敦煌地块寒武纪—早奥陶世中酸性侵入体:古亚洲洋南缘古生代早期俯冲的记录  

Cambrian-Early Ordovician intrusive bodies in Dunhuang Block: Records of Paleo-Asian Ocean subduction and implications for regional Early Paleozoic tectonic evolution

作　　者：康磊[1,2] 王涛[3] 李天虎[2] 计文化[2] 王杰 董浩强 张玉[6] 张超 KANG Lei;WANG Tao;LI TianHu;JI WenHua;WANG Jie;DONG HaoQiang;ZHANG Yu;ZHANG Chao(Department of Geology,Northwest University,Xi an 710069,China;Centre of Orogenic Belt Geology,CGS,MNR Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,Xi'an Center of Geological Survey,CGS,Xi'an 710054,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Xi an Institute of Geological and Mineral Exploration,Xi'an 710054,China;School of Earth Sciences,China University of Geosciences,Beijing 100083,China;School of Earth Sciences and Resources,Chang an University,Xi'an 710054,China)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [2]中国地质调查局造山带地质研究中心,自然资源部岩浆作用成矿与找矿重点实验室,中国地质调查局西安地质调查中心,西安710054 [3]中国地质科学院地质研究所,北京100037 [4]西安地质矿产勘察开发院,西安710054 [5]中国地质大学地球科学学院,北京100083 [6]长安大学地球科学与资源学院,西安710054

出　　处：《岩石学报》2023年第3期823-844,共22页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41202044、41002063);中国地质调查局二级项目(DD20160009、DD20179607、DD20190370);陕西省自然科学基金项目(2012JM5004)联合资助。

摘　　要：一直以来,敦煌地块缺少1.6-0.46Ga的地质记录,从而严重制约了对该地块在新元古代和早古生代期间地质构造演化的全面认识。通过1:5万区域地质调查,本次工作在敦煌地块东北缘新发现了寒武纪-早奥陶世小宛山岩体、截山子岩体和小宛南岩体等多个中酸性侵入体,测得其LA-ICP-MS锆石U-Pb年龄分别为517±3Ma、480±3Ma和473±3Ma,由此厘定出敦煌地块目前古生代最古老的侵入岩体及早奥陶世侵入岩体。通过这些岩体的岩石岩相学、岩石地球化学特征、岩石成因及大地构造环境分析,表明它们属于与洋壳俯冲消减作用有关的活动陆缘环境下形成的富钠质I型花岗岩。其中,小宛山花岗闪长质岩体是在低压低温条件下由玄武质地幔楔部分熔融而成,同时受到俯冲流体的强烈交代;截山子岩体和小宛南岩体则是在高压低温富水条件下,由新生镁铁质洋壳发生部分熔融并受到地幔楔强烈混染而形成,虽然它们均属于(类)O型埃达克岩,但其部分熔融的压力及其残留矿物组合不同。上述研究揭示敦煌地块北缘早古生代517Ma就存在俯冲作用,且至少持续了44Myr。结合区域地质资料和以往研究成果,敦煌地块北缘早古生代洋陆转换过程可分为三个阶段:(1)晚震旦世-早寒武世(574-518Ma),敦煌地块北缘被动陆缘演化阶段;(2)寒武纪第二世-早奥陶世(517-471Ma),敦煌地块北缘活动陆缘演化阶段,期间,古亚洲洋南支洋分别向敦煌地块和石板山地块/马鬃山地块发生双向俯冲消减;(3)中奥陶世-早泥盆世(464-412Ma),敦煌地块与石板山地块/马鬃山地块碰撞造山阶段,期间古亚洲洋南支洋闭合。The lack of 1.6-0.46 Ga geological records in the Dunhuang Block badly restricted the comprehensive understanding of its Early Paleozoic tectonic evolution. In 1/50,000 regional geological survey, three Cambrian-Early Ordovician intermediate-acid intrusive bodies, namely the Xiaowanshan, the Shuishanzi and the Xiaowannan plutons, were discovered in the northeastern margin of the Dunhuang Block. The LA-ICP-MS zircon U-Pb ages of these plutons are 517±3 Ma, 480±3 Ma and 473±3 Ma, respectively, and thus determined an earliest Early Paleozoic magmatism and Early Ordovician magmatism in the Dunhuang Block. Based on the analysis of petrography, petrogeochemical characteristics, petrogenesis and tectonic setting, these intrusions are sodium-rich I-type granites formed in the active continental margin environment related to oceanic crust subduction. Among them, the Xiaowanshan Pluton was formed by partial melting of a basaltic mantle wedge under low pressure and low temperature with a strong metasomatization by subduction fluids;while the Jieshanzi and Xiaowannan plutons were formed by partial melting of a new mafic oceanic crust under a condition of high pressure and low temperature together with rich water, and subsequently strongly contaminated by a mantle wedge. Although both of the later two plutons belong to a type of classic O-type adakite, their formation pressure and residual minerals during the partial melting were different. Combined with the regional geological information, the Early Paleozoic ocean-continent transition on the northern margin of Dunhuang Block can be divided into three stages:(1) the Late Sinian-Early Cambrian(574-518 Ma): the passive continental margin stage of the Dunhuang Block;(2) the Cambrian II-Early Ordovician(517-471 Ma): the active continental margin satge of the northern margin of the Dunhuang Block, when the ancient Asian Ocean subducted to the Dunhuang Block and the Shibanshan/Mazongshan blocks in two directions;(3) the Middle Ordovician-Early Devonian(464-412 Ma): a satge of c

关 键 词：寒武纪-早奥陶世 侵入体 敦煌地块 早古生代 古亚洲洋俯冲 大地构造演化 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]