华北东南缘五河杂岩中镁铁质麻粒岩的变质演化  

Metamorphic Evolution of Mafic Granulites from the Wuhe Complex at the Southeastern Margin of the North China Craton

作　　者：王程程[1] 刘贻灿[1] 杨阳 张品刚[1,2] 聂佳珍 

机构地区：[1]中国科学院壳幔物质与环境重点实验室中国科学技术大学地球和空间科学学院,安徽合肥230026 [2]安徽省煤田地质局勘察研究院,安徽合肥230088

出　　处：《地球科学》2018年第1期296-316,共21页Earth Science

基　　金：国家自然科学基金项目(No.41773020);国家重点基础研究发展计划(973计划)项目(No.2015CB856104);高等学校博士学科点专项科研基金(No.20133402130008)

摘　　要：华北东南缘五河杂岩的变质演化过程研究有助于揭示研究区前寒武纪变质基底的形成与演化历史.基于对五河杂岩中镁铁质麻粒岩进行的详细岩相学观察、矿物电子探针及锆石LA-ICP-MS U-Pb定年和微量元素分析,识别出古元古代变质演化的3个阶段,重建了峰期后近等温减压及降压冷却的顺时针P-T-t轨迹.峰期高压麻粒岩相变质阶段的代表性矿物组合为石榴子石(富Ca核部)+单斜辉石(富Al)+斜长石+石英+金红石±角闪石(富Ti),所记录的峰期温压条件为850~900℃、1.5GPa;峰期后近等温减压麻粒岩相变质阶段,富Ti角闪石分解在周围形成石榴子石+斜方辉石+斜长石±单斜辉石的矿物组合,所记录的温压条件为~900℃、1.1~1.2GPa;晚期角闪岩相退变质阶段,石榴子石分解产生角闪石+斜长石±石英,所记录的温压条件为600~680℃、0.65~0.75GPa.锆石U-Pb定年结果表明,高压麻粒岩相、中压麻粒岩相和角闪岩相变质时代分别为~1.90Ga、~1.85Ga和~1.78Ga.因此,研究区镁铁质麻粒岩的变质演化过程与胶北地体可以对比,结合已有的2.1Ga花岗质岩石的成因和锆石年代学等方面研究成果,进一步证明五河杂岩属于胶-辽-吉带的西延,二者共同构成了华北克拉通东部一条古元古代碰撞造山带.Investigations on metamorphic processes of the Wuhe complex provide new insights into the formation and evolution of Precambrian metamorphic basement at the southeastern margin of the North China Craton（NCC）.In this paper,three Paleoproterozoic stages of metamorphic assemblages from mafic granulites in the Wuhe complex is recognized and a clockwise P-T-t path characterized by post-peak near-isothermal decompression and subsequent decompression-cooling by conducting detailed petrographic observations,mineral electron microprobe analysis,zircon LA-ICP-MS U-Pb dating and trace element analysis is reconstructed.The peak HP granulite-facies metamorphism（M1）is characterized by high-Ca cores in granet,highAl cores in clinopyrexene,plagioclase,quartz and rutile,yielding P-T conditions of 850-900℃ and 1.5 GPa.The mediumpressure（MP）granulite facies assemblage（M2）mainly consists of garnet＋orthopyrexene＋plagioclase±clinopyrexene surrounding the amphibole porphyroblasts,recording P-Tconditions of -900℃ and 1.1-1.2 GPa.Symplectites or coronas com-posed of hornblende＋plagioclase（M3）surrounding the garnet porphyroblasts indicate garnet decompressional reactions occurred at 600-680℃ and 0.65-0.75 GPa.The zircon dating results can be categorized into three groups of -1.90 Ga,-1.85 Ga and-1.78 Ga,corresponding to the time of HP granulite facies,MP granulite facies and amphibolite facies metamorphism.The comparable metamorphic evolution of mafic granulites from the Wuhe complex to Jiaobei terrane,combined with previous studies on petrogenesis and U-Pb ages of 2.1 Ga granitic rocks,suggest that the Wuhe complex is the west extension of the Jiao-Liao-Ji belt（JLJB）and they constitute a Paleoproterozoic collisional orogen as a whole in the eastern block of the NCC.

关 键 词：镁铁质麻粒岩 高压麻粒岩相 前寒武纪变质基底 古元古代 五河杂岩 岩石学 

分 类 号：P588.34[天文地球—岩石学] P586[天文地球—地质学]