Structural pattern in the Precambrian rocks of Sonua-Lotapahar region,North Singhbhum,eastern India     

Dhruba Mukhopadhyay  Tapas Bhattacharya  Tapan Chakraborty  Arun Kanti Dey 《Journal of Earth System Science》1990,99(2):249-268

In the western part of the North Singhbhum fold belt near Lotapahar and Sonua the remobilized basement block of Chakradharpur Gneiss is overlain by a metasedimentary assemblage consisting of quartz arenite, conglomerate, slate-phyllite, greywacke with volcanogenic material, volcaniclastic rocks and chert. The rock assemblage suggests an association of volcanism, turbidite deposition and debris flow in the basin. The grade of metamorphism is very low, the common metamorphic minerals being muscovite, chlorite, biotite and stilpnomelane. Three phases of deformation have affected the rocks. The principal D1 structure is a penetrative planar fabric, parallel to or at low angle to bedding. No D1 major fold is observed and the regional importance of this deformation is uncertain. The D2 deformation has given rise to a number of northerly plunging major folds on E-W axial planes. These have nearly reclined geometry and theL ₂lineation is mostly downdip on theS ₂surface, though some variation in pitch is observed. The morphology of D2 planar fabric varies from slaty cleavage/schistosity to crenulation cleavage and solution cleavage. D3 deformation is weak and has given rise to puckers and broad warps on schistosity and bedding. The D2 major folds south of Lotapahar are second order folds in the core of the Ongarbira syncline whose easterly closure is exposed east of the mapped area. Photogeological study suggests that the easterly and westerly closing folds together form a large synclinal sheath fold. There is a continuity of structures from north to south and no mylonite belt is present, though there is attenuation and disruption along the fold limbs. Therefore, the Singhbhum shear zone cannot be extended westwards in the present area. There is no evidence that in this area a discontinuity surface separates two orogenic belts of Archaean and Proterozoic age.  相似文献   

湖北浠水蓝晶石铝直闪石片岩中的冠状体结构的研究   总被引：11，自引：3，他引：11  

游振东  吕学淼 《地球科学》1990,15(4):345-356

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Sedimentational,structural and migmatitic history of the Archaean Dharwar tectonic province,southern India     

K. Naha  R. Srinivasan  S. Jayaram 《Journal of Earth System Science》1991,100(4):413-433

The earliest decipherable record of the Dharwar tectonic province is left in the 3.3 Ga old gneissic pebbles in some conglomerates of the Dharwar Group, in addition to the 3.3–3.4 Ga old gneisses in some areas. A sialic crust as the basement for Dharwar sedimentation is also indicated by the presence of quartz schists and quartzites throughout the Dharwar succession. Clean quartzites and orthoquartzite-carbonate association in the lower part of the Dharwar sequence point to relatively stable platform and shelf conditions. This is succeeded by sedimentation in a rapidly subsiding trough as indicated by the turbidite-volcanic rock association. Although conglomerates in some places point to an erosional surface at the contact between the gneisses and the Dharwar supracrustal rocks, extensive remobilization of the basement during the deformation of the cover rocks has largely blurred this interface. This has also resulted in accordant style and sequence of structures in the basement and cover rocks in a major part of the Dharwar tectonic province. Isoclinal folds with attendant axial planar schistosity, coaxial open folds, followed in turn by non-coaxial upright folds on axial planes striking nearly N-S, are decipherable both in the “basement” gneisses and the schistose cover rocks. The imprint of this sequence of superposed deformation is registered in some of the charnockitic terranes also, particularly in the Biligirirangan Hills, Shivasamudram and Arakalgud areas. The Closepet Granite, with alignment of feldspar megacrysts parallel to the axial planes of the latest folds in the adjacent schistose rocks, together with discrete veins of Closepet Granite affinity emplaced parallel to the axial planes of late folds in the Peninsular Gneiss enclaves, suggest that this granite is late-tectonic with reference to the last deformation in the Dharwar tectonic province. Enclaves of tonalite and migmatized amphibolite a few metres across, with a fabric athwart to and overprinted by the earliest structures traceable in the supracrustal rocks as well as in a major part of the Peninsular Gneiss, point to at least one deformation, an episode of migmatization and one metamorphic event preceding the first folding in the Dharwar sequence. This record of pre-Dharwar deformation and metamorphism is corroborated also by the pebbles of gneisses and schists in the conglomerates of the Dharwar Group. Volcanic rocks within the Dharwar succession as well as some of the components of the Peninsular Gneiss give ages of about 3.0 Ga. A still younger age of about 2.6 Ga is recorded in some volcanic rocks of the Dharwar sequence, a part of the Peninsular Gneiss, Closepet Granite and some charnockites. These, together with the 3.3 Ga old gneisses and 3.4 Ga old ages of zircons in some charnockites, furnish evidence for three major thermal events during the 700 million year history of the Archaean Dharwar tectonic province.  相似文献   

山东灵山沟金矿床的矿化阶段划分及成矿意义     

张均 《矿产与地质》1991,5(1):33-41

灵山沟金矿床位于招掖成矿带中部,是一个兼具“玲珑式”“焦家式”双重矿化特征的典型矿床.该矿床的成矿演化过程大致可划分为4个矿化阶段:I.微量金一黄铁矿一石英阶段;Ⅱ.金一石英一黄铁矿阶段;Ⅲ.金一石英一多金属硫化物阶段;Ⅳ.少量金一黄铁矿一石英一碳酸盐阶段.不同阶段具有不同的矿化特征和成矿意义.Ⅱ、Ⅲ矿化阶段为主成矿阶段.上述认识在整个胶东金矿化集中区具普遍性意义.  相似文献   

中国东部地洼阶段应力场与锡成矿     

王开怡 《大地构造与成矿学》1991,15(2):138-143

中国东部地壳地洼阶段的热塑性变形应力场有利于锡成矿。构造应力场对锡成矿的控制作用,表现为对成矿域的矿液运移势和能量场的控制。推导获得矿液运移势的计算公式:Vi=-(a·K_0/u)·[exp(σ_1-σ_2)]·(σ_1+σ_2),表明地壳构造应力场对成矿域矿液的运移和成矿部位的选择提供了有利的动力学条件。  相似文献   

云南金顶铅锌矿床碎屑岩地层中铅锌活化迁移的实验研究   总被引：2，自引：0，他引：2  

姚志健  唐宏 《地球科学》1991,16(2):181-188

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570矿床地质特征及成矿条件   总被引：2，自引：0，他引：2  

陈迪云  章邦桐 《华东地质学院学报》1994,17(3):212-218

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康滇地轴石棉—会理段金矿化同位素地质研究   总被引：9，自引：0，他引：9  

王小春 《矿物岩石》1994,14(1):74-82

本文在研究康滇地轴石棉－会理段金矿化地质特征的基础上，分析了各类金矿化的同位素年龄、氢、氧、碳、硫和铅同位素的变化特征。指出了它们的流体类型、碳、硫、铅及金等成矿物质的来源，从而建立了本区金矿化的成矿序列。  相似文献   

造盆作用及成矿盆地的历史──动力综合分类   总被引：5，自引：4，他引：5  

陈国达 《大地构造与成矿学》1994,18(1):1-23

关于盆地的分类，不少学者提出过有意义的方案。它们主要是从某个单一角度进行：或者是从历史角度分析，或者是从动力角度分析，为了更较全面地认识它们，以求得更有效地指导找矿勘探，作者把两种分析方法结合起来，提出一个综合分类方案。按历史－动力综合分类，造盆作用及盆地可划分为三大类：大洋壳型、雏陆壳（过渡壳）型及大陆壳型。大洋壳型中可细分为活动区型（主要为拉张式）和稳定区型。雏陆壳型包括前地槽型（其中可分出多种活动区型及稳定区型，有待详究；活动区型中拉张式多见）及地槽前期型（主为拉张式）．大陆壳型中计有地槽后期（褶皱带）型（挤压式或拉张式）、地台型（主为陷落式，偶为张陷式－－断拉谷Ｑｕｌａｃｏｇｅｎ）和地洼型（挤压式、拉张式或压张式）。  相似文献   

热液成矿作用的一般动力学方程   总被引：3，自引：1，他引：3       下载免费PDF全文

鲍征宇  唐促华 《地球科学》1994,19(3):313-319

分析了热液成矿作用的基本特点和研究现状，推导出热液成矿作用动力学体系的一般方程，并着重讨论了方程中表征热液与围岩之间化学反应的速率项，除目前一般采用动力学实验实测反应速率常数外，作者根据局域平衡原理，认为成矿作用可视为体系内各点随着温度和压力的变化不断重建平衡的过程，可用温度和压力变化时成矿反应的平衡常数的变化速度表征成矿反应的动力学行为，成矿化学反应的速率还可用主要成矿物质的溶解的变化率来表征。  相似文献