华北克拉通怀安杂岩中“MORB”型高压基性麻粒岩的成因及其构造意义  

Petrogenesis of the MORB type highpressure mafic granulite from the Huai’an complex in North China Craton and its tectonic implications

作　　者：张家辉 王惠初 田辉[1,2] 任云伟 常青松 施建荣 相振群[1,2] ZHANG JiaHui;WANG HuiChu;TIAN Hui;REN YunWei;CHANG QingSong;SHI JianRong;XIANG ZhenQun(Tianjin Centre,China Geological Survey,Tianjin 300110,China;Precambrain Geological Research Centre,China Geological Survey,Tianjin 300170,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]中国地质调查局前寒武纪地质研究中心,天津300170 [3]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029

出　　处：《岩石学报》2019年第11期3506-3528,共23页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(41902196);中国地质调查局地调项目(DD20160042、D20190035、DD20190472)联合资助

摘　　要：古元古代是华北克拉通重要的构造演化阶段,现已识别出多条碰撞造山带,但这些造山带的构造边界、演化时限以及地球动力学过程仍存在争议。本文报道了在怀安杂岩中新发现的一套高压基性麻粒岩-大理岩-富铝片麻岩表壳岩组合,原岩为一套基性火山岩-碳酸盐岩-砂/泥岩建造。高压基性麻粒岩记录了峰期高压麻粒岩相变质和麻粒岩相-角闪岩相退变质过程;地球化学研究表明其原岩为亚碱性拉斑玄武岩,具有平坦的稀土元素配分模式((La/Yb)N=1. 35~1. 79),轻稀土相对亏损((La/Sm)N=0. 83~1. 13),弱的正铕异常(δEu=1. 0~1. 22),无Nb、Ta负异常,与洋中脊玄武岩(MORB)地球化学特征类似;岩石组合和产状特征与晋冀蒙交界地区广泛分布的具有岛弧拉斑玄武岩性质的岩墙型高压基性麻粒岩明显不同。高压基性麻粒岩锆石εHf(t)为正值(+2. 6^+11. 5),单阶段模式年龄(tDM)介于2065~2250Ma之间,可能来源于尖晶石稳定域的浅层地幔源区。综合来看,这套含高压基性麻粒岩组合可能是古洋壳残片。SHRIMP U-Pb定年和Hf同位素研究表明,高压基性麻粒岩的原岩可能形成于2. 15~2. 2Ga,峰期高压麻粒岩相变质年龄为~1. 95Ga,1. 83~1. 82Ga代表麻粒岩相退变质作用和减压熔融时限。本文研究表明,该套表壳岩组合记录了古元古代俯冲-碰撞-折返等一系列造山构造演化过程,可为恢复古元古代造山带早期构造环境提供证据。The Paleoproterozoic is an important era in the tectonic evolution of North China Craton. Several collisional orogenic belts have been recognized, but their tectonic boundaries, temporal evolution and geodynamic process are still controversial. This contribution reports a new supracrustal rock association which consists of high-pressure mafic granulite,marble and aluminium-rich gneiss in the Huai’an complex. The protolith rock is a set of basic volcanic rocks-carbonate-sand/mudstone. The high-pressure mafic granulite has a typical mineral assemblage of high-pressure granulite facies,and recorded a granulite-amphibolite facies retrograde metamorphism. Geochemical studies show that the original rock of the high-pressure mafic granulite is a sub-alkaline tholeiite with a nearly flat rare earth pattern(( La/Yb)_N= 1. 35 ~ 1. 79),light rare earth element( LREE) depleted(( La/Sm)_N= 0. 83 ~ 1. 13),and shows weakly positive Eu anomalies( δEu = 1. 0 ~ 1. 22) and markedly negative anomalies in Na-Ta,which has similar geochemical characteristics as mid-ocean ridge basalt( MORB). Their rock association and occurrence characteristics are significantly different from the dyke-type high-pressure basic granulite with island arc basalt properties which widely distributed in the border area of Shanxi,Hebei and Inner Mongolia provinces. The high-pressure mafic granulite display positive zircon εHf( t) values( + 2. 6 ^+ 11. 5) with model ages of 2065 ~ 2250 Ma,and which may be derived from the shallow mantle source of the spinel stability domain.This supracrustal rock association is probably a paleo-oceanic remnant. SHRIMP U-Pb dating results and Hf isotope studies indicate that age of the protolith of high-pressure granulite may be 2. 15 ~ 2. 2 Ga, ~ 1. 95 Ga represents the peak age of the high-pressure granulite facies metamorphism,and 1. 83 ~ 1. 82 Ga is the timing of granulite facies retrograde metamorphism and decompression melting. This study shows that the supracrustal rock association recorded Paleoproterozoic orogenic

关 键 词：高压基性麻粒岩 MORB 古元古代 造山作用 怀安杂岩 华北克拉通 

分 类 号：P588.347[天文地球—岩石学] P597.3[天文地球—地质学]