Caledonian Low-Temperature Granulite-Facies Metamorphism in the West Kunlun Orogenic Belt—SHRIMP Chronological Evidence from Zircon

The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system. Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz. The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun Early Paleozoic. Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program “ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National Geological Surveying Bureau.     

中国与蒙古之地质

东昆仑中部缝合带清水泉一带发育石榴斜长紫苏麻粒岩、紫苏辉石黑云母石榴子石麻粒岩、石榴二辉斜长麻粒岩和石榴单斜辉石麻粒岩,它们与混合岩化黑云母石榴子石变粒岩、黑云母辉石变粒岩、石墨大理岩、含透辉石透闪石大理岩、透辉石大理岩、黑云斜长角闪岩和片麻岩等高级变质岩系以及纯橄岩、辉橄岩、橄长岩、辉长岩、辉绿岩和玄武岩等共同构成蛇绿混杂岩。麻粒岩相变质作用的温压条件为T=760~880℃,p=830~1200MPa,为高温中高压麻粒岩相变质作用,估算其形成深度为40~45km。麻粒岩相变质作用的SHRIMP锆石U-Pb年龄为(507·7±8·3)Ma。清水泉地区蛇绿岩形成于~520Ma,到~508Ma时俯冲至地下40~45km深处而发生中高压麻粒岩相变质作用,然后发生构造折返而剥露至地表。证实了清水泉高级变质岩和基性—超基性岩片是形成于早—中寒武世的蛇绿混杂岩,标志一个古生代早期的非常重要的板块汇聚边界,这对于进一步研究东昆仑造山带构造演化、乃至中国西部大地构造格局具有非常重要的意义。     

中国早元古代区域变质建造及构造环境的初步研究

根据中国早元古代变质建造研究表明，早元古时期，中朝变质地区华北分区是中国陆壳中可确认的最主要相对稳定的隆起区。其它变质地区及中朝变质地区的其它分区相对于华北分区为较活动的构造区。吕梁运动之后中朝变质地区为相对稳定的准地台，而其它变质地区一般仍一度处于较活动的构造环境。     

西昆仑布伦阔勒岩群中泥质高压麻粒岩的岩石学、年代学及其地质意义

西昆仑的深变质岩类主要发育于布伦阔勒岩群之中,其中的高压麻粒岩是西昆仑造山带中目前已知的变质程度最高的岩石。本文以其中的泥质高压麻粒岩为研究对象,结合岩相学、相平衡模拟以及锆石年代学分析等方法进行研究。结果显示其峰期变质矿物组合蓝晶石+石榴石+钾长石,是典型的泥质高压麻粒岩岩石组合。根据相平衡模拟估算,高压麻粒岩相峰期变质的温压条件高于850℃及1.4GPa,退变质的温压条件约为650℃和0.6GPa。SHRIMP U-Pb锆石定年结果显示泥质高压麻粒岩记录了两期变质,第一期暗色变质锆石年龄为ca.185Ma,代表岩石从高压麻粒岩相峰期变质退变至近固相线阶段的年龄;第二期亮色变质增生边年龄为ca.166Ma,代表后期退变质年龄;而高压麻粒岩相峰期变质时代应在200~185Ma之间。高压麻粒岩的变质条件、顺时针的P-T轨迹及锆石年代学的结果指示了晚三叠世-早侏罗世的碰撞造山事件(ca.200~166Ma)。结合区域地质资料,推断在西昆仑山内存在一条中生代的中-高压变质带,这条变质带代表了古特提斯洋关闭塔里木与羌塘地块碰撞拼合的位置。     

华北中部造山带五台-恒山地区古元古代变质作用与构造演化

华北克拉通古元古代造山带的时空分布与构造属性尚有很大争论,一种观点认为华北克拉通从新太古代至古元古代受大洋俯冲闭合控制,在1.85~1.95 Ga之间先后发生3次陆-陆碰撞形成3条造山带,即孔兹岩带、胶-辽-吉带和中部造山带;另一种观点强调华北克拉通这3条元古代造山带在1.80~1.98 Ga之间经历了相同的漫长演化过程,指示当时特有的热俯冲和碰撞环境.通过总结中部造山带中的五台-恒山地区变质作用研究进展,阐述该区古元古代造山时代与构造属性.五台-恒山地区的主要变质岩石-构造单元包括恒山杂岩、五台杂岩和滹沱群.恒山杂岩和五台杂岩主体为新太古代TTG片麻岩和表壳岩,它们在古元古代晚期经历了两期变质作用改造.第一期变质作用为中压型,是由于陆-陆碰撞导致弧后伸展盆地闭合、地壳加厚造山所致,从南向北形成一个递增序列:包括五台群下部和南恒山杂岩南部的低角闪岩相、南恒山杂岩北部高角闪岩相和北恒山杂岩的高压麻粒岩相,其压力峰期所对应的地热梯度为~15 ℃/km.变质锆石所记录的年龄峰值随着变质程度增高而降低,依次为~1.95 Ga、~1.92 Ga和~1.85 Ga,这是因为在变质过程中锆石生长受流体和熔体行为控制:在亚固相线下,变质锆石可记录峰期变质年龄,而在超固相线条件下记录伴随熔体结晶的退变质年龄.由此确定该区中压相系变质作用压力峰期时间为~1.95 Ga,对应地壳加厚造山的峰期.加厚地壳由于重力均衡导致变质岩从深部地壳折返至中部地壳,在P-T轨迹上表现为压力峰期之后发生等温减压（ITD）至0.5~0.7 GPa,岩相学上表现为峰期石榴石分解形成斜长石"白眼圈"等,指示缺流体条件.南恒山北部高角闪岩相岩石中的变质锆石记录的折返时间为~1.92 Ga,指示第一次造山结束.第二期变质作用为中-低压型,系为板内变形所致,表现为折返至中地壳的岩石伴随挤压型剪切变形和流体注入形成平衡矿物组合.朱家坊韧性剪切带就是这次板内变形的强构造域,其中也记录了顺时针型P-T轨迹,但所反映的地壳加厚程度有限,第二期变质-变形峰期时间为~1.85 Ga.由于朱家坊韧性剪切带左行走滑,导致北恒山麻粒岩地体抬升.五台-恒山地区在1.80~1.96 Ga之间经历两期变质-变形事件,这一认识或对讨论华北克拉通其他地区的古元古代造山带演化有一定启示意义.      

阿尔泰造山带喀纳斯群变质碎屑岩地球化学特征及年代学研究

喀纳斯群为一套巨厚的中低压型浅变质碎屑岩系,主要由片岩、片麻岩、变质砂岩等组成,其形成时代未有统一的认识,致使阿尔泰构造带的构造演化过程争议较大。对喀纳斯群变质岩进行原岩恢复,认为该套变质岩为副变质岩,考虑到变质碎屑岩的成岩物质继承母岩特征和变质程度的影响,利用碎屑岩研究方法对元素地球化学特征进行探讨,显示出喀纳斯群变质碎屑岩原岩形成环境以大陆岛弧为主,兼有活动大陆边缘的特征,CIA、ICV指数反应出原岩经历了相对温暖、湿润的风化作用,成熟度较低。锆石U-Pb定年结果表明,最年轻的锆石年龄集中在(500±3.0)Ma,代表喀纳斯群的上限年龄,认为该套地层形成于晚寒武世晚期之前,为一套形成于大陆岛弧或活动大陆边缘的复理石建造。新元古代青白口纪初期基底裂解事件,暗示着阿尔泰构造带存在前寒武纪大陆地壳基底。     

Ultrahigh Pressure Metamorphism and Tectonic Evolution of Southwestern Tianshan Orogenic Belt,China: A Comprehensive Review

Recently, a huge ultrahigh‐pressure (UHP) metamorphic belt of oceanic‐type has been recognized in southwestern (SW) Tianshan, China. Petrological studies show that the UHP metamorphic rocks of SW Tianshan orogenic belt include mafic eclogites and blueschists, felsic garnet phengite schists, marbles and serpentinites. The well‐preserved coesite inclusions were commonly found in eclogites, garnet phengite schists and marbles. Ti‐clinohumite and Ti‐chondrodite have been identified in UHP metamorphic serpentinites. Based on the PT pseudosection calculation and combined U‐Pb zircon dating, the P‐T‐t path has been outlined as four stages: cold subduction to UHP conditions before ～320 Ma whose peak ultrahigh pressure is about 30 kbar at 500oC, heating decompression from the Pmax to the Tmax stage before 305 Ma whose peak temperature is about 600oC at 22kbar, then the early cold exhumation from amphibolite eclogite facies to epidote‐amphibolite facies metamorphism characterized by ITD PT path before 220 Ma and the last tectonic exhumation from epidote amphibolite facies to greenschist facies metamorphism. Combining with the syn‐subduction arc‐like 333‐326 Ma granitic rocks and 280‐260 Ma S‐type granites in the coeval low‐pressure and high‐temperature (LP‐HT) metamorphic belt, the tectonic evolution of Tianshan UHP metamorphic belt during late Cambrian to early Triassic has been proposed.     

Geodynamics of the origin of granulites in the Sangilen block of the Tuva–Mongolian terrane,Central Asian Orogenic Belt

The Tuva–Mongolian terrane of the Central Asian Orogenic Belt is a composite structure with a Vendian–Cambrian terrigenous–carbonate cover. The Sangilen block in the southern part of the belt is a smaller composite structure, in which tectono–stratigraphic complexes of different age that were produced under various conditions were amalgamated in the course of Early Paleozoic tectonic cycle. The P–T parameters of the Early Paleozoic metamorphism in the western part of the Sangilen block corresponded to the amphibolite facies. The gneisses of the Erzin Complex contain relict granulite-facies mineral assemblages. The granulites are dominated by metasediments typical of deep-water basins on passive continental margins. The only exception is granulites of the Lower Erzin tectonic nappe of the Chinchlig thrust system: these rocks are metatholeiites, tonalites, and trondhjemites, whose REE patterns are similar to those of MORB. The composition of these granulites and their high Sm/Nd ratios indicate that the rocks were derived from juvenile crust that had been formed in an environment of a mature island arc or backarc basin. It is reasonable to believe that these rocks are fragments of the Late Riphean basement of the Sangilen block. The average ²⁰⁶Pb/²³⁸U zircon age of the garnet–hypersthene granulites is 494 ± 11 Ma. With regard for the zircon age of the postmetamorphic granitoids, the granulite-facies metamorphism occurred within the age range of 505–495 Ma. The peak metamorphic temperature reached 910–950°C, and the pressure was 3–4 kbar, which corresponds to ultrahigh-temperature/low-pressure (UHT–LP) metamorphism. The garnet–hypersthene orthogranulites were formed at a temperature that decreased to ~850°C and pressure that increased to ~5.5?7 kbar. It can be hypothesized that the earlier UHT–LP granulites were produced at an elevated heat flux and were later (in the course of continuing collision) overlain by a relatively cold tectonic slab, and this leads to a certain temperature decrease and pressure increase. This relatively cold slab could consist of fragments of the Vendian elevated-pressure metamorphic belt whose development terminated at the Vendian–Cambrian boundary before the onset of the Early Paleozoic regional metamorphism.     

大别山北部榴辉岩和英云闪长质片麻岩锆石U-Pb年龄及多期变质增生

大别山北部榴辉岩及英云闪长质片麻岩的锆石U-Pb年龄分析表明：北部榴辉岩相峰期变质时代为226～230Ma左右;北部塔儿河一带英云闪长质片麻岩经历过印支期变质事件;大别山北部与南部超高压岩石中一致的（226～230Ma）高压或超高压变质年龄表明,北部镁铁-超镁铁质岩带中部分岩石也曾作为扬子俯冲陆壳的一部分,在印支期发生过高压或超高压变质作用;本区锆石发生过两期变质增生事件,一是印支期高压或超高压变质,另一期是燕山期热变质事件;榴辉岩及英云闪长质片麻岩的原岩形成时代为晚元古代;锆石U-Pb年龄可用多期变质增生模型来解释。     

东昆仑南缘布青山地区得力斯坦花岗闪长岩LA-ICP-MS锆石U-Pb年龄及其地质意义

布青山构造混杂岩带地处青藏高原东北缘,是东昆仑南缘一条重要的构造单元边界,带内构造岩浆活动强烈,早古生代—晚古生代中酸性侵入岩较发育。采用LA-ICP-MS锆石U-Pb同位素测年技术,对研究区内得力斯坦花岗闪长岩进行高精度的年代学测试,获得~(206)Pb/~(238)U年龄加权平均值为414.3±1.8Ma,表明其侵位时间为晚志留世—早泥盆世。结合前人研究成果,认为得力斯坦花岗闪长岩是洋壳俯冲板块部分熔融的产物,暗示布青山地区原特提斯洋向北俯冲可能持续到晚志留世—早泥盆世,进而为研究东昆仑地区的地质构造演化提供新的约束。     

大别山碧溪岭未经历超高压变质的片麻状花岗岩

关于大别山超高压变质带中与榴辉岩密切伴生的花岗片麻岩是否也经历了超高压变质作用一直是个争议的问题。笔者最近在碧溪岭片麻状花岗岩中首次发现了可靠的岩相学和矿物学证据 ,证明该岩石只遭受到绿片岩相变质作用的改造 ,而未曾记录超高压变质矿物组合。根据片麻状花岗岩与围岩接触部位强烈糜棱岩化的发育 ,认为超高压岩石在抬升到地壳范围时与以花岗质岩石为主构成的扬子陆壳发生了大规模的构造并置。     

青藏高原东缘哀牢山 金沙江构造带糜棱状花岗岩的 LA ICP MS U Pb 定年及其构造意义

哀牢山—金沙江构造带糜棱状花岗岩位于哀牢山深变质带中部。锆石LA-ICP-MS U-Pb定年结果显示两个样品(08Q2-22和08Q2-15)锆石新生边的年龄分别为250.2±2.1Ma(MSWD=2.5)和247.2±2.3Ma(MSWD=0.15)。石英C轴组构测定(EBSD)结果表明韧性变形变质作用形成于角闪岩相条件(500～630℃),远低于锆石结晶温度(675～864℃)和U-Pb体系的封闭温度(800℃),对锆石内部的U-Th-Pb组成不会产生影响,结合锆石的阴极发光图像及U-Pb协和图的特点分析认为锆石LA-ICP-MS U-Pb定年结果(247～250Ma)是对岩浆侵位时代的体现。花岗岩中白云母等过铝质矿物的出现、低钠高钾、A/CNK和A/NK都1.0、稀土和微量元素配分模式与上地壳相似,以及大离子亲石元素和亲岩浆元素强烈富集,Sm和Y明显亏损的特征展示出过铝质、S型花岗岩的地球化学性质。(Yb+Ta)-Rb、Nb-Y、(Y+Nb)-Rb和CaO-(TFeO+MgO)构造环境判别图解及构造带曾经历早中生代俯冲碰撞作用的历史,表明该花岗岩体形成于俯冲碰撞型构造环境。结合前人在哀牢山、点苍山深变质带中相继发现的早三叠世糜棱岩化花岗岩,以及长英质岩石韧性变形变质作用发生于中下地壳(10～15km以下)的特点,分析认为哀牢山—金沙江深变质带是早三叠世及其以前的岩石被俯冲到中下地壳发生韧性变形变质后被挤出或隆升到上地壳的,深变质变形作用形成于中生代或新生代,而非元古宙,它不是,或至少不完全是扬子地块的结晶基底。     

1∶25万大同幅区域地质调查项目成果

通过对1∶25万大同市幅地质概况的介绍,重点论述了所取得的主要成果: ①对区内构造单元进行了划分,查明了各个构造单元的物质组成及变质、变形特点,建立了早前寒武纪地质构造事件演化序列及其地质构造演化模式,恢复了本区的地质构造发展史; ②对前人所称集宁群进行了重新认识和解体,认为原集宁群由变质深成岩与变质表壳岩系组成,同时针对区内的沉积盖层,系统地建立了岩石地层格架,为生物地层、年代地层划分提供了新资料; ③将区内变质深成岩划分为4个岩浆岩带,对各个岩浆岩带的变质深成岩进行了详细解体与划分; ④针对区内的中生代侵入岩,查明了其空间分布、岩石特征、岩石化学及地球化学特征,探讨了岩石成因,研究了其构造背景; ⑤针对区内早前寒武纪变质岩系变质矿物,查明了不同变质体的变质矿物组合特点和矿物世代关系; ⑥针对区内的构造形迹,建立了本区构造格架,将早前寒武纪的构造变形划分为五台期早晚2次变形,吕梁期早晚2次变形,并针对区内中生代构造,查明了各个盆地的盆缘构造特征和不同方向、不同期次、不同性质断裂的分期配套关系,尤其是查明了大同盆地西缘大型构造带的空间展布、性质、断裂组合及运动学特征,对探讨山西中—新生代盆地的演化发展具有重要意义。     

晋北早前寒武纪变质岩区构造相研究

晋北地区出露有不同层次的地壳,是研究构造相最理想的地区之一。本文以构造分析为主线,结合当前地壳流变学研究进展,对该区早前寒武纪构造特征进行了分析,初步建立了早前寒武纪地质事件序列。提出了该区北部（大同-集宁）麻粒岩相变质岩代表下地壳的物质组成,中部（恒山）中深变质岩代表典型的中下地壳过渡带的特征（早前寒武纪一个重要的软...     

U–Pb zircon study of tectonically bounded blocks of 2940–2840 Ma crust with different metamorphic histories,Paamiut region,South-West Greenland: implications for the tectonic assembly of the North Atlantic craton

New fieldwork, map interpretation, petrography and single zircon U–Pb geochronology has allowed the identification of different crustal blocks in the Paamiut region, in the southern portion of the West Greenland Archaean Craton. Changes of metamorphic grade from only amphibolite facies to granulite facies (some subsequently retrogressed) corresponds with zones of Archaean high strain ductile deformation ± mylonites. U–Pb zircon dates are presented for the TTG (tonalite, trondhjemite, granodiorite) protoliths from each block in the Paamiut region, and the southern portion of the previously identified Tasiusarsuaq terrane lying to the north. The southern part of the Tasiusarsuaq terrane contains 2880–2860 Ma TTG rocks and underwent amphibolite facies metamorphism. Structurally underneath the Tasiusarsuaq terrane to the south is the Sioraq block containing 2870–2830 Ma TTG rocks partly retrogressed from granulite facies. Structurally underneath and to the south is the Paamiut block, dominated by 2850–2770 Ma granodioritic rocks that have only undergone amphibolite facies metamorphism. Also structurally overlying the Paamiut block, but cropping out separately from the Sioraq block, is the Neria block. This appears to be dominated by 2940–2920 Ma gneisses that have been totally retrogressed from granulite facies and strongly deformed. In the southernmost part of the region the Neria block overlies the greenschist to lowermost amphibolite facies Sermiligaarsuk block that contains the ⩾2945 Ma Tartoq Group. Rocks from all the blocks record ancient loss of Pb from zircons and some new zircon growth at 2820 Ma, interpreted to indicate a high grade metamorphic event at that time, including granulite facies metamorphism in the Sioraq and Neria blocks. The blocks of different metamorphic grade are interpreted to have moved to their current positions after the 2820 Ma metamorphism, explaining the change in metamorphic history across some mylonites and ductile shear zones which deform and retrogress granulite facies textures. The juxtaposed blocks and their contacts were subsequently folded under amphibolite facies conditions. The contacts are cut by undeformed Palaeoproterozoic dolerite dykes which post-date amphibolite facies metamorphism. These results, together with previously published data from the Godthåbsfjord region (north of Paamiut) shows that the North Atlantic Craton in West Greenland from Ivittuut in the south to Maniitsoq in the north (∼550 km) consists of a mosaic of ductile fault-bounded packages that attained their present relative positions in the late Archaean.     

Ultrahigh-pressure eclogite transformed from mafic granulite in the Dabie orogen, east-central China

Although ultrahigh‐pressure (UHP) metamorphic rocks are present in many collisional orogenic belts, almost all exposed UHP metamorphic rocks are subducted upper or felsic lower continental crust with minor mafic boudins. Eclogites formed by subduction of mafic lower continental crust have not been identified yet. Here an eclogite occurrence that formed during subduction of the mafic lower continental crust in the Dabie orogen, east‐central China is reported. At least four generations of metamorphic mineral assemblages can be discerned: (i) hypersthene + plagioclase ± garnet; (ii) omphacite + garnet + rutile + quartz; (iii) symplectite stage of garnet + diopside + hypersthene + ilmenite + plagioclase; (iv) amphibole + plagioclase + magnetite, which correspond to four metamorphic stages: (a) an early granulite facies, (b) eclogite facies, (c) retrograde metamorphism of high‐pressure granulite facies and (d) retrograde metamorphism of amphibolite facies. Mineral inclusion assemblages and cathodoluminescence images show that zircon is characterized by distinctive domains of core and a thin overgrowth rim. The zircon core domains are classified into two types: the first is igneous with clear oscillatory zonation ± apatite and quartz inclusions; and the second is metamorphic containing a granulite facies mineral assemblage of garnet, hypersthene and plagioclase (andesine). The zircon rims contain garnet, omphacite and rutile inclusions, indicating a metamorphic overgrowth at eclogite facies. The almost identical ages of the two types of core domains (magmatic = 791 ± 9 Ma and granulite facies metamorphic zircon = 794 ± 10 Ma), and the Triassic age (212 ± 10 Ma) of eclogitic facies metamorphic overgrowth zircon rim are interpreted as indicating that the protolith of the eclogite is mafic granulite that originated from underplating of mantle‐derived magma onto the base of continental crust during the Neoproterozoic (c. 800 Ma) and then subducted during the Triassic, experiencing UHP eclogite facies metamorphism at mantle depths. The new finding has two‐fold significance: (i) voluminous mafic lower continental crust can increase the average density of subducted continental lithosphere, thus promoting its deep subduction; (ii) because of the current absence of mafic lower continental crust in the Dabie orogen, delamination or recycling of subducted mafic lower continental crust can be inferred as the geochemical cause for the mantle heterogeneity and the unusually evolved crustal composition.     

徐淮地区中生代侵入杂岩中角闪岩和片麻岩类捕虏体的岩石学和地球化学:对深部地壳物质组成的制约

徐淮地区中生代侵入杂岩中角闪岩和片麻岩类捕虏体的主要元素、微量元素地球化学特征及其岩相学的研究表明,它们经历了两期变质作用的改造,即早期的榴辉岩相变质和晚期的角闪岩相退化变质。其原岩为拉斑玄武质岩石,在其形成过程中有较强的陆壳物质混染;部分捕虏体可能代表了本区深部地壳的物质组成,且具有华北地块基底的性质。中生代早期该区上地幔是多种岩石构成的构造混杂岩带,深部地壳主要由片麻岩类、角闪岩类和少量石榴辉石岩类组成。早白垩世时期深部地壳主要由一套快速折返至下地壳的榴辉岩相变质岩石所构成,它们普遍发生了角闪岩相退化变质,并与原下部地壳的深变质岩(片麻岩和角闪岩)混杂在一起,构成了一个构造混杂体。     

Structure and metamorphism of the Antarctic Shield

The information on the composition, structure, P-T conditions of metamorphic facies, evolution, and time of the metamorphic events in the largest Precambrian tectonic provinces of the Antarctic Crystalline Shield gained over more than a half-century is summarized in this paper. The joining up of the ortho- and paracrystalline rocks into complexes and groups according to their geographic position, composition, age, and the character of their metamorphism allowed us to consider the main features of the structure and evolution of the provinces including (1) the near-latitudinal polycyclic Late Precambrian-Early Paleozoic Wegener-Mawson Mobile Belt, extended for more than 4000 km, which started to evolve in the Mesoproterozoic and stabilized only at the end of Cambrian; (2) the Early Precambrian relict crystalline protocratonic blocks adjoining this mobile belt; their history is traced from the Eoarchean; and (3) the near-latitudinal Late Precambrian-Early Paleozoic aulacogen in the southern protocratonic block. The P-T conditions of the metamorphism from the pyroxene-granulite subfacies in the protocratonic blocks to the greenschist facies in aulacogen, as well as the age of the magmatic and metamorphic events in all the tectonic provinces of the shield, are characterized. This made it possible to consider the metamorphic history and conditions of the continental crust’s formation in Antarctica, where the oldest crystalline rocks are dated to the Eoarchean (4060–3850 Ma) and the youngest rocks are ～500 Ma old.     

北祁连东段米家山地区碰撞变质作用研究

:米家山地区位于北祁连东段 ,区内下奥陶统阴沟群为一套海相火山—碎屑岩建造。在加里东末期 ,米家山岩体最终定位。通过填图发现 ,岩体与阴沟群变质地层呈“互层状”产出。在岩体的中心部位发育两条角闪岩相变质带 ,其变质条件由早期中—高压中温向晚期低压高温演化 ,变质作用为多期碰撞变质作用。这一现象不仅反映了造山作用是一个连续过程 ,同时也说明了与其相伴的变质作用必然是一个变化的过程。在与花岗岩相伴的地区 ,严格地用区域变质作用和接触变质作用来解释变质成因是与板块构造观点不相符合的 ,它们可能是一个起因的不同结果 ,是相互联系的