U-Pb zircon geochronological evidence for Neoproterozoic events in the Glenfinnan Group (Moine Supergroup): the formation of the Ardgour granite gneiss, north-west Scotland

The age and Precambrian history of the Moine Supergroup within the Caledonide belt of north-west Scotland have long been contentious issues. The Ardgour granite gneiss is essentially an in situ anatectic granite formed during deformation and regional high-grade metamorphism from Moine metasediments. High-precision TIMS and SHRIMP U-Pb zircon dating shows that the age of the anatectic Ardgour granite gneiss and its enclosed segregation pegmatites is 873 ± 7 Ma. This demonstrates the reality of a Neoproterozoic episode of high-grade metamorphism in the Glenfinnan Group Moine and, contrary to previous evidence, the absence of Grenvillian-aged metamorphism. This conclusion places constraints on Neoproterozoic palaeogeographic reconstructions of the North Atlantic region, indicating that the Moine rocks cannot be used as a link between the Grenvillian belt of North America and the Sveconorwegian orogen in Scandinavia. SHRIMP ages of between c. 1100 and 1900 Ma were obtained from detrital, inherited zircons and reflect the provenance of the Glenfinnan Group Moine sediments which must, therefore, have been deposited between c. 1100 and 870 Ma. Potential sources are found as relatively minor, tectonically bounded basement inliers within the British Caledonides, although more widespread source areas occur outside Britain in both Laurentia and Baltica. The most important feature of the provenance is the absence of detrital Archaean grains. This suggests that the Archaean Lewisian gneiss complex, which forms the basement component of the western foreland to the Caledonides in Britain, was not a major contributor to the Glenfinnan Group basin. Received: 16 June 1996 / Accepted: 29 January 1997     

地史早期岩石中的铅锌演化--狼山-渣尔泰山中元古代铅锌成矿的物质基础

以中国内蒙古狼山一渣尔泰山中元古代SEDEX型铅．锌成矿带为例，研究了该区从太古代到中元古代地壳岩石的铅锌含量和变化关系以及与成矿的关系。研究发现，从早到晚，岩石SiO2和K2O含量升高，铅含量也与二者同步增加；FeO、MgO、CaO及Na20含量呈下降趋势，锌含量也同步降低。在太古代时，岩石的Zn／Pb比值一般〉8，中元古代时这一比值降低为2～4。矿石的Zn／Pb比值与基底岩石Zn／Pb比值具有很好的一致性。铅锌这种随时间的变化与中元古代铅的暴发性成矿及大规模铅锌共生矿床的形成是同步的，说明基底岩石中的铅和锌是该成矿带SEDEX矿床成矿的物质基础。     

Banded iron formations in Proterozoic greenstone belts: Call for further studies

Banded iron formations occur in greenstone belts in which volcanic rocks are predominant. Greenstone belts are not restricted to the Archaean (>2500 Ma), as is commonly perceived, but they continued to form, albeit in lesser abundance, in the Proterozoic. Thus, banded iron formations which are closely associated with volcanic sequences occur in several well-documented early-mid Proterozoic greenstone belts. Examples are the Yavapai belts at Jerome in Arizona, the Trans-Amazonian belts in Guiana, and the Dalma belts of the Singhbhum region of NE India. Stratigraphic and sedimentological studies are needed to establish the similarities and differences of these iron formations with those in Archaean greenstone belts, and with the banded iron formations which were common in cratonic-shelf environments in the early-mid Proterozoic.     

马坑铁矿火山沉积成因探讨

<正> 地处闽西南—粤东地区,以加里东褶皱带为基底的永(安)—梅(县)上古生代拗陷,又分为中间基底隆起带和两翼基底凹陷带。南东翼阳山—龙岩—梅县基底凹陷带是一个重要的铁成矿带,在福建有阳山、潘田、洛阳、中甲、马坑等,粤东有铁坑拗、铁山峰、尖山等铁矿,其中大中型矿床沿北东向略呈等间距分布,主要基底构造线方向为北东向和东西向。     

海相火山-沉积建造铁铜矿床类型及地质特征

铁-铜型矿床产出的时代从元古宙到新生代均有，与其有关的火山岩大多数为中基性与中酸性或偏碱性岩石。作者以镜的山桦树沟、陇山陈家庙和陕西铜厂不同时代的铁-铜矿床为例，概述了该类型矿床的地质特征、成矿环境并着重探了铁-铜矿床的成因机制，认为该类型矿床是与火山作用有关的喷气-沉积型矿床，同时指出柳沟峡地区及其以西（东缰地区）铁-铜型铜矿化带的发现，是进一步寻找铁-铜-金矿床的有利地段。     

Gravity and magnetic joint modeling of the Potiguar Rift Basin (NE Brazil): Basement control during Neocomian extension and deformation

A 2.5D gravity and magnetic investigation was conducted along five transects across the Potiguar Basin in the Borborema Province, NE Brazil. The objective of the study is to model the internal architecture of this intracontinental rift basin, which represents the interaction between the heterogeneous Precambrian basement and the Neocomian extensional tectonics, which led to the South Atlantic opening.Joint modeling of the gravity and magnetic data was constrained by Euler deconvolution results, seismic data, well logs and geologic mapping. This integrated approach allowed to determine the rift architecture that is inserted in a complex tectonic and structural framework. Results from joint modeling show that a series of asymmetric half-grabens is oriented in the NE–SW direction and controlled by a system of normal faults with throw greater than 5.5 km. High-density and low-magnetized material constitutes the footwall and intrarift horsts. These supracrustal heterogeneities in association with preexisting shear zones probably guided the Mesozoic rifting process in NE Brazil. Their composition seems to be related to metamorphic rocks of the Proterozoic basement, as suggested by gravity and magnetic anomalies and the geology of the exposed basement. Our interpretation is supported by geophysical studies carried out in the Benue Trough, the counterpart of the Potiguar Basin in West Africa.     

冀东探区潜山油藏形成条件及分布规律研究

冀东地区发育有多个潜山,潜山地层由中生界、古生界、元古界及太古界-下元古界结晶基底组成,潜山发育有侏罗系、奥陶系、寒武系和太古界花岗岩四大套储层,以及上第三系明化镇组、上第三系馆陶组、白垩系泥岩、侏罗系煤系地层,寒武系徐庄组、毛庄组、馒头组泥页岩盖层,且储盖组合良好,油气成藏的关键因素是油源,并以南堡凹陷下第三系烃源岩最佳;总结了潜山的新生古储型成藏组合和单侧-它源-侧向-潜山成藏模式,认为南堡凹陷下第三系生成的油气可以通过深大断裂和不整合面运移到潜山有利部位的多个目的层中聚集成藏;潜山油藏的分布规律是沿富油凹陷周边潜山的大断裂和不整合面发育带分布,在油源断层的交汇处附近富集.     

Metallogeny and lead isotopic composition of base metal sulfide deposits in the Rappen area,northern Sweden

Early Proterozoic volcanic and sedimentary rocks of the Rappen district in northern Sweden were deposited at a destructive plate margin to the south of the Archaean craton of the western Baltic Shield. The volcano-sedimentary suite was intruded by two generations of early Proterozoic granites at ca. 1.89–1.85 Ga and ca.1.82–1.78 Ga, respectively, and metamorphosed at upper amphibolite facies conditions. Small stratabound iron, copper, and zinc deposits occur in felsic to mafic tuffs and arkosic sediments. Small deposits of molybdenum, tungsten, and uranium formed during the emplacement of the younger granites. The lead isotopic compositions of sulfide trace lead from the various deposits are highly heterogeneous. In the ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb diagram they fall on mixing arrays between little evolved early Proterozoic lead and highly radiogenic Caledonian lead. The least radiogenic lead isotopic compositions from the various deposits have a wide range of ²⁰⁷Pb/²⁰⁴Pb ratios and thus indicate variable involvement of Archaean crustal lead in the Proterozoic deposits. Deposits hosted by siliciclastic rocks have higher ²⁰⁷Pb/²⁰⁴Pb ratios than deposits hosted in mafic to felsic tuffites. The lead isotopic heterogeneity suggests that the lead in the various deposits was locally derived and, furthermore, that the sedimentary rocks in part originated from the Archaean craton to the north. Lead mixing arrays in the ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb diagram demonstrate that in Paleozoic time radiogenic lead was mobilized and transported in the basement. Source ages calculated from the mixing arrays (ca.1.9 Ga and ca.1.8 Ga) correspond to the age of the Early Proterozoic volcanism and metamorphism respectively. One group of deposits includes lead from at least three sources and illustrates that radiogenic lead was multiply mobilized and transported in the Proterozoic basement. It occurs in deposits that occur in zones that became permeable during the reactivations of the basement.     

北祁连造山带东段上奥陶统一下、中泥盆统砂岩碎屑组分与物源分析

北祁连造山带东部武威斜豪-古浪石城子-靖远水泉-带上奥陶统一下、中泥盆统砂岩碎屑组分源区大地构造背景的判别结果表明,上奥陶统砂岩中的沉积物主要来自弧造山带内的过渡岛弧源区,并且早期可能含有较多的来自未分割岛弧源区的物质,下志留统砂岩中的沉积物主要来自碰撞造山带,而下、中泥盆统砂岩中的沉积物主要来自卷入碰撞造山带内的分割...     

柴达木盆地北缘早古生代碰撞造山系统

柴达木盆地北缘在早古生代形成了一条碰撞造山带，该造山带结构保存较完整，可分辨出深俯冲板片、火山岛弧带、蛇绿杂岩带、岛弧深成岩带等组成单元。其中，俯冲板块主要由中元古代鱼卡河岩群和中新元古代花岗片麻岩构成，在寒武纪末-奥陶纪可能全部或部分俯冲到岩石圈深部，发生了高压-超高压变质作用。火山岛弧主要由中基性火山岩、细碎屑岩等组成，成岩时代为晚寒武世-奥陶纪。蛇绿杂岩带由超镁铁质岩、辉长岩、玄武岩和少量硅质岩组成，形成于弧后扩张脊构造背景，成岩时代为寒武纪-奥陶纪。岛弧深成岩成分变化较大，由闪长岩变化到花岗岩，成岩时代为奥陶纪。而造山带北侧的欧龙布鲁克微陆块则具有双层结构，由德令哈杂岩和达肯大坂岩群构成基底，盖层为全吉群。     

An Andean type Palaeozoic convergence in the Bohemian Massif

The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.     

Granite diapirism in the Rum Jungle area,Northern Australia

Early studies in the Rum Jungle area suggested an intrusive relationship between the Rum Jungle and Waterhouse “Granites”, and the overlying sediments. It was later shown that the granitic “intrusions” were Archaean basement complexes onto which Lower Proterozoic sediments had been deposited. Polyphase folding was postulated as being responsible for doming of the basement and cover rocks.This paper proposes to show that the domed structures in the Rum Jungle area, and the emplacement of Middle Proterozoic granites in the Pine Creek Geosyncline were related, and caused by diapiric intrusion of granites, in a solid state, into basement complexes and cover rocks.Structural and metamorphic evidence in support of diapiric intrusion in the Rum Jungle area includes: pebble deformation within steeply dipping beds of quartz conglomerate; disappearance of polyphase fold structures away from the basement complexes; bending of folded country-rock strata into concordance with the complex—sediment contact; and metamorphic and metasomatic alteration of sediments in contact with the basement complexes. Gravity data show mass deficiencies in the Archaean complexes which possibly coincide with young granite diapirs.     

桦甸—和龙北西向金矿密集带基本地质特征及资源远景

金矿密集带位于太古宙中朝古陆板块与元古宙蒙古海板块之间的缝合线上，受北西向的富尔河－古洞河岩石圈断裂带控制。金矿床普遍产在上述相邻二板块构造的边缘，与成矿有关的中酸性侵入杂岩体多为深熔花岗岩浆的产物，容矿构造往往为韧性剪切带或脆性构造破腑带内的片理化带。金矿床主要为少硫化物型，次为构造蚀变岩型，该带有优异的成矿条件，是吉林省金矿的主要远景区。     

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     

桦甸─和龙北西向金矿密集带基本地质特征及资源远景

金矿密集带位于太古宙中朝古陆板块与元古宙蒙古海板块之间的缝合线上，受北西向的富尔河－古洞河岩石圈断裂带控制。金矿床普遍产在上述相邻二板块构造的边缘，与成矿有关的中酸性侵入杂岩体多为深熔花岗岩浆的产物，容矿构造往往为韧性剪切带或脆性构造破碎带内的片理化带。金矿床主要为少硫化物型，次为构造蚀变岩型，该带有优异的成矿条件，是吉林省金矿的主要远景区。     

Silurian Sedimentation in the South Qilian Belt: Arc-Continent Collision-related Deposition in the NE Tibet Plateau?

The South Qilian belt mainly comprises an early Paleozoic arc-ophiolite complex, accretionary prism, microcontinental block, and foreland basin. These elements represent accretion-collision during Cambrian to Silurian time in response to closure of the Proto-Tethyan Ocean in the NE of the present-day Tibet Plateau. Closure of the Proto-Tethyan Ocean between the Central Qilian block and the Oulongbuluke block and the associated collision took place from NE to SW in a zipper-like style. Sediment would have been dispersed longitudinally SW-ward with a progressive facies migration from marginal alluvial sediments toward slope deep-water and deep-sea turbidites. This migration path indicates an ocean basin that shrank toward the SW. The Balonggongga'er Formation in the western South Qilian belt represents the fill of a latest Ordovician-Silurian remnant ocean basin that separated the Oulongbuluke block from the Central Qilian block, and records Silurian closure of the Proto-Tethyan Ocean and subduction beneath the Central Qilian block. However, alluvial deposits in the Lajishan area were accumulated in a retro-foreland basin, indicating that continent-continent collision in the eastern South Qilian belt occurred at c. 450–440 Ma. These results demonstrate that the Proto-Tethyan Ocean closed diachronously during early Paleozoic time.     

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     

Distribution Characteristics and Metallogenic Regularity of Graphite Deposits in Qinling Orogen, China

Qinling orogen is one of the five main repository distribution provinces of large scale graphite resources. Graphite occurrence strata are multitudinous including Neo Archaean group to Neopaleozoic. Mineral deposit types are complete consisting of crystal flaky graphite deposit and aphanitic graphite deposit, ore types of the former are main graphite gneiss, graphite schist and graphitized marble, and ore types of the latter are main graphite layer metamorphosised from coal bed and graphitic carbargilite. At present, most graphite deposits with low research degree only implement preliminary investigations of the graphite resource, which has a good prospect. Based on the basic material of dozens of graphite deposits, spots and plays discovered in the Qinling orogen, this paper applied geologic multidisciplinary analysis method to disclose the graphite deposit types of the Qinling orogen, mainly through outdoors geologic survey and specimen examination with analysis of some typical deposits: regional metamorphism crystal graphite deposits and thermo-contact metamorphic aphanitic graphite deposits, with the control of latitudinally trending regional tectonic, graphite deposits of the Qinling orogen distribute sublatitudinally trending three large ore belts: I the Neoarchean–Proterozoic basement crystal graphite enrichment deposits zone along the south margin of North China plate; II the Carboniferous intermountain basin group aphanitic graphite enrichment deposits zone near the Shangdan suture of the West Qinling; III Paleozoic crystal graphite enrichment deposits zone in the Qinling paleomicroplate of the west part of the East Qinling.Conclusions are reached from multiple inquiries: Qinling multi-cycle complex continental collision orogen zone has experienced multiple tectonic framework transformation and polyphase tectonic thermal event from Neo Archean Erathem adjointing multiple graphite tectonic mineralization cycle. In the light of chief control of mineralization and ore types, each of the three large graphite deposits belts of the Qinling orogen has its own genesis: I graphite deposits enriched metallogenetic zone is that regional tectogenetic movement from Neo Archaean caused polyphase metapepsis, which superimposed up and reconstructed Neo Archean Erathem to Proterozoic basement, forming regional metamorphic big flake crystal graphite deposits; II graphite deposits enriched metallogenetic zone is that polyphase regional tectogenetic movement associated with multiple heating caused by multiphase igneous intrusion, which resulted in original coal layers emerging multiple thermo-contact metamorphisms and formed thermo-contact metamorphic aphanitic graphite deposits. III graphite deposits enriched metallogenetic zone is that Palaeozoic cap–rock experienced polyphase metapepsis, forming regional metamorphic finely flake crystal graphite deposits. Comprehensive research of metallogenetic mechanism in graphite deposits and its associated profitable deposits of the Qinling orogen is importance for future exploration.     

The crustal evolution of South America from a zircon Hf‐isotope perspective

Hf‐isotope data of >1100 detrital zircon grains from the Palaeozoic, south‐central Andean Gondwana margin record the complete crustal evolution of South America, which was the predominant source. The oldest grains, with crustal residence ages of 3.8–4.0 Ga, are consistent with complete recycling of existing continental crust around 4 Ga. We confirm three major Archaean, Palaeoproterozoic (Transamazonian) and late Mesoproterozoic to early Neoproterozoic crust‐addition phases as well as six igneous phases during Proterozoic to Palaeozoic time involving mixing of juvenile and crustally reworked material. A late Mesoproterozoic to early Neoproterozoic, Grenville‐age igneous belt can be postulated along the palaeo‐margin of South America. This belt was the basement for later magmatic arcs and accreted allochthonous microcontinents as recorded by similar crustal residence ages. Crustal reworking likely dominated over juvenile addition during the Palaeozoic era, and Proterozoic and Archaean zircon was mainly crustally reworked from the eroding, thickened Ordovician Famatinian arc.     

闽中尤溪－德化－永泰地区金矿地质特征、成矿条件及成矿规律

闽中尤溪－德化－永泰地区中元古界基底变质岩在火山岩中呈“天窗”断续出露，火山－侵入岩浆活动强烈，北东、北西向断裂发育，是我省金矿潜在的有找矿远景的地区之一。本文通过对控制成矿的地质因素的分析研究，认为：含基性－中酸性火山沉积建造的中元古界卓地组、葛坑组基底变质岩是金的重要矿源层，是成矿的前提条件；各种构造，尤其是断裂构造，控制了成矿带的展布和矿床（点）的形成，并决定了矿（化）体的定位空间，是成矿的先决条件；多期次的岩浆活动为成矿提供热源、热液源的部分矿源，是成矿的必要条件。成矿时期始于晋宁期，印支期有明显的矿化活动，燕山期为主要的成矿时期。同时，阐述了由控矿因素所制约的若干成矿规律，进而提出该地区金的区域成矿模式，并对金的潜在资源和找矿远景进行了初步预测和评价。