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1.
The Oman‐Emirates is the largest and best‐exposed ophiolite; consequently, it has attracted significant interest among scientists, together with serious conflicts. Most geologists regard this ophiolite as having formed in an intra‐oceanic subduction zone before being accreted to the Arabian continent. Here, we propose an alternative scenario, supported by detailed field observations and integrated geophysics. The smaller Emirates part of the ophiolite was forced into a nearby continent, in the pre‐collision stage of Tethyan closure. The contraction led to the exhumation of the mantle floor of segmented basins accreted in a rifted system similar to the present‐day Gulf of California. The implied high temperature–high pressure metamorphism and the range of geochemical signatures were introduced during the process of rifting, whereas the larger Oman ophiolite was emplaced by obduction onto and along the subducting continental shore. This Ridge–Trench–Transform system might call for a new process to obduct over continents in particular Tethyan ophiolites. 相似文献
2.
J.F. Dewey 《Tectonophysics》1976,31(1-2)
If ophiolite complexes originate as oceanic crust and mantle generated by sea-floor spreading at oceanic ridges or in marginal basins, the tectonic emplacement (obduction) of ophiolite sheets and slices must involve some form of decoupling of oceanic lithosphere prior to emplacement and the expulsion of relatively dense oceanic rocks onto lighter continental rocks. The major problems are the mechanism by which this decoupling takes place, the extent to which the decoupling fractures penetrate the entire lithosphere, and the mechanism and geometry of the tectonic emplacement process, that is — the extent to which compressional versus gravity-sliding mechanisms predominate. Several writers (Coleman, 1971; Stevens, 1970; Church and Stevens, 1971; Temple and Zimmerman, 1969; Dewey and Bird, 1970, 1971; Williams, 1971) have discussed these obduction problems and offered various kinds of solution. These solutions, among others, are discussed in this paper. It is concluded that several convergent plate-margin mechanisms may be responsible for ophiolite obduction, none of which involve gravity sliding. 相似文献
3.
Uncertainty about the timing and location of the initiation of convergence in the western and south‐western Pacific greatly hinders accurate plate tectonic reconstructions of subduction systems in that area. The chemistry and age of dikes intruding mantle peridotite in the ophiolite of New Caledonia infer that subduction‐related magmatism began before 53 Ma. These new results infer that obduction in the south‐west Pacific is unrelated to the reorientation of the Pacific plate motion that occurred c. 43 Ma and confirm new interpretations showing that changes in mantle flow, hotspot and plate motion may have occurred as soon as late Paleocene or early Eocene. 相似文献
4.
本文将全球洋中脊系统作为研究整体,根据洋中脊的全球分布、运动学特征及其初始形成时与泛大陆的构造几何关系,将全球现今的洋中脊系统划分为内、外支洋中脊。外支洋中脊为探索者洋中脊-太平洋洋隆-东南印度洋中脊-西北印度洋中脊,起源于泛大洋及冈瓦纳大陆内部;内支洋中脊为西南印度洋中脊-大西洋中脊-北冰洋加科尔洋中脊,起源于泛大陆内部。两者之间通过俯冲带、转换断层以及弥散性板块边界实现全球板块构造在运动上的平衡,并保持地球的球形几何形态恒定。外支洋中脊在全球板块构造上造成泛大洋缩减,并持续被太平洋取代,直接推动了环太平洋俯冲带的形成;内支洋中脊造成大西洋盆、印度洋盆中生代以来持续扩张。中生代以来,外支洋中脊和内支洋中脊共同作用引起非洲板块、印度澳大利亚板块向北运动,新特提斯洋盆关闭,形成特提斯(阿尔卑斯山-喀尔巴阡山-扎格罗斯山-喜马拉雅山)碰撞造山带,并通过洋中脊扩张平衡了相关的岩石圈缩短。 相似文献
5.
吉林延边开山屯地区地层时代的新证据 总被引：11，自引：1，他引：10
吉林延边开山屯地区古生代地层,在构造地层学研究的基础上,取得一些地层时代的新资料在混杂岩中新发现中二叠世北方型动物群化石;对混杂岩中的花岗岩砾石,测得SHRIMP锆石U-Pb年龄(286.8±5.6Ma),代表岛弧岩浆岩结晶时间;在变蛇绿岩和糜棱岩中采取白云母样品,测得40Ar-39Ar年龄,分别为408Ma和205.7Ma。由此,可以得出开山屯地区地层时代和混杂岩形成与演化的时间表泥盆纪洋壳形成;在中石炭世—中二叠世由南向北的运移过程中,洋壳之上发生硅质和碳酸盐沉积,形成海山;洋壳与由北向南移动的兴凯地块相对运动,二叠纪时向大陆俯冲,在兴凯地块西缘(现代方位)发育岛弧活动,并在中、晚二叠世形成滑塌堆积。可能与晚三叠世的洋壳俯冲作用有关,在兴凯地块前陆边缘发生逆冲作用,形成构造岩片。 相似文献
6.
内蒙古索伦山地区出露蛇绿岩,其研究对探讨古亚洲洋演化具有重要意义。对内蒙古索伦山地区蛇绿岩进行了系统的调查和研究,探讨了其就位机制与时限。 结合索伦山蛇绿岩地质特征和区域地质背景综合分析,认为研究区蛇绿岩组合包括地幔与洋壳组分。索伦山地区蛇绿岩存在较为完整的蛇绿岩组合模式,出露地幔岩石组合为蛇纹石化纯橄榄岩、蛇纹石化二辉-方辉橄榄岩、橄榄辉石岩和硅化碳酸盐化蚀变超基性岩(风化壳)等。蛇绿岩组合中洋壳组分为辉长岩、辉绿岩、玄武岩和硅质岩。蛇绿岩就位机制划分为4种,即碰撞仰冲型、增生底垫型、俯冲剥离型和角流型。其中,俯冲剥离型就位机制表现为岩石组合齐全完整的特征,产出形态为岩块、岩片,其中岩块、岩片与基质为构造断层接触;在俯冲带近大陆一侧常形成岛弧岩浆岩等特征。索伦山蛇绿岩地质特征与俯冲剥离型就位机制特征完全相符,故索伦山蛇绿岩就位机制大致为洋中脊俯冲剥离型。根据大洋岩石圈形成之后在10 Ma之内就位这一原则,结合索伦山地区辉长岩SHRIMP锆石U Pb年龄为(2807±53) Ma,认为索伦山蛇绿岩就位时限在270 Ma左右。 相似文献
7.
Y. Ota Dr. 《GeoJournal》1980,4(2):111-124
The study of tectonic landforms is one of the main themes of geomophological research in Japan, characterized as a tectonically active area along the subducting oceanic plates. The recent trends in the studies of tectonic landforms which include an arrangement or distribution of major ranges and plains, vertical displacement of low-relief erosion surfaces and of marine terraces, and various kinds of deformed features due to active faulting or folding, are introduced here with special reference to the Quaternary geomorphic development. A regionality of each tectonic landforms is also summarized. Further, some fundamental concept of the Quaternary tectonics, for instance, an accumulative character of each type of deformation and sequence of rate of tectonic movement, reconstruction of former stress field as well as a relation between the Quaternary tectonic movement and seismic deformation in present and historic time are discussed on the basis of analysis of the tectonic landforms. The Quaternary tectonics of the Japanese Islands are essentially characterized by the compressional stress, originated from the subduction of oceanic plates, and regionality can be interpreted as the result of the different response of each tectonic region to island arc tectonics. 相似文献
8.
The reason for obduction, or tectonic transport of oceanic lithosphere onto continents, is investigated by two‐dimensional thermo‐mechanical numerical modelling based on the geology of the Anatolia–Lesser Caucasus ophiolites. Heating of the oceanic domain and extension induced by far‐field plate kinematics appear to be essential for the obduction of ~80‐Ma‐old oceanic crust over distances exceeding 200 km. Heating of the oceanic lithosphere by mantle upwelling is evidenced by a thick alkaline volcanic series emplaced on top of the oceanic crust 10–20 Ma before obduction, at the onset of Africa–Eurasia convergence. Regional heating reduced the negative buoyancy and strength of the magmatically old lithosphere. Extension facilitated the propagation of obduction by reducing the mantle lithosphere thickness, which led to the exhumation of eclogite‐free continental crust previously underthrusted beneath the ophiolites. This extensional event is ascribed to far‐field plate kinematics resulting from renewed Neotethys oceanic subduction beneath Eurasia. 相似文献
9.
Petrological evidence for stepwise accretion of metamorphic soles during subduction infancy (Semail ophiolite,Oman and UAE) 
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下载免费PDF全文 Mathieu Soret Philippe Agard Benoît Dubacq Alexis Plunder Philippe Yamato 《Journal of Metamorphic Geology》2017,35(9):1051-1080
Metamorphic soles are tectonic slices welded beneath most large‐scale ophiolites. These slivers of oceanic crust metamorphosed up to granulite facies conditions are interpreted as forming during the first million years of intraoceanic subduction following heat transfer from the incipient mantle wedge towards the top of the subducting plate. This study reappraises the formation of metamorphic soles through detailed field and petrological work on three key sections from the Semail ophiolite (Oman and United Arab Emirates). Based on thermobarometry and thermodynamic modelling, it is shown that metamorphic soles do not record a continuous temperature gradient, as expected from simple heating by the upper plate or by shear heating as proposed in previous studies. The upper, high‐T metamorphic sole is subdivided in at least two units, testifying to the stepwise formation, detachment and accretion of successive slices from the down‐going slab to the mylonitic base of the ophiolite. Estimated peak pressure–temperature conditions through the metamorphic sole, from top to bottom, are 850°C and 1 GPa, 725°C and 0.8 GPa and 530°C and 0.5 GPa. These estimates appear constant within each unit but differing between units by 100–200°C and ~0.2 GPa. Despite being separated by hundreds of kilometres below the Semail ophiolite and having contrasting locations with respect to the ridge axis position, metamorphic soles show no evidence for significant petrological variations along strike. These constraints allow us to refine the tectonic–petrological model for the genesis of metamorphic soles, formed via the stepwise stacking of several homogeneous slivers of oceanic crust and its sedimentary cover. Metamorphic soles result not so much from downward heat transfer (ironing effect) as from progressive metamorphism during strain localization and cooling of the plate interface. The successive thrusts originate from rheological contrasts between the sole, initially the top of the subducting slab, and the peridotite above as the plate interface progressively cools. These findings have implications for the thickness, the scale and the coupling state at the plate interface during the early history of subduction/obduction systems. 相似文献
10.
Hydrous partial melting within the lower oceanic crust 总被引：1，自引：0，他引：1
We studied more than 60 oceanic gabbros from the recent oceanic crust and from ophiolites (East Pacific Rise, Mid-Atlantic Ridge, Southwest Indian Ridge, Oman ophiolite) by scanning electron microscopy and found in nearly all samples microstructures suggesting that hydrous partial melting reactions proceeded. The characteristic paragenesis consists of orthopyroxene and pargasite rimming olivine and clinopyroxene primocrysts in intimate contact with neoblastic plagioclase strongly enriched in anorthite. This is in agreement with recent water-saturated melting experiments on a variety of natural gabbros between 900 and 1000 °C. The observed microtextures in the natural gabbros imply the propagation of water-rich fluids on grain boundaries in a ductile regime causing hydrous partial melting. Thus, this type of hydrothermal activity proceeds within the deep oceanic crust at very high temperatures (900–1000 °C) without a crack system, a prerequisite in current models for enabling hydrothermal circulation. 相似文献
11.
A recent re-evaluation of the Late Mesozoic and Cenozoic sea-floor spreading data in the eastern Pacific has allowed us to make a new interpretation of the timing and sequence of the tectonic events which produced the present configuration of the plates (Whitman and Harrison, 1981; Whitman, 1981). Rotation parameters specifying the relative motion between all pairs of plates in the ocean basin have been calculated from the best fit of oceanic magnetic anomalies, with additional input from bathymetry and crustal ages of the Deep Sea Drilling Project sites. The rotation parameters for the relative motion between the Pacific and Antarctic plates are taken from Weissel et al. (1977) and the continental rotation parameters are from Barron et al. (1981).Plate motions have been determined back to 74 Ma. This time marks the initiation of spreading at the Pacific-Antarctic Ridge which caused the separation of the Campbell Plateau from Antarctica (Barron et al., 1981). Thus, this time is the earliest fix on the position of the Pacific plate relative to the continents surrounding the Pacific Ocean basin using sea-floor spreading. Since it is not possible to derive quantitative information about the relative motion between two plates separated by a trench, all rotations for the oceanic plates of the Pacific basin have been calculated relative to the Pacific plate and then relative to North America through the plate circuit: Pacific-Antarctica-Africa-North AmericaSince we also know the relative position of North America with respect to the other continents, we can show the relative position of the Pacific plate and the other oceanic plates with respect to all of the continental plates surrounding the Pacific Ocean basin. 相似文献
12.
John A. Katili 《Tectonophysics》1978,45(4):289-322
Sulawesi with its peculiar K-shaped pattern is situated in an area where the Eurasian, Indian—Australian and Pacific plates interact and collide.Complex geological processess in this area resulted in the transformation of a normal island-arc structure into an inverted one, deformation of an already tectonized belt, sweeping of fragments against unrelated terrain, thrusting of oceanic and mantle material over the island arc, closing of deep-sea basins behind the arc, trapping of old oceanic crust caused by the rolling up of an island arc, formation of a marginal basin by the spreading of the sea floor behind the arc, development of small subduction zones with reverse polarities etc.Small deep-sea basins surrounding Sulawesi such as the Gulf of Bone and the Gulf of Gorontalo originally formed the arc—trench gap of the Sulawesi island arc.The Banda Sea is considered as an oceanic crust trapped by the bending of the east—west trending Banda arc due to the northward drift of Australia combined with the westward movement of the Pacific plate. Similarly the Sulawesi Sea consists of an old Pacific crust trapped by the westward bending of the Sulawesi island arc, caused by the spearheading westward thrust along the Sorong transform-fault system, in which later a minor spreading center became active in its central part. The Molucca Sea comprises tectonic mélange in which presumably a small spreading center developed between the two colliding arcs of northern Sulawesi and western Halmahera. While the Benioff zones dip under the northern Sulawesi and Halmahera arcs in normal fashion, the mélange thrusts over them. The Strait of Makassar is a marginal basin which was brought into existence by the spreading of the sea floor between Kalimantan and Sulawesi.The evolution of Sulawesi started in Miocene time or even earlier when 800 km east of Kalimantan a north—south trending east-facing island arc came into existence, originating from a spreading center located in the Pacific Ocean. Volcanism and plutonism accompanied this subduction process.Collision between Sulawesi and the Australian—New Guinea plate which occurred in early Pliocene time severely transformed Sulawesi into an island with its convex side turned towards the continent, at the same time causing obduction of ophiolite in the eastern arc of this island.The movement of the Pacific plate continued and gradually pushed Sulawesi towards the Asian continent, resulting in the closing of the sea between Kalimantan and Sulawesi islands separated by small straits and deep seas resembling the complicated pattern of the Philippine Archipelago, in which the original double island-arc structure can no longer be recognized. 相似文献
13.
北补连蛇绿岩的特征,形成环境及其构造意义 总被引：23，自引：4，他引：23
文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产生，形成在弧后和岛弧环境，北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带，部分蛇绿岩之上整合产出一套沉积一火山岩系，称为蛇绿岩的上覆岩系，指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义，还讨论了北祁连早古生代板块构造格局，认为 相似文献
14.
蛇绿岩侵位机制是板块构造理论中一直没有得到合理阐释的科学问题,制约了许多次级问题的解决。本文综述了已发表的关键资料和地质观察,提出了一个新的分析模型。蛇绿岩带的长距离延伸表明其形成过程与板块汇聚过程紧密相关;冈底斯岩浆弧的两期弧岩浆活动暗示汇聚板块边缘的构造性质曾经发生过转换;前人报道的玻安岩缺乏充分的地质学、岩石学和矿物学约束;强还原晶体群的普遍性暗示蛇绿岩侵位过程与大规模流体活动有关。据此,本文提出了一个由流体协助的蛇绿岩侵位模型,认为俯冲板块回卷、断离、流体-岩石圈相互作用、大洋岩石圈穹隆等过程是蛇绿岩侵位的基本控制因素。 相似文献
15.
北祁连蛇绿岩的特征、形成环境及其构造意义 总被引：58，自引：1，他引：58
文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产出，形成在弧后和岛弧环境。北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带。部分蛇绿岩之上整合产出一套沉积－火山岩系，称为蛇绿岩的上覆岩系。指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义。还讨论了北祁连早古生代板块构造格局，认为北祁连洋盆属于古亚洲洋的一部分，可能曾经是一个较大规模的洋盆。献中通常把它当成增生或俯冲杂岩带的一部分来看待〔１３，１６－１７〕；大岔大坂蛇绿岩带，其向两侧的延伸情况不清楚；九个泉（或塔墩沟）蛇绿岩带，向东可连到景泰县老虎山蛇绿岩，有人认为，向西可与榆树沟蛇绿岩相连〔２０〕。早先认为，北祁连存在新元古代、中寒武和早－中奥陶世三个时代的蛇绿岩〔２，１１〕，经过多年研究，目前大多数同意蛇绿岩主要是晚寒武－奥陶纪的〔１３，１６〕。图１北祁连早古生代蛇绿岩分布图１．前寒武纪基底；２．俯冲杂岩带；３．蛇绿岩。图中数字：１．九个泉；２．大岔大坂；３．边马沟；４．玉石沟；５．小八宝；６．百经寺；７．老虎山；８．榆树沟山２北祁连几 相似文献
16.
《International Geology Review》2012,54(5):437-447
Subduction-zone magmatism became extensive along the west coast of South America during the Ordovician, soon after Gondwana was assembled. During the remainder of the Paleozoic and the early Mesozoic, eastward subduction of the Farallon plate led to emplacement of a succession of granitic and volcanic rocks. During the Cretaceous, when South America broke away from Africa and began moving independently toward the Pacific Basin, the resulting opposite motions of the South American and Farallon plates toward the subduction zone caused vigorous tectonic mountain building. But by the Oligocene, South America had advanced more than 2000 km beyond the position of the Cretaceous subduction zone's root in the lower mantle. The South American plate, moving westward over the subducting plate, pushed down and flattened the curved top of the subducting slab, as indicated by today's flattened earthquake zone under South America. I hypothesize that this flattening increased the subducting slab's resistance with the underlying lower mantle. Crustal deformation slowed, and the mountains built during the Cretaceous and later were eroded to a peneplane. During the Oligocene, about 25 Ma, the Farallon plate broke into the Cocos and Nazca plates, and I suggest that along the west coast of South America a shear at a slope of about 30° cut through the subducting slab. The oceanic (Nazca) part of the slab then entered the lower mantle below the Andes with a steeper dip than before. As the newly sheared obtuse upper corner of the Nazca plate pushed eastward and downward, it buckled the rigid edge of the continent and began the folding and thrusting of the Andean (Quechua) orogeny. The orogeny continues, but earthquake foci indicate that as South America continues to move westward, the subduction zone once again is flattening; in the future we can expect the Nazca slab to shear once more and its new wedge-shaped end to enter the lower mantle again. 相似文献
17.
R.S. Thorpe 《Tectonophysics》1977,40(3-4):T19-T26
The Mexican Volcanic Belt of active, mainly andesite volcanoes extends from the Pacific coast, through central Mexico, to the Caribbean coast. The setting of the Belt is linked with subduction of the oceanic Cocos plate below continental Mexico. The eastern-most volcano in the Belt is part of the Tuxtla volcanic area on the Caribbean coast. Volcanics from this area belong to a picrite basalt—basanitoid-alkali basalt—hawaiite association, in contrast to the calc-alkaline association of the remainder of the Volcanic Belt, and are linked with lithospheric fracturing in the tectonic setting of a destructive-type continental plate margin. 相似文献
18.
The outer arc of the costa rican orogen (oceanic basement complexes of the Nicoya and Santa Elena Peninsulas) 总被引：1，自引：0，他引：1
J. de Boer 《Tectonophysics》1979,56(3-4)
The basement of the Costa Rican outer arc consists of two major complexes. The older is composed of peridotite-serpentinite, pillow lava and radiolarite; the younger is made up of gabbro-diorite, pillow lava, pyroclastic rocks and siliceous limestone.The observational data are interpreted as follows. The older pillow lavas are believed to be oceanic crust generated along the north-south-spreading Carnegie Ridge during the late Coniacian. The younger lavas flowed from fissures along a west-northwest-trending volcanic belt (Culebra arc) which developed in this crust during early to middle Campanian time, when it collided with the Chortis block. Paleomagnetic evidence suggests that the older sequence originated on the Southern Hemisphere, and the younger in the Northern.During the Paleocene, the crust fragmented and separated into the Caribbean and Cocos plates, probably as a result of the outer arc escaping the tectonic influence of the Carnegie Ridge and entering that of the ancestral East Pacific Rise. This fragmentation resulted in the formation of two parallel volcanic belts (San Antonio and Cachimbas arcs) in the inner deep (Tempisque Valley), which remained active throughout the Eocene. It is postulated that subduction of the Cocos beneath the Caribbean plate was initiated during Oligocene time and resulted in the formation of yet another volcanic belt (Tilarán-Talamanca arc). The outer arc was uplifted, folded, and thrust south westward. The resulting pattern shows a gradual clockwise rotation west to northwest, and north-astward migration of the volcanic arcs through time. Aeromagnetic and tectonic data indicate that differential uplift and later gravitational décollement of the sedimentary rock blanket characterize the tectonic deformation of singular volcanic belts, and that tectonic overprinting is usually restricted to one major phase. 相似文献
19.
20.
The Tertiary Mineoka ophiolite occurs in a fault zone at the intersection of the Honshu and Izu forearcs in central Japan and displays structural evidence for three major phases of deformation: normal and oblique-slip faults and hydrothermal veins formed during the seafloor spreading evolution of the ophiolite at a ridge-transform fault intersection. These structures may represent repeated changes in differential stress and pore-fluid pressures during their formation. The second series of deformation is characterized by oblique thrust faults with Riedel shears and no significant mineral veining, and is interpreted to have resulted from transpressional dextral faulting during the obduction of the ophiolite through oblique convergence and tectonic accretion. This deformation occurred at the NW corner of a TTT-type (trench–trench–trench) triple junction in the NW Pacific rim before the middle Miocene. The third series of deformation of the ophiolite is marked by contractional and oblique shear zones, Riedel shears, and thrust faults that crosscut and offset earlier structures, and that give the Mineoka fault zone its lenticular (phacoidal) fabric at all scales. This deformation phase was associated with the establishment and the southward migration of the TTT Boso triple junction and with the kinematics of oblique subduction and forearc sliver fault development. The composite Mineoka ophiolite hence displays rocks and structures that evolved during its complex geodynamic history involving seafloor spreading, tectonic accretion, and triple junction evolution in the NW Pacific Rim. 相似文献