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1.
The evolution of the Indian Shield has been envisaged from the analysis of available tectono-lithostratigraphic, geochronological, geochemical and geophysical data. It appears that the Dharwar schist belts and their equivalents, except the Kolar schist belt, are not typical greenstone belts, but are representative of a transitional era of rapid transformation from simatic to sialic crust. In the Archaean—Proterozoic tract of India, relics of rocks older than 3.0 b.y. are identified in five widely separated regions of distinct tectono-litho-stratigraphic assemblages which probably represent the primordial continental nucleii. It is suggested that the growth of the Indian Shield has taken place through nucleation, accretion and merger into three protocontinents named Dharwar, Aravalli and Singhbhum. The cratonisation of the Indian unit seems to have been rapid and almost completed by the middle Proterozoic, as there is no significant variation in the composition of the clastic sediments and basalts from middle Proterozoic onwards. The continental nucleii appear to merge along the deep-seated lineaments, which are reflected on the tectonic map of India. Further, the Dharwar, Aravalli and Singhbhum protocontinents also seem to merge along a Y=shaped Narmada—Son—Godavari lineament which along with the Mahanadi lineament, between the two continental nucleii of the Singhbhum protocontinent have later developed into rift valleys.  相似文献   

2.
印度克拉通位于喜马拉雅山前断裂以南,与欧亚大陆相连,是一独立的地质构造单元,主要由Aravalli微陆块、Bundelkhand微陆块、Singhbhum微陆块、Bastar微陆块、东Dharwar微陆块、西Dharwar微陆块及南部麻粒岩微陆块7个太古宙微陆块与Satpura活动带、东Ghats活动带2个元古宙活动带组成。在前期项目的基础上,通过梳理印度克拉通各个构造单元的地质特征,笔者认为：印度克拉通基底在2.50 Ga左右趋于稳定;其主要由TTG片麻岩、花岗岩及不同变质程度的变质岩系组成;元古宙发育的Vindhyan盆地、Chhattisgarh盆地、Cuddapah盆地、Godavari盆地、Indravati盆地及Bhima-Kaladgi盆地浅海相碎屑岩-碳酸盐岩沉积是组成印度克拉通前寒武纪的盖层。  相似文献   

3.
Aravalli fold belt has witnessed major tectonism resulting in intense deformation and associated mafic magmatism. Recently acquired high resolution aeromagnetic data over central Aravalli fold belt brought out a conspicuous E-W trending magnetic anomaly extending for more than 35 km in length cutting across the whole succession of Aravalli Supergroup. This anomaly on ground is manifested as undeformed basic dyke intruding into metasediments of Aravalli Supergroup. The E-W trend and undeformed nature of these dykes suggest that they represent post Aravalli mafic magmatism which are emplaced sympathetic to the axial plane of F3 folding.  相似文献   

4.
The mafic dyke swarms are important feature of the Proterozoic and in parts of some stabilised cratonic areas. The early Proterozoic Bundelkhand massif of Central India is extensively intruded by suites of NW-SE and NE-SW trending mafic and ultramafic dykes. These dykes are mostly dolerites with subordinate pyroxenite, or lamproites, moreover, geochemical signatures of the two compositional types are different for the NW-SE and NE-SW trending suites. 40Ar/39Ar age determinations of the dolerite dykes suggest two phases of dyke activity at c.2150Ma and c.2000 Ma in this region. The dolerites are typically tholeiites and quartz normative types represented by Group I and Group II, whilst the ultramafics are komatiite or basaltic komatiite in composition and show an olivine-normative character. Rare earth element (REE) patterns show some enrichment of LREE and exhibit both positive and negative Eu anomalies. Most of the tholeiites display incompatible elements patterns indicative of an enriched mantle source, whilst those of the ultramafics indicate a depleted source. The 2 Ga event is a global event and well documented in various parts of Singhbhum, Aravalli terrane, Tamilnadu, Andhra Pradesh and Kerala regions of Indian Peninsular Shield and many parts of globe. The genesis of these dyke swarms clearly constitutes a major thermal event affecting the Earth's mantle during that period.  相似文献   

5.
The Satpura Mountain Belt (also referred as Central Indian Tectonic Zone in recent literature) forms an important morphotectonic unit in the central part of India. Some of the recent workers have reported an orogenic event at ∼1000–900 Ma (termed “Sausar orogeny”) which led to amalgamation of the North Indian Block and the South Indian Block and formation of the Satpura Mountain Belt. In this model the stratigraphic relations of two important lithostratigraphic units on either side of the Satpura Mountain Belt (the Sausar Group in the south and the Vindhyan Supergroup on the north) are suggested to be revised from previously held ideas. Critical analyses of available published work in the region to assess the status of the Sausar Group vis a vis the Vindhyan Supergroup was carried out. It is found that the ideas proposed by the recent workers stem from an earlier interpretation that the Sausar Group has monocyclic evolution and the earliest fabric in the Sausar Group is marked by a schistosity with EW strike. Re-mapping of the gneissic rocks and adjacent matasedimentary rocks of Khawasa, Deolapar, and Kandri–Mansar areas revealed presence of gneissic rocks and granulites of two generations, and of four phases of superposed deformations in the metasediments and gneisses. The older gneisses and granulites constitute the basement over which the rocks of the Sausar Group were deposited; and the younger gneisses developed by metamorphism and migmatisation of the rocks of the Sausar Group. The latter types are found in the Khawasa–Ramakona areas. Contrary to the belief of the recent workers that no volcanic activity is present in the Sausar Group, volcanic rocks marked by amygdular basic flows and tuffs have been mapped from different parts of the Sausar Group. Migmatisation and metamorphism of these volcanic rocks (of the Sausar Group) have given rise to amphibolites and granulites in Khawasa and Ramakona areas. Therefore, the use of fabric patterns in these areas to suggest that the granulite facies metamorphism in the Ramakona–Katangi granulite domain was pre-Sausar in age is debatable.Available geochronological data of the Satpura Mountain Belt and its eastward continuation into the Chhotanagpur Gneiss terrain indicate that the basement and cover rocks of these areas were subjected to multiple deformation and metamorphic episodes of similar style and nature. The earliest deformation and metamorphism of the rocks of the Sausar Group and its equivalent rocks to the east took place at ∼2100–1900 Ma. The regional EW trend of the belt developed during the second deformation at ∼1800–1700 Ma and again at ∼1600–1500 Ma. This deformation was accompanied by migmatisation and granulite facies metamorphism in the northern domain of the Sausar Belt and in the Chhotanagpur Gneiss region. Late phase low intensity deformations in the region were associated with thermal events at ∼1100–1000 Ma and ∼900–800 Ma.The ∼EW trending fabric, referred as “Satpura orogenic trend” in Indian literature marks a major compressional tectonic event, developed during the second deformation of the Sausar Group. This has its counter part in Western Australia as the Capricorn orogeny (∼1780–1830 Ma). The development of the Satpura Mountain Belt during the Grenvillian orogeny is ruled out from the synthesis of event stratigraphic data of the region and from its comparison with the Western Australian Craton.  相似文献   

6.
黔西北纳雍-水城一带位于扬子板块西南缘,区内断裂和褶皱极为发育。通过详细野外地质调查,并结合沉积地层接触关系,对区内构造行迹及其组合特征、构造变形期次和构造演化进行探讨。研究表明,震旦纪末至中侏罗世纳雍-水城一带经历了多次构造事件,特别是广西构造事件和印支期构造事件,导致明显的差异剥蚀,但均未造成地层褶皱变形,地层间表现为平行不整合接触。晚侏罗世以后的燕山构造期和喜山构造期才是区内发生构造变形的重要时期。纳雍-水城一带发育的NE-SW、NW-SE及近E-W向三组构造以及在NE-SW、NW-SE向两组构造交接转换部位发育的穹窿构造、构造盆地,均为侏罗纪晚期至早白垩世时期强烈构造事件的产物。其中NE-SW向褶皱及近E-W向断层先期形成,NW-SE向褶皱后期形成,并对先期形成的NE-SW向褶皱进行叠加改造。  相似文献   

7.
在对沁水盆地北端发育的中生代褶皱、断层和节理等构造研究的基础上,分析并总结了区内的构造变形及构造应力场特征,。结果表明:研究区西部构造线以NE-SW向为主;东部构造线以近SN或NW-SE向为主;两者之间的构造线方向主要表现为近EW向。研究区内的褶皱、断裂、节理以及水系的发育特征均表明:本区在晚古生代—中生代经历过一期近SN向的挤压作用,其最大主应力方位为161°~174°,倾角在10°以内,这期挤压作用可能是对印支期构造活动的响应;此外,在距今165±5 Ma至136 Ma期间,本区可能还经历过一期NW–SE向的挤压作用,其最大主应力方位为152°,倾角1°。   相似文献   

8.
河西走廊北部的平山湖盆地,被围限于龙首山、北大山和合黎山之间,是一个在早白垩世受南北两侧逆冲断层共同控制形成并发展的盆地。笔者通过研究盆地内下白垩统沉积特征、构造变形、生长地层以及碎屑锆石U-Pb年代学特征,划分了平山湖盆地在早白垩世的构造演化期次,并恢复其形成演化过程。盆地内发育一套由下向上总体变细的下白垩统庙沟群沉积序列,盆地内构造变形以NE-SW向挤压和近E-W向伸展为主,庙沟群上岩组的碎屑锆石最小年龄为(129.3±1.8)Ma,可能代表了地层沉积和同期地堑发育的最早时间。由此得出,在早白垩世早期发育挤压构造盆地,同构造生长地层为挤压盆地的形成与构造演化提供了时代约束;在早白垩世晚期发育伸展断陷盆地,由挤压到伸展的转换时间晚于129.3 Ma。  相似文献   

9.
Semi-detailed gravity investigations were carried out over an area of approximately 2750 sq km with maximum N-S and E-W extents of 55 and 50 km respectively in the Gadag region in the Dharwar craton with a view to obtain a clearer perception of the structural configuration of the region. From qualitative analysis of the gravity data, several tectonic features are inferred: the high density Gadag schist belt is characterized by a gravity high and occurs in two discontinuous segments — the main N-S trending segment, and its thinner NW-SE trending extension, the two separated by a NE-SW trending deep seated fault. While the N-S trend of the Gadag schist belt is bounded on its east by the NW-SE trending Chitradurga thrust fault and on its west by another major NNWSSE trending fault, the NW-SE extension is likewise bounded by two other NW-SE major faults. Quantitative evaluation from forward modeling/inversion of five profiles in the region, assuming a density contrast of 0.29gm/cc of the anomalous schistose body with the gneissic host rocks indicated a synclinal structure plunging to the southeast along its axis for the Gadag schist belt. The maximum width and depth from surface of the schist belt are 22 km and 5.6 km respectively.  相似文献   

10.
中国大陆及邻区中生代—新生代大地构造与环境变迁   总被引：68，自引：12，他引：68  
万天丰  朱鸿 《现代地质》2002,16(2):107-120
在系统研究古地磁、周边板块的运动学特征、板内变形、构造应力场和沉积古地理资料的基础上 ,恢复了中国大陆及邻区中、新生代 6个时期的大地构造演化特征、构造古地理 ,并进而探讨了对环境变迁的影响。 6个时期的划分、构造特征及其古地理环境分别为 :印支期 (2 5 0～ 2 0 8Ma) ,NE -SW向缩短 ,中国大部分大陆完成拼合 ,南方以海为主 ,北方以陆地为主 ;燕山期 (2 0 8～ 135Ma) ,NW -SE向缩短 ,大陆地块逆时针旋转 2 0°～ 30° ,东部形成高地 ,西部为低地 ;四川期 (135～ 5 2Ma) ,NE -SW向缩短 ,以盆岭地形为主 ;华北期 (5 2～ 2 3 3Ma) ,太平洋板块第一次向西俯冲、挤压 ,中国东部形成 3条东西向山脉和 4个汇水盆地 ;喜马拉雅期 (2 3 3～ 0 78Ma) ,印度板块与欧亚大陆碰撞 ,青藏高原隆升 ,其他地块相对沉降 ;新构造期 (0 78Ma以来 ) ,周边各板块保持相对均衡状态 ,逐步构成现代地貌。研究表明 ,大地构造是古地理环境变化的主要控制因素。  相似文献   

11.
The pelitic schists of the area around Kandra, Singhbhum district, Jharkhand belong to the Chaibasa Formation of the Singhbhum Group, which constitute a part of the youngest Precambrian orogenic cycle of the Singhbhum region. Structurally, the area represents the Singhbhum anticlinorium and is overlain by Dalma traps which form the synclinorium towards the north of the area around Kandra. This area mainly consists of medium to high grade rocks belonging to greenschist and amphibolite facies. These rocks are folded in the E-W trending doubly plunging folds (F1) overturned towards the south with low plunges and superposed by cross-folds (F2). The spatial distribution of the index minerals in the pelitic schists of the area shows Barrovian type of metamorphism. Four isograds, viz. biotite, garnet, staurolite and sillimanite have been delineated by the first appearance of the index minerals and also by isograd reactions. The textural relation suggests that sillimanite is formed from staurolite consumption reaction instead of kyanite consumption.  相似文献   

12.
《Tectonophysics》1987,135(4):307-327
The Kutch-Saurashtra, Cambay and Narmada basins are pericontinental rift basins in the western margin of the Indian craton. These basins were formed by rifting along Precambrian tectonic trends. Interplay of three major Precambrian tectonic trends of western India, Dharwar (NNW-SSE), Aravalli-Delhi (NE-SW) and Satpura (ENE-WSW), controlled the tectonic style of the basins. The geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults. The Kutch basin opened up first in the Early Jurassic (rifting was initiated in Late Triassic) along the Delhi trend followed by the Cambay basin in the Early Cretaceous along the Dharwar trend and the Narmada basin in Late Cretaceous time along the Satpura trend. The evolution of the basins took place in four stages. These stages are synchronous with the important events in the evolution of the Indian sub-continent—its breakup from Gondwanaland in the Late Triassic-Early Jurassic, its northward drifting during the Jurassic-Cretaceous and collision with the Asian continent in the Early Tertiary. The most important tectonic events occurred in Late Cretaceous time. The present style of the continental margins of India evolved during Early Tertiary time.The Saurashtra arch, the extension of the Aravalli Range across the western continental shelf, subsided along the eastern margin fault of the Cambay basin during the Early Cretaceous. It formed an extensive depositional platform continuous with the Kutch shelf, for the accumulation of thick deltaic sediments. A part of the Saurashtra arch was uplifted as a horst during the main tectonic phase in the Late Cretaceous.The present high thermal regime of the Cambay-Bombay High region is suggestive of a renewed rifting phase.  相似文献   

13.
The Archaean Peninsular Gneiss of southern India is considered by a number of workers to be the basement upon which the Dharwar supracrustal rocks were deposited. However, the Peninsular Gneiss in its present state is a composite gneiss formed by synkinematic migmatization during successive episodes of folding (DhF1, DhF1a and DhF2) that affected the Dharwar supracrustal rocks. An even earlier phase of migmatization and deformation (DhF*) is evident from relict fabrics in small enclaves of gneissic tonalites and amphibolites within the Peninsular Gneiss. We consider these enclaves to represent the original basement for the Dharwar supracrustal rocks. Tonalitic pebbles in conglomerates of the Dharwar Supergroup confirm the inference that the supracrustal rocks were deposited on a gneissic basement. Whole rock Rb-Sr ages of gneisses showing only the DhF1 structures fall in the range of 3100–3200 Ma. Where the later deformation (DhF2) has been associated with considerable recrystallization, the Rb-Sr ages are between 2500 Ma and 2700 Ma. Significantly, a new Rb-Sr analysis of tonalitic gneiss pebbles in the Kaldurga conglomerate of the Dharwar sequence is consistent with an age of ～2500 Ma and not that of 3300 Ma reported earlier by Venkatasubramanian and Narayanaswamy (1974). Pb-Pb ages based on direct evaporation of detrital zircon grains from the metasedimentary rocks of the Dharwar sequence fall into two groups, 3300–3100 Ma, and 2800–3000 Ma. Stratigraphic, structural, textural and geochronologic data, therefore, indicate that the Peninsular Gneiss of the Dharwar craton evolved over a protracted period of time ranging from > 3300 Ma to 2500 Ma.  相似文献   

14.
Multiple deformation in all the Precambrian metamorphic-migmatitic rocks has been reported from Rajasthan during the last three decades. But, whereas the Aravalli Group and the Banded Gneissic Complex show similarity in the style and sequence of structures in all their details, the rocks of the Delhi Group trace a partly independent trend. Isoclinal folds of the first generation (AF1) in the rocks of the Aravalli Group had gentle westerly plunge prior to later deformations. These folds show reclined, inclined, and upright attitude as a result of coaxial upright folding (AFla). Superposition of upright folds (AF2) of varying tightness, with axial plane striking N to NNE, has resulted in interference patterns of diverse types in the scale of maps, and deformation of earlier planar and linear structures in the scale of hand specimens. The structures of the third generation (AF3) are either open recumbent folds or reclined conjugate folds with axial planes dipping gently towards NE or SW. Structures of the last phase are upright conjugate folds (AF4) with axial planes striking NNE-SSW and E-W. The Banded Gneissic Complex (BGC) underlies the Aravalli Group with a conglomerate horizon at the contact, especially in southern Rajasthan. But, for a major part of central and southern Rajasthan, migmatites representing BGC show a structural style and sequence identical with those in the Aravalli Group. Migmatization, broadly synkinematic with the AF1 folding, suggests extensive remobilization of the basement. Very rare relict fabric athwart to and overprinted by structures of AF, generation provide tangible evidence for a basement. Although the structures of later phases in the rocks of the Delhi Group (DF3 and DF4) match with the late-phase structures in the Aravalli Group (AF3 and AF4), there is a contrast in the structural history of the early stages in the rocks of the two groups. The folds of the first generation in the Delhi Group (DF1) were recumbent to reclined with gentle plunge towards N to NNE or S to SSW. These were followed by coaxial upright folds of varying tightness (DF2). Absence of westerly trending AF1 folds in the Delhi Group, and extreme variation in plunge of the AF2 folds in contrast with the fairly constant plunge of the DF2 folds, provide evidence for an angular unconformity between the Aravalli and the Delhi Groups. Depending on the importance of flattening attendant with and following buckling during AF2 deformation, the lineations of AF1 generation show different patterns. Where the AF1 lineations are distributed in circular cones around AF2 axes because of flexural-slip folding in layered rocks with high viscosity contrast, loci of early lineations indicate that the initial orientation of the AF1 axes were subhorizontal, trending towards N280°. The orientation of the axial planes of the earlier folds has controlled the development of the later folds. In sectors where the AF, axial planes had N-S strike and gentle dips, or E-W strike with gentle to steep dips, nearly E-W horizontal compression during AF2 deformation resulted in well-developed AF2 folds. By contrast, where the AF, axial planes were striking nearly N-S with steep dips, E-W horizontal compression resulted in tightening (flattening) of the already isoclinal AF1 folds, and probably boudinage structures in some instances, without the development of any AF2 folds. A similar situation obtains when DF4 deformation is superposed on earlier structures. Where the dominant S-planes were subhorizontal, N-S compression during DF4 deformation resulted in either chevron folds with E-W striking axial plane or conjugate folds with axial plane striking NE and NW. In zones with S-planes striking E-W and dipping steeply, the N-S compression resulted in flattening of the earlier folds without development of DF4 folds.  相似文献   

15.
Widespread distribution of mafic dykes and scanty occurrence of ultrabasic intrusives of kimberlitic affinity around Proterozoic Cuddapah basin, parts of Eastern Dharwar craton of south India has been the focus of attention since their discovery, to understand the structural fabric in relation to their emplacement in geological time. Satellite Imagery, geomorphological, geophysical and radiometric age data of Narayanpet area, northwest of Cuddappah basin, have clearly displayed the alignments and structures of geological significance, such as deep seated fault / fracture / shear zones, stratigraphic / lithological contacts, basic / ultrabasic intrusives and younger granites etc,. Based on the field observations such as emplacement of mafic dykes, their cross cutting relationship, study of morphological and geophysical signatures, inferred linears drawn from satellite imagery, aeromagnetic and gravity maps are arranged in a chronological order. A system of long, narrow and widely spaced dykes trending NW-SE direction conformable to gneissic foliation, typically associated with migmatites in the southwestern part of the study area are the oldest. Followed by E-W dykes, cut across by the sparsely distributed dykes associated with NW-SE and N-S features and in turn off set by dykes of NE-SW trends are the youngest. Kimberlites of Narayanpet area, belongs to hypabysal facies, which are essentially controlled by E-W to ENE-WSW deep seated fault / fracture zone, their intersection with NW-SE, NE-SW to N-S trends, which may have been reactivated during Proterozoic period as indicated by the intrusion of mafic dykes (～2270 to 1701 Ma) and emplacement of kimberlitic magmatism (～1300 to 1100 Ma) suggesting different intrusive episodes. Kimberlite pipes of Narayanpet field, falls in an ellipsoid form trending WNW-ESE direction in the northern part of the area, associated with radial drainage / topographic high and a gravity low. In addition, physical properties such as density and magnetic susceptibilities of mafic dykes and kimberlites, their geophysical signatures, emplacement of kimberlites at the close vicinity of mafic dykes or at their intersections have also been discussed.  相似文献   

16.
特提斯喜马拉雅带以广泛发育近E-W向和近S-N向断裂以及北喜马拉雅片麻岩穹隆带为典型特征.藏南错那洞穹隆位于特提斯喜马拉带的东部,是近两年新发现并厘定的穹隆构造.该穹隆从外向内主要由3部分组成:上部单元（盖层）、中部单元（滑脱系）和下部单元（核部）,其中滑脱系主要由一套强烈变形的片岩、伟晶岩、花岗岩、大理岩和矽卡岩组成,片岩包括含石榴石云母片岩、含石榴石十字石云母片岩、含蓝晶石石榴石十字石片岩、含矽线石蓝晶石石榴石片岩和云母石英片岩.野外构造变形特征表明滑脱系为一条强烈变形的韧性剪切带,发育大量的鞘褶皱、"Z"形揉褶皱和眼球状构造、石榴石的旋转碎斑、S-C组构和压力影构造.错那洞穹隆记录了4期构造变形:第1期由北向南的逆冲挤压构造、第2期由南向北的韧性伸展构造、第3期近E-W向的韧性伸展构造变形和第4期成穹后的脆性垮塌构造.通过对滑脱系中含石榴石云母片岩的白云母进行Ar-Ar同位素测年,获得坪年龄为14.0±0.2 Ma,等时线年龄为13.7±0.5 Ma,二者基本一致,同时微观构造特征显示石英呈亚颗粒旋转重结晶（SGR）,其韧性变形的温度为450~550℃,该变形温度高于白云母的封闭温度.因此,白云母Ar-Ar坪年龄（14.0±0.2 Ma）代表错那洞穹隆近E-W向伸展变形的时间,也即近S-N向桑日-错那裂谷的活动时间.结合构造变形和年代学特征,认为错那洞穹隆是STDS向北伸展拆离的主导机制叠加后期近E-W向韧性伸展活动的结果.   相似文献   

17.
The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated forming the Greater Indian Landmass. In this study, we use the metamorphic and geochronological evolution of the Gangpur Schist Belt (GSB) and neighbouring crustal units to constrain crustal accretion processes associated with the amalgamation of the Northern and Southern Indian Blocks. The GSB sandwiched between the Bonai Granite pluton of the Singhbhum craton and granite gneisses of the Chhotanagpur Gneiss Complex (CGC) links the CITZ and the North Singhbhum Mobile Belt. New zircon age data constrain the emplacement of the Bonai Granite at 3,370 ± 10 Ma, while the magmatic protoliths of the Chhotanagpur gneisses were emplaced at c. 1.65 Ga. The sediments in the southern part of the Gangpur basin were derived from the Singhbhum craton, whereas those in the northern part were derived dominantly from the CGC. Sedimentation is estimated to have taken place between c. 1.65 and c. 1.45 Ga. The Upper Bonai/Darjing Group rocks of the basin underwent major metamorphic episodes at c. 1.56 and c. 1.45 Ga, while the Gangpur Group of rocks were metamorphosed at c. 1.45 and c. 0.97 Ga. Based on thermobarometric studies and zircon–monazite geochronology, we infer that the geological history of the GSB is similar to that of the North Singhbhum Mobile Belt with the Upper Bonai/Darjing and the Gangpur Groups being the westward extensions of the southern and northern domains of the North Singhbhum Mobile Belt respectively. We propose a three‐stage model of crustal accretion across the Singhbhum craton—GSB/North Singhbhum Mobile Belt—CGC contact. The magmatic protoliths of the Chhotanagpur Gneisses were emplaced at c. 1.65 Ga in an arc setting. The earliest accretion event at c. 1.56 Ga involved northward subduction and amalgamation of the Upper Bonai Group with the Singhbhum craton followed by accretion of the Gangpur Group with the Singhbhum craton–Upper Bonai Group composite at c. 1.45 Ga. Finally, continent–continent collision at c. 0.96 Ga led to the accretion of the CGC with the Singhbhum craton–Upper Bonai Group–Gangpur Group crustal units, synchronous with emplacement of pegmatitic granites. The geological events recorded in the GSB and other units of the CITZ only partially overlap with those in the Trans North China Orogen and the Capricorn Orogen of Western Australia, indicating that these suture zones are not correlatable.  相似文献   

18.
西昆仑山前冲断带断裂特征及构造单元划分   总被引：3，自引：1，他引：2  
受新生代帕米尔构造结大幅度向北推移、旋转的影响,形成了弧形的西昆仑山前冲断带.本文主要通过野外地质调查、地震反射剖面的精细解释,对西昆仑山前冲断带最基本的组成部分-断裂进行系统研究.西昆仑山前冲断带内以发育与其弧形形态一致的逆冲断裂为主,但弧形冲断带中段的断裂具有挤压逆冲的同时兼有右行走滑性质.冲断带内还发育了NE 向和近EW向的走滑断裂,它们的发育时间和成因不尽相同,它们控制了冲断带内的变形,调节和改造了早期形成的构造.在对断裂系统研究的基础上,结合冲断带各个部位的结构特征和变形时间,将冲断带划分为9个次级构造单元.西昆仑山前冲断带开始发育于中新世中晚期,此后经历了上新世早期、上新世中晚期、早更新世早中期以及早更新世晚期四个演化阶段.  相似文献   

19.
Reappraisal of field relationships between the different lithological ensembles supported by available geochronological data, and taking due note of the tectono-metamorphic, magmatic and sedimentation history helped to build up a coherent crustal evolutionary history of the Singhbhum Archaean craton, eastern India. The evolution of the earliest sialic crust, as the isotope ages suggest, was around 3700 Ma or even earlier. Deposition of the oldest, dominantly metasedimentary supracrustals, the Older Metamorphic Group (OMG), was initiated at around 3380 Ma, i.e. after a gap of about 320 million years. The closing of OMG basins synchronously with the emplacement of a granitoid phase was at ca.3285 Ma. No other fabric-forming ductile deformation and metamorphism associated with the development of foliation and mineral lineation is known in the rocks of the Singhbhum Archaean craton subsequent to this event. Formation of the succeeding geological ensembles including the deposition of BIF-bearing Iron Ore Group (IOG) and the emplacement of the post-IOG granitoids at ca.3100 Ma can be described as ??lsnon-orogenic?? event taking place during the phase of tectonic quiescence. Supracrustals like the Dhanjori and Simlipal mafic volcanics with intercalated beds of arenite evolved later during the phase of Plume outburst at around 2800 Ma. The end-Archaean intrusion of Newer Dolerite dykes in conjugate sets and the deposition of Kolhan Group in an N-S oriented basin during an E-W stress system mark the culmination of the Archaean crust-building activity in the Singhbhum Archaean craton.  相似文献   

20.
In the Beaujolais-Lyonnais area of the northeastern Massif Central accretion of continental and possibly oceanic crustal fragments occurred between Cambrian (?) and early Carboniferous time. Three distinct lithotectonic units (terranes?) have been recognized. The southern (Lyonnais-) Unit consists of medium- to high-grade metamorphics and includes eclogites; it formed in the early Paleozoic. The Brévenne-Unit to the north contains low- to medium-grade metamorphic mafic and felsic volcanics and subordinate sedimentary rocks which possibly originated during the early Paleozoic until Devonian time, in a sialic back-arc environment or along an active continental margin. The Beaujolais-Unit is represented by volcanics on the south and predominantly shallow marine clastics and carbonates on the north. It developed in a late Devonian or early Carboniferous ensialic marginal basin. The peak of metamorphism in the Lyonnais-unit (HP/HT) was reached in Silurian time. Subsequent NW-SE to E-W oriented convergence produced mylonitic foliation, structural imbrication of the Lyonnais basement rocks with the Brévenne-Unit and SE-vergent folds accompanied by low- to medium-grade metamorphism. Late Visean to Namurian N-S to NW-SE directed N-vergent thrusting produced tectonic imbrication of the metamorphic northern Brévenne-Unit with the nonmetamorphic Beaujolais-Unit. In the southern Brévenne-Unit and in the Lyonnais-Unit updoming along right-lateral high-angle normal faults was followed by emplacement of voluminous granitic plutons of crustal origin. Late Carboniferous to early Permian crustal thinning in the Beaujolais-Lyonnais area was associated with N-S trending left-lateral strike-slip faults and E-W to NE-SW trending right-lateral strike-slip faults. Basins that developed along these faults contain continental red beds.  相似文献   

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