Progresses and overviews of voluminous meta-sedimentary series within the Paleoproterozoic Jiao-Liao-Ji orogenic / mobile belt,North China Craton
Progresses and overviews of voluminous meta-sedimentary series within the Paleoproterozoic Jiao-Liao-Ji orogenic / mobile belt,North China Craton
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作者：
L. Fu
华北克拉通内确定了3条古元古代构造带，即东部地块的胶辽集构造带、西部地块的孔雀岩构造带和东西地块之间的跨华北造山带。近20年来，人们对这些古元古代构造带进行了广泛的构造、变质、岩浆、地球化学、年代学和地球物理等方面的研究，获得了大量的新资料和相互矛盾的解释，对华北克拉通的形成和演化以及古元古代的合并有了重要的重新解释。胶辽集带是华北克拉通中最重要的古元古代造山带/活动带，该区不仅接收了大量的古元古代陆壳沉积，而且经历了非常复杂的构造演化，同时伴有多期岩浆变质事件。根据前人的研究，位于东部地块的胶辽集造山带/活动带将地块细分为龙岗和朗林地块。该带主要由大量的变质沉积和火山序列组成，并伴有花岗岩和基性侵入岩。北韩的马川营群、吉林南部的吉安群和老岭群、辽宁半岛东南部的北辽河群和南辽河群、胶北地块的粉子山群和井上群、安徽的五河群等沉积和火山序列，是由基底富碎屑层序和下双峰火山层序，经过中部富碳酸盐岩层序到上部富泥岩层序的过渡。与胶辽-基造山带/活动带的沉积岩和火山岩伴生有丰富的古元古代花岗岩体和基性岩体，其中花岗岩体由变形的a型花岗岩和未变形的碱性正长岩和拉帕基花岗岩组成，基性岩体由变质辉长岩和白云岩组成。总的来说，胶辽基造山带/活动带为北东向，长约1000公里。从岩石组合和空间分布上看，景山组与南辽河组、吉安组具有可比性，汾子山组与北辽河组、老岭组具有可比性。然而，由于多期剧烈变形，各群/组原有的层序和接触关系已被完全破坏，目前露出以断裂或韧性剪切带分隔的不同规模的构造片。块状沉积岩主要来源于造山带/活动带内的古元古代花岗质岩石和周围古地块的变质基底，原岩形成于2 ~ 2℃之间。15ga和1。95 Ga。以往研究表明，胶辽基造山带古元古代变质作用非常不均匀，其中（中高压）麻粒岩相变质作用仅局限于景山群及其邻岩内。而汾子山组、南辽河组和北辽河组、吉安组和老岭组只经历了角闪岩相变质作用和局部绿片岩相变质作用。粉子山群、北辽河群和老岭群的变质演化以顺时针的P-T-t路径为特征，而景山群、南辽河群和吉安群的变质演化以逆时针的P-T-t路径为特征。在南辽河组和吉安组中发现了古元古代麻粒岩相变质作用的各种岩石学证据，其P-T-t顺时针路径与景山组的泥质麻粒岩和基性麻粒岩具有相似的近等温减压（ITD）特征。丰富的年代学资料表明，麻粒岩相变质作用的峰值年龄在1岁左右。90 ~ 1。整个胶辽-吉造山带/活动带。野外观察和岩石学研究表明，景山组、南辽河组和吉安组的泥质麻粒岩经历了广泛的深熔（或部分熔融）作用，各种长英质脉在围岩中以不规则脉状、链状和透镜状露头，呈渐变关系。深熔锆石丰富的U-Pb测年结果表明，该区1月1日发生了区域性部分熔融事件。84ga到1。表明广泛的深熔作用应发生在胶辽基造山带/活动带发掘的峰后低压麻粒岩相变质阶段。迄今为止，对胶辽造山带/活动带的空间分布、南北边界、伸展模式和构造背景等方面存在着明显的分歧和争议。最近的研究表明，蚌埠—霍丘地区的露头、花岗质麻粒岩、基性麻粒岩和富铝片麻岩岩心记录了麻粒岩相变质作用，发生在~ 1℃。85ga到1。表明该带可能穿过郯庐断裂，穿过山东西南部，到达第四纪盖层下的蚌埠-霍丘变质基底。古元古代（~ 1）的广泛叠印。85 Ga to1。95Ga)变质事件和~ 2的两期岩浆事件。1Ga和1。8Ga到1。辽南和朗林地块9Ga的构造演化表明，这两个地块（至少部分变质基底）都参与了胶辽基造山带/活动带的古元古代构造演化。关于胶辽造山带古元古代的构造演化，人们提出了多种模式，包括弧-陆碰撞模式和陆内裂谷的开闭模式。近年来，学者们提出了古元古代胶辽基造山带/活动带的新模式，即裂谷盆地的打开，随后是初期洋盆的发育，洋盆通过俯冲和碰撞最终闭合。然而，这些模型都难以解释胶辽-基造山带内异常复杂、巨大的火山-沉积岩、多期岩浆事件、不同类型的变质作用和不同的变质P-T-t路径以及多期变形。因此，在确定其南部边界、确定辽南地块和朗林地块的构造属性，特别是确定古元古代胶辽-集造山带/活动带的构造背景和演化等方面，还需进一步研究。
Three Paleoproterozoic tectonic belts have been identified within the North China Craton,including the Jiao-Liao-Ji belt in the Eastern Block,the Khondalite belt in the Western Block,and the Trans-North China Orogen between the Eastern and Western blocks. In the last two decades,extensive structural, metamorphic, magmatic, geochemical, geochronological and geophysical investigations have been carried out on these Paleoproterozoic tectonic belts,producing an abundant amount of new data and competing interpretations,which have resulted in significant reinterpretations of the formation and evolution of three tectonic belts and the Paleoproterozoic amalgamation of the North China Craton. The Jiao-Liao-Ji belt is the most important Paleoproterozoic orogenic / mobile belt in the North China Craton,which has not only received huge mount of Paleoproterozoic continental crust deposits,but also experienced a very complex tectonic evolution, accompanied with multi-stage magmatic-metamorphic events simultaneously. As previous studies,the Jiao-Liao-Ji orogenic / mobile belt located in the Eastern Block subdivides the block into the Longgang and Langrim blocks. The belt consists mainly of voluminous meta-sedimentary and volcanic successions with associated granitic and mafic intrusions.The sedimentary and volcanic successions,including the Macheonayeong Group in North Korea,the Ji'an and Laoling groups in the southern Jilin,the North and South Liaohe groups in the southeastern Liaoning Peninsula,the Fenzishan and Jingshang groups in the Jiaobei massif,and the Wuhe Group in Anhui Province,are transitional from a basal clastic-rich sequence and a lower bimodalvolcanic sequence,through a middle carbonate-rich sequence,to an upper pelite-rich sequence. Associated with the sedimentary and volcanic rocks in the Jiao-Liao-Ji orogenic / mobile belt are abundant Paleoproterozoic granitoid and mafic intrusions,of which the granitoid plutons are composed of deformed A-type granites and undeformed alkaline syenites and rapakivi granites,and mafic intrusions consist of meta-gabbros and-dolerites. In general,the Jiao-Liao-Ji orogenic / mobile belt is NE-trending and is ca. 1000 km long. Based on the rock assemblage and spatial distribution,the Jingshan Group is comparable with the South Liaohe and Ji'an groups,whereas the Fenzishan group is comparable with the North Liaohe and Laoling groups. However,the original stratigraphic sequences and contact relationships for each group / formation have been completely destroyed due to the multi-stage intensive deformation,which outcrop currently as varying scale of tectonic slices separated by faults or ductile shear zones. The massive sedimentary rocks are mainly sourced from the Paleoproterozoic granitic rocks within the orogenic / mobile belt and the metamorphic basement of the surrounding ancient blocks,and the protoliths were formed between 2. 15 Ga and 1. 95 Ga. Previous studies show that the Paleoproterozoic metamorphism is very heterogeneous across the Jiao-Liao-Ji orogenic / mobile zone,in which the( medium to high pressure) granulite-facies metamorphism is only constrained within the Jingshan Group and adjacent rocks. However,the Fenzishan,South and North Liaohe,Ji'an and Laoling groups only experienced amphibolite-facies and locally greenschist-facies metamorphism.The metamorphic evolution for the Fenzishan,North Liaohe and Laoling groups are characterized by similar clockwise metamorphic P-Tt paths,whereas the Jingshan,South Liaohe and Ji'an groups are featured by counterclockwise P-T-t paths. It is noted that various petrographic evidence for the Paleoproterozoic granulite-facies metamorphism have been identified throughout the South Liaohe and Ji'an groups,which have similar clockwise P-T-t paths with near-isothermal decompression( ITD) to those of the pelitic and mafic granulites of the Jingshan Group. Abundant geochronological data show that the peak metamorphic age of the granulite-facies metamorphism is around 1. 90 ~ 1. 95 Ga throughout the Jiao-Liao-Ji orogenic / mobile belt. Field observations and petrographic studies show that the pelitic granulites of the Jingshan,South Liaohe and Ji 'an groups have experienced widespread anatexis( or partial melting),and various felsic veins outcrop as irregular veinlets,stockworks and lenticular in the host rocks with gradual transition relationships. Abundant U-Pb dating results of anatexis zircons show that an regional partial melting event happened at 1. 84 Ga to 1. 86 Ga,indicating that the widespread anatexis should occur at the post-peak low-pressure granulite-facies metamorphic stage during exhumation of the Jiao-Liao-Ji orogenic / mobile belt.Up to now,there have been distinct disagreements and controversies about spatial distribution,north and south boundaries,extension pattern and tectonic setting of the Jiao-Liao-Ji orogenic / mobile belt. Recent studies show that the outcrops,and granitic,mafic granulite and Al-rich gneissic cores in the Bengbu-Huoqiu area recorded a granulite facies-metamorphism occurring at ~ 1. 85 Ga to 1. 95 Ga,suggesting that the belt likely extends across the Tan-Lu fault,through the southwestern Shandong Province and to the Bengbu-Huoqiu metamorphic basement beneath the Quaternary coverage. A widespread overprint of a Paleoproterozoic( ~ 1. 85 Ga to1. 95Ga) metamorphic event and two stages of magmatic events at ~ 2. 1Ga and 1. 8Ga to 1. 9Ga in the Southern Liaoning and Langrim blocks suggest that both of them( at least part of the metamorphic basement) have been involved in the Paleoproterozoic tectonic evolution of the Jiao-Liao-Ji orogenic / mobile belt. A variety of models have been proposed for the Paleoproterozoic tectonic evolution of the Jiao-Liao-Ji orogenic / mobile belt,including those invoking arc-continent collision and those involving the opening and closing of an intra-continental rift. Recently,a newly model for the Paleoproterozoic Jiao-Liao-Ji orogenic / mobile belt have been proposed,including the opening of a rift basin,followed by the development of an initial ocean basin,and the final closure of the ocean basin through subduction and collision. However,it is difficult to adopt any of these models to explain the extremely complex and massive volcanicsedimentary rocks,multi-stage magmatic events,different types of metamorphism and various metamorphic P-T-t paths and multi-stage deformation within the Jiao-Liao-Ji orogenic / mobile belt. Thus,further studies should be carried out about determination of its southern boundary,tectonic attribution of the Southern Liaoning and Langrim blocks and especially the tectonic setting and evolution for the JiaoLiao-Ji orogenic / mobile belt at the Paleoproterozoic.