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An assessment of the southern Betsimisaraka Suture (B.S.) of southeastern Madagascar using remote sensing and field investigation reveals a complex deformation history. Image processing of Landsat ETM+data and JERS-I Synthetic Aperture Radar (SAR) imagery was integrated with field observations of structural geology and field petrography. The southern B.S. divides the Precambrian basement rocks of Madagascar in two parts. The western part includes Proterozoic rocks whereas the eastern part is an Archean block, named the Masora block. The southern part of the B.S. includes high-grade metamorphic rocks, recording strong deformation and has mineral deposits including chromite, nickel, and emerald, characteristic of oceanic material that is compatible with a suture zone.Large-scale structural features indicate ductile deformation including three generations of folding (F1, F2, and F3) associated with dextral shearing. The first folding event (F1) shows a succession of folds with NE striking axial planes. The second folding event (F2) mainly has north–south striking axial planes and the last event (F3) is represented by mega folds that have ENE–WSW axial plane directions and have NNW and SSE contractional strain patterns. Closure of the Mozambique Ocean between two components of Gondwana sandwiched rocks of the B.S. and formed upright folds and shortening zones which produced N–S trending lineaments. Later dextral movements followed the contraction and formed NW–SE trending lineaments and N–S trending normal faults associated with dextral strike slip faults and fractures. 相似文献
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We investigate the mantle dynamics beneath the North China Craton (NCC) and surrounding regions based on a synthesis of recent P-wave mantle tomographic data down to depths of 600–800 km and their correlation with the surface geological features, with particular reference to the Paleoproterozoic tectonic events associated with the incorporation of the NCC within the Columbia supercontinent amalgam. From the tomographic images, we identify a hot corridor in the mantle transition zone beneath the central region of the Western Block of the NCC sandwiched between two cold corridors. This scenario is similar to the donut-shaped high-velocity anomaly surrounding a region of low-velocity anomaly in the lowermost mantle under the Pacific and suggests that the cold regions might represent slab graveyards which provide the fuel for the plumes rising from the center. A tomographic transect along the collisional suture of the NCC with the Columbia supercontinent, covering the Yinshan-Ordos Blocks in the Western Block through the Central Orogenic Belt and into the Eastern Block of the NCC reveals a ca. 250 km thick lithospheric keel below the Ordos Block defined by a prominent high-velocity anomaly. We identify slab break-off and asthenospheric upwelling in this region and suggest that this process probably initiated the thermal and material erosion of the tectosphere beneath the Eastern Block from the Paleoproterozoic, which was further intensified during the Mesozoic when a substantial part of the sub-continental mantle lithosphere was lost. We visualize heat input from asthenosphere and interaction between asthenosphere and overlying carbonated tectosphere releasing CO2-rich fluids for the preservation of ultra-high temperature (ca. 1000 °C) metamorphic rocks enriched in CO2 as well as high-pressure mafic granulites as a paired suite in this region. We also identify a hot swell of the asthenosphere rooted to more than 200 km depth and reaching up to the shallow mantle in the tomographic section along 35°N latitude at a depth of 800 km. This zone represents a cross-section through the southern part of the NCC. The surface distribution of Paleoproterozoic Xiong’er lavas and mafic dykes in this region would indicate that this region might have evidenced similar upwellings in the past. Our study has important implications in understanding the evolution of the NCC and suggests that the extensive modification of the mantle architecture and lithospheric structure beneath one of the fundamental Precambrian nuclei of Asia had a prolonged history probably dating from the Paleoproterozoic suturing of the NCC within the Columbia supercontinent amalgam. 相似文献
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井间断层分析的研究,是油气储层地质研究的一项重要基础性工作,对油气的运移和聚集其中重要的控制作用。它是利用测井资料,以地层分层为基础,采用计算机技术实现井间断层分析的一种井间断层自动分析方法。动态波形匹配算法是本次研究采用的主要算法,它能够很好地建立井间地层之间的对比关系,通过曲线拟合、特征提取、匹配代价计算等步骤,自动绘制井间地层对比的路径图解。本文在对各种构造的路径图分析的基础上,总结出正断层、逆断层、不整合、同沉积断层、犁式断层和地层尖灭等30种情况下的路径图模式,提出路径图模式及相关概念。在大港油田的实例分析中取得了很好的效果。 相似文献
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Collision leading to multiple-stage large-scale extrusion in the Qinling orogen: Insights from the Mianlue suture 总被引：10，自引：5，他引：10
Sanzhong Li Timothy M. Kusky Lu Wang Guowei Zhang Shaocong Lai Xiaochun Liu Shuwen Dong Guochun Zhao 《Gondwana Research》2007,12(1-2):121
The geologic framework of the Phanerozoic Qinling–Dabie orogen was built up through two major suturing events of three blocks. From north to south these include the North China craton (including the north Qinling block), the Qinling–Dabie microblock, and the South China craton (including the Bikou block), separated by the Shangdan and Mianlue sutures. The Mianlue suture zone contains evidence for Mesozoic extrusion tectonics in the form of major strike–slip border faults surrounding basement blocks, a Late Paleozoic ophiolite and a ca. 240–200 Ma thrust belt that reformed by 200–150 Ma thrusts during A-type (intracontinental) subduction. The regional map pattern shows that the blocks are surrounded by complexly deformed Devonian to Early Triassic metasandstones and metapelites, forming a regional-scale block-in-matrix mélange fabric. Five distinct tectonic units have been recognized in the belt: (1) basement blocks including two types of Precambrian basement, crystalline and transitional; (2) continental margin slices including Early Paleozoic strata, and Late Paleozoic fluviodeltaic sedimentary rocks, proximal and distal fan clastics, reflecting the development of a north-facing rift margin on the edge of the South China plate; (3) out of sequence oceanic crustal slices including strongly deformed postrift, deep-water sedimentary rocks, sheeted dikes, basalts, and mafic–ultramafic cumulates of a Late Paleozoic ophiolite suite, developing independent of the rift margin in a separate basin; (4) out-of-sequence island-arc slices; (5) accretionary wedge slices. All the tectonic units were deformed during three geometrically distinct deformation episodes (D1, D2 and D3 during 240–200 Ma). Units 2–4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the D1 episode. Thrust slices 20 km south of the Mianlue suture are related to this vertical extrusion due to the same rock assemblages, ages and kinematics. The D2 and D3 episodes folded all the units in a thick-skinned style about east–west (D2) and west–northwest (D3) axes in the Mianlue suture zone. An early foreland propagating sequence of accretion of Late Paleozoic rocks deposited above the Yangtze craton is not involved in D1 deformation but is temporally equivalent to the D2 and D3 deformation in the Mianlue suture. Two stages of strike–slip faulting mainly occurred at the end of D2 and D3, respectively. During D2 deformation, the Bikou block was obliquely indented to the ESE into the Mianlue suture, rather than being thrust over the Mianlue suture from the north as a part of the Qinling–Dabie microblock. During D3 deformation, however, the Bikou block was bounded by the south boundary fault of the Mianlue suture, and the Yangpingguan fault on the south. These faults are coeval strike–slip faults, but of opposite senses, and accommodated minor southwestward extrusion of the Bikou block into Songpan–Ganze orogen. The other basement blocks north of the Mianlue suture were extruded eastward by about 20 km of lateral displacement, based on the offset of the Wudang dome, during the D3 episode due to the northeastward indentation of the Hannan complex of the South China craton. Post-D3 emplacement of granite, cutting across the strike–slip faults such as the Mianlue suture, provides a minimum age of 200 Ma for D3 deformation. Therefore, based on insights from the evolution of the Mianlue suture, the D2 and D3 episodes in the Mianlue suture and its neighbors are not responsible for and associated with the two-stage extrusion of the Dabie UHP-HP terranes from the Foping dome to the present erosional surface (more than 350 km). 相似文献
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Tectonic evolution of China and adjacent crustal fragments 总被引：6，自引：6，他引：6
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The South China fold belt has experienced a complex series of tectonic events that span 1.0 billion years of earth history. Longhushan (龙虎山) World Geopark is located on the Proterozoic suture between the Yangtze craton and Cathyasia block and highlights the long history of this belt. Collision of the Cathyasia and Yangtze cratons 1.0 billion years ago was associated with the formation of the Rodinian supercontinent where most of the planet's landmasses were amalgamated into one block. Jurassic through Early... 相似文献
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Ultrahigh-temperature (UHT) and high pressure (HP) metamorphic rocks generated at different times in Earth history form paired suites within the same tectonic belts in several regions. We evaluate the thermal regimes and fluid circulation patters in different plate tectonic settings and propose a new model involving ridge subduction where the slab window places hot asthenosphere against the base of the overlying plate and provides an ideal setting for the supply of heat and CO2 -rich fluids at relatively shallow domains, which can explain the formation and preservation of UHT metamorphic rocks in the roots of the arc and forearc. The plate geometry below the slab window would inhibit the normal cooling induced by the slab, and a temporary deprivation of slab-derived sediments and hydrous fluids. Our analysis provides a unified model for paired UHT and HP metamorphic orogens and presents a key to the associated thermal and fluid regimes. 相似文献
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Permian to Cretaceous mélange of the McHugh Complex on the Kenai Peninsula, south-central Alaska includes blocks and belts of graywacke, argillite, limestone, chert, basalt, gabbro, and ultramafic rocks, intruded by a variety of igneous rocks. An oceanic plate stratigraphy is repeated hundreds of times across the map area, but most structures at the outcrop scale extend lithological layering. Strong rheological units occur as blocks within a matrix that flowed around the competent blocks during deformation, forming broken formation and mélange. Deformation was noncoaxial, and disruption of primary layering was a consequence of general strain driven by plate convergence in a relatively narrow zone between the overriding accretionary wedge and the downgoing, generally thinly sedimented oceanic plate. Soft-sediment deformation processes do not appear to have played a major role in the formation of the mélange. A model for deformation at the toe of the wedge is proposed in which layers oriented at low angles to σ1 are contracted in both the brittle and ductile regimes, layers at 30–45° to σ1 are extended in the brittle regime and contracted in the ductile regime, and layers at angles greater than 45° to σ1 are extended in both the brittle and ductile regimes. Imbrication in thrust duplexes occurs at deeper levels within the wedge. Many structures within mélange of the McHugh Complex are asymmetric and record kinematic information consistent with the inferred structural setting in an accretionary wedge. A displacement field for the McHugh Complex on the lower Kenai Peninsula includes three belts: an inboard belt of Late Triassic rocks records west-to-east-directed slip of hanging walls, a central belt of predominantly Early Jurassic rocks records north–south directed displacements, and Early Cretaceous rocks in an outboard belt preserve southwest–northeast directed slip vectors. Although precise ages of accretion are unknown, slip directions are compatible with inferred plate motions during the general time frame of accretion of the McHugh Complex. The slip vectors are interpreted to preserve the convergence directions between the overriding and underriding plates, which became more oblique with time. They are not considered indicative of strain partitioning into belts of orogen-parallel and orogen-perpendicular displacements, because the kinematic data are derived from the earliest preserved structures, whereas fabrics related to strain partitioning would be expected to be superimposed on earlier accretion-related fabrics. 相似文献
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The Betsimisaraka Suture (B.S.) of Madagascar is an important structural zone defining the collision between Eastern and Western Gondwana. It is represented by highly deformed high-grade metamorphic rocks with mineral assemblages typical of ophiolitic material, including chromitite and nickel bearing rocks consistent with a suture zone setting. Analysis of satellite imagery coupled with field investigations has helped to elucidate the structure and evolution of the B.S. Digital image processing of Landsat ETM+ data was integrated with Synthetic Aperture Radar (SAR) to reduce the effects of the dense vegetation cover. Enhanced false color composite (7-4-2 and 4-2-3), single Landsat bands and band ratio composites including 2/7-1/7-2/5, 5/3-5/1-7/3, 5/1-7/1-4/1 and 5/7-5/1-5/4 × 3/4 (in RGB) improve the lithologic contrast, reduce the effects of topography and enhance the structural lineaments. Ductile deformation deduced from structural features mapped on Landsat enhanced images indicates three generations of folding (F1, F2, and F3) coupled with shearing: (1) F1 folds with NE striking axial surfaces; (2) F2 related with N–S striking axial surfaces, (3) and F3 associated with ENE–WSW axial surfaces, indicating NNW and SSE contractional strain similar to the deformation in the southern B.S. Mapping these structures enables three types of shearing to be delineated: (1) NW–SE dextral shearing as seen in the Befandriana region; (2) NW–SE sinistral shearing defined by sigmoidal bodies in Mandritsara and Ankijanilava-Marotandrano regions, (3) and NE–SW striking dextral shears recorded in the Lake Alaotra region. Several faults, joints and fractures represent brittle deformation events. Lineaments analyzed within the B.S. are divisible into two groups of brittle structures: (1) N–S trending lineaments correlated with the Gondwanan collision events and (2) much younger NE and NW trending lineaments that are mainly found in the Antananarivo block. The latter may represent an active tectonic event in the central plateau that bounds the western part of the B.S. 相似文献