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41.
R. O. Greiling M. M. Abdeen A. A. Dardir H. El Akhal M. F. El Ramly G. M. El Din Kamal A. F. Osman A. A. Rashwan A. H. N. Rice M. F. Sadek 《International Journal of Earth Sciences》1994,83(3):484-501
Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 615-600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 – 595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent NNW-SSE shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane boundaries can be defined, the Allaqi and South Hafafit Sutures, which are apparently linked by the high angle sinistral strike-slip Wadi Kharit-Wadi Hodein shear zone with a tectonic transport of about 300 km towards the W/NW. In general, the tectonic evolution shows that extensional collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The late Pan-African high angle faults were reactivated during Red Sea tectonics both as Riedel shears and normal faults, where they were oriented favourably with respect to the actual stress regime. 相似文献
42.
43.
碳同位素与早元古代地层对比 总被引:2,自引:0,他引:2
本文首次较详细地研究了早元古代碳酸盐地层的碳同位素组成,样品采自华北早元古代标准地层单元──山西五台地区滹沱群,结果表明碳同位素组成随地质时代有明显的变化,并与地层层位有很好的对应关系。作者认为,碳同位素对于早元古代碳酸盐地层的对比是很有用的。 相似文献
44.
皖南和赣东北蛇绿岩成因及其构造意义:元素和Sm-Nd同位素制约 总被引:32,自引:0,他引:32
本文对扬子块体南缘构造侵位于板溪群(及相应地层)的皖南和赣东北晚元古代蛇绿岩进行了系统的元素和Sm-Nd同位素地球化学研究,结果表明两套蛇绿岩具有类似的元素地球化学特征,即二者的火山岩元素地球化学特征均类似于形成于弧后盆地构造环境的拉斑玄武岩。但是,两套蛇绿岩的Nd同位素组成明显不同。赣东北蛇绿岩具有相当均一的高εNd(T)值(+5.5±1.2),表明来源于一较亏损的上地幔源区,并且没有受到明显的较成熟地壳物质的混染。相反,皖南蛇绿岩的εNd(T)值低,并有较大的变化范围(+4.5──1.0),并和Sm/Nd、Nd、MgO、SiO2呈明显的二元混合相关关系,表明蛇绿岩是由亏损幔源岩浆(初始εNd(T)≈+5.5)在结晶分异过程中与地壳组分(初始εNd(T)≈-1)混合形成的。皖南和赣东北蛇绿岩的Nd同位素和元素地球化学特征以及该地区的同时代花岗岩和火山岩的时空分布特征,可以用华南和扬子元古宙陆-弧-陆碰撞模式来解释。大约在1.0Ga前,扬子和华南块体之间存在一多岛弧洋盆。大陆边缘岛弧和大洋岛弧在扬子块体南缘发育演化。皖南和赣东北蛇绿岩就是在大陆边缘盆地和弧间盆地演化过程中形成的洋壳构造侵位的碎片。该地区I型 相似文献
45.
V. N. Sergeev M. A. Semikhatov M. A. Fedonkin A. F. Veis N. G. Vorob’eva 《Stratigraphy and Geological Correlation》2007,15(2):141-160
Expounded in this work are the results of critical consideration of published and original data on biologic nature and appearance chronology of different groups of Archean and Lower Proterozoic (3.5–1.65 Ga) paleontological remains known from geological record. Conclusions are substantiated by morphological analysis of structurally preserved microfossils, their facies distribution, and by inferable genesis and principal evolutionary trends of Archean stromatolites. A special attention is paid to variations of organic and carbonate carbon isotope composition in sedimentary successions with paleontological remains and to recent information about discovered, most ancient biomarkers of large groups of organic world. As a result of this approach, a detailed model of Precambrian organic world evolution is suggested. 相似文献
46.
北京十三陵地区中—新元古界碳酸盐岩Pb—Pb年龄研究 总被引:8,自引:0,他引:8
对北京十三陵地区中一新元古界碳酸盐岩进行了系统地采样和207pb/204pb-206Pb/204Pb年龄测定.共测定了63个样品(大部分样品采取两种溶解方式),得到中元古界雾迷山组第三段的207Pb/204pb-206Pb/204pb等时线年龄为1373±92Ma(95%置信度误差,下同,MSWD=4.7),杨庄组为1488±55Ma(MSWD=14),高于庄组第三段为1608±74Ma(MSWD=8.1).这些年龄数据与目前已有地质记录相吻合.串岭沟组的碳酸盐相的206Pb/204Pb-207Pb/204Pb未构成等时线,但全岩的206Pb/204pb-207Pb/204Pb比碳酸盐相具有更明显的线性趋势,其原因尚待进一步研究.另外,根据同一个样品用稀盐酸溶解和用氢氟酸加硝酸混合酸溶解的铅同位素比值的接近的现象,显示碳酸盐岩中的硅质没有陆源的特征,是沉积盆地中的产物. 相似文献
47.
华北陆块南部熊耳群火山岩的地球化学特征与成因 总被引:16,自引:12,他引:16
分布于华北陆块南部的熊耳群火山岩由玄武质到流纹质火山岩组成,并以玄武安山岩、安山岩为主,次为英安-流纹岩,SiO2=62%±的岩石较少,显示双峰特点。中基性熔岩的主要造岩矿物是辉石和斜长石,没有角闪石和黑云母,表明熊耳群火山岩形成于相对无水的环境。岩石地球化学上的显著特点是,富K2O、FeO,低Al2O3、MgO、CaO;富含大离子亲石元素(LILE,如K、Rb、Ba)和轻稀土元素(LREE),相对亏损高场强元素(HFSE,Nb、Ta、Ti),表现出岛弧型火山岩的地球化学亲合性。文中详细的岩石地球化学证据表明,熊耳群火山岩具有岛弧型地球化学特征的主要原因是其地幔源区遭受俯冲带组分的改造,而岩浆在上升到地表的过程中混染地壳物质是次要的。基于熊耳群及下伏结晶基底的地质学和地球化学特征,表明熊耳群形成于夭折的三叉裂谷环境,推断俯冲带组分的改造和富集事件发生在华北陆块南部古元古代大陆壳的形成和 拼贴过程中,由于洋壳和地壳物质再循环到上地幔中,使陆下岩石圈地幔源区富集LILE、LREE并亏损HFSE。熊耳期岩浆作用正是源于这样的保留有早期俯冲带组分改造特征的陆下岩石圈富集地幔。 相似文献
48.
Wang Siyuan Xiao Qibing Zeng Jianguo Faculty of Earth Resources China University of Geosciences Wuhan 《中国地质大学学报(英文版)》2001,12(1)
-,The well-known Suichang silvengold field is located inZhejiang Province of SOutheast China. It is the largest silver-gold deposit associated with copper and zinc in the Cathaysianmetallogenic province.There are a series of silver-gold dePOsits in the shear zonesof Proterozoic gneiss terrene, Suichang region. The volcanicapparatus at Mesozoic has complicated rpineralization. Respectively, there are two pieces of understanding on the origin ofore-formigg nuid: (l ) metamorphic fluid (Lia… 相似文献
49.
鄂东北早元古代沉积变质锰矿是我国时代最古老的锰矿之一,是由早元古代锰质碳酸盐岩经区域变质作用而成,后又经风化富集形成工业矿床。由于特殊的地质构造背景和成矿作用的多阶段性,元素和矿物组合复杂,具有独特性。本文研究了各种组分的演变关系和元素集散因素,为锰质碳酸盐岩在高压绿片岩相区域动力变质及其后表生作用中的演变提供了一个实例。 相似文献
50.
The Upper-Middle Proterozoic epimetamorphic rock series in northern Guangxi is a suite of volcanic-terrigenous clastic formations transforming in facies from mobile to stable, which is similar to Eparchean normal argillo-arenaceous sediments both in petrochemistry and in REE geochemistry.The Upper-Middle Proterozoic Suberathem in northern Guangxi is characterized by primordial enrichment of As and Sb, significant depletion in Sr and Hg, bimodal or polymodal distribution of Au and other ore-forming elements, and high variation coefficients and strong mobilities of Sn,Cu,Ni,Au,Ag,As and Sb.The trace element association is characterized by the predominance of siderophile and chalcophile elements occurring in the Middle Proterozoic and that of lithophile ele-ments occurring in the Upper Proterozoic .It is suggested that in northern Guangxi is developed a series of ore-bearing formations with the Sibao Group as the protogenous basement and the Danzhou Group and Lower Sinian series as the derivative cap strata. 相似文献