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1.
The Proterozoic basins of India adjoining the Eastern Ghats Granulite Belt (EGGB) in eastern and southern India contain both Mesproterozoic and Neoproterozoic successions. The intracratonic set-up and contractional deformation fo the Neoproterozoc successions in the Paland sub-basin in the northeastern part of Cuddapah basin and similar crustal shortening in contemporaneous successions lying west of the EGGB and Nellore Schist Belt (NSB) are considered in relation to the proposed geodynamic evolution of the the Rodinia and Gondwana supercontinents. Tectonic shortening in the Palnad sub-basin (northeast Cuddapah), partitioned into top-to-westnorthwest thrust shear, flexural folds and cleavage development under overall E-W contraction, suggests foreland style continental shortening within an intracratonic set-up. A thrust sheet containing the Nallamalai rocks and overlying the Kurnool rocks in the northeastern part of Palnad sub-basin exhibits early tight to isoclinal folds and slaty (phylllitic) cleavage, which can be correlated with early Mesoproterozoic deformation structures in the nothern Nallamalai Fold Belt (NFB). NNE-SSW trending folds and cleavage affect the Kurnool Group and overprint earlier structures in the thrust sheet. Thrusting of the Nallamalai rocks and the later structures may have been related to convergence of the Eastern Ghats terrane and the East-Dharwar-Bastar craton during Early Neoproterozoic (Greenvillian) and/or later rejuvenation related to Pan-African amalgamation of East and West Gondwana. 相似文献
2.
塔里木盆地南部玛东早古生代褶皱-冲断带 总被引：2，自引：0，他引：2
玛东褶皱-冲断带位于塔里木盆地南部,走向NE-SW,由NW向SE方向冲断。褶皱冲断带发育于寒武-奥陶系,以中寒武统膏-盐层为主滑脱面。中志留统及其以上地层不整合于褶皱冲断带之上。它是世界上保存最好的早古生代褶皱冲断带之一。根据卷入变形最新地层、不整合于褶皱-冲断带之上的最老地层和上奥陶统上部的生长地层,玛东褶皱-冲断带的变形时间为晚奥陶世-早志留世。玛东褶皱-冲断带与其东南侧的塘南褶皱-冲断带同为塔里木盆地南缘早古生代前陆褶皱-冲断带的组成部分,塘南褶皱-冲断带是该早古生代前陆褶皱-冲断带主体的残余,其向NW的主冲断方向代表该前陆褶皱-冲断带的主冲断方向;玛东褶皱-冲断带是该早古生代前陆褶皱-冲断带的前锋,其向SE的冲断具有反冲性质。它们是昆仑早古生代造山作用的重要记录,也是昆仑早古生代碰撞造山带的组成部分,现今保存最好的部分。 相似文献
3.
《International Geology Review》2012,54(8):661-735
The Longmen Shan region includes, from west to east, the northeastern part of the Tibetan Plateau, the Sichuan Basin, and the eastern part of the eastern Sichuan fold-and-thrust belt. In the northeast, it merges with the Micang Shan, a part of the Qinling Mountains. The Longmen Shan region can be divided into two major tectonic elements: (1) an autochthon/parautochthon, which underlies the easternmost part of the Tibetan Plateau, the Sichuan Basin, and the eastern Sichuan fold-and-thrust belt; and (2) a complex allochthon, which underlies the eastern part of the Tibetan Plateau. The allochthon was emplaced toward the southeast during Late Triassic time, and it and the western part of the autochthon/parautochthon were modified by Cenozoic deformation. The autochthon/parautochthon was formed from the western part of the Yangtze platform and consists of a Proterozoic basement covered by a thin, incomplete succession of Late Proterozoic to Middle Triassic shallow-marine and nonmarine sedimentary rocks interrupted by Permian extension and basic magmatism in the southwest. The platform is bounded by continental margins that formed in Silurian time to the west and in Late Proterozoic time to the north. Within the southwestern part of the platform is the narrow N-trending Kungdian high, a paleogeographic unit that was positive during part of Paleozoic time and whose crest is characterized by nonmarine Upper Triassic rocks unconformably overlying Proterozoic basement. In the western part of the Longmen Shan region, the allochthon is composed mainly of a very thick succession of strongly folded Middle and Upper Triassic Songpan Ganzi flysch. Along the eastern side and at the base of the allochthon, pre-Upper Triassic rocks crop out, forming the only exposures of the western margin of the Yangtze platform. Here, Upper Proterozoic to Ordovician, mainly shallow-marine rocks unconformably overlie Yangtze-type Proterozic basement rocks, but in Silurian time a thick section of fine-grained clastic and carbonate rocks were deposited, marking the initial subsidence of the western Yangtze platform and formation of a continental margin. Similar deep-water rocks were deposited throughout Devonian to Middle Triassic time, when Songpan Ganzi flysch deposition began. Permian conglomerate and basic volcanic rocks in the southeastern part of the allochthon indicate a second period of extension along the continental margin. Evidence suggests that the deep-water region along and west of the Yangtze continental margin was underlain mostly by thin continental crust, but its westernmost part may have contained areas underlain by oceanic crust. In the northern part of the Longmen Shan allochthon, thick Devonian to Upper Triassic shallow-water deposits of the Xue Shan platform are flanked by deep-marine rocks and the platform is interpreted to be a fragment of the Qinling continental margin transported westward during early Mesozoic transpressive tectonism. In the Longmen Shan region, the allochthon, carrying the western part of the Yangtze continental margin and Songpan Ganzi flysch, was emplaced to the southeast above rocks of the Yangtze platform autochthon. The eastern margin of the allochthon in the northern Longmen Shan is unconformably overlapped by both Lower and Middle Jurassic strata that are continuous with rocks of the autochthon. Folded rocks of the allochthon are unconformably overlapped by Lower and Middle Jurassic rocks in rare outcrops in the northern part of the region. They also are extensively intruded by a poorly dated, generally undeformed belt, of plutons whose ages (mostly K/Ar ages) range from Late Triassic to early Cenozoic, but most of the reliable ages are early Mesozoic. All evidence indicates that the major deformation within the allochthon is Late Triassic/Early Jurassic in age (Indosinian). The eastern front of the allochthon trends southwest across the present mountain front, so it lies along the mountain front in the northeast, but is located well to the west of the present mountain front on the south. The Late Triassic deformation is characterized by upright to overturned folded and refolded Triassic flysch, with generally NW-trending axial traces in the western part of the region. Folds and thrust faults curve to the north when traced to the east, so that along the eastern front of the allochthon structures trend northeast, involve pre-Triassic rocks, and parallel the eastern boundary of the allochthon. The curvature of structural trends is interpreted as forming part of a left-lateral transpressive boundary developed during emplacement of the allochthon. Regionally, the Longmen Shan lies along a NE-trending transpressive margin of the Yangtze platform within a broad zone of generally N-S shortening. North of the Longmen Shan region, northward subduction led to collision of the South and North China continental fragments along the Qinling Mountains, but northwest of the Longmen Shan region, subduction led to shortening within the Songpan Ganzi flysch basin, forming a detached fold-and-thrust belt. South of the Longmen Shan region, the flysch basin is bounded by the Shaluli Shan/Chola Shan arc—an originally Sfacing arc that reversed polarity in Late Triassic time, leading to shortening along the southern margin of the Songpan Ganzi flysch belt. Shortening within the flysch belt was oblique to the Yangtze continental margin such that the allochthon in the Longmen Shan region was emplaced within a left-lateral transpressive environment. Possible clockwise rotation of the Yangtze platform (part of the South China continental fragment) also may have contributed to left-lateral transpression with SE-directed shortening. During left-lateral transpression, the Xue Shan platform was displaced southwestward from the Qinling orogen and incorporated into the Longmen Shan allochthon. Westward movement of the platform caused complex refolding in the northern part of the Longmen Shan region. Emplacement of the allochthon flexurally loaded the western part of the Yangtze platform autochthon, forming a Late Triassic foredeep. Foredeep deposition, often involving thick conglomerate units derived from the west, continued from Middle Jurassic into Cretaceous time, although evidence for deformation of this age in the allochthon is generally lacking. Folding in the eastern Sichuan fold-and-thrust belt along the eastern side of the Sichuan Basin can be dated as Late Jurassic or Early Cretaceous in age, but only in areas 100 km east of the westernmost folds. Folding and thrusting was related to convergent activity far to the east along the eastern margin of South China. The westernmost folds trend southwest and merge to the south with folds and locally form refolded folds that involve Upper Cretaceous and lower Cenozoic rocks. The boundary between Cenozoic and late Mesozoic folding on the eastern and southern margins of the Sichuan Basin remains poorly determined. The present mountainous eastern margin of the Tibetan Plateau in the Longmen Shan region is a consequence of Cenozoic deformation. It rises within 100 km from 500–600 m in the Sichuan Basin to peaks in the west reaching 5500 m and 7500 m in the north and south, respectively. West of these high peaks is the eastern part of the Tibetan Plateau, an area of low relief at an elevations of about 4000 m. Cenozoic deformation can be demonstrated in the autochthon of the southern Longmen Shan, where the stratigraphic sequence is without an angular unconformity from Paleozoic to Eocene or Oligocene time. During Cenozoic deformation, the western part of the Yangtze platform (part of the autochthon for Late Triassic deformation) was deformed into a N- to NE-trending foldandthrust belt. In its eastern part the fold-thrust belt is detached near the base of the platform succession and affects rocks within and along the western and southern margin of the Sichuan Basin, but to the west and south the detachment is within Proterozoic basement rocks. The westernmost structures of the fold-thrust belt form a belt of exposed basement massifs. During the middle and later part of the Cenozoic deformation, strike-slip faulting became important; the fold-thrust belt became partly right-lateral transpressive in the central and northeastern Longmen Shan. The southern part of the fold-thrust belt has a more complex evolution. Early Nto NE-trending folds and thrust faults are deformed by NW-trending basementinvolved folds and thrust faults that intersect with the NE-trending right-lateral strike-slip faults. Youngest structures in this southern area are dominated by left-lateral transpression related to movement on the Xianshuihe fault system. The extent of Cenozoic deformation within the area underlain by the early Mesozoic allochthon remains unknown, because of the absence of rocks of the appropriate age to date Cenozoic deformation. Klippen of the allochthon were emplaced above the Cenozoic fold-andthrust belt in the central part of the eastern Longmen Shan, indicating that the allochthon was at least partly reactivated during Cenozoic time. Only in the Min Shan in the northern part of the allochthon is Cenozoic deformation demonstrated along two active zones of E-W shortening and associated left-slip. These structures trend obliquely across early Mesozoic structures and are probably related to shortening transferred from a major zone of active left-slip faulting that trends through the western Qinling Mountains. Active deformation is along the left-slip transpressive NW-trending Xianshuihe fault zone in the south, right-slip transpression along several major NE-trending faults in the central and northeastern Longmen Shan, and E-W shortening with minor left-slip movement along the Min Jiang and Huya fault zones in the north. Our estimates of Cenozoic shortening along the eastern margin of the Tibetan Plateau appear to be inadequate to account for the thick crust and high elevation of the plateau. We suggest here that the thick crust and high elevation is caused by lateral flow of the middle and lower crust eastward from the central part of the plateau and only minor crustal shortening in the upper crust. Upper crustal structure is largely controlled in the Longmen Shan region by older crustal anisotropics; thus shortening and eastward movement of upper crustal material is characterized by irregular deformation localized along older structural boundaries. 相似文献
4.
Arlo Brandon Weil Gabriel Gutiérrez-Alonso David Wicks 《International Journal of Earth Sciences》2013,102(1):43-60
The Esla tectonic unit lies along the southern boundary of the Cantabrian–Asturian Arc, a highly curved foreland fold-thrust belt that was deformed during the final amalgamation of the Pangea supercontinent. Previous structural and paleomagnetic analyses of the Cantabrian–Asturian Arc suggest a two-stage tectonic history in which an originally linear belt was bent into its present configuration, creating an orocline. The Esla tectonic unit is a particularly complex region due to the interaction of rotating thrust sheets from the southern limb of the arc and the southward-directed thrusts of the Picos de Europa tectonic domain during late-stage north–south shortening and oroclinal bending. These structural interactions resulted in intense modification of early-phase thin-skinned tectonic structures that were previously affected by a deeper out-of-sequence antiformal stack that passively deformed the early thrust stack. A total of 75 paleomagnetic sites were collected from the Portilla and Santa Lucia formations, two carbonate passive-margin reef platform units from the middle Devonian. Similar to other regions of the Cantabrian–Asturian Arc, Esla Unit samples carry a secondary remanent magnetization that was acquired after initial thrusting and folding of Variscan deformation in the late Carboniferous. Protracted deformation during late-stage oroclinal bending caused reactivation of existing thrust sheets that include the Esla and younger Corniero and Valbuena thrusts. When combined with existing structural data and interpretations, these data indicate that the present-day sinuosity of the Esla Unit is the consequence of both secondary rotation of originally linear features in the western Esla exposures (e.g., frontal thrusts), and secondary modification and tightening of originally curvilinear features in the eastern Esla exposures (e.g., hanging-wall lateral/oblique ramps). Differences in structural style between the Esla and other tectonic units of the arc highlight the complex kinematics of oroclinal bending, which at the orogen-scale buckled an originally linear, north–south (in present-day coordinates) trending Cantabrian–Asturian thrust belt during the final stages of Pangea amalgamation. 相似文献
5.
Deformational, metamorphic, monazite age and fabric data from Rengali Province, eastern India converge towards a multi-scale transpressional deformational episode at ca. 498–521 Ma which is linked with the latest phase of tectonic processes operative at proto-India-Antarctica join. Detailed sector wise study on mutual overprinting relationships of macro-to microstructural elements suggest that deformation was regionally partitioned into fold-thrust dominated shortening zones alternating with zones of dominant transcurrent deformation bounded between the thrust sense Barkot Shear Zone in the north and the dextral Kerajang Fault Zone in the south. The strain partitioned zones are further restricted between two regional transverse shear zones, the sinistral Riamol Shear Zone in the west and the dextral Akul Fault Zone in the east which are interpreted as synthetic R and antithetic R' Riedel shear plane, respectively. The overall structural disposition has been interpreted as a positive flower structure bounded between the longitudinal and transverse faults with vertical extrusion and symmetric juxtaposition of mid-crustal amphibolite grade basement gneisses over low-grade upper crustal rocks emanating from the central axis of the transpressional belt. 相似文献
6.
Joyjit Dey R Jayangonda Perumal Subham Sarkar Anamitra Bhowmik 《Journal of Earth System Science》2017,126(6):83
In the NW Sub-Himalayan frontal thrust belt in India, seismic interpretation of subsurface geometry of the Kangra and Dehradun re-entrant mismatch with the previously proposed models. These procedures lack direct quantitative measurement on the seismic profile required for subsurface structural architecture. Here we use a predictive angular function for establishing quantitative geometric relationships between fault and fold shapes with ‘Distance–displacement method’ (D–d method). It is a prognostic straightforward mechanism to probe the possible structural network from a seismic profile. Two seismic profiles Kangra-2 and Kangra-4 of Kangra re-entrant, Himachal Pradesh (India), are investigated for the fault-related folds associated with the Balh and Paror anticlines. For Paror anticline, the final cut-off angle \(\beta =35{^{\circ }}\) was obtained by transforming the seismic time profile into depth profile to corroborate the interpreted structures. Also, the estimated shortening along the Jawalamukhi Thrust and Jhor Fault, lying between the Himalayan Frontal Thrust (HFT) and the Main Boundary Thrust (MBT) in the frontal fold-thrust belt, were found to be 6.06 and 0.25 km, respectively. Lastly, the geometric method of fold-fault relationship has been exercised to document the existence of a fault-bend fold above the Himalayan Frontal Thrust (HFT). Measurement of shortening along the fault plane is employed as an ancillary tool to prove the multi-bending geometry of the blind thrust of the Dehradun re-entrant. 相似文献
7.
《International Geology Review》2012,54(16):1992-2027
An Archaean continent ‘SIWA’, an acronym for South India–Western Australia, comprising the Bastar–Dharwar craton, the Yilgarn craton, the Napier Complex, and the Vestfold Hills has been identified from palaeomagnetic and spatio-temporal data. This assembly was dispersed in three phases with the development of the proto-Indian ocean. The first and second events ~2350 and ~2000 Ma were related to the separation of the Yilgarn craton and the Napier Complex, respectively, to form a proto-Indo-Antarctic ocean and the Cuddapah basin. The proto-ocean was closed ~1650 Ma by the collision of the Lambert Terrane of East Antarctica and the Bastar–Dharwar craton. This collision, associated with ultra-high temperature (UHT) granulite facies metamorphism, is identified in the southern domain of the Eastern Ghats and the Oygardens domain of East Antarctica. The third extensional event between 1500 and 1200 Ma was associated with the separation of the Vestfold Hills block and a second phase of opening of the proto-Indian ocean, and the development of a series of basins on the western side of the Eastern Ghats (the Chhatisgarh, Khariar, Ampani, Indravati, and Sabari basins). The closing of this ocean basin during the Eastern Ghats–Rayner orogeny at ~950 Ma was related to the amalgamation of India and East Antarctica to form the supercontinent Rodinia. During the Neoproterozoic, this part of Rodinia was involved in orogenic collapse/extension and deposition of the Sodruzhesvo Group. The Pan-African Prydz Bay orogeny at ~550 Ma caused the closing of the basin to form East Gondwanaland. 相似文献
8.
Dilip Saha S. Chakraborti V. Tripathy 《Journal of the Geological Society of India》2010,75(1):323-337
Recent works suggest Proterozoic plate convergence along the southeastern margin of India which led to amalgamation of the
high grade Eastern Ghats belt (EGB) and adjoining fold-and-thrust belts to the East Dhrawar craton. Two major thrusts namely
the Vellikonda thrust at the western margin of the Nellore Schist belt (NSB) and the Maidukuru thrust at the western margin
of the Nallamalai fold belt (NFB) accommodate significant upper crustal shortening, which is indicated by juxtaposition of
geological terranes with distinct tectonostratigraphy, varying deformation intensity, structural styles and metamorphic grade.
Kinematic analysis of structures and fabric of the fault zone rocks in these intracontinental thrust zones and the hanging
wall and footwall rocks suggest spatially heterogeneous partitioning of strain into various combinations of E-W shortening,
top-to-west shear on stratum parallel subhorizontal detachments or on easterly dipping thrusts, and a strike slip component.
Although relatively less prominent than the other two components of the strain triangle, non-orthogonal slickenfibres associated with flexural slip folds and mylonitic foliation-stretching lineation orientation
geometry within the arcuate NSB and NFB indicate left lateral strike slip subparallel to the overall N-S trend. On the whole
an inclined transpression is inferred to have controlled the spatially heterogeneous development of thrust related fabric
in the terrane between the Eastern Ghats belt south of the Godavari graben and the East Dharwar craton. 相似文献
9.
传统上认为前陆冲断带内部的背斜构造具有"成排成带分段"的特征,在表观认识和宏观尺度上讲,容易理解这一特征,并且通过"成排成带分段"的解剖,直接为含油气区带评价和地震解释方案的落实提供指导作用。随着前陆冲断带深层结构的精细解剖和三维空间内构造变形的准确刻画,发现前陆冲断带深层构造变形的分布并非成排成带分段的特征,褶皱构造的发育与分布明显受前陆冲断构造位移量及各个断层位移量的大小所控制,各个断层控制的逆冲岩席在垂向上相互叠置、侧向上交叉对接、走向上错落有致, 3D立体空间内由多个次级弧形体组成鳞片状分布。本文以中国天然气勘探最为成功、勘探资料最为详实的库车坳陷克拉苏构造带为例,通过地震剖面精细构造解释,揭示出构造变形的运动学特征及其构造位移量在传播过程中的分异和转换,进而控制冲断带内部构造岩席的生长发育和空间展布特征,并在3D立体空间内揭示冲断岩席受构造位移量的控制而成鳞片状分布的规律,控制这一分布规律的主控因素是冲断构造位移量与冲断岩席长度之间定量的几何关系。这一认识提升了油气藏评价和构造圈闭描述的精度。 相似文献
10.
基于复杂构造解析和实验模拟研究,揭示了中西部前陆褶皱冲断构造带主要表现为受侧向挤压形成的滑脱冲断构造变形过程和结构样式;明确了单层滑脱挤压冲断构造变形存在临界增生和非临界增生两种变形机制,发育脆性拆离型、塑性滑移型和黏性流动型3种作用类型,并受滑脱层强度、地层厚度、底部边界和外动力过程等4种主要因素影响。复杂冲断构造带基本上表现为受多层单滑脱作用控制形成的垂向叠置组合结构,本文提出了复杂滑脱冲断变形结构的可分解性以及受不同性质的滑脱层组合控制形成特征结构模式,并揭示了前陆冲断带前缘多滑脱构造变形结构中由浅层向深层逐渐发育的变形时序;建立了中西部再生前陆冲断带结构模型、构造单元以及基本构造类型;并基于前陆盆地多阶段构造演化过程以及晚期的隆升剥蚀-沉降沉积过程,提出了中西部两种类型冲断带的控油气作用及其勘探领域。 相似文献
11.
对川东-湘鄂西断褶带内鄂西地区的弧形构造,从构造剖面特征、叠加褶皱样式和断裂性质入手进行几何学和运动学分析。结果发现鄂西弧形构造具有多期变形特征:早期普遍为北东东向的直线型褶皱,随着弧形带扩展,在东、西两翼分别发育右行和左行的逆冲-走滑断裂,同时分别形成北北东向和北西西向的弧形褶皱。晚期弧形带中部发育北北东向构造并叠加改造了早期北东东和北西西向褶皱,同时在黄陵背斜以西还发育交切早期构造的北北西向仙女山右行走滑断裂。根据弧形带扩展的几何学-运动学分类原则,并结合前人的古地磁研究结果,推测鄂西弧形构造应属于构造弯曲形成的弯曲弧。区域滑脱层和黄陵隆起阻挡可能是控制弧形样式的主要原因。区域滑脱层控制了拆离滑脱褶皱的构造样式; 黄陵基底隆起的阻挡作用使弧形带东翼进一步弯曲变形,并导致了构造应力场方向发生改变,造成了晚期北北东向与早期北东东向构造的叠加。由此恢复的鄂西弧形构造变形过程对于揭示川东-湘鄂西断褶带构造演化具有重要的指示意义。 相似文献
12.
Late Cenozoic Deformation Sequence of a Thrust System along the Eastern Margin of Pamir, Northwest China 总被引：1，自引：1，他引：0
A thrust belt formed in the basin along the eastern margin of Pamir. The thrust belt is about 50 km wide, extends about 200 km, and includes three compressive structures from south to north: the blind Qipan structural wedge and Qimugen structural wedge, and the exposed Yengisar anticline. The thrust belt displays a right-stepping en echelon pattern. The Qipan structural wedge dies out northward to the west of the Qimugen structural wedge, and the Qimugen structural wedge dies out northward to the west of the Yengisar anticline. Detailed analysis of seismic reflection profiles of the western Tarim Basin reveal that fan-shaped growth strata were deposited in the shallow part of the thrust belt, recording the deformation sequence of the thrust belt. The depth of the Cenozoic growth strata decreases from south to north. The growth strata of the Qipan structural wedge is located in the middle-lower section of the Pliocene Artux Formation (N2a), the growth strata of the Qimugen structural wedge is close to the bottom of the Pleistocene Xiyu Formation (Q1x), and the growth strata of the Yengisar anticline is located in the middle section of the Xiyu Formation (Q1x). Combined with magnetostratigraphic studies in the western Tarim basin, it can be preliminarily inferred that the deformation sequence of the thrust belt along the eastern margin of Pamir is progressively younger northward. The geometry and kinematic evolution of the thrust belt in the eastern margin of Pamir can be compared with previous analogue modeling experiments of transpressional deformation, suggesting that the thrust belt was formed in a transpressional tectonic setting. 相似文献
13.
Detrital zircon geochronology of quartzites from the southern Madurai Block,India: Implications for Gondwana reconstruction 总被引：1，自引：1，他引：0
Detrital zircons are important proxies for crustal provenance and have been widely used in tracing source characteristics and continental reconstructions. Southern Peninsular India constituted the central segment of the late Neoproterozoic supercontinent Gondwana and is composed of crustal blocks ranging in age from Mesoarchean to late Neoproterozoic–Cambrian. Here we investigate detrital zircon grains from a suite of quartzites accreted along the southern part of the Madurai Block. Our LA-ICPMS U-Pb dating reveals multiple populations of magmatic zircons, among which the oldest group ranges in age from Mesoarchean to Paleoproterozoic (ca. 2980–1670 Ma, with peaks at 2900–2800 Ma, 2700–2600 Ma, 2500–2300 Ma, 2100–2000 Ma). Zircons in two samples show magmatic zircons with dominantly Neoproterozoic (950–550 Ma) ages. The metamorphic zircons from the quartzites define ages in the range of 580–500 Ma, correlating with the timing of metamorphism reported from the adjacent Trivandrum Block as well as from other adjacent crustal fragments within the Gondwana assembly. The zircon trace element data are mostly characterized by LREE depletion and HREE enrichment, positive Ce, Sm anomalies and negative Eu, Pr, Nd anomalies. The Mesoarchean to Neoproterozoic age range and the contrasting petrogenetic features as indicated from zircon chemistry suggest that the detritus were sourced from multiple provenances involving a range of lithologies of varying ages. Since the exposed basement of the southern Madurai Block is largely composed of Neoproterozoic orthogneisses, the data presented in our study indicate derivation of the detritus from distal source regions implying an open ocean environment. Samples carrying exclusive Neoproterozoic detrital zircon population in the absence of older zircons suggest proximal sources in the southern Madurai Block. Our results suggest that a branch of the Mozambique ocean might have separated the southern Madurai Block to the north and the Nagercoil Block to the south, with the metasediments of the khondalite belt in Trivandrum Block marking the zone of ocean closure, part of which were accreted onto the southern Madurai Block during the collisional amalgamation of the Gondwana supercontinent in latest Neoproterozoic–Cambrian. 相似文献
14.
We use scaled physical analog (centrifuge) modeling to investigate along- and across-strike structural variations in the Salt Range and Potwar Plateau of the Himalayan foreland fold-thrust belt of Pakistan. The models, composed of interlayered plasticine and silicone putty laminae, comprise four mechanical units representing the Neoproterozoic Salt Range Formation (basal detachment), Cambrian–Eocene carapace sequence, and Rawalpindi and Siwalik Groups (Neogene molasse), on a rigid base representing the Indian craton. Pre-cut ramps simulate basement faults with various structural geometries.A pre-existing north-dipping basement normal fault under the model foreland induces a frontal ramp and a prominent fault-bend-fold culmination, simulating the Salt Range. The ramp localizes displacement on a frontal thrust that occurs out-of-sequence with respect to other foreland folds and thrusts. With a frontal basement fault terminating to the east against a right-stepping, east-dipping lateral ramp, deformation propagates further south in the east; strata to the east of the lateral ramp are telescoped in ENE-trending detachment folds, fault-propagation folds and pop-up structures above a thick basal detachment (Salt Range Formation), in contrast to translated but less-deformed strata with E–W-trending Salt-Range structures to the west. The models are consistent with Salt Range–Potwar Plateau structural style contrasts being due to basement fault geometry and variation in detachment thickness. 相似文献
15.
塔里木盆地库车、塔西南和塔东南山前带在构造变形和活动强度等方面存在较大的差异性,这也决定了油气地质条件与油气分布的不均衡性。通过对3个山前带地质剖面的对比研究,结合对典型成藏模式的剖析,探讨山前带差异构造变形特征对油气成藏的控制作用。库车山前带以逆冲推覆及盐构造为主,构造圈闭规模大、幅度高;主要有盐下和盐上两种成藏模式,通源断裂十分发育,库姆格列木组膏盐岩对盐下油气的保存非常有利。塔西南山前带变形分段特征明显,包括三角带构造、双重逆冲、叠加背斜等,构造圈闭规模和完整性不如库车山前带;成藏模式也体现出分段差异,上白垩统-阿尔塔什组膏泥岩和普司格组泥岩的封闭效果较好,但运移路径复杂,先存油气易遭受后期调整和破坏。塔东南山前带具有一定构造分段性,若羌凹陷山前以冲断变形为主,远离山前的第二排背斜、断背斜圈闭具备基本的成藏条件;民丰凹陷山前以叠瓦逆冲和三角带构造为主,古近系膏泥岩封盖能力有限,深部逆冲断块及凹陷内部的低幅度背斜等是较现实的勘探目标。 相似文献
16.
前陆冲断带可以分为3种基本类型:弧后前陆型、周缘前陆型和再生前陆型冲断带。相对国外典型前陆冲断带,中国中西部前陆冲断带在构造演化和变形方面具有独特性,属于再生前陆型冲断带,普遍经历了两期逆冲构造变形、或者"伸展-挤压-伸展-挤压"多期构造变形的叠加。中国中西部的再生前陆冲断带多具有"分带、分段和分层"的结构特征,表现出以主干断裂为界往往可以划分为若干个冲断变形带,沿走向方向表现为几个在构造变形上具有明显差异的变形区段,在垂向上由于滑脱层的发育表现出不协调的分层收缩、上下叠置的变形特征。 相似文献
17.
《Gondwana Research》2015,27(3-4):888-906
The Ongole Domain in the southern Eastern Ghats Belt of India formed during the final stages of Columbia amalgamation at ca. 1600 Ma. Yet very little is known about the protolith ages, tectonic evolution or geographic affinity of the region. We present new detrital and igneous U–Pb–Hf zircon data and in-situ monazite data to further understand the tectonic evolution of this Columbia-forming orogen.Detrital zircon patterns from the metasedimentary rocks are dominated by major populations of Palaeoproterozoic grains (ca. 2460, 2320, 2260, 2200–2100, 2080–2010, 1980–1920, 1850 and 1750 Ma), and minor Archaean grains (ca. 2850, 2740, 2600 and 2550 Ma). Combined U–Pb ages and Lu–Hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent Dharwar Craton. Instead they were likely derived from East Antarctica, possibly the same source as parts of Proterozoic Australia. Magmatism occurred episodically between 1.64 and 1.57 Ga in the Ongole Domain, forming felsic orthopyroxene-bearing granitoids. Isotopically, the granitoids are evolved, producing εHf values between − 2 and − 12. The magmatism is interpreted to have been derived from the reworking of Archaean crust with only a minor juvenile input. Metamorphism between 1.68 and 1.60 Ga resulted in the partial to complete resetting of detrital zircon grains, as well as the growth of new metamorphic zircon at 1.67 and 1.63 Ga. In-situ monazite geochronology indicates metamorphism occurred between 1.68 and 1.59 Ga.The Ongole Domain is interpreted to represent part of an exotic terrane, which was transferred to proto-India in the late Palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south-west Baltica and south-eastern Laurentia. Given the isotopic, geological and geochemical similarities, the proposed exotic terrane is interpreted to be an extension of the Napier Complex, Antarctica, and may also have been connected to Proterozoic Australia (North Australian Craton and Gawler Craton). 相似文献
18.
准噶尔盆地南缘褶皱-逆冲断层带分析 总被引：13，自引：0，他引：13
讨论了与准噶尔盆地南缘褶皱-逆冲断层带有关的4个问题。(1)准噶尔盆地南缘褶皱-逆冲断层带具有纵向分带、横向分段和垂向构造分层的特征:纵向上由南至北可分为逆冲推覆构造带、基底卷入褶皱-冲断带和滑脱型褶皱-冲断带三个带;横向上,基底卷入褶皱-冲断带从西至东按横向调节带分为5个段,构造特征表现为反冲断层从不发育到向南反冲的位移逐渐增大、反冲断层所滑脱的层位亦逐渐加深;滑脱型褶皱-冲断带以红车断裂为界划分为西段和东段,西段构造运动弱,构造变形具双层结构;东段构造运动较强,发育大型冲向后陆的反向逆冲断层,构造变形多具有3层结构。(2)逆冲断层-褶皱类型按其形成机制分为基底卷入型冲断-褶皱、滑脱型冲断-褶皱以及基底卷入-滑脱混合型冲断-褶皱3大类,其中,基底卷入型冲断-褶皱的特征是褶皱作用发生在逆冲断裂之前,而滑脱型冲断-褶皱以冲断和褶皱同时或冲断层先于褶皱形成为特征。(3)本区存在横向和纵向传递带。横向调节带一般分布于基底卷入型褶皱-冲断带,主要为左旋走滑断层;纵向传递带分布于滑脱型褶皱-冲断带,以逆冲断层系斜列分布和位移纵向斜列传递为特征。(4)褶皱-冲断带形成的主控因素主要有:近南北向的水平挤压作用,上新世末—早更新世末和晚侏罗世末发生的构造变形以及古近系、下白垩统和下—中侏罗统发育的三套异常高压泥岩层相关的滑脱作用。 相似文献
19.
In southern India the older Precambrian is overlain unconformably in the Cuddapah Basin by the Cuddapah and Kurnool Systems. The former is tilted and unmetamorphosed in the west but eastwards becomes strongly folded and metamorphosed. It contains lavas and sills, particularly in the lower two groups, is intruded by dolerites and at Chelima by diatremes of kimberlitic affinities related to those intruding the older gneisses west of the Cuddapah Basin in the Wajrakarur area. The Kurnool System lacks any igneous rocks; its basal conglomerate is diamondi‐ferous. Rb‐Sr dating of lava samples from the lowest group of the Cuddapah System shows that the age of the base of the system may be as great as 1,700 m.y. Together with data for a granite which intrudes probable Cuddapah rocks near the disturbed eastern margin of the basin the data imply that the base is unlikely to be younger than 1,555 m.y. Metamorphism affected some lavas at about 1,360 m.y. The diatremes have two ages of intrusion, about 1,225 m.y. and 1,140 m.y., the latter being the age of the Majhgawan pipe near Panna in northern India. Pre‐Kurnool dolerites have an age of 980 ±110 m.y. The lavas and dolerites show a range of initial 87Sr/86Rb ratios from about 0.704 to 0.708 and possibly 0.712. The age data suggest that no simple correlation can be made with other Precambrian sequences in northern peninsular India. Deposition of the Cuddapah System appears to have started well before the start of the deposition of the Vindhyan System, while the Kurnool System is coeval with only part of the Upper Vindhyan. The data also suggest that present interpretations of the structural development of the Cuddapah Basin may need some revision. 相似文献
20.
The Nellore Schist Belt (NSB) is a curvilinear Archaean schist belt, approximately 350 km long and 8–50 km wide. The Nellore Schist Belt is considered to be Neoarchean in age and stratigraphically NSB is classified as the western Udayagiri group (dominated by metasediments) and underlying eastern Vinjamuru group (dominated by metabasalts). There is a long controversy regarding the contact relationship between Udayagiri and Vinjamuru groups. Earlier researchers regarded the contact between two groups as tectonic on the basis of metamorphism. A shear zone and a possible thrust contact between the two groups have also been reported. On the basis of present study, an NNW–SSE trending, westerly dipping inclined transpressional zone is found at the contact between Udayagiri and Vinjamuru groups in the central western part of the NSB. Kinematic analysis of both the hanging wall and foot wall of the westerly dipping thrust zone shows presence of strong S1 schistosity, shear bands and S-C fabric in both strike and dip section along with east-verging overturned fold, westerly dipping inverted beds, suggesting partitioning of non-coaxial deformation in strike-slip and dip-slip component along with a pure shear component. Strike-slip is more prominent in the northern part of the contact than the southern part. The presence of steep to moderate northerly plunging non-orthogonal stretching/mineral elongation lineation all along the contact and clockwise shift of plot of the same in stereo net from its orthogonal position and presence of other kinematic indicators in plan suggests a right lateral strike-slip component. As a whole, it is suggested that Udayagiri group is thrusted over Vinjamuru group along a westerly dipping thrust plane with a right lateral strike-slip motion and simultaneous E–W contraction. 相似文献