwent widespread Middle to Late Ordovician HT/LP metamorphism,with corresponding ages concentrated between ca.475～440 Ma.This period is notably confined to the late stage of oceanic subduction recorded by arc magmatism(ca.510～450 Ma),and is nearly synchronous with the eclogite-facies metamorphism associated with subduction of oceanic crust documented in the Dulan UHP unit.Integrating these data with previous studies on metamorphic P-T evolution,we suggest that the HT/LP metamorphism occurred within an extensional environment at the continental marginal arc,and was triggered by slab rollback during the late stage of plate convergence.This highlights the critical role of studying the metamorphism in overriding plates within subduction zones to reconstruct the tectonic evolution of oceanic subduction.关键词
柴北缘构造带/乌北地体/变质岩/年代学/地球化学/板片回卷Key words
North Qaidam tectonic belt/North Wulan Terrane/metamorphic rock/geochronology/geochemistry/slab rollback引用本文复制引用
周凯,高一杰,孔会磊,张江伟,赵民,荆德龙,贺永康,谢春林..柴北缘乌北地体早古生代变质岩年代学、地球化学及其构造意义[J].地质学报,2026,100(8):2789-2808,20.基金项目
本文为国家自然科学基金项目(编号42402063,42202102)、陕西省自然科学基金项目(编号2024JC-YBQN-0344)和中国地质调查局地质调查项目(编号DD20190143,DD202402046)联合资助的成果. （编号42402063,42202102）
