华北地台南缘金矿床的成因和成矿模式   总被引：3，自引：0，他引：3  

邵世才 《华北地质矿产杂志》1997,12(4):358-364

本文阐述了华北地台南缘金矿床构造一半和地质地球化学条件，认为该区金矿具有形成多期性，成因多重性和物质多源性的特征，它们构成了一个完整的成矿系列，据此建立了成矿模式。  相似文献   

华北地台北部晚石炭世古植被演替及其古气候解释   总被引：2，自引：0，他引：2  

张泓  何宗莲  王安民 《西北地质科学》1997,(2)

拴马桩煤系植物化石研究结果表明，华北地台北部晚石炭世的古植被在维斯发期和斯蒂芬期之交发生了重要变化：斯蒂芬期以前，种子蕨类占主导地位，随后是以Ｐｅｃｏｐｔｅｒｉｓ为代表的树蕨真蕨类植物和有节类成了植被的主要类群。这种型式的古植被改变不仅与华北晚古生代植物群成分在本溪组与太原组界线上出现的真蕨类、有节类＂新生峰点＂相一致，而且与欧美基本植被在维斯发Ｄ期－斯蒂芬期的改组大体吻合。据叶相及煤中的碳同位素分析，晚石炭世晚期存在一个古气候升温事件。上述古植被的改组可能是这个升温事件的正反馈。  相似文献   

华北地台太古宙地壳生长机制与构造体制转换     

吴福元  葛文春  孙德有  林强 《吉林大学学报(地球科学版)》1995,(3)

Ｓｍ－Ｎｄ同位素研究结果显示，华北地台太古宙构造体制与地壳生长可分为二个发展阶段：２８００Ｍａ以前，地壳以幔源物质垂向增生为主；进入２８００Ｍａ以后，地壳物质开始进入地幔，并以水平运动为主要构造体制，反映板块构造机制在太古宙晚期地质演化中具有十分重要的作用。  相似文献   

华北地台铀成矿条件及成矿远景分析   总被引：2，自引：0，他引：2  

胡绍康 《铀矿地质》1988,(3)

就全球而言,前寒武纪是铀元素的一个非常重要的成矿期。华北地台是我国出露面积最广、形成时代最老、具有找矿前景的唯一占地台。在综合大量普查、区调资料的基础上,本文详细地论述了华北地台的基本地质特征,并与国外主要产铀占地台进行了对比,强调了地台基底,即原始古陆壳演化成熟程度及成熟期早、晚与铀矿化的关系。据此、并参考其它条件将华北地台划分为6类地区,指出了这些地区的不同找矿前景以及应着重寻找和探索的铀矿类型。  相似文献   

松潘甘孜地块与秦岭褶皱带、扬子地台的关系及其发展史   总被引：30，自引：9，他引：30  

杨逢清  殷鸿福  杨恒书  赖旭龙 《地质学报》1994,68(3):208-218

松潘甘孜地块存在与否是个有争议的问题。本文论证了地块的古老基底为前震旦纪花岗质岩系。地块与南秦岭褶皱带可能都是古扬子地台的一部分。由于早古生代末的加里东运动造成的裂陷,使地块从扬子地台的西北部解体出来,但这次解体并不彻底,裂陷槽后来逐渐被弥合填平。茅口期开始的峨眉地裂运动使地块再次从扬子地台解体出来,裂陷线大致沿木里、平武一线。这次裂陷是扬子地台周缘及内部同期张裂的一部分,反映扬子地台迅速北移造成的后缘、侧缘及内部的拉张作用,使地块连同南秦岭地区一起与邻区割裂开来。拉丁期时,松潘甘孜地块与南秦岭区整体强烈下陷,直至晚三叠世末晚印支运动将其海槽关闭,全部褶皱隆起成山。  相似文献   

The Late Jurassic Tithonian, a greenhouse phase in the Middle Jurassic–Early Cretaceous 'cool' mode: evidence from the cyclic Adriatic Platform, Croatia     

ANTUN HUSINEC  J. FRED READ† 《Sedimentology》2007,54(2):317-337

Well‐exposed Mesozoic sections of the Bahama‐like Adriatic Platform along the Dalmatian coast (southern Croatia) reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding Late Jurassic (Tithonian) shallow platform‐interior (over 750 m thick, ca 5–6 Myr duration). Facies within parasequences include dasyclad‐oncoid mudstone‐wackestone‐floatstone and skeletal‐peloid wackestone‐packstone (shallow lagoon), intraclast‐peloid packstone and grainstone (shoal), radial‐ooid grainstone (hypersaline shallow subtidal/intertidal shoals and ponds), lime mudstone (restricted lagoon), fenestral carbonates and microbial laminites (tidal flat). Parasequences in the overall transgressive Lower Tithonian sections are 1–4·5 m thick, and dominated by subtidal facies, some of which are capped by very shallow‐water grainstone‐packstone or restricted lime mudstone; laminated tidal caps become common only towards the interior of the platform. Parasequences in the regressive Upper Tithonian are dominated by peritidal facies with distinctive basal oolite units and well‐developed laminate caps. Maximum water depths of facies within parasequences (estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences) were generally <4 m, and facies show strongly overlapping depth ranges suggesting facies mosaics. Parasequences were formed by precessional (20 kyr) orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles. Parasequences are arranged in third‐order sequences that lack significant bounding disconformities, and are evident on accommodation (Fischer) plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position. Modelling suggests that precessional sea‐level changes were small (several metres) as were eccentricity sea‐level changes (or precessional sea‐level changes modulated by eccentricity), supporting a global, hot greenhouse climate for the Late Jurassic (Tithonian) within the overall ‘cool’ mode of the Middle Jurassic to Early Cretaceous.  相似文献   

Seismic crustal structure between the Transylvanian Basin and the Black Sea, Romania     

F. Hauser  V. Raileanu  W. Fielitz  C. Dinu  M. Landes  A. Bala  C. Prodehl 《Tectonophysics》2007,430(1-4):1-25

In order to study the lithospheric structure in Romania a 450 km long WNW–ESE trending seismic refraction project was carried out in August/September 2001. It runs from the Transylvanian Basin across the East Carpathian Orogen and the Vrancea seismic region to the foreland areas with the very deep Neogene Focsani Basin and the North Dobrogea Orogen on the Black Sea. A total of ten shots with charge sizes 300–1500 kg were recorded by over 700 geophones. The data quality of the experiment was variable, depending primarily on charge size but also on local geological conditions. The data interpretation indicates a multi-layered structure with variable thicknesses and velocities. The sedimentary stack comprises up to 7 layers with seismic velocities of 2.0–5.9 km/s. It reaches a maximum thickness of about 22 km within the Focsani Basin area. The sedimentary succession is composed of (1) the Carpathian nappe pile, (2) the post-collisional Neogene Transylvanian Basin, which covers the local Late Cretaceous to Paleogene Tarnava Basin, (3) the Neogene Focsani Basin in the foredeep area, which covers autochthonous Mesozoic and Palaeozoic sedimentary rocks as well as a probably Permo-Triassic graben structure of the Moesian Platform, and (4) the Palaeozoic and Mesozoic rocks of the North Dobrogea Orogen. The underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions, which correlate well with the Tisza-Dacia, Moesian and North Dobrogea crustal blocks. The lateral velocity structure of these blocks along the seismic line remains constant with about 6.0 km/s along the basement top and 7.0 km/s above the Moho. The Tisza-Dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km, which are presumably due to basement thrusts imbricated with sedimentary successions related to the Carpathian Orogen. The crystalline crust of Moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks. The North Dobrogea crust reaches a thickness of about 44 km and is probably composed of thick Eastern European crust overthrusted by a thin 1–2 km thick wedge of the North Dobrogea Orogen.  相似文献   

The Genesis,Classification, Problems and Prospects of Microbial Carbonates:Implications from the Cambrian Carbonate of North China Platform     

Long Wang  Latif Khalid  Riaz Muhammad  Xiaoye Liu 《地球科学进展》2018,33(10):1005-1023

Currently, sedimentologists focus on the challenging issue of microbial carbonates, which are regarded as "one of the sedimentary rocks most difficult to study", having complicated sedimentary fabric. Their characteristic features closely related to microbial activity, distributed over a long period of geological time, and formed in diversified sedimentary environments. The main research concentrations are the calcified microbial mats and biofilms in geological records as the products of lithification and diagenesis. Starting from the origin, this paper systematically reviewed and explained the processes dwelling within two types of microbial communities, the thinner biofilm and the thicker microbial mat, which enabled them to convert into microbial carbonates through biomineralization and lithification. This study proposed that the existence of multiple microbial mats was another important cause for the diversification and complexity of microbial carbonates in addition to its complex depositional process. Moreover, the sedimentary characteristics and classification of different types of microbial carbonates were reviewed, exemplifying the Cambrian microbial carbonates in the North China Platform. These microbial carbonates are suggested to be placed under "bindstone" after Embry and Kloven, which can be further divided into 5 types, stromatolites, thrombolites, oncolites, laminites and leiolites. Dendrolite is not categorized as a separate class, instead attributed to thrombolites. The microbial carbonates may possess good source rock potential because of the enriched organic content, and may also serve as hydrocarbon reservoirs because of certain microbial textures and fabrics leading to significant porosity and permeability. Because of their biomineralization processes related to microbial activity, the microbial carbonates are not only an important window to understand the evolution of the earth's surface environment, but also capable of forming large-scale reservoirs, and their scientific and economic values are self-evident.  相似文献   

Prospects of search for diamondiferous kimberlites in the northeastern Siberian Platform     

N.V. Sobolev  A.V. Sobolev  A.A. Tomilenko  D.V. Kuz’min  S.A. Grakhanov  V.G. Batanova  A.M. Logvinova  T.A. Bul’bak  S.I. Kostrovitskii  D.A. Yakovlev  E.N. Fedorova  G.F. Anastasenko  E.I. Nikolenko  A.V. Tolstov  V.N. Reutskii 《Russian Geology and Geophysics》2018,59(10):1365-1379

The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns in about 1000 olivine macrocryst samples with a forsterite content Fo = (100Mg/(Mg + Fe)) of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown predominant hydrocarbons of a wide range of compositions and subordinate contents of N₂, H₂O, and CO₂. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and the basal horizon of the Carnian Stage.  相似文献   

寒武纪丝状蓝细菌生物膜主导和诱发的巨型鲕粒:以河南新安县石井剖面苗岭统徐庄组为例^*          下载免费PDF全文

梅冥相 《古地理学报》2021,23(1):105-124

多样化的产出环境和30×10⁸年的分布历史表明,鲕粒成因一直是一个谜一样的沉积学难题,争论的关键问题是其究竟是有机(微生物)成因还是无机成因。来自于华北地台寒武系苗岭统徐庄组鲕粒滩相灰岩顶部的方解石巨鲕表现出同心状、放射—同心状和泥晶质的沉积组构,在鲕粒核心和鲕粒皮层中保存着精美的葛万菌(Girvanella)化石所主导的光合作用生物膜的钙化作用残余物,这为研究鲕粒形成与光合作用生物膜之间复杂的成因联系提供了一个较为直接的微生物证据,因为葛万菌可相对较为肯定地类比于近代的钙化织线菌(Plectonema)丝状蓝细菌化石。所以说,在伴随着后生动物辐射的寒武纪蓝细菌繁盛的方解石海中,尽管形成放射状鲕粒皮层的放射纤维状方解石的沉淀作用机理还没有得到完全彻底的了解,但是这些巨鲕确实表现出光合作用生物膜诱发、滋养并促进了鲕粒形成的直接证据,进一步支持了“鲕粒沉积可以作为一种不同的微生物岩体系新类型”的重要科学理念。  相似文献