中国地质科学院地质研究所成立于1956年4月.当时名为地质部地质矿产研究所,1957年更名为地质部地质研究所.由于隶属部门职责和名称的变更,研究所的名称几经变更,2000年正式更名为中国地质科学院地质研究所.

This paper systematically sorts out the Meso-Neoproterozoic stratigraphic problems on the Stratigraphic Chart of China (2014), based on the achievements of relevant experts and the author's team in stratigraphic chronology in the past 10 years. By combining the results with the spatio-temporal development and correlation relationship of geological events, the study focuses on studying the definition of the bottom boundary of the Mesoproterozoic and the Mesoproterozoic Undefined System, the stratigraphic relationship in the Meso-Neoproterozoic transition period, and the division of the lower boundary of the Cryogenian, as well as the timing of the Tonian Luoquan glaciation. On this basis a subdivision and correlation framework of the Meso-Neoproterozoic strata of China are presented and the similarities and differences among the North China, Yangtze, and Tarim block discussed. The research indicates that it is more reasonable to set 1800 Ma (or 1780 Ma) as the lower boundary of the Mesoproterozoic than 1600 Ma. Although the Mesoproterozoic Undefined System is developed in both the northern and southern margins of North China and South China block, the Shennongjia Group in the northern margin of the Yangtze block is more favorable than others and as a result, suggested as the temporary stratotype of the Undefined System in China for focused research. The proto-Qingbaikou System in Jiao-Liao-Xuhuai-Ji-Yu of the North China block, is probably older than 1000 similar to 820 Ma), i. e., parts of it belong to the Mesoproterozoic. We propose that the proto-Nanhuan System corresponds to the international Cryogenian (720 similar to 635 Ma). The Qingbaikou System is bounded by a tectonic plane dated to 820 Ma-its lower part is named as the Lower Series of the Qingbaikou System (1000-820 Ma), and the upper part is named as the Upper Series of the Qingbaikou System (820 similar to 20 Ma). The decision on whether to divide these into two systems will be made when more evidence becomes available. The Luoquan Formation and coeval strata in the southern margin of North China block probably belong to the upper Sinian (Ediacaran). Our research provide data, evidence and the reference subdivision, to revise and improve for "the Meso-Neoproterozoic" division and correlation in the Stratigraphic Chart of China.

程裕淇院士是我国著名的变质岩石学家、矿床学家和前寒武纪地质学家.中国科学院学部委员(院士),中国人民政治协商会议第四届、第五届全国委员会委员,第六届、第七届全国政协常务委员会委员.程裕淇先生开拓了我国变质岩研究领域,提出了矿床成矿系列理论,发展了我国前寒武纪地质学.他在管理上积极推进地质行业的对外开放,促进国际合作交流,为建立中央直属的野战军队伍建言献策;在政协多次提案,推动了我国矿产资源法的立法和实施.

Paleoproterozoic (similar to 2.3) Ga metavolcanic rocks occur in the Lengkou area, northern Zhongtiao Mountains of the North China Craton (NCC). The area is dominated by metabasic volcanic rocks, intercalated with metamorphosed intermediate to acid volcanic rocks. The Lengkou metavolcanic rocks have a magmatic zircon U-Pb age of 2317 +/- 13 Ma, but also contain some 2508 Ma inherited zircons. The Lengkou metabasic and intermediate volcanic rocks are calc-alkaline with high SiO2 and K2O contents. They display fractionation of the HREE relative to the LREE, relative enrichments in large ion lithophile elements and depletion in high field strength elements resulting in negative Nb-Ta-Ti and Zr-Hf anomalies. Therefore, they are inferred to have formed in a volcanic arc setting. The meta-acid volcanic rocks of the Lengkou series have geochemical features similar to the surrounding Sushui Complex (Neoarchaean tonalitic gneiss), resulting from partial melting of ancient crust. The Lengkou metabasic volcanic rocks have a low Nd-143/Nd-144 ratio and epsilon(Nd)(t) value of 0.8-1.5, with T-DM of 2.57-2.63 Ga, indicating the mantle-derived mafic rocks were variably contaminated by older continental material. The integrated data from the Lengkou metavolcanic rocks indicate a convergent subduction-related regime in the early Paleoproterozoic. The isotopic signatures and the xenocrystic zircons demonstrate that subduction occurred at a margin of continental crust, rather than within intra-ocean, exploring an Andean-like setting in the NCC at that time.

在全球岩浆活动静寂期,人们在华北克拉通内相继识别出大量～2.3 Ga的地质体,对探讨华北克拉通古元古代地质演化过程具有十分重要的意义.选择中条山地区横岭关二长花岗岩进行了地球化学、锆石U?Pb年代学和Hf同位素研究.横岭关二长花岗岩LA-ICPMS锆石U?Pb年龄结果为2308±12 Ma,代表岩体的形成时代.横岭关二长花岗岩高硅、高钾、高铝、富碱,贫钙、低钠和低钛,A/CNK主要集中在1.0～1.1之间,为高钾钙碱性偏铝-过铝质花岗岩系列.岩石的稀土元素含量相对高,轻重稀土元素分异强烈,并具有明显的Eu负异常.高场强元素Nb、Ta、Zr、Hf、U和大离子亲石元素Rb等相对富集,亏损V、Cr、Co、Ni等相容元素,具有I型花岗岩的特征.横岭关二长花岗岩锆石εHf(t)为0.52～6.24,平均值为2.06,单阶段和两阶段模式年龄分别为2419～2642 Ma和2438～2738 Ma.横岭关二长花岗岩具有同碰撞花岗岩的特征,推测来源于～2.5 Ga古老地壳岩石在挤压碰撞环境下的部分熔融,揭示了华北克拉通在古元古代全球岩浆静寂期并不静寂.

华北克拉通中部阜平地区的阜平岩群是该区分布较广的太古宙地层,经历了角闪岩相-麻粒岩相变质,其时代限定对研究阜平杂岩的早期演化过程具有重要意义.本文利用LA-MC-ICP-MS(多接收激光剥蚀电感耦合等离子体质谱仪)对阜平岩群元坊岩组中的浅粒岩进行了锆石U-Pb-Hf同位素原位分析,获得两期变质锆石年龄分别为2 531±15 Ma和1 943±16 Ma,并根据碎屑锆石内部结构特征和年龄结果,认为核部年龄在2 549～2 500 Ma的碎屑锆石中最大207Pb/206Pb年龄2 549±4 Ma可以代表原岩的最大沉积年龄,初步限定元坊岩组浅粒岩原岩沉积时代为2 550～2 530 Ma.锆石Lu-Hf同位素结果中,176 Lu/177 Hf值为0.000 289 ～0.004 262,176 Hf/177 Hf值为0.281 255～0.281 791.176 Hf/177 Hfi值为0.281 230～0.281 623,εHf(t)值为-5.86～13.62,变化范围较大.单阶段和两阶段模式年龄分别为2 748 ～2 242 Ma和2 810～2 272 Ma.根据锆石U-Pb年龄和Hf同位素结果,提出元坊岩组浅粒岩物源区主要来自新太古代TTG质片麻岩,2.8～2.6 Ga为阜平地区强烈的地壳生长阶段,阜平地区2.5 Ga和1.95 Ga变质信息分别代表华北初步克拉通化和最终克拉通化过程中的变质作用.

Diamictites of late Ediacaran to early Cambrian age (ca. 551-518 Ma) are widespread across Southeast-Central Asia, with the Luoquan Formation particularly well preserved along the southern margin of the North China craton. A basal unconformity, comprising striations and p-forms interpreted to have been produced subglacially, was cut into Mesoproterozoic basement. Integrating new observations on the basal unconformity with the stratigraphy and sedimentology of the Luoquan Formation, an unequivocal glacial origin is demonstrated. The succession evolves from massive or stratified diamictite at the base to laminated fine-siltstone with dropstones upward, and is capped by siltstone with or without dropstones on the top. These lithological combinations represent a glacial sedimentary succession deposited recording progressive retreat of the ice margin. Based on multiple palaeoflow measurements, data from 7 new measured sections, and facies analysis, a new paleogeo-graphic model is proposed. This model envisages the expansion of a large continental ice sheet from north to south at the southern flank of the North China Craton (NCC).

Meso-Neoproterozoic magmatic rocks widely occur in three Chinese blocks of China ( North China, South China and Tarim blocks) . Based on a large number of geochronologic data, the Meso-Neoproterozoic magmatic events in the North China Block can be divided into seven stages ( 1. 78Ga, 1. 70Ga , 1. 63Ga, 1. 32Ga, 1. 23Ga , 0. 93Ga and 0. 83Ga) , in which 1. 78Ga and 1. 32Ga magmas have a large influence range and form the large igneous provinces, respectively. The Meso-Neoproterozoic magmatic rocks in the North China Block formed in the intracontinental extensional environment indcating that North China Block was not involved in the assembly process of the Rodinia supercontinent. The Meso-Neoproterozoic magmatic events in the South China Block can be divided into eight stages (1. 78Ga, 1. 72Ga , 1. 67Ga, 1. 5Ga, 1. 42Ga , 1. OGa, 0. 84Ga and 0. 77Ga) , the four stages of magmatic events from 1. 78Ga to 1. 5Ga were formed in extensional environment. The sporadic 1. 4 Ga magmatic rocks likely formed in an assembly setting in local area. The magmatic stages around 1. OGa performed differently in different parts of the South China Block, indicating the different blocks have been aggregated together. Magmatic events from 0. 95Ga to 0. 82Ga , mainly distributed in the Jiangnan Orogen and the northern margin of the Yangtze massif, led to the coherent Yangtze massif ( or Yangtze Block) and Cathaysia massif ( or Cathaysia Block) into the South China Block. Subsequently, magmatic events from 0. 78Ga to 0. 72Ga were almost all over the South China Block, reflecting the extensional process after the formation of the entire continental block. The Meso-Neoproterozoic magmatic events in the Tarim block can be subdivided into eight stages ( 1. 78Ga, 1. 5Ga, 1. 43Ga, 1. 1Ga, 0. 92Ga , 0. 83Ga, 0. 74Ga and 0. 65 Ga) . The magmatic events of 1. 78Ga and 1. 5Ga are only locally distributed, and they formed in the extensional setting. 1. 4Ga magmatic events performed differently in the northern and southwestern margins of the Tarim Block. Calc-alkaline magmatic rocks in the northern margin emplaced in the continental arc setting, while A2 type granites in the southwestern margin were formed in the tensional setting. During the period of 0. 96 similar to 0. 88Ga, the granites in the southeastern and northern margins of Tarim Block are dominated by I-type and S-type and formed in the active continental margin, while in the southwestern margin of Tarim Block, bimodal volcanic rocks in the Sailajiazitage Group formed in the intra-continental rift environment. During 0. 88 similar to 0. 82Ga , magmatic sequences, related to subduction and accretion, were formed in Kuruktagh area on the northern margin, while bimodal volcanic rocks related to extensional tectonic setting were formed on the southeastern margin. The difference of magmatic rock assemblages in different locations and stages of the Tarim Block denotes that the Tarim Block originally is not originally a unified block, but likey assembled by different massifs in different periods. The differential evolutions of the Meso-Neoproterozoic magmatic rocks reveal their independent processes in the North China, South China and Tarim blocks in this period.

太古宙末期钾质花岗岩的广泛发育是陆壳成熟和稳定化的重要标志,对了解早期陆壳的形成与演化具有重要的意义.发育于华北克拉通南缘中条山地区涑水杂岩中的烟庄正长花岗岩的形成年龄和成因还没有被很好地限定,构造背景还存在争议.对烟庄花岗岩进行了锆石U?Pb年代学和Hf同位素以及全岩地球化学和Nd同位素研究.烟庄花岗岩锆石SHRIMP U?Pb年龄为2515±7 Ma.岩石具有高硅(SiO2=73.05％～74.85％)、高钾(K2O=4.46％～5.86％)、富碱(ALK=8.32％～9.36％)、贫钙(CaO=0.55％～0.98％)、低TFeO*(0.73％～1.28％)和MgO(0.31％～0.52％)的特征,A/CNK=1.01～1.04,为弱过铝质的钾玄系列.稀土总量变化较大(ΣREE=63.80×10-6～250.02×10-6)),轻重稀土元素分异明显((La/Yb)N=25.44～92.87),Eu异常变化较大(Eu/Eu*=0.47～0.79).岩石低Sr、Ba,富集Rb、Th、U等元素,亏损Nb、Zr、Y、Yb、Cr、Co、Ni等元素,具有较高的Rb/Sr、Rb/Ba和Sr/Yb比值以及较低Sm/Nd和Nd/Th比值,具有高分异I型花岗岩的特征.烟庄花岗岩具有0附近的全岩εNd(t)值,岩浆锆石具有正的εHf(t)值(2.85～3.66),两阶段Hf模式年龄为2258～2883 Ma,多数在2600～2883 Ma之间.结合其他方面研究,烟庄花岗岩具有同碰撞和后碰撞花岗岩的特征,推测为新生地壳在由挤压向伸展转换的构造背景下部分熔融所形成,可能有少量地幔物质添加.这期钾质花岗岩的形成,标志着华北克拉通太古宙末期强烈岩浆活动的结束以及稳定陆壳的形成.

This paper presents some data of the Jiaopingdu gabbro and Caiyuanzi granite at the southwestern margin of the Yangtze Block, on the geochemical compositions, zircon LA–ICP–MS U–Pb ages and Hf isotopic data. The Jiaopingdu gabbro gives the age of 1721 ± 5 Ma, the Caiyuanzi granite 1732 ± 6 Ma and 1735 ± 4 Ma, and the Wenjiacun porphyry granite 1713 ± 4 Ma, suggesting nearly contemporaneous formation time of the gabbro and granite. The bimodal feature is demonstrated by the gabbro SiO2 content of 44.64–46.87 wt% and granite 73.81–77.03 wt%. In addition, the granite has high content of SiO2 and Na2O + K2O, low content of Al2O3 and CaO, enriched in REEs (except Eu) and Zr, Nb, Ga and Y, depleted in Sr, implying it belongs to A‐type granite geochemistry and origin of within‐plate environment. The zircon ∊Hf(t) of the granite and gabbro is at the range of 2–6, which is near the 2.0 Ga evolution line of the crust, implying the parent magma of the gabbro being derived from the depleted mantle and a small amount of crustal material, and the parent magma of the granite from partial melting of the juvenile crust and some ancient crustal material at the same time. Compared with 1.8–1.7 Ga magmatism during breakup of other cratons in the world, we can deduce that the Columbia has initially broken since ca. 1.8 Ga, and some continental marginal or intra‐continental rifts occurred at ca. 1.73 Ga.

本文收集了阜平杂岩新太古代早期?古元古代晚期基底岩石的岩石地球化学、锆石U?Pb年代学、同位素地球化学和变质作用资料,以期对阜平杂岩早寒武纪演化历史进行初步总结.阜平新太古代早期～2.7 Ga片麻岩原岩为英云闪长岩,具有TTG质片麻岩的地球化学特征;其锆石εHf(t)具有较高的正值(+5.44～+7.50),单阶段模式年龄为2745～2824 Ma,表明新太古代早期为阜平杂岩强烈的地壳生长时期.新太古代晚期片麻岩的时代集中于2543～2484 Ma,主要岩石类型为英云闪长岩?奥长花岗岩?花岗闪长岩(TTG),同时区域内还存在二长花岗岩.TTG质片麻岩的εNd(t)值为?1.64～+0.96,单阶段模式年龄为2.76～3.04 Ga;锆石εHf(t)值为?1.9～+7.91,单阶段和两阶段模式年龄分别为2546～2888 Ma和2548～3119 Ma.这些TTG岩石主要为新太古代早期岩石的部分熔融,并有少量中太古代地壳物质参与.近于同期具有岛弧性质的辉长岩和变质作用暗示阜平杂岩新太古代晚期可能经历了俯冲和弧?陆或陆?陆碰撞.古元古代中期(2.1～2.0 Ga)阜平地区花岗质岩浆活动强烈.该阶段花岗岩具有A型花岗岩特征,与同期的火山?沉积岩系形成于华北克拉通古元古代中期伸展的陆内裂谷环境中.阜平杂岩中基性麻粒岩包体记录的变质作用时代为1.89～1.85 Ga,并具有顺时针演化的P?T轨迹,其代表了古元古代晚期裂谷闭合的陆内造山过程,表明华北最终克拉通化.

The chronostratigraphic chart describes the timescale of the geological evolutions in the Earth's history, records our understanding of the global evolution, and carries a series of key scientific questions. There are many problems in the current Precambrian Geological Time Scale, yet no new chart has been widely accepted by far. 2.0 similar to 1.8Ga, 1.8 similar to 1.6Ga and 1.6 similar to 1.4Ga are referred as the Orosirian, Statherian and Calymmian in the international chronostratigraphic chart (IUGS 1989-2004), respectively. That is, the transition between the end of orogenesis and the development of stable sedimentary covers is termed Statherian, while the widely development of stable sedimentary covers represents the start of the Mesoproterozoic. The "Lvliang Event" is usually considered as the symbolic tectono-thermal event marking the final solidification of the crystalline basement of the North China Craton (NCC), which was followed by development of extensive platform-type sedimentary covers collectively known as the Changcheng-Jixian-Qingbaikou systems. The deposition of the Changcheng System has long been considered as the beginning of the Mesoproterozoic in China. The boundary between Paleoproterozoic and Mesoproterozoic was set at 1.8Ga according to the end time of the "Lvliang Event". The International Stratigraphic Commission (ISC) launched a new proposal in 2012 for the global Geochronological Time Scale, in which the 2060 similar to 1780Ma period is called the "Columbian", followed by the "Rodinian", the long historical stage from the break-up of the Columbia Supercontinent to the assembly of the Rodinia Supercontinent (1.78 similar to 8.5 Ga). That is, the boundary between Paleoproterozoic and Mesoproterozoic of this new proposal global Geochronologic Time Scale is 1.78Ga, which is largely consistent with the boundary that Chinese scholars have long insisted on. The termination of the "Lvliang Movement" in the NCC is at ca. 1.8Ga. Subsequently, the NCC has been in an intra-continental extension environment until the Late Neoproterozoic. The Changcheng and Jixian systems are basically continental epicontinental deposit. Recent studies showed that the initial age of the Changcheng System in the Yanshan area is ca. 1.7Ga and the boundary between the Changcheng System and Jixian System is 1.6Ga. It is obviously inappropriate to regard the Changcheng System and Jixian System boundary (1.6Ga) as the Paleo-Mesoproterozoic boundary considering the successive sedimentation of these two systems. It is noteworthy that the volcanic rocks of the Xiaoliangling Formation distributed in the Lvliang area in central NCC and the Xiong'er Group in the southern NCC, the largest volcanic-sedimentary rocks globally at that time, are the earliest sedimentary covers overlying the crystalline basement of the NCC dated at 1.8Ga, which is quite close to the new proposed Paleo-Mesoproterozoic boundary. The period between 1.8Ga and 1.6Ga witnesses significant geological changes globally. The orogenic process terminated, the Columbia Supercontinent began to break-up, and the magmatism model, magmatic rock assemblage types and their geochemical characteristics changed significantly, characterized by the development of anorthosite and rappakivi granite in many cratons. Meanwhile, stable sedimentary covers began to develop worldwide, the banded iron formation (BIF) disappeared, shallow-sea iron-rich deposits consisting of oolitic and granular mineral aggregates and marine sulphide deposits and eukaryotes first appeared. All these features marked that the earth's lithosphere, hydrosphere and atmosphere have undergone major turning points, and the biosphere has entered a new evolutionary stage, indicating that the Earth entered into an evolution stage of "middle age". The major reason and detailed information for the Earth turning into the "middle age" are still unclear and further in-depth study is requested, yet the initial point or foremost turning period of this transformation is at ca. 1.8Ga, which should be regarded as the global Paleo-Mesoproterozoic boundary.

In the International Precambrian Stratigraphic Chart, the Paleo-/Mesoproterozoic boundary is always set at 1.6Ga while in Chinese literatures, this boundary is always placed at 1.8Ga. The fundamental reason for this difference is the understanding of the nature of the geological events in this period. This paper focuses on discussing the boundary between Paleoproterozoic and Mesoproterozoic from the nature of the geological events during 1.8 similar to 1.6Ga. A large amount of geological data shows that the Columbia/Nuna supercontinent began to stretch and breakup from 1.8Ga to 1.75Ga and formed a series of intracontinental rifting-sag basins, such as Thelon basin in North America (Laurentia), Leichhardt superbasin in northern Australia, Sao Francisco basin in South America, Xiong'er rifting basin in the southern margin of the North China Craton, Dongchuan basin in the southwestern margin of the Yangtze Block, and others. During the early stage of basin formation, the clastic rocks of alluvial fan facies and fluvial facies were deposited, followed by extensive volcanic eruptions. During the middle and late stage, the ealier fluvial facies and lacustrine facies rocks were overlied by carbonate platform sediments deposited in shallow sea, which reflects a process of stretching and breakup. Anorogenic magmatic rocks of 1.78 similar to 1.72Ga distributed widely in continents/blocks that formed the Columbia supercontinent, including bimodal igneous rocks, AMCG assemblages (anorthosite, mangerite, charnockite and granite), rapakivi granite, A-type granite, etc., as well as widely distributed mafic dyke swarms. All these igneous rocks reflect the stretching and breaking process. During 1.8 similar to 1.6Ga, both sedimentary events and magmatic events were related to the stretching and breaking of the supercontinent, but did not show the characteristics of orogeny, continental solidation and cratonization. Therefore, it is not appropriate to use the Statherian to summarize the nature of the geological events in this stage. In Columbia supercongtinent, many intracontinental basins experienced a wide uplift at around 1.6Ga, resulting in a short interval of sedimentation. After that, the original basins continued to develop and accepted a wider range of sedimentation, which sustained until about 1.4 similar to 1.3Ga. Magmatic events related to supercontinental stretching and breaking can also be intermittent from 1.78Ga to 1.4 similar to 1.32Ga. From 1.8Ga (or 1.78Ga) to 1.4 similar to 1.3Ga, both sedimentary events in the basins and magmatic events related to stretching and breaking are basically continuous. Therefore, the set of Paleo-Mesoproterozoic boundary at 1.6Ga artificially destroys the continuity of global sedimentary events and magmatic events, which were obviously contrary to the principle that the major sequences of sedimentation, igneous emplacement, or orogeny should be cut off as little as possible in the Precambrian stratigraphic division. Since the time of the successive depositional events in rifting-basins and of the anorogenic magmatic events in continents can be traced back to 1.8Ga (or 1.78Ga), we propose to place the Paleo-Mesoproterozoic boundary at 1.8Ga or 1.78Ga, rather then 1.6Ga. Considering that the rifting process leads to the development of the overlying strata on the preexisting supercontinent or craton, we suggest classifying the sediments of ca. 1.8 similar to 1.4Ga into the Calymmian.

Three supercontinents occurred during the evolution of the Earth. Development of two of them (Columbia and Rodinia) span part of the age range of the Meso-Neoproterozoic. Their formation was related to a series of regional events, leading to a supercontinent evolution model containing multiple for-mation mechanisms. The sedimentary events in the middle and eastern North China Craton, and the rifting and snowball events in Yangtze and Tarim Cratons during the Neoproterozoic are all considered as the response to the break-up of the Rodinia supercontinent. These events help to decode the location of the three cratonic basins in the supercontinent and to decipher their relative positions to each other. Evolution of the Columbia and Rodinia supercontinents was accompanied by several events including development of thick dolomite, microbiolite, red bed, and black shale of regional or global significance, as well as the globally distributed molar tooth and Ediacaran cap carbonate. Geochemical events also occurred, reflected by abnormal excursions of some isotopes and element abundances. The mineralization events result in ore deposition of phosphorite, manganese and BIF related iron. These events are important to the reconstruction of the paleocontinents and paleogeographic scenarios. Based on an overview of the development and distribution of the events related to supercontinent evolution and our own data, this paper aims to clarify the relationship between the evolution of supercontinent and the occurrence of the geological events, which aids the analysis of the cyclic formation and break-up of supercontinents, help to locate the supercontinent position, and assists the interpretation of the development of the prototype basins.

神农架群的底界问题一直以来悬而未决.神农架群底界能否获取,已成为神农架群能否完美成为待建系候选层型的关键.距神农架东南几十公里的黄陵穹隆东北部地区自下而上发育中—新元古代西汊河组、吴家台组、浇园山组、南沱组和陡山沱组等地层,且胡正祥等(2012)认为该地吴家台组为神农架群中下部地层,那么该地是否存在神农架群的底界自然就引起大家的极大关注.本文基于该地浇园山剖面西汊河组石英片岩样品(0529-1),吴家台组底部砾岩(0228-4)和砂岩(0228-5)3件样品,应用LA-ICP-MS方法进行了碎屑锆石年龄的测试分析,同时结合地层单元间接触关系和岩石学与沉积学特征等标志,最终约束吴家台组形成时代.结果表明,崆岭北部樟村坪以北浇园山剖面西汊河组与上覆吴家台组呈不整合接触;西汊河组碎屑锆石年龄谱仅显示太古宙和2.0Ga两个明显的峰值;但吴家台组碎屑锆石年龄谱不仅包含了与西汉河组相同的太古宙和2.0Ga两个年龄峰值,而且还含有0.8Ga的弱峰值,由此断定西汊河组和吴家台组形成时限是完全不同的.前者应年轻于2.0Ga,但由于其为角闪岩相变质岩,又不同于扬子克拉通最终(1.8Ga)固结前的变质结晶基底岩石组合,因此推测西汊河组大致为中元古代,同理,吴家台组应形成于0.8Ga以后,结合吴家台组之上具有典型的南沱组冰碛杂砾岩,因此其时代应界于青白口纪晚期—南华纪早期之间,进一步结合各岩组砾岩中砾石组分的证据认为,吴家台组应相当于区域上莲沱组.同时研究表明,西汊河组和吴家台组物源主要来自黄陵穹隆核部中太古代TTG片麻岩和新太古代的花岗质片麻岩,古元古代碎屑锆石主要来源于崆岭杂岩中部的火山—岩浆岩以及黄陵穹隆南翼的新元古代岩浆岩.

华北克拉通南缘汝阳群中以大型具刺疑源类为代表的真核生物群的时代归属问题一直存在争议.新近在豫西汝州阳坡村洛峪群洛峪口组中获得的凝灰岩锆石SHRIMP U-Pb年龄为1639±13 Ma,结合熊耳群和汝阳群已获得的其他年龄数据,将这类形态复杂的真核生物群出现的时间限定在1.75-1.64 Ga,即中元古代的早期.这说明,过去一直被认为的代表进化程度较高但仅属于新元古代的一些真核生物群,其实在中元古代早期就已经出现了;由此可以进一步推测,在更古老的地层中应有更原始的微体化石出现,从而华北克拉通南缘中元古界(＞1.60 Ga)将成为探寻最古老真核生物祖先的重要窗口.同时,将这些在中元古代早期就已经出现并在以后较长地史时期都存在的真核生物群用于标定地层形成时代或作为相关地层的对比标志,值得重新考虑和商榷.

Amphibolites (basic volcanics), TTG gneisses and hypersthene-diorite/charnockite of Late Neoarchean age are widely distributed throughout the Zunhua-Qianxi-Qian' an area in eastern Hebei, North China Craton. SHRIMP zircon U-Pb isotopic dating reveals that amphibolites, TTG gneisses and hypersthene-diorite/charnockites were synchronously from 2529 +/- 30Ma to 2555 +/- 14Ma, reflecting an important Late Neoarchean magmatic event in the North China Craton, followed by sequential granulite facies metamorphism at similar to 2.5Ga. CL images exhibed that some cores of zircons from TTG gneisses and hypersthene-diorite/charnockites are black-gray with fir-leaf structure or structureless, implying that the U-Th-Pb isotopic system of the cores of the zircons have been turbulenced or reseted during metamorphism, so the Pb-207/Pb-206 weighted mean ages in cores of magamatic zircons are generally interpreted as the youngest age of magmatic event. Magmatic zircons of the Late Neoarchean TTG gneisses and charnockites have positive epsilon(Hf)(t) values of -0.08 similar to 9.49 and calculated t(DM1) (Hf) ages from 2572Ma to 2896Ma with a peak age of 2.72Ga, suggesting that the TTG gneissic and charnockitic magma were direved from depleted mantal source, and 2.7Ga was an important crustal growth event in the studed area and the North China Craton. Geochemical and petrogenetic studies revel that the TTG gneisses and hypersthene-diorite/charnockites in the area were formed by fractional crystaollization in the magmas direved from juvenile crustal rocks with hornblende as the primary frantionated phase. A mantle plume model is favored from petrogenesis of TTG gneisses and hypersthene-diorite/charnockite which explains the many other gellogical features in the eastern Hebei of the North China Craton as well.

Metamorphic rock series of the Guanghua Group occurs as a block in Archean TTG gneiss in Tonghua area of Jilin Province,whose forming age remains controversial for a long time.Using SHRIMP and LA-ICPMS zircon U-Pb dating techniques,representative rock samples from the Guanghua Group were analyzed,including garnet biotite schist,biotite monzogneiss,garnet hornblende schist and potassium granite intruding into the bottom of the Guanghua Group.The results show that four metamorphic rock samples have similar detrital zircon ages (concordant ages are between 2.6 Ga and 2.5 Ga) though they were collected from different strata.Most detrital zircons from four samples yeild concordant mean ages of 2 529 ± 7 Ma,2 568±4 Ma,2 526±11 Ma and 2 530±6 Ma,respectively,suggesting a derivation from Neoarchean magmatic unit.Some zircons from metamorphic rocks record 3 stages metamorphic age (2 525±10 Ma,1 926±40 Ma and 1 878±16 Ma),indicating that the Guanghua Group experienced both Neoarchean and Paleoproterozoic thermo-tectonic events.Zircons from the potassium granite yield a concordant mean age of 2 154±7 Ma,which is interpreted as intruding time of the ploton.The potassium granite has not suffered any deformation,suggesting a intracontinental rift tectonic setting.

For summarizing the historical experiences of the study of metamorphic rocks in China,this paper presents a review on the advances from metamorphic petrology to metamorphic geology in the past nearly 70 years.These advances are discussed in three stages and eight aspects.On the basis of reviewing a huge number of literatures,we propose that our researches on ultrahigh pressure metamorphism,Precambrian metamorphic geology,metamorphic chronology,and metamorphic phase modeling are internationally advanced,and researches on blueschist,metamorphic fluids and metamorphic chemical kinetics are synchronized with the world,but the researches on very low-grade metamorphism and some other fields have not attracted enough attention,having large gaps with the international advanced level.It is concluded that the study on metamorphic rocks in China has changed from metamorphic petrology to metamorphic geology,that is,from mono-disciplinary petrology study to multi-disciplinary researches of metamorphic rocks,including metamorphic minerals,geochemistry,isotopic geology,tectonic geology and some other disciplines.Although we have some location advantages in the study of metamorphic rocks,independent innovative researches are still required to turn the location advantages into academic advantages.In addition,as the development of various analytical experimental techniques has accelerated scientific researches,metamorphic geology will advance greatly with the advent of new technologies and the application of big data technology.

This paper has predominantly discussed four aspects in the study of very low-grade metamorphism:① The major features of very low-grade metamorphism and research contents;② The significance and necessity to strengthen the study of very low-grade metamorphism;③ Current research status and existing problems both in China and abroad;④ Main problems in strengthening the study of very low-grade metamorphism:the first is seting up projects,the second is continuous projects funds,the third is talent training,the fourth is providing advanced instruments and equipment.