华北克拉通孔兹岩带磴口和佘太地区花岗片麻岩和斜长角闪岩变质锆石对其北界位置的再约束  

Studies on Metamorphic Zircons of Granitic Gneisses and Amphibolites in the Dengkou and Shetai Areas of the Khondalite Belt of the North China Craton:More Constraints on Its Northern Boundary

作　　者：段瑞涵 刘超辉[1] 施建荣[2] Duan Ruihan;Liu Chaohui;Shi Jianrong(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Tianjin Center,China Geological Survey,Tianjin 300170,CAzwa)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]天津地质调查中心,天津300170

出　　处：《地球科学》2020年第9期3386-3402,共17页Earth Science

基　　金：国家自然科学基金委重大项目(No.41890833);国家重点研发计划深地专项(No.2017YFC0601301);中国地质调查局公益性基础地质调查项目(No.DD20190003)。

摘　　要：准确限定古老陆块及其之间造山带或缝合带的位置一直是早前寒武纪研究的难点和热点之一.前人对华北克拉通西部孔兹岩带边界在磴口地区的延伸方向以及在佘太地区的具体位置一直存在着争议.基于此,本次研究对孔兹岩带西部磴口地区的花岗片麻岩和中部佘太地区的斜长角闪岩中的变质锆石进行了矿物包裹体、U-Pb同位素以及微量元素的研究.结果表明磴口地区一个花岗片麻岩岩浆锆石的U-Pb年龄为2 549±14 Ma,变质锆石年龄为1 874±26 Ma,另一个花岗片麻岩变质锆石的U-Pb年龄为1 877±25 Ma,锆石的稀土元素整体呈现出左倾的特征.佘太地区北部一个斜长角闪岩样品变质锆石的UPb年龄为2 469±15 Ma,南部两个样品的变质年龄为1 924±25 Ma和1 800±20 Ma,锆石的稀土元素同样表现为左倾的特征.结合岩石组合、新太古代末和古元古代两期变质事件的空间分布及前人的研究成果,表明在磴口地区孔兹岩带与阴山陆块的边界更有可能向西延伸,而非以往认为的向西南方向延伸,而在佘太地区这条边界应沿武川-固阳-佘太分布,而非以往认为的沿武川-固阳-乌拉特后旗分布.This paper presents a study of the mineral inclusions, U-Pb isotopes and trace elements of the metamorphic zircons from the granitic gneisses in the Dengkou area and the amphibolites in the Shetai area. The results show that the U-Pb age of one granite gneiss magmatic zircon in Dengkou area is 2 549±14 Ma, the age of metamorphic zircon is 1 874 ± 26 Ma, and that of another granite gneiss metamorphic zircon is 1 877 ± 25 Ma, and their REE patterns are generally left-leaning. On the other hand, the metamorphic zircons of the amphibolites in the Shetai area yield U-Pb ages of 1 924±25 Ma and 1 800±20 Ma in the south and2 469±15 Ma in the north, respectively and they also show left-leaning REE patterns. Based on the rock assemblage, spatial distribution of the late Neoarchean and Paleoproterozoic metamorphic events, and the previous research results, we suggest that the north boundary of the Khondalite Belt in the Dengkou area more likely extends to the west, rather than the southwest as previously thought and the boundary in the Shetai area is distributed along the Wuchuan-Guyang-Shetai instead of along the Wuchuan-Guyang-Urad Houqi.

关 键 词：华北克拉通 孔兹岩带 古元古代 锆石U-PB定年 微量元素 锆石包裹体 岩石学 

分 类 号：P597[天文地球—地球化学]