红安造山带南缘古元古代杂岩体的发现对扬子板块古元古代造山事件的约束  

A Paleoproterozoic complex in the Hong'an orogenic belt,central China:New evidence for a Paleoproterozoic collisional orogenic belt in the Yangtze Block

作　　者：尹须伟 徐扬 杨坤光[2] 邓新[1] 魏运许 刘雨 YIN XuWei;XU Yang;YANG KunGuang;DENG Xin;WEI YunXu;LIU Yu(Wuhan Center of Geological Survey,China Geological Survey,Wuhan 430205,China;MOE Key Laboratory of Tectonics and Petroleum Resources,China University of Geosciences,Wuhan 430074,China;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]中国地质调查局武汉地质调查中心(中南地质科技创新中心),武汉430205 [2]中国地质大学,构造与油气资源教育部重点实验室,武汉430074 [3]中国地质大学(北京)地球科学与资源学院,北京100083 [4]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640

出　　处：《岩石学报》2021年第7期2123-2152,I0011-I0019,共39页Acta Petrologica Sinica

基　　金：湖北省自然科学基金项目(2020CFB344);中国地质大学构造与油气资源教育部重点实验室开放基金项目(TPR-2019-07);同位素地球化学国家重点实验室(中国科学院广州地球化学研究所)开放-合作基金项目(SKLabIG-KF-18-13);中国地质调查局地质调查项目(DD20190050)联合资助。

摘　　要：识别并研究扬子板块古元古代的岩浆-变质-沉积事件,是探讨扬子板块古元古代构造演化的基础,也是重建该陆块在Columbia超大陆中位置的前提。新发现的金盆杂岩体为进一步揭示扬子板块古元古代岩浆事件和造山过程提供了新的制约信息。锆石U-Pb定年结果表明,金盆片麻状二长花岗岩、奥长花岗岩和基性岩脉的形成年龄分别为-2478Ma、-2049Ma和-1999Ma。奥长花岗岩具有高的SiO_(2)(71.62%-76.92%)、Na_(2)O(4.58%-6.47%)含量,低的K2O(0.50%-1.06%)、FeOT+MgO(0.81%-3.86%)、Y(5.34×10^(-6)-14.7×10^(-6))和Yb(0.55×10^(-6)-1.07×10^(-6))含量,显示变化的Sr/Y(10.9-28.5)和(La/Yb)_(N)(4.7-21.6)比值和负的锆石εHf(t)值(-13.1--3.4)。这些特征表明,金盆奥长花岗岩可能为陆壳物质在加厚地壳源区部分熔融的产物,其类似TTG岩的地球化学特征主要受控于部分熔融过程中石榴石+角闪石在源区的残留。基性岩脉具有相对富集轻稀土和大离子亲石元素、亏损重稀土和高场强元素的微量元素配分模式,以及富集的Nd-Hf同位素组成(全岩εNd(t)=-3.47--2.47、锆石εHf(t)=-11--5.6),这样的弧型地球化学特征和富集的同位素组成是由地壳混染和富集地幔源区共同造成。高的Nb含量(11.4×10^(-6)-14.8×10^(-6))以及Nb/U(19.2-23.6)、Nb/La(0.53-0.65)和Nb/Th(3.71-4.67)比值指示其源区遭受了再循环沉积物熔体的交代。综合本文和前人的数据推测,扬子东、西陆块在2.15-2.0Ga不断汇聚,并可能在2.0-1.95Ga沿着黄陵-钟祥一线拼贴,最终形成古元古代统一的基底,这一过程可能与全球Columbia超大陆的形成有关。The relationship between the Yangtze Block(YTB)and the supercontinent Columbia remains unclear.Our new identification of Jinpen Complex in the southern Hong'an orogenic belt provides new constraints on the Palaeoproterozoic tectonic evolution of the YTB.Emplacement ages of the gneissic monzogranite,trondhjemite and mafic dyke are 2478±5Ma,2049±16Ma,and 1999±8Ma,respectively.Trondhjemites are rich in SiO_(2)(71.62%-76.92%)and Na_(2)O(4.58%-6.47%),depleted in K2O(0.50%-1.06%),FeOT+MgO(0.81%-3.86%),Y(5.34×10^(-6)-14.7×10^(-6))and Yb(0.55×10^(-6)-1.07×10^(-6)),with variable Sr/Y(10.9-28.5)and(La/Yb)N(4.7-21.6)ratios and enriched zircon Hf isotope values(εHf(t)=-13.1--3.4).These features suggest that the trondhjemites were derived from partial melting of a basaltic source at the base of a thickened magmatic arc,with garnet and amphibole in residuals.The mafic dykes have high Nb contents(11.4×10^(-6)-14.8×10^(-6))with high Nb/U(19.2-23.6),Nb/La(0.53-0.65)and Nb/Th(3.71-4.67)ratios.Their primitive mantle-normalized trace element patterns are characterized by enrichment of light rare-earth element and large-ion lithophile elements,but depletion of HREE and HFSE.Zircons from the mafic dyke display negativeεHf(t)values(-11--5.6),and whole-rock samples show negativeεNd(t)values(-3.47--2.47).Geochemical signatures suggest that mafic dyke in this study were derived from an enriched subarc mantle and underwent some degrees of crustal contamination.On the basis of our new data and the data from Paleoproterozoic rocks in the YTB,we propose a 2.15-1.95Ga subduction-collision zone along Huangling-Zhongxiang.The western YTB finally collided with the eastern YTB along this zone during 2.0-1.95Ga to form the united YTB,favoring tight linkage between YTB and the proposed Columbia.

关 键 词：锆石U-Pb-Hf同位素 古元古代 Columbia超大陆 红安造山带 

分 类 号：P542[天文地球—构造地质学] P588.12[天文地球—地质学]