Metallogenic Systems on the Paleocontinental Margin of the North China Craton

The North China Craton (NCC) is one of the largest blocks composing the continent. Different types of continental margins well developed around the NCC, along with lots of metallogenic systems of different metals and different times. Based on the study on the structural evolution of the NCC, the authors made a new division of tectonic units of the NCC. Through an analysis of the data of 1:25000 geochemical survey on stream sediments, regional geochemical features of main ore-forming elements including Au, Ag, Cu, Pb, Zn, W, Ni, Co and Mo of the NCC are discussed in the paper. Then different metallogenic systems and their forming processes and geodynamics are discussed in detail. At last, temporal and spatial distribution regularities are summarized and ten favorable ore-control factors on the paleocontinental margins are put forward, including (1) abundance of ore sources; (2) rendezvous of ore-forming fluids; (3) high thermo-dynamic anomaly; (4) remarkable Earth crust-mantle interaction; (5) cluster of macroscopic structures and their long activities; (6) diversity of ore-forming environments; (7) long geohistory; (8) multiforms of critical transitional ore-forming mechanisms; (9) multi-staged and superimposed ore-formation; and (10) suitable preservation condition.

Paleoproterozoic juvenile magmatism within the northeastern sector of the Sao Francisco paleocontinent:Insights from the shoshonitic high Ba-Sr Montezuma granitoids

New,integrated petrographic,mineral chemistry,whole rock geochemical,zircon and titanite UPb geochronology,and zircon Hf isotopic data from the Montezuma granitoids,as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex,provides new insights into the late-to post-collisional evolution of the northeastern Sao Francisco paleocontinent.U-Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca.2.2 Ga to 1.8 Ga and comprise distinct groups.Group I have crystallization ages between ca.2.15 Ga and 2.05 Ga and are interpreted as inherited grains.Group II zircon dates vary from 2.04 Ga to1.9 Ga and corresponds to the crystallization of the Montezuma granitoids,which were constrained at ca.2.03 Ga by the titanite U-Pb age.Inverse age zoning is common within the ca.1.8 Ga Group III zircon ages,being related to fluid isotopic re-setting during the Espinhaco rifiting event.ZirconεHf(t)analysis show dominantly positive values for both Group I(-4 to+9)andⅡ(-3 to+8)zircons and TDM2 model ages of 2.7-2.1 Ga and 2.5-1.95 Ga,respectively.Geochemically,the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids,enriched in LILES and LREE,with high to moderate Mg#and depleted in some of the HFSE.Their lithochemical signature,added to the juvenile signature of both inherited and crystallized zircons,allowed its classification as a shoshonitic high Ba-Sr granitoid related to a late-to post-collisional lithosphere delamination followed by asthenospheric upwelling.In this scenario,the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc,being these hybrid magma interpreted as the source of the Montezuma granitoids.The Corrego Tingui Complex host rocks are akin to a syn-to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks.The results presented in this study have revealed the occurrence of juvenile rocks,probably related to an island arc environment,that are exotic in relation to the Paleo-to Neoarchean crust from the Sao Francisco paleocontinent’s core.

Characteristics of the Composite Metallogenic System along the Jilin Paleocontinental Margin and the Evolution of Continental Dynamic Regimes

In view of the existing problems about the metallogenic epoch and origin of the complex along the Jilin paleocontinental margin, we propose the composite metallogenic system of the Jilin old land, based on the theory of metallogeny and from the continental dynamics and comprehensive analysis on the metallogenic characteristics. Its scientific theory is demonstrated by the following aspects: (1) Screening and analysis of the multi-stage super-imposition and sequences. The composite ore-forming system consists mainly of three types: the divergent-type epicontinental metallogenic system on the southern margin, the convergent-type epicontinental metallogenic system on the northern margin and the strike-slip-type epicontinental metallogenic system on the northeastern margin. Their major metallogenic epochs are Archean-Proterozoic, Variscan and Yanshanian respectively. (2) Comprehensive analysis of the genetic relations of the complicated deposits. The above-mentioned three types all indicate a consanguinity among granites, vein rocks and gold deposits, correspondence with geochemical elements, and unicity showing the same activities of mantle derived fluids and multi-source origin of ore-forming substances. (3) As to the mechanisms for mineral concentration, in addition to the sources, we also focus on the co-actions of permeability, vibration, gas-liquid state alternation and abrupt changes of flow velocity during the movement of ore-forming liquids, as well as the extraction and communication of multi-sequence circulating liquids. (4) It is helpful for establishing the relationship between metallogeny and the evolution of continental dynamic regimes, i.e., the ore-controlling correlations between the ore-forming elements-metallogenic series-metallogenic systems-composite metallogenic system and ore-controlling structural features (stratabound, primary and branching types)-regional faulting or secondary continental extension and collision-transformation of different continental dynamic types (divergent, convergent and strike-slip)-the evolution process of the whole old land for the Jilin old land margin. All these are helpful for further researches on the continental metallogenic dynamics.

A perspective on potassic and ultrapotassic rocks:Constraints on the Paleoproterozoic late to post-collisional event in the São Francisco paleocontinent

The late-to post-collisional stage in orogenic systems is characterized by the coeval existence of bimodal potassic to ultrapotassic magmatic activity related to partial melting of an enriched lithospheric mantle together with crustal derived melts.In this paper,we present new whole rock geochemical analyses combined with zircon and titanite U–Pb and zircon Hf isotopic data from potassic to ultrapotassic rocks from six plutons that occur within the Archean Itacambira-Monte Azul block(BIMA),to discuss their petrogenesis and the tectonic implications for the São Francisco paleocontinent.The new U–Pb ages range from ca.2.06 Ga to 1.98 Ga and reveal long-lasting potassic magmatism within the BIMA,which is within the late-to-post-collisional stage of the São Francisco paleocontinent evolution.The ultrapotassic rocks are compatible with a fluid-related metasomatized mantle source enriched by previous subduction events,whereas the potassic rocks are bimodal and have a transitional shoshonitic to A-type affinity.These rocks have a hybrid nature,possible related to the mixing between the mafic potassic/ultrapotassic rocks and high temperature crustal melts of the Archean continental crust.Our results also show an increase of within-plate signature towards the younger potassic magmas.The participation of an important Archean crustal component in the genesis of these rocks is highlighted by the common and occasionally abundant occurrence of Archean inherited zircons.The Hf isotopic record shows that most of the zircon inheritance has dominantly subchondriticεHf(t)values,which fits a crustal reworking derivation from a similar Eo-to Paleoarchean precursor crust.However,the presence of juvenile 2.36 Ga zircon inheritance in an ultrapotassic sample reveal the existence of a hidden reservoir that is somewhat similar to the described for the Mineiro Belt in southern São Francisco paleocontinent.

Paleocontinental Reconstruction:Methodology,Computer Software and an Example of Application

Paleocontinental reconstruction is of the nature of multidisciplinary analysis . This paper discusses the significance of some more important disciplines , including paleomagnetism , paleoclimatology and paleobiogeography. Top attention should be paid to the synthetic analysis and geological explanation of geophysical data . Reassembling of the paleocontinents by geometric similarities is preliminary, geological considerations should receive more attention . Several rules constraining the reconstruction are proposed and Eider poles used to reassemble some separated Precambrian median massifs to their mother continents are given . A computer software for paleocontinental reconstruction , GUDALU , is introduced . The software is flexible in that it gives the user maximum freedom to demonstrate his or her geological opinions by providing means of organizing geographic data and rotational parameters ,many kinds of map projection of different features and dynamic editing of the reconstruction maps . Finally, an example of Mesoproterozoic reconstruction is demonstrated .

Record of Early Tonian mafic magmatism in the central Espinhaco(Brazil):New insights for break-up of the Neoproterozoic landmass ancestor of Sao Francisco-Congo paleocontinent

Petrological characterization,U-Pb geochronology,Lu-Hf analyses and major and trace element data from mafic intrusions in the Central Espinhaco(central portion of the Brazilian shield)are used here to investigate the geological significance of the Early Neoproterozoic magmatism in the context of the Sao Francisco-Congo paleocontinent.These mafic bodies are represented by medium to coarse-grained metagabbros with plagioclase,amphibole and clinopyroxene.Zircon U-Pb isotopic data from two samples yielded weighted mean 206pb/238U ages of 895±3.4 Ma(MSWD=1.7)and 896±2.4 Ma(MSWD=0.64),regarded as the best estimates for the crystallization age of these mafic rocks.Major and trace element data(including REEs)show that the gabbros originated from a subalkaline tholeiitic magma,typical of intraplate magmatism.Such rocks are slightly enriched in LREEs and LILEs and depleted in HFSEs.Our new isotope and geochemical data,along with regional knowledge,indicate that these metagabbros mark the beginning of an important Tonian-age extensional tectonic event of the landmass of which the Sao Francisco-Congo paleocontinent was part(Rodinia supercontinent or Central African block?).We furthermore suggest that these rocks belong to a prominent suite of Tonian-age mafic rocks that mark a diachronic breakup attempt of this landmass which may have occurred from south to north along the Espinhaco mountain range.

A Lower Ordovician Carbonate Contourite Drift on the Margin of the South China Paleocontinent at Jiuxi,Northern Hunan

Carbonate contourite drift at Jiuxi. Taoyuan, northern Hunan, was developed in a deepwater area ofnorthern Hunan on the margin of the Early Ordovician South China palcocontinent. The Lower Ordoviciansequence in the area is more than 350 m thick and contains well-developed contourites that can be groupedinto the following five types: the calcilutitic, the arenitic, the siltitic. the fine ruditic and the bioclastic. Thefirst three often constitute a complete or incomplete contourite succession. The arenitic contourite is nearlyuniformly distributed as interlayers throughout the succession, creating a monotonously rhythmic texture inthe contourite drift. The pattern of spatial distribution of the succession shows that the contourite drift is ahuge ridge-like sedimentary body extending along the trend of paleoslope. Numerous marks of flow direc-tion have pointed to an eastward paleoflow direction along the slope.

An Overview of the Amazonian Craton Evolution: Insights for Paleocontinental Reconstruction

The Amazonian craton major accretionary and collisional processes may be correlated to supercontinent assemblies developed at several times in the Earth history. Based on geologic, structural and paleomagnetic evidence paleocontinent reconstructions have been proposed for Archean to younger times. The oldest continent (Ur) was formed probably by five Achaean cratonic areas (Kaapvaal, Western Dhawar, Bhandara, Singhhum and Pilbara cratons). Geologic evidences suggest the participation of the Archaean rocks of the Carajás region in the Ur landmass. Supercontinental 2.45 Ga Kenorland amalgamation is indicated by paleomagnetic data including Laurentia, Baltica, Australia, and Kalahari and Kaapvaal cratons. There is no evidence indicating that Amazonian craton was part of the Kenorland supercontinent. From 1.83 Ga to 1.25 Ga Columbia and Hudsonland supercontinents including Amazonian craton were proposed based on NE portion of the Amazonian craton (Maroni/Itacaiunas province) connection with West Africa and Kalahari cratons. Rodinia supercontinent reconstructions show Amazonia joined to Laurentia-Baltica as result of 1.1 Ga to 1.0 Ga fusion based on the Sunsas-Aguapei belts and Greenville and Sveconorwegian belts, respectivelly. The large Late Mesoproterozoic landmass included also Siberia, East Antartica, West Nile, Kalahari, Congo/Sao Francisco and Greenland. The 750 - 520 Ma Gondwana assembly includes most of the continental fragments rifted apart during the break-up of Rodinia followed by diachronic collisions (Araguaia, Paraguay and Tucavaca belts). The supercontinent Pangea is comprised of Gondwana and Laurentia formed at about 300 - 180 Ma ago. The Amazonian craton margins probably were not envolved in the collisional processes during Pangea because it was embebed in Neoproterozoic materials. As consequence, Amazonian craton borders have no record of the orogenic processes responsible for the Pangea amalgamation.

活动古地理重建的实践与思考——以青藏特提斯为例

由于石油工业的推动,特提斯构造域一直作为活动古地理重建的重点研究地区,并取得大量研究成果,直接推动了全球古地理研究工作的深入。近年来对位于该构造域东部的青藏高原地区进行了活动古地理重建的研究工作实践,其主要思路是:在古地理重建数据库和古地理重建模拟系统开发的基础上,依据古地磁学运动轨迹研究古大陆位置,结合古构造和古生物对青藏高原喜马拉雅(印度北缘)、拉萨、东和西羌塘地体的古大陆位置进行复位;利用深部地球物理、地表地质断裂证据,借助生物古地理资料,对古大陆和盆地的边界、规模予以限制;利用变形缩短率、构造平衡剖面恢复技术等对原型盆地进行复原;在沉积和生物环境识别划分基础上,编绘基于古大陆重建的岩相和生物古地理图;进一步通过沉积学、沉积地球化学、古生物有关方法和技术,对古海洋海水参数特征、海洋气候参数进行分析研究,探讨古地理和古构造格局控制下的古海洋、古气候条件与盆地、储集岩和烃源岩的形成环境。通过活动古地理重建的研究趋势分析和青藏特提斯的实践认为,古地理重建是现代地质科学的集成,是一项复杂的系统工程。它的研究不仅具有从过去走向未来,从固定走向活动,从古大陆再造到古地理重建,从示意性的小比例尺到大比例尺,以及模拟技术、信息技术、全球定位技术(GPS)等特点;而且具有从单一沉积学要素到古环境、古气候、古海洋等多种要素,可以表现地质历史中各种地质作用及其结果(如古构造和地貌、岩浆和变质作用与各种岩体的剥露)的优势。我们相信,活动古地理重建研究将会成为未来我国沉积地质学重点研究领域之一。

华北古大陆南缘的金属成矿作用

东秦岭大部分金属矿床集中分布于华北古大陆南部边缘 ,以陆缘构造发展阶段的赋矿沉积建造和岩石组合划分成矿系统 :前长城纪陆核活动性边缘沉积成矿系统 ;中、新元古代被动大陆边缘成矿系统 ;早加里东期构造体制转换期成矿系统 ;中生代陆内碰撞造山成矿系统。按矿床形成作用方式可以划分为 :①构造 岩浆 流体成矿作用 ,主要以洛南 栾川钼 (钨 )多金属斑岩组合成矿系统为主 ,成岩方式为壳幔同熔的燕山期中酸性岩浆的浅成侵入与定位 ;②构造 建造 流体成矿作用 ,按不同构造作用层次再细分为中深层次的构造作用 (主要形成韧性剪切带型矿床 )、浅层次构造作用 (主要形成构造蚀变岩型矿床 )。主要的成矿作用发生在燕山期。

中国前寒武纪矿床时空分布

文章详细地分析研究了中国前寒武纪矿床的时空分布。指出中国前寒武纪蕴藏着丰富的矿产资源,形成了众多的铁、铜、铅锌、镍、金、稀土、锰、石墨、菱镁矿、滑石、硼、磷、硫铁矿、金红石、蛭石等大型-超大型矿床。成矿时代从古太古代到震旦纪,但以新太古代、古元古代、中元古代-青白口纪3个地质时期为成矿高峰期。随着中国前寒武纪地史的演化,成矿物质种类和矿床类型具有明显的变化和增多。中国前寒武纪矿床主要分布在陆块区,尤以华北陆块、扬子陆块较多,较少分布在造山带。而陆块边缘和陆块内部裂谷是前寒武纪矿床产出的十分有利的空间。

古大陆再造的回顾与展望

最早的古大陆再造基于大陆轮廓的拼接、古生物区系以及古气候方面资料的对比。20世纪50年代古地磁技术的突破为确定大陆的古地理位置、古陆块之间的相互关系以及大陆裂解和大洋扩张的历史提供了更有说服力的证据。60年代,板块构造成为古大陆再造的理论基础,由此推动了技术的发展、观念的更新和学科之间的交融。在成图方面,完善了球面坐标系下古大陆移动、拼合的计算机软件;建成了一系列全球性的古大陆再造基础资料数据库。按照板块构造理论,超级大陆的形成是古大陆拼合的结果,所以对造山带的分析正在成为古大陆再造中最重要的方法,由此也推动了古大陆再造与地质、地球物理、地球化学等多学科理论、技术之间的交叉和集成。主要根据同位素年代学证据和造山带全球性分布的特征,人们推测地质历史上可能发生过多次超级大陆(Supercontinent)或泛大陆(Pangea)聚散事件,但目前对其古地理和构造格局已基本研究清楚的只有古生代的超级大陆冈瓦那(Gondwana)和晚古生代—早中生代的泛大陆。90年代初提出的Rodinia超级大陆,尚处在完善证据和修订模式的阶段。中国古大陆再造研究的主要问题包括:中国古陆块之间的关系、中国古陆块和造山带与冈瓦那大陆及特提斯演化的关系、与欧亚大陆增生演化的关系以及最近提出的中国?

东秦岭沉积建造演化与成矿

在华北古大陆南缘,以控制不同构造单元的断裂为界,构造格局自北而南划分如下:古大陆边缘的基底与盖层单元(华-熊陆缘带),宽坪群构造单元,二郎坪群构造单元,北秦岭(秦岭群)构造单元和南秦岭(刘岭群)构造单元。据陆缘构造发展阶段的沉积建造和岩石组合控矿因素,划分该区沉积建造演化阶段:①前长城纪陆核活动性边缘沉积建造;②中、新元古代被动大陆边缘沉积建造;③早加里东期构造体制转换期演化阶段;④古生代活动大陆边缘沉积建造;⑤中生代陆内碰撞演化阶段。从时间与空间角度,分别研究了不同构造演化阶段的成矿问题。

Tectonic Setting and Metallogenic System of North China Block Margins

The paleocontinental margins have frequent and intensive tectonic movement and various ore forming processes. According to their tectono dynamic characteristics, the paleocontinental margins can be classified into three types: the divergent, the convergent and the transformational. Each type has its specific geological geochemical processes and metallogenic system. The paper discusses the tectonic evolution and ore forming features of the North China block margins, puts forward conceptions such as complexity, variety and multi stage development of metallogenic evolution in the paleocontinental margins, and expounds five factors controlling the formation of large superlarge ore deposits in the paleocontinental margins: (1) channelway, (2) rendezvous of fluids, (3) abundance of ore source, (4) thermo dynamic anomaly, (5) long duration of structural activities.

吉林古陆成岩背景及边缘金构造-成矿系统

吉林克拉通广泛出露的粗粒黑云长英片麻岩是以英云闪长岩为主的TTG深成侵入体 ,原始岩浆来自幔源物质的部分熔融作用 ,同源岩浆不同演化阶段形成多种岩石类型 (Gnbd、GnblⅠ、GnblⅡ ) ,后经变质构成统一古陆。古陆隆升 ,边缘滑脱和裂解并接受元古宙地层沉积。层间滑动和韧性剪切达上地幔 ,使部分太古宙黑云长英片麻岩被卷进地层 ,幔源物质加入成矿。这使人们打破原层控金矿的认识 ,将整个古陆边缘金矿床统归于构造 -成矿系统 ,依构造动力学特征的不同划分为三类 :离散型陆缘构造 -成矿系统 ,以中型金矿和Fe、Al、P、B为主 ;会聚型陆缘构造 -成矿系统 ,以金矿化和Ni、Cr为主 ;走滑型陆缘构造 -成矿系统 ,以大型金矿和Cu、Pb、Zn为主 ,该系统有助于全面认识构造特征和矿床分布规律 ,为区域成矿预测和勘查提供科学依据。

Late Permian Sequence Stratigraphic Framework and Controlling Factors in Southern Yangtze Platform and Its Margin

Late Permian stratigraphic, sedimentary and paleotectonic studies along a corridor profile across the Yangtze paleocontinent and its southern margin reveal the sedimentary evolution, subdivide the depositional sequences, and reconstruct the stratigraphic framework based on lateral correlation and tracing of the bounding surfaces and depositional systems. This corridor profile transects the Yangtze craton and a molasse sag zone in its southern margin. It is demonstrated that the Late Permian sedimentary evolution along the investigated profile evidently resulted from the interplay of sea level change, differential subsidence and sediment supply within the given tectonic units. In the cratonic interior, high frequency sea level fluctuation exerts an important control on the formation of the third order and fourth order sequences, and is the basis for transfacies correlation. The evolution of sequence succession in the taphrogenic zone is so much affected by the intense tectonic subsidence that it is hardly correlatable to that in the cratonic interior.

Rhyacian-Orosirian tectonic history of the Juiz de Fora Complex:Evidence for an Archean crustal reservoir within an island-arc system

The southern São Francisco Paleocontinent(SFP)comprises Archean nuclei and Paleoproterozoic complexes encompassing magmatic arcs juxtaposed during a Rhyacian to Orosirian orogenic event.The Juiz de Fora Complex(JFC)represents an imbricated thrust system that comprises orthogranulites with a wide compositional range formed in an intra-oceanic setting during the Siderian to the Orosirian and later accreted to the southeastern margin of the SFP.Here we report new petrological,geochemical,whole-rock Nd and Sr data,as well as zircon U–Pb ages from felsic and mafic orthogranulites from the JFC.The new data is combined with a regional compilation that enables an evaluation of the interaction between magmatism and orogenetic episodes in the context of the consolidation of São Francisco Paleocontinent during the Rhyacian–Orosirian.Pre collisional Island Arc tholeiites(IAT),Tonalites-Tron dhjemites-Granodiorites(TTGs)and sanukitoid magmatism occurred from 2200 Ma to 2085 Ma.This was followed by post-collisional magmatism,which is represented by hybrid granitoids coeval with the emplacement of E-MORB basic rocks.Crustal signatures for the Rhyacian to Orosirian evolution are highlighted by the dominance of negativeεNd(t)associated with Meso-to Neoarchean Nd TDMmodel ages as well as inherited zircon grains from the hybrid granitoids.The JFC is extensively highlighted in the literature as a primitive intra-oceanic arc,but here we propose the reworking or recycling of ancient crustal segments within the mature arc stage of the JFC,suggesting a Mesoarchean crustal source involved in the JFC evolution.

球面几何构建欧拉极的方法

欧拉旋转可用来描绘刚性板块在球体上的运动,并用于古大陆的再造.一般构建欧拉极的方法是通过匹配等时线、海底磁异常、转换断层和古地磁数据等来确定的.但是在一些地质环境下,不能直接构建欧拉极.本文直接根据古板块位置图,从几何上构建欧拉极,从而为古大陆重建提供了一个新途径.本文主要介绍了在球面几何上构建欧拉极的方法原理,并编写了相应的程序功能.选取了印度大陆0 Ma和50 Ma的位置图作为实例计算了欧拉极.由本方法计算得到的欧拉极将板块旋转后的位置,与原始古板块位置图几乎完全重合.说明本文构建欧拉极的方法是正确而有效的.

华北古大陆西南边缘构造格架与成矿系统

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