冀北康保芦家营巨斑状花岗岩:华北克拉通北缘中段1.3~1.2 Ga B.P.伸展-裂解事件的地质记录  

The Lujiaying megaporphyric granite in Kangbao area,North Hebei:A geological record of extension and breakup event at 1.3~1.2 Ga B.P.in the central segment of northern margin of North China Craton

作　　者：牛腾 倪志耀[1] 孟宝航 潘登 胡军亮 田涛[1] NIU Teng;NI Zhiyao;MENG Baohang;PAN Deng;HU Junliang;TIAN Tao(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]成都理工大学地球科学学院,成都610059

出　　处：《成都理工大学学报（自然科学版）》2023年第4期486-503,共18页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：国家自然科学基金资助项目(41272087,41072050,40472041)。

摘　　要：以冀北康保芦家营巨斑状花岗岩为对象,进行了岩相学、地球化学、锆石U-Pb年代学研究,探讨其构造属性、形成时代,进而为华北克拉通北缘1.3~1.2 Ga B.P.伸展-裂解事件研究提供新的证据。巨斑状花岗岩体主要出露在康保芦家营、小英图及永德堂一带,呈北东-南西向展布,侵位于中元古代化德群之中,而后又被晚古生代-中生代花岗岩体所侵入。花岗岩体的岩性单一,为片麻状-弱片麻状似斑状黑云二长花岗岩,以含有许多不等量且个体粗大(较大者可达5~10 cm,多数在3~5 cm)、呈板柱状或眼球状产出的微斜长石巨斑(可有少量斜长石巨斑)及黑云母成团分布为特征。巨斑状花岗岩具有铝质A型花岗岩(A 2亚类)的地球化学属性,形成于陆缘裂谷(裂陷槽)的构造环境,可能属于中-上地壳钙碱性花岗质岩石部分熔融、冷凝结晶形成的板内花岗岩。巨斑状花岗岩的锆石LA-ICP-MS U-Pb年龄为(1235±7.9)Ma,表明其形成于中元古代晚期,应该是华北克拉通北缘1.3~1.2 Ga B.P.伸展-裂解事件的地质记录,可与华北克拉通广泛存在的1.3~1.2 Ga B.P.基性岩墙群相对应。从全球范围内广泛存在的1.3~1.2 Ga B.P.伸展-裂解事件来看,华北克拉通北缘中段1.3~1.2 Ga B.P.伸展-裂解事件应与哥伦比亚超大陆的最后一次裂解有关,是华北克拉通对哥伦比亚超大陆晚期裂解事件的响应。Based on petrography,geochemistry and zircon U-Pb chronology,the megaporphyritic granites in the Lujiaying area,Kangbao County,northern Hebei Province,are studied in order to investigate their tectonic properties and forming ages,and thus provide new evidence for the extension-breakup events at 1.3~1.2 Ga B.P.in the northern margin of North China Craton.The megaporphyritic granites mainly occur in Lujiaying,Xiaoyingtu and Yongdetang areas of Kangbao County,cropping out from northeast to southwest,invading in the Middle Proterozoic Huade Group,and then invaded by late Paleozoic to Mesozoic granites.Lujiaying granite is a porphyritic monzogranite,with gneissic-weak gneissic structure,in which phenocrysts are mainly microcline,with a small amount of plagioclase.The phenocrysts are coarse,(the larger ones can reach 5~10 cm,most of them are between 3~5 cm)with column and augen shape.Biotite occurs as clumps scattered in the rock.Geochemical analysis shows that the megaporphyritic granite has the property of aluminous A-type granite(A 2 subclass),formed in the tectonic environment of continental margin rift(rifting trough),and may belong to the intra-plate granite formed by partial melting and condensation crystallization of calc-alkaline granitic rocks in the middle-upper crust.Zircon LA-ICP-MS U-Pb age of the megaporphyritic granite is 1235±7.9 Ma,indicating that the granite was formed in the late Mesoproterozoic and representing a geological record of extension-breakup event at 1.3~1.2 Ga B.P.in the northern margin of North China Craton,which is consistent with the formation of widespread basic dike swarm at 1.3~1.2 Ga B.P.in the area.It is considered that the widespread worldwide 1.3~1.2 Ga B.P.extension-cracking event is related to the last breakup of the Columbia supercontinent,while the extension-breakup event occurred in the middle section of the North China Craton at 1.3~1.2 Ga B.P.should be the response of the North China Craton to the late breakup event of the Columbia supercontinent.

关 键 词：铝质A型花岗岩 裂陷槽 中元古代晚期 巨斑状花岗岩 冀北 

分 类 号：P588.121[天文地球—岩石学]