辽北地区克拉通与造山带边界的限定:来自晚古生代-早中生代花岗质岩石锆石Hf同位素证据  

Constraints on the craton-orogen boundary in the northern Liaoning Province:Evidence from zircon Hf isotopes of the late Paleozoic-early Mesozoic granitoids

作　　者：张琪琪 张拴宏[1,2] 赵越 胡国辉[1,2] ZHANG Qiqi;ZHANG Shuanhong;ZHAO Yue;HU Guohui(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Beijing 100081,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081

出　　处：《地质学报》2024年第6期1715-1731,共17页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号U2244213,41920104004,41725011)资助的成果。

摘　　要：华北地块北缘主要由北侧白乃庙弧带和南侧华北克拉通组成,尽管白云鄂博-多伦-赤峰-开原断裂被认为是克拉通与造山带边界,但在辽北地区该断裂带的具体位置并不明确。华北克拉通与白乃庙弧不同的基底属性和演化历史导致了两大构造单元内岩浆岩(主要为中酸性岩石)具有不同的Nd-Hf同位素组成。本文以辽北地区广泛出露的晚古生代—早中生代花岗质岩石为研究对象,通过对其进行年代学和Hf同位素研究,以此来限定辽北地区克拉通与造山带的边界位置。研究结果表明:位于白乃庙弧与华北克拉通北缘之上的石炭纪和二叠纪—早三叠世花岗质岩石锆石Hf同位素组成具有明显差异,具体表现为前者ε_(Hf)(t)值均为正值且平均地壳模式年龄T^(C)_(DM)普遍小于1.0Ga,后者ε_(Hf)(t)值均为负值且平均地壳模式年龄T^(C)_(DM)普遍大于2.2Ga。尽管中三叠世花岗质岩石锆石Hf同位素组成变化范围较大且有少量区域重合,但总体上仍表现出不同的特征。本文通过对比辽北地区石炭纪-中三叠世花岗质岩石锆石Hf同位素组成,结合太古宙-古元古代变质结晶基底岩系的分布范围,初步限定了辽北地区古老克拉通(华北克拉通)与年轻造山带(白乃庙弧)的边界位置:阜新北约60km-彰武西南部-新民北部-法库南部-铁岭西部-开原东部-清河断裂。The northern margin of the North China Block consists of the Bainaimiao arc belt in the north,and the North China Craton in the south with the Bayan Obo-Duolun-Chifeng-Kaiyuan fault as the cratonorogen boundary.However,the location of this boundary in the northern Liaoning Province has not been well constrained.The Bainaimiao arc is an island arc with different basement compositions and evolution history from the North China Craton,and the magmatic rocks(mainly intermediate-acid magmatic rocks)have different Nd-Hf isotopic compositions in these two tectonic units.This paper presents new LA-ICPMS zircon U-Pb geochronological and Hf isotopic data of late Paleozoic-early Mesozoic granitoids widely exposed in the northern Liaoning Province.The Hf isotopic composition of zircons from Carboniferous and Permian-Early Triassic granitoid rocks located on the Bainaimiao arc and the northern North China Craton is significantly different.The ε_(Hf)(t)values of the former are positive and the mean crustal model ages T^(C)_(DM) are generally less than 1.0 Ga.The ε_(Hf)(t)values of the latter are negative and the mean crustal model ages T^(C)_(DM) are generally greater than 2.2 Ga.Although the Hf isotopic composition of zircons from the middle Triassic granitic rocks varies widely,and there are a few overlapping regions,they still show different characteristics in general.The zircon Hf isotopic compositions of Carboniferous-middle Triassic granitoids from the northern Liaoning Province,combined with the distribution range of Archean-Paleoproterozoic metamorphic crystalline basement rocks,showing that the craton-orogen boundary in the northern Liaoning Province is located 60 km to the north of Fuxin-southwest Zhangwu-northern Xinmin-southern Faku-western Tieling-eastern Kaiyuan-Qinghe fault.

关 键 词：华北克拉通 白乃庙弧 克拉通与造山带边界 花岗质岩石 锆石HF同位素 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]