The Early Precambrian Rocks,Their Ages,Division and Correlation of the Taihang-Wutai Region, the Yanshan Region and the Eastern Sector of the Yinshan Mountains

According to differences of the protolith formations, the early Precambrian strata in the northern part ofthe North China platform may be divided into the stable stratigraphic region in the west and the mobilestratigraphic region in the east. Based on unconformities, either stratiragphic or tectonic, as well as significantmetamorphic thermal events, the two regions may be stratigraphically defined as follows: 1) the middleArchaean Fuping Supergroup composed of the Chenzhuang and Wanzi Groups (stable areas), and the middleArchaean Qianxi Group (mobile area), whose upper limits are all dated at 2800 Ma; and 2) the upper ArchaeanWutai Supergroup composed of the Longquanguan, Shizui and Taihuai Groups (stable areas), and the upperArchaean Zunhua, Dantazi and Zhuzhangzi Groups (mobile areas). whose upper limits are all dated at 2500Ma. A correlation of the above-mentioned units is also made. The lower Proterozoic Hutuo Group of the sta-ble region is adjusted to comprise the Gaofan, Doucun, Dongye and Guojiazhai Groups. The upper limit of theGaofan Group is placed at 2350 Ma, Dongye 1850 Ma and Guojiazhai (the lower limit of the Changcheng Sys-tem) 1700 Ma.     

A New Progress of the Proterozoic Chronostratigraphical Division

The Precambrian, an informal chronostratigraphical unit, represents the period of Earth history from the start of the Cambrian at ca. 541 Ma back to the formation of the planet at 4567 Ma. It was originally conceptualized as a "Cryptozoic Eon" that was contrasted with the Phanerozoic Eon from the Cambrian to the Quaternary, which is now known as the Precambrian and can be subdivided into three eons, i.e., the Hadean, the Archean and the Proterozoic. The Precambrian is currently divided chronometrically into convenient boundaries, including for the establishment of the Proterozoic periods that were chosen to reflect large-scale tectonic or sedimentary features(except for the Ediacaran Period). This chronometric arrangement might represent the second progress on the study of chronostratigraphy of the Precambrian after its separation from the Phanerozoic. Upon further study of the evolutionary history of the Precambrian Earth, applying new geodynamic and geobiological knowledge and information, a revised division of Precambrian time has led to the third conceptual progress on the study of Precambrian chronostratigraphy. In the current scheme, the Proterozoic Eon began at 2500 Ma, which is the approximate time by which most granite-greenstone crust had formed, and can be subdivided into ten periods of typically 200 Ma duration grouped into three eras(except for the Ediacaran Period). Within this current scheme, the Ediacaran Period was ratified in 2004, the first period-level addition to the geologic time scale in more than a century, an important advancement in stratigraphy. There are two main problems in the current scheme of Proterozoic chronostratigraphical division:(1) the definition of the Archean–Proterozoic boundary at 2500 Ma, which does not reflect a unique time of synchronous global change in tectonic style and does not correspond with a major change in lithology;(2) the round number subdivision of the Proterozoic into several periods based on broad orogenic characteristics, which has not met with requests on the concept of modern stratigraphy, except for the Ediacaran Period. In the revised chronostratigraphic scheme for the Proterozoic, the Archean–Proterozoic boundary is placed at the major change from a reducing early Earth to a cooler, more modern Earth characterized by the supercontinent cycle, a major change that occurred at ca. 2420 Ma. Thus, a revised Proterozoic Eon(2420–542 Ma) is envisaged to extend from the Archean–Proterozoic boundary at ca. 2420 Ma to the end of the Ediacaran Period, i.e., a period marked by the progressive rise in atmospheric oxygen, supercontinent cyclicity, and the evolution of more complex(eukaryotic) life. As with the current Proterozoic Eon, a revised Proterozoic Eon based on chronostratigraphy is envisaged to consist of three eras(Paleoproterozoic, Mesoproterozoic, and Neoproterozoic), but the boundary ages for these divisions differ from their current ages and their subdivisions into periods would also differ from current practice. A scheme is proposed for the chronostratigraphic division of the Proterozoic, based principally on geodynamic and geobiological events and their expressions in the stratigraphic record. Importantly, this revision of the Proterozoic time scale will be of significant benefit to the community as a whole and will help to drive new research that will unveil new information about the history of our planet, since the Proterozoic is a significant connecting link between the preceding Precambrian and the following Phanerozoic.     

华北板块北缘活动带元古宙构造岩片

新的研究证实 ,华北板块北缘残存一条元古宙构造岩片堆集带 ,包括古元古代、中元古代、新元古代等多期构造岩片。并相伴有 180 0Ma±、140 0Ma±、10 0 0Ma±、6 5 0Ma±的花岗岩类的侵入活动和构造变质成矿等热事件的年代记录 ,并在华北板块北部金镶边带中保存了相一致的信息 ,揭示了它们是陆缘多期拼贴造山的产物。这为超大陆旋回 ,特别是元古宙两次超大陆的聚合与裂解及其构造演化过程的研究提供了良好的野外实验园地 ,并为元古宙、特别是古元古代大陆的增生及Rodinia超大陆在北半球的存在或构造响应提出新的课题。     

Geochronological constraints on early volcanic evolution of the Pilbara Block,Western Australia

U‐Pb isotopic systems of zircons from the Boobina and Spinaway Porphyries from the Precambrian Pilbara Block of Western Australia indicate ages of 3307± 19 Ma and 2768 ± 16 Ma, respectively. The Boobina Porphyry intrudes upper members of the Archaean greenstones of the Warrawoona Group. The Spinaway Porphyry intrudes basal units of the unconformably overlying volcanics and sediments of the Mt Bruce Supergroup. The age of the Boobina Porphyry, together with previous zircon U‐Pb and whole rock Sm‐Nd age determinations on stratigraphically older units, indicate that early Archaean volcanism in the Pilbara took place between 3560 Ma and 3300 Ma. On the basis of the age determination of the Spinaway Porphyry, and the chronometric definition of 2500 Ma for the Archaean—Proterozoic boundary, by the International Subcommis‐sion on Precambrian Stratigraphy (James H. L. 1978, Precambrian Res. 7, 193–204), the lower units of the Mt Bruce Supergroup should now be assigned to the Archaean.     

阴山东段(冀北及冀晋内蒙古接壤地带)的太古宙地层问题讨论

在对区内太古宙地层的原岩性质、大的层序、同位素地质测年值的地质意义 (主要是 H2 O、CO2 流体作用在变质作用中能否造成同位素的开放及 TDM值能否反映为变质年龄 )等众多认识分歧进行剖析的基础上 ,将其自下而上划分为桑干岩群、集宁群、单塔子群、红旗营子群 (或称乌拉山群 ) ,其时代依次归属中太古代早期 (330 0—30 0 0 Ma)、晚期 (30 0 0— 2 80 0 Ma)及新太古代早期 (2 80 0— 2 6 5 0 Ma)、中期 (2 6 5 0— 2 5 6 0 Ma)     

华北地台的元古宙构造演化

华北地台在前寒武纪经历过三个大构造阶段,即太古初始克拉通、早元古代原地台和中—晚元古代地台的形成阶段,每个阶段都有各具特点的构造演化史。发生在太古宙末期的阜平运动,是一次强烈的构造-热事件,造成太古岩层的变质、变形等和形成初始的克拉通基底,早元古时出现了裂陷形成了克拉通内或边缘的内硅铝盆地或海槽。早元古末期的吕梁-中条运动是另一次重要的构造-热事件,此后,原地台最终固化,华北地台的主要构造格架基本成型。中—晚元古时期在华北地台的不同部位发育了三个主要构造盆地。     

吉林南部变质岩太古宙—元古宙分界时限的确定及过渡性构造演化

吉林南部古老岩石测年数据偏新和太古宙与元古宙之间分界时限的混乱,本文运用Ｓｍ－Ｎｄ等时线法和锆石Ｕ－Ｐｂ法将吉林南部变质岩系划分为４个年龄段：前阜平旋回（〉２６００Ｍａ）;阜平旋回第一幕（２６００￣２５００Ｍａ）;阜平旋回第二幕（２５００￣２４００Ｍａ）;阜平旋回第三幕（２４００￣２３５０Ｍａ）。阜平旋回第三幕归入太古宙并作为太古宙－元古宙之间分界时限,吉林南部古陆构造环境由活动趋向于稳定,新、老     

东昆仑造山带花岗岩及地壳生长

东昆仑造山带是青藏高原内可与冈底斯相媲美的又一条巨型构造岩浆岩带。该带内的花岗岩形成可以划分为4个时段,分别与4个造山旋回相对应：前寒武纪（元古宙）;早古生代;晚古生代—早中生代;晚中生代—新生代。其中,以晚古生代—早中生代（或称华力西—印支旋回）、特别是三叠纪的花岗岩最为发育。东昆仑造山带基底主要形成于古元古代晚期。其早古生代构造-岩浆事件序列与北祁连造山带可以对比,属祁连—东昆仑加里东造山系统的一部分。到晚古生代—早中生代时东昆仑卷入古特提斯构造体制,属于古特提斯造山系统的北缘。华力西—印支是一个完整的造山旋回,与西南“三江”古特提斯的演化历史相似。昆南缝合带是当时中国南北大陆的主要构造分界线。新生代印度—欧亚大陆的碰撞,使东昆仑造山带又卷入了青藏大陆碰撞造山系统,但对东昆仑的影响是一种远程效应。 　　东昆仑造山带大陆地壳主要形成于古元古代晚期,但在显生宙还有新生地壳 （juvenile crust） 产生,与兴蒙、冈底斯、安第斯等造山带相似。东昆仑花岗岩带中丰富的幔源岩浆底侵作用与壳-幔源岩浆混合作用的证据,以及花岗岩类的Nd、Sr同位素成份（87Sr/ 86Sr初始值多数小于0.710;εNd（t ）值变化于－9.2和＋3.6之间）,说明 地幔物质的注入及其与地壳物质的混合,对显生宙地壳的形成演化起着重要作用,是显生宙东昆仑地壳生长的重要方式。根据花岗质寄主岩、镁铁质暗色微粒包体（MME）及底侵辉长岩的锆石SHRIMP U-Pb定年,东昆仑造山带在显生宙发生过两次大规模的底侵作用与岩浆混合作用,一次在早-中泥盆世（394~403 Ma）,另一次在中三叠世（239～242 Ma）,分别相当于加里东旋回、华力西-印支旋回的俯冲结束/碰撞开始阶段。     

Discussion on Relationship Between Western Margin of Yangtze Block and Southwestern Sanjiang Region in Proterozoic

DISCUSSION ON RELATIONSHIP BETWEEN WESTERN MARGIN OF YANGTZE BLOCK AND SOUTHWESTERN SANJIANG REGION IN PROTEROZOIC     

Geochronology,geochemistry and tectonics of the NE Bayuda Desert,N Sudan: Implications for the western margin of the late Proterozoic fold belt of NE Africa

Five suites of rocks collected from the Precambrian basement in the NE Bayuda Desert of central northern Sudan give late Proterozoic whole-rock $\text{Rb}\text{Sr}$ isochron ages. The Abu Harik Complex, thought by some previous workers to be an older basement, gives an age of 898 ± 51 Ma. Upper amphibolite-facies metasediments give a metamorphic age of 761 ± 22 Ma. The supposedly younger greenschist-facies El Koro Volcanic Series were erupted 800 ± 83 Ma ago. These are chemically similar to the volcanics which unconformably overlie the Sol Hamed ophiolite in the Red Sea Hills of NE Sudan and to some modern island are volcanics. The metasediments were intruded 678 ± 43 Ma ago by the Diefallab Granite, which is itself deformed. The younger, weakly-deformed Amaki Series, with a basal conglomerate containing basement clasts overlain by purple grits, is probably equivalent to the molasse-type Hammamat Group of the Eastern Desert of Egypt which was deposited between 616 and 596 Ma ago. Finally, the post-tectonic Shallal Granite, with within-plate geochemistry, was intruded 549 ± 12 Ma ago. Geochemical data suggest that the Abu Harik Complex, the El Koro Volcanic Series and the Diefallab Granite are arc-related magmatic rocks. They were intruded into, or thrust onto, shallow-water, shelf sediments during subduction and then collision, between c. 900 and 550 Ma. The data presented here give no support to previous views that the high-grade metasediments were metamorphosed prior to the late Proterozoic events, that they unconformably overlie a still older, perhaps Archaean, basement or that they are unconformably overlain by younger late Proterozoic low-grade volcanics. The Precambrian rocks along the E side of the Bayuda Desert must now all be assigned to the late Proterozoic and the boundary between this late Proterozoic fold belt and an older craton, known to crop out at Jebel Uweinat, must lie farther to the W.     

内蒙大青山早前寒武纪变质岩和早期陆壳的演化

将大青山地区早前寒武纪变质岩石分成三个岩性构造组合.即(1)麻粒岩—紫苏花岗岩组合;(2)角闪片麻岩—英云闪长岩组合;(3)富铝片麻岩—钾质花岗岩组合.其中,组合(1)是区内最古老的物质组成,其形成时代至少应在晚太古代以前(>2800Ma).组合(2)是具花岗—绿岩带特征的晚太古代中、低级变质岩系.组合(3)是经早元古造山变质作用形成的岩石组合.根据重新排定的地质事件顺序,对本区早期地壳演化的有关问题进行了讨论.     

论中国前寒武纪地质时代及年代地层的划分

本文讨论了前寒武纪地质时代和年代地层划分的原则和命名,提出建立隐生宙、原生宙和显生宙。隐生宙包括冥古代和太古代;原生宙分始元代、中元代和新元代。划分中的重要改变是根据新的年龄值数据将五台群归入太古代,将长城系底界改为1700Ma;并根据蠕虫-须腕动物群的出现,将震旦纪归入古生代。文中还阐述了作者对前寒武纪时代划分的新观点。     

Precambrian crustal contribution to the Variscan accretionary prism of the Kaczawa Mountains (Sudetes,SW Poland): evidence from SHRIMP dating of detrital zircons

SHRIMP dating of detrital zircons from sandstones of the Gackowa Formation (Kaczawa Complex, Sudetes, SW Poland) indicates input from late (550–750 Ma) and early Proterozoic to Archaean sources (∼2.0–3.4 Ga, the latter being the oldest recorded age from the Sudetic region). These dates preclude within-terrane derivation from seemingly correlatory acid volcanic rocks of early Palaeozoic age. Rather, they indicate provenance from Cadomian and older rocks that currently form part of other, geographically distant terranes; the most likely source identified to date is the Lusatian Block in the Saxothuringian Zone. Hence, the Gackowa Formation may be late Proterozoic rather than early Palaeozoic in depositional age, possibly coeval with the late Proterozoic (pre-Cadomian) greywackes of Lusatia, being subsequently tectonically interleaved with early Palaeozoic volcanic rocks into the Kaczawa accretionary prism during the Variscan orogeny. However, correlation with the lithologically similar early Ordovician Dubrau Quartzite of Saxothuringia, and so assignation to the early Paleozoic (post-Cadomian) rift succession deposited at the northern margin of Gondwana, cannot yet be precluded.     

Late Archaean—early proterozoic source ages of zircons in rocks from the Paleozoic orogen of western Galicia,NW Spain

U-Pb data are reported for nine suites of zircons and three monazites from the Paleozoic orogen in western Galicia (NW Spain): one paragneiss and six orthogneisses from the early Paleozoic basement, and two Carboniferous (ca. 310 Ma old) intrusions of two-mica granite. New whole-rock Rb-Sr analyses, along with earlier data, indicate an age of ca. 470-440 Ma (Ordovician) for the emplacement of the granitic precursors of the orthogneisses. Monazite from the paragneiss also yields an U-Pb age of ca. 470 Ma. For all nine investigated suites of zircons the U-Pb systematics signal the presence of a minor proportion of Precambrian zircon. The zircon data from two orthogneisses and the paragneiss display roughly linear arrays with upper intercepts between about 3.0 Ga and 2.0 Ga, and lower intercepts between ca. 480 and 460 Ma; the former are interpreted as approaching the age of the old zircon component, and the latter as reflecting either the time of crystallization of new zircons from the magma (orthogneisses), or the time of radiogenic lead loss from the old zircons (paragneiss). The suites of zircons from all other investigated orthogneisses suffered isotopic disturbance posterior to the granite emplacement 470-440 Ma ago, in most cases leading to ‘false’ discordias without geochronological significance. Similarly, the zircons of the two investigated two-mica granites do not produce meaningful discordias because of post-Paleozoic disturbance. The monazite U-Pb systems of the latter granites indicate (sub)recent lead loss.From the high initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios an involvement of Precambrian continental crust material is evident in the generation of the early Paleozoic suite of granites, while the zircon U-Pb data give evidence of the presence of about 3.0-2.0 Ga old (late Archaean—early Proterozoic) components in the source material. Zircons from the oldest sedimentary rocks in the area, now present as catazonal paragneisses and a likely source for the granites, likewise reveal a provenance age of 3.0-2.0 Ga. The late Archaean—early Proterozoic source rocks in western Galicia probably formed part of an Archaean continental crust underlying much of western Europe, but mostly modified beyond recognition by younger events.     

太行山—五台山区前寒武纪变质岩系同位素地质年代学研究

<正> 中国北方河北、山西两省交界地带的太行—五台山区,早前寒武纪变质岩系十分发育,分布面积达20,000平方公里,为华北地块的重要组成部分。在这一地区内,保留了早前寒武纪不同发展阶段的种种地质作用的记录。深入研究其地质历史,将对阐明华北地块的形成和演化具有重要的典型意义。作者正是基于这一目的,在该区进行了同位素地质年代学的研究。     

陕西南秦岭地质组成及其演化

综合分析南秦岭地质组成与构造特征，显示出区内经历了太古－早、中元古代基底形成阶段，晚元古－早古生代统一扬子大陆北缘演化阶段，古生代勉略－石泉海槽的形成、闭合造山阶段和燕山以来的陆内造山4个大的演化阶段，并形成了相应的岩石建造与构造变形组合。     

Tectonic Development of the Proterozoic Continental Margins in East Qinling and Adjacent Regions

The East Qinling and adjacent cratonic regions belong to two geotectonicunits,the Sinokorean Subdomain including the Sinokorean Platform and itssouthern continental margin the North Qinling Belt,and the YangtzeanSubdomain comprising the Yangtze Platform and its northern continental mar-gin the South Qinling Belt.The Qinling region may thus be subdivided into twocontinental margin belts separated from each other by the Proterozoic Qinlingmarine realm,which did not disappear until Late Triassic.The convergentcrustal consumption zone,the megasuture between the two belts,lies betweenthe Fengxian-Shangnan line in the north and the Shanyang-Xijia line in thesouth and was much deformed and displaced through Mesozoic intracratoniccollision and compression.In the northern subdomain the Lower Proterozoic is representedby protoaulacogen volcano-sediments,the inner Tiedonggou Group and theouter marginal Qinling Group,which were folded and metamorphosed in theLuliangian orogeny,a general process of aggregation and s     

新疆北部前寒武系划分和对比

库鲁克塔格是新疆北部前寒武系分布较广,地层层序相对完整的地区.作者以库鲁克塔格为地层模型区,以同位素第龄为格架,初步确定了本区群级地层单元的界线及归属.在岩石地层、生物地层、化学地层等各种方法相互印证的基础上,建立并完善了前寒武纪的地层层序.     

中国中-新元古代地层年表的修正——锆石U-Pb年龄对年代地层的制约

报道了全国地层委员会的中-新元古代地层年表新标定的方案:即长城系限定在1.8～1.6 Ga;蓟县系限定在1.6～1.4 Ga;待建系1.4～1.0 Ga;青白口系限定在1.0～0.78 Ga;南华系限定在780～635 Ma及震旦系限定在635～542 Ma.新年表突出3个方面的标定:1)对长城系和蓟县系的年代学限定;...     

Proterozoic links between Northeastern Brazil and West Africa: A plate tectonic model based on gravity data

Using the Bullard predrift reconstruction for the southern Atlantic, analysis of the major gravimetric trends of the West African craton (2000 Ma) and the surrounding mobile belts allows us to delineate the upper Proterozoic shield boundary and to put forward an evolutionary model for late Precambrian time.Over the cratonic area gravimetric anomalies are related to a basement framework or to sedimentary basins whose geometry is linked to reactivation of ancient faults. Gravity anomalies and LANDSAT imagery show a NE-SW lineament in West Africa which can be correlated with a variety of geologic features, the largest being the late Precambrian Gourma aulacogen.At the margins of the craton the deformation patterns and gravity signatures associated with the 600 Ma orogeny were largely controlled by the geometry of the stable craton itself. On the eastern edge (Pan-African belt and Brazilian belt east of the São Luis and Amazonian cratons), the distribution of the anomalies and deduced structures can be explained by a continental collision process. On the western and southern edge (Brazilian belt between the São Luis and Amazonian cratons, Rokelide belt, Mauritanide belt) the gravity signature is different, suggesting a large amount of intensely tectonized basic rocks. A limited spreading process followed by an intense compressional episode is suggested.