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1.
The Taitao ophiolite of southern Chile lies 10 km from the buried extension of the Peru-Chile trench, and less than 50 km from the present position of the Nazca/South America/Antarctica triple junction. Plio-Pleistocene radiometric and paleontologic ages indicate its formation during ridge subduction, and an ultramafic rock, gabbro, sheeted dike, volcanic and sedimentary rock psuedostratigraphy suggests formation by typical accretionary processes for oceanic lithosphere. Yet major and trace element data show that mafic dikes and volcanic units are transitional from MORB to IAT, and there are abundant silicic volcanic units of calc-alkaline character that have high LIL element and light REE concentrations relative to oceanic plagiogranites. Sr and Nd isotopic data are consistent with that of modern oceanic suites, even though having a greater internal variability. Silicic volcanic units show the more enriched Sr and depleted Nd isotopic ratios relative to dike and gabbro samples. In addition to chemical distinctions, paleobathymetric data support a shallow water origin for some of the upper volcanic units and, assuming local compensation, suggest crustal thicknesses of continental proportion. In the vicinity of the Taitao ophiolite, and extending some 40 km landward of the plate margin, are a series of silicic stocks, sills, and plutons that were intruded into the forearc at the time of ridge collision and ophiolite generation. These calc-alkaline I-type granitoids are light REE enriched and have Sr and Nd isotopic compositions similar to those of the main volcanic chain 200 km landward. Chemically, some of the silicic intrusions are indistinguishable from volcanic units of the ophiolite. In general, major, trace, REE, and isotopic variations of both the ophiolite and the distributed intrusions are atypical of simple fractionation trends for basaltic liquids. Intermediate to silicic units lie along mixing hyperbolae between Taitao gabbro and either forearc sediment or metamorphic basement on a Nd---Sr correlation diagram, and these two crustal components support, respectively, either a 10–25% or 5–10% assimilation. Shutdown of magmatism, and therefore probably partial melting as well, appears to occur within 40 km of the trench, roughly spanning the depth interval for the disappearance of the plagioclase-lherzolite stability field as the zone of mantle upwelling is overridden by an increasing thickness of continental lithosphere. A deeper and more landward absence of partial melt related to the subducted ridge is supported by the correlation of the shutoff and re-initiation of arc volcanism over the northern and southern trailing edges of the postulated subcontinental asthenospheric window. Here, as well as elsewhere in the circum-Pacific, the general restriction of magmatism related to ridge subduction to near-trench settings supports a shallow (0 to 15 km) shutoff mechanism for adiabatic decompressive melting and a rather abrupt return to single-phase (solid) convective rise of mantle into an evolving asthenospheric window. 相似文献
2.
新疆西准噶尔达拉布特蛇绿岩E-MORB型镁铁质岩的地球化学、年代学及其地质意义 总被引：28，自引：12，他引：16
新疆西准噶尔地区是古生代经过俯冲-增生形成的复合造山带,该地区分布有多条蛇绿岩带,其中之一的西准噶尔达拉布特蛇绿岩被认为是最大的一条蛇绿岩带,可能代表了古亚洲洋壳的残余。本文的资料显示蛇绿岩带内的镁铁质岩呈现出N-MORB、E-MORB和似OIB的地球化学特征,通过对阿克巴斯套岩体中的浅色辉长岩LA-ICP-MS锆石年龄测定,获得达拉布特蛇绿岩E-MORB型镁铁质岩的年龄为302±1.7Ma。鉴于达拉布特蛇绿岩中E-MORB和似OIB型镁铁质岩成因的复杂性,结合前人研究成果,对辉长岩锆石U-Pb年龄所代表的意义存在两种可能性：（1）E-MORB型和似OIB型镁铁质岩可能是弧后盆地扩张后期的产物,代表蛇绿岩的年龄,其表明西准噶尔地区可能晚石炭纪还有洋盆存在;（2）E-MORB型镁铁质岩是蛇绿岩消亡阶段由于扩张脊和俯冲带碰撞作用而形成的弧前海山,形成时代晚于达拉布特主体蛇绿岩,但其成因与蛇绿岩的演化密切相关。本文侵向于第二种可能性,认为新疆北部晚石炭-早二叠可能仍存在活动陆缘,俯冲作用仍然存在,扩张脊俯冲形成的板片窗效应导致地幔楔、俯冲板片和沉积物等熔融促使基性岩浆向长英质酸性岩浆转变,从而引发了二叠纪大规模玄武质岩浆底侵,导致了该时期的构造-岩浆-成矿-造山作用的发生。 相似文献
3.
An active oceanic spreading ridge is being subducted beneath the South American continent at the Chile Triple Junction. Mass balance estimations to characterize temporal and spatial variations in the frontal accretion, or underplating and subduction of sediments since the Late Miocene, were made using seismic and drill-hole data. At 200 km north of the triple junction, almost 80% of the sediment on the downgoing Nazca plate are subducted. Sediment subduction rate decreases towards the triple junction because of a low in sedimentation rates as the flank of the spreading ridge approaches the trench. At the triple junction, the forearc is almost completely destroyed by spreading ridge collision and subduction erosion. Less than 12% of the available sedimentary input is accreted. South of the triple junction, where the spreading ridge passed 6 Ma ago, a large fraction (>60%) of the sediment on the incoming Antarctic plate has been scraped off and was frontally accreted to the Chile forearc. Spreading ridge subduction leaves a distinctive geological fingerprint, and has a large impact on the mass balance of the subduction zone. However, the high rates of change in the process may make this fingerprint hard to detect in fossil convergent orogens. In the ridge collision zone the sediment supplied to the trench, and the amount of sediment subducted, show strong and distinctive variations on a 1- to 5-million-year time scale. On a 10-million-year time scale, sediment subduction to the Earth's mantle is reduced by spreading ridge collision, caused by the need of the overriding forearc to regain a low angle of taper by frontal accretion. 相似文献
4.
An active oceanic spreading ridge is being subducted beneath the South American continent at the Chile Triple Junction. This process has played a major part in the evolution of most of the continental margins that border the Pacific Ocean basin. A combination of high resolution swath bathymetric maps, seismic reflection profiles and drillhole and core data from five sites drilled during Ocean Drilling Program (ODP) Leg 141 provide important data that define the tectonic, structural and stratigraphic effects of this modern example of spreading ridge subduction.A change from subduction accretion to subduction erosion occurs along-strike of the South American forearc. This change is prominently expressed by normal faulting, forearc subsidence, oversteepening of topographic slopes and intensive sedimentary mass wasting, overprinted on older signatures of sediment accretion, overthrusting and uplift processes in the forearc. Data from drill sites north of the triple junction (Sites 859–861) show that after an important phase of forearc building in the early to late Pliocene, subduction accretion had ceased in the late Pliocene. Since that time sediment on the downgoing oceanic Nazca plate has been subducted. Site 863 was drilled into the forearc in the immediate vicinity of the triple junction above the subducted spreading ridge axis. Here, thick and intensely folded and faulted trench slope sediments of Pleistocene age are currently involved in the frontal deformation of the forearc. Early faults with thrust and reverse kinematics are overprinted by later normal faults.The Chile Triple Junction is also the site of apparent ophiolite emplacement into the South American forearc. Drilling at Site 862 on the Taitao Ridge revealed an offshore volcanic sequence of Plio-Pleistocene age associated with the Taitao Fracture Zone, adjacent to exposures of the Pliocene-aged Taitao ophiolite onshore. Despite the large-scale loss of material from the forearc at the triple junction, ophiolite emplacement produces a large topographic promontory in the forearc immediately after ridge subduction, and represents the first stage of forearc rebuilding. 相似文献
5.
Mesozoic rocks of the Baja California Peninsula form one of the most areally extensive, best-exposed, longest-lived (160 my), least-tectonized and least-metamorphosed convergent-margin basin complexes in the world. This convergent margin shows an evolutionary trend that may be typical of arc systems facing large ocean basins: a progression from highly extensional (phase 1) through mildly extensional (phase 2) to compressional (phase 3) strain regimes. This trend is largely due to the progressively decreasing age of lithosphere that is subducted, which causes a gradual decrease in slab dip angle (and concomitant increase in coupling between lower and upper plates), as well as progressive inboard migration of the arc axis.This paper emphasizes the usefulness of sedimentary and volcanic basin analysis for reconstructing the tectonic evolution of a convergent continental margin. Phase 1 consists of Late Triassic to Late Jurassic oceanic intra-arc to backarc basins that were isolated from continental sediment sources. New, progressively widening basins were created by arc rifting and sea floor spreading, and these were largely filled with progradational backarc arc-apron deposits that record the growth of adjacent volcanoes up to and above sea level. Inboard migration of the backarc spreading center ultimately results in renewed arc rifting, producing an influx of silicic pyroclastics to the backarc basin. Rifting succeeds in conversion of the active backarc basin into a remnant backarc basin, which is blanketed by epiclastic sands.Phase 1 oceanic arc–backarc terranes were amalgamated by Late Jurassic sinistral strike slip faults. They form the forearc substrate for phase 2, indicating inboard migration of the arc axis due to decrease in slab dip. Phase 2 consists of Early Cretaceous extensional fringing arc basins adjacent to a continent. Phase 2 forearc basins consist of grabens that stepped downward toward the trench, filled with coarse-grained slope apron deposits. Phase 2 intra-arc basins show a cycle of (1) arc extension, characterized by intermediate to silicic explosive and effusive volcanism, culminating in caldera-forming silicic ignimbrite eruptions, followed by (2) arc rifting, characterized by widespread dike swarms and extensive mafic lavas and hyaloclastites. This extensional-rifting cycle was followed by mid-Cretaceous backarc basin closure and thrusting of the fringing arc beneath the edge of the continent, caused by a decrease in slab dip as well as a possible increase in convergence rate.Phase 2 fringing arc terranes form the substrate for phase 3, which consists of a Late Cretaceous high-standing, compressional continental arc that migrated inboard with time. Strongly coupled subduction resulted in accretion of blueschist metamorphic rocks, with development of a broad residual forearc basin behind the growing accretionary wedge, and development of extensional forearc (trench–slope) basins atop the gravitationally collapsing accretionary wedge. Inboard of this, ongoing phase 3 strongly coupled subduction, together with oblique convergence, resulted in development of forearc strike-slip basins upon arc basement.The modern Earth is strongly biased toward long-lived arc–trench systems, which are compressional; therefore, evolutionary models for convergent margins must be constructed from well-preserved ancient examples like Baja California. This convergent margin is typical of many others, where the early to middle stages of convergence (phases 1 and 2) create nonsubductable arc–ophiolite terranes (and their basin fills) in the upper plate. These become accreted to the continental margin in the late stage of convergence (phase 3), resulting in significant continental growth. 相似文献
6.
The subduction of spreading ridges creates a special geodynamic setting distinguished by the interference of convergent and
divergent boundaries between lithospheric plates and their long-term interaction accompanied by the formation of characteristic
geological complexes and structures. The available data on subduction of the contemporary Chile Ridge make it possible to
reconstruct such settings in the geological past. The subduction of the spreading ridge leads to uplift of the continental
margin, cut off the accretionary wedge by means of tectonic erosion, emplacement of a fold-thrust structure and longitudinal
strike-slip faults, and creates settings favorable for obduction of the young oceanic lithosphere. A lithospheric window expressed
in geological and geophysical features opens beneath the continental margin at the continuation of the ridge axis. The subduction-related
volcanic activity ceases above this window, giving way to specific proximal magmatism close to the boundary with the ocean and distal magmatism at a distance from this boundary. The proximal bimodal magmatism was related to the sources of tholeiitic basalts
characteristic of the ridge involved in subduction and to the partial melting of its oceanic crust and sediments. The distal
basaltic magmatism is a product of melting of the fertile oceanic asthenosphere ascending through the lithospheric window
with subsequent transformation of magma in the mantle wedge and the continental crust. The use of the Chilean tectonotype
for paleoreconstructions is limited by the diverse settings of ridge subduction. The Paleogene magmatism at the Pacific margin
of Alaska, where the kinematics of subduction was close to the Chilean subduction, is similar to the proximal igneous rocks
of Chile in composition and zoning, retaining some geological differences. Another aspect of the paleoreconstruction is discussed
on the basis of Jurassic and Cretaceous granitoids of the Ekonai Terrane of the Anadyr-Koryak System and terranes of southern
Alaska. These localities are known for a special, accretionary type of granitoids in the forearc region related to anatectic
magma formation without participation of the plunging ridge. Proceeding from comparison with the Chilean tectonotype, the
criteria for the identification of granitoids varying in their origin are considered. The effect of subducting ridges on continental
margins changed over geologic time and was subject to the rhythm of supercontinental cycles. 相似文献
7.
Gondwana breakup via double-saloon-door rifting and seafloor spreading in a backarc basin during subduction rollback 总被引：1，自引：0，他引：1
A model has been developed where two arc-parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback. The resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double-saloon-doors about their hinges. As movement proceeds and the two terranes rotate, a gap begins to extend between them, where a third rift initiates and propagates in the opposite direction to subduction rollback. Observations from the Oligocene to Recent Western Mediterranean, the Miocene to Recent Carpathians, the Miocene to Recent Aegean and the Oligocene to Recent Caribbean point to a two-stage process. Initially, pairs of terranes comprising a pre-existing retro-arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents. Terrane docking reduces the width of the subduction zone, leading to a second phase during which subduction to strike-slip transitions initiate. The clockwise rotated terrane is caught up in a dextral strike-slip zone, whereas the counterclockwise rotated terrane is entrained in a sinistral strike-slip fault system. The likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline.By analogy with the above model, a revised five-stage Early Jurassic to Early Cretaceous Gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the Weddell Sea area. Seven features are considered diagnostic of double-saloon-door rifting and seafloor spreading:
- i) earliest movement involves clockwise and counterclockwise rotations of the Falkland Islands Block and the Ellsworth Whitmore Terrane respectively;
- ii) terranes comprise areas of a pre-existing retro-arc fold thrust belt (the Permo-Triassic Gondwanide Orogeny) attached to an accretionary wedge/magmatic arc; the Falklands Islands Block is initially attached to Southern Patagonia/West Antarctic Peninsula, while the Ellsworth Whitmore Terrane is combined with the Thurston Island Block;
- iii) paleogeographies demonstrate rifting and extension in a backarc environment relative to a Pacific margin subduction zone/accretionary wedge where simultaneous crustal shortening occurs;
- iv) a ridge jump towards the subduction zone from east of the Falkland Islands to the Rocas Verdes Basin evinces subduction rollback;
- v) this ridge jump combined with backarc extension isolated an area of thicker continental crust — The Falkland Islands Block;
- vi) well-documented EW oriented seafloor spreading anomalies in the Weddell Sea are perpendicular to the subduction zone and propagate in the opposite direction to rollback;
- vii) the dextral strike-slip Gastre and sub-parallel faults form one boundary of the Gondwana subduction rollback, whereas the other boundary may be formed by inferred sinistral strike-slip motion between a combined Thurston Island/Ellsworth Whitmore Terrane and Marie Byrd Land/East Antarctica.
Keywords: Gondwana breakup; Double-saloon-door seafloor spreading; Plate tectonics; Backarc basin; Subduction rollback; Opposite rotations of terranes 相似文献
8.
The continental growth mechanism of the Altaids in Central Asia is still in controversy between models of continuous subduction–accretion versus punctuated accretion by closure of multiple oceanic basins. The Beishan orogenic belt, located in the southern Altaids, is a natural laboratory to address this controversy. Key questions that are heavily debated are: the closure time and subduction polarity of former oceans, the emplacement time of ophiolites, and the styles of accretion and collision. This paper reports new structural data, U- Pb and Ar–Ar ages from the eastern Beishan orogen that provide information on the accretion process and tectonic affiliation of various terranes. Our geochronological and structural results show that the younging direction of accretion was northwards and the subduction zone dipped southwards under the northern margin of the Shuangyingshan micro-continent. This long-lived and continuous accretion process formed the Hanshan accretionary prism. Our field investigations show that the emplacement of the Xiaohuangshan ophiolite was controlled by oceanic crust subduction beneath the forearc accretionary prism of the Shuangyingshan–Mazongshan composite arc to the south. Moreover, we address the age and terrane affiliation of lithologies in the eastern Beishan orogen through detrital zircon geochronology of meta-sedimentary rocks. We provide new information on the ages, subduction polarities, and affiliation of constituent structural units, as well as a new model of tectonic evolution of the eastern Beishan orogen. The accretionary processes and crustal growth of Central Asia were the result of multiple sequences of accretion and collision of manifold terranes. 相似文献
9.
Subduction of active spreading ridges most likely occurs throughout Earth's history. Interaction or collision between spreading center and trench, with the active spreading ridge downgoing and shallowly being buried in subduction zone, results in low-pressure but high-temperature near-trench magmatism in the forearc and accretionary prism setting. The Central Asian region, a complex orogenic belt created during the evolution and closure of the Paleo-Asian Ocean (PAO) at ~ 1000–300 Ma, provides an ideal place to study the subduction of PAO spreading ridges beneath ancient continental margins. It had been suggested that the low-pressure and high-temperature mafic and intermediate to felsic magmas from the Karamaili ophiolite (KO) in the NE corner of the Junggar basin (NW China) in Central Asia were likely produced by ridge subduction (Liu et al., 2007). In this paper, we combine our new geochemical data with previous results to show that the geochemical characteristics of the bulk of KO mafic rocks range from arc basalt-like to mid-ocean ridge basalt-like and ocean island basalt-like. Their trace element patterns range from depleted to enriched in highly incompatible elements, but depleted in Nb and Ta, indicating a subduction-influenced origin. The KO intermediate to felsic rocks are calc-alkaline and boninitic in composition and have trace element signatures similar to the associated mafic rocks. The low Nb/Ta ratios of some of the mafic rocks and boninitic character of some of the intermediate to felsic rocks reflect a highly depleted source, perhaps due to prior backarc magmatism. Major and trace element models indicate complex fractional crystallization histories of parental KO magmas to generate both the mafic and intermediate to felsic rocks, but in general, crystal fractionation occurred at 1000 to 1200 °C and moderate to low (0.5 kbar to 10 kbar) pressure or < 23 km depth. We conclude that the KO was formed in a forearc region of a subduction system that experienced ridge subduction. 相似文献
10.
俯冲带地幔演化与岩浆作用是地球各固体圈层之间发生物质和能量交换的重要地质过程.西太平洋雅浦海沟因其极短的沟-弧距离和洋脊碰撞等独特的地质构造特征成为研究复杂条件下俯冲带演化的理想场所.为了探究雅浦海沟地幔演化与岩浆作用,本文将前人对雅浦海沟火成岩的研究数据进行整合,分析了雅浦海沟火成岩的成因,并根据火成岩形成的制约条件,对卡罗琳板块俯冲到菲律宾海板块的地幔演化与岩浆作用过程进行了讨论.结果显示雅浦海沟火成岩均具有与俯冲相关火成岩的典型特征.橄榄岩地球化学特征指示雅浦海沟地幔熔融程度为20%~25%,地幔在部分熔融过程中受到了流体与熔体的双重交代作用.Re-Os同位素特征指示雅浦海沟地幔中存在约1.16 Ga非常古老的残余地幔,表明地幔可能经历过多期熔融事件,从而导致雅浦海沟地幔非常亏损.雅浦岛弧成因至今仍存争议,主要包括:(1)现今雅浦岛弧为帕里希维拉海盆洋壳的一部分,在中新世因卡罗琳洋脊的碰撞导致帕里希维拉海盆洋壳逆冲到原雅浦岛弧之上.(2)雅浦岛弧在不同构造时期经历过多期岛弧岩浆作用,包括俯冲初始阶段(~52 Ma)的弧前玄武岩、俯冲开始后的岛弧玄武岩(~25 Ma)、与卡罗琳洋脊碰撞(21 Ma)后的岛弧拉斑玄武岩(7~11 Ma).其中7~11 Ma的岛弧拉斑玄武岩指示雅浦岛弧岩浆活动并未因卡罗琳洋脊的碰撞完全停止,很有可能在晚中新世短暂恢复活动. 相似文献
11.
中亚大陆古生代构造形成及演化 总被引：8，自引：3，他引：8
西伯利亚、塔里木及哈萨克斯坦诸古板块中的微陆和地体构造了中亚十分复杂的拼贴构造图案。古生代时，南天巴准洋－阿萨伊锡弧沟弧系和额尔齐斯洋－成田弧沟弧系构成了哈萨克斯坦板块的原型，塔里木板块陆壳块体在泥盆纪相对于阿萨伊锡岛弧的左行低角度斜俯冲和碰撞，造成此弧的解体、走滑堆叠和山弯构造。与此同时，成田岛弧南北两侧分别受到南天巴准洋和额尔齐斯洋的俯冲。在晚古生代晚期这两个沟弧系演变为哈萨克斯坦板块的基本构 相似文献
12.
C. G. Murray 《Australian Journal of Earth Sciences》2013,60(7):899-925
The Princhester Serpentinite of the Marlborough terrane of the northern New England Orogen is a remnant of upper mantle peridotite that was partially melted at an oceanic spreading centre at 562 Ma, and subsequently interacted with Late Devonian island arc basalts in an intra-oceanic supra-subduction zone (SSZ) setting. The full range of rare-earth element (REE) contents, including U-shaped patterns, can be explained by a single process of reaction of partially melted, depleted peridotite with Late Devonian calc-alkaline and island arc tholeiite magmas by equilibrium porous flow, fractionating the REE by a chromatographic column effect. The Northumberland Serpentinite on South Island of the Percy Group has similar REE and high field strength element (HFSE) contents to the most depleted samples of the Princhester Serpentinite, supporting a common origin. However, spinel compositions suggest that the Northumberland Serpentinite interacted with boninitic magmas. The REE and mineral geochemistry indicates that the Princhester and Northumberland Serpentinites both represent part of the mantle component of a disrupted SSZ ophiolite. The ophiolite is considered to have formed above an east-dipping subduction zone, based on the geochemistry of Devonian island arc basalts between Mt Morgan and Monto, which include compositions identical to dykes and gabbroic blocks within the Princhester Serpentinite. Blockage of the subduction zone by collision with the Australian continent during the Late Devonian led to slab breakoff and the reversal of subduction direction, trapping the Late Devonian ophiolite in a forearc position. Its location, in a forearc setting above a growing accretionary wedge, conforms to the definition of a Cordilleran-type ophiolite. This interpretation is consistent with current views that most ophiolites are formed from young, hot and thin oceanic lithosphere at forearc, intra-arc and backarc spreading centres in a SSZ setting, and that emplacement follows genesis by 10 million years or less. Late Devonian crustal growth may have been widespread in the New England Orogen, because the disrupted ophiolite assemblage of the Yarras complex in the southern New England Orogen is probably of this age. Extensional tectonism at the end of the Carboniferous dismembered the Princhester – Northumberland ophiolite, removed the crustal section, and produced windows of accretionary wedge rocks within the fragmented ophiolite. The Princhester Serpentinite, together with fault slices of metasedimentary rocks, was thrust westward as a flat sheet over folded strata of the Yarrol Forearc Basin by a Late Permian out-of-sequence thrust during the Hunter – Bowen Orogeny, completing the emplacement of the Marlborough terrane. The Princhester and Northumberland Serpentinites could have been displaced by strike-slip movement along the Stanage Fault Zone or an equivalent structure. There is no record in the northern New England Orogen of SSZ ophiolites and volcanic arc deposits of Cambrian age, as exposed along the Peel Fault. Partial melting of the Princhester Serpentinite at an oceanic spreading centre at 562 Ma, recorded by mafic intrusives displaying N-MORB chemistry, was an earlier event that was outboard of any Early Paleozoic subduction zone along the margin of the Australian continent, and cannot be regarded as representing the early history of the New England Orogen. It is possible that the formation of intra-oceanic arcs in latest Silurian and Devonian time was the first tectonic event common to both the southern and northern New England Orogen. 相似文献
13.
青藏高原各地体的地壳-上地幔结构及其东西向的变化特征 总被引：1，自引：0，他引：1
青藏高原是由多个地体拼合而成的,在印度板块向北俯冲的长期作用下,各地体被挤压,地壳缩短,高原隆升。尽管在北北东向挤压作用下发生了高原的近南北向的断裂活动,但各地体本身的结构整体上保持相对稳定,不仅地壳浅部的地层、岩石、古生物保持着各自的特征,而且深部Moho面的变化和岩石圈的特征也是相似的。青藏高原的相距500km以上的2条宽频地震探测剖面的接收函数结果证实:高喜马拉雅地体、特提斯喜马拉雅地体、冈底斯地体、羌塘地体和巴颜喀拉地体在东西方向上保持着相近的速度特征。这充分说明,印度板块向北俯冲与青藏高原碰撞,引发各地体碰撞造山与高原隆升是地壳和岩石圈的整体构造运动,高原各地体,至少高原腹地仍然保持着大致相同的深部结构,Moho面、岩石圈底界面的深度和产状变化不大。 相似文献
14.
15.
青藏高原南部拉萨地体的变质作用与动力学 总被引：3，自引：0，他引：3
拉萨地体位于欧亚板块的最南缘,它在新生代与印度大陆的碰撞形成了青藏高原和喜马拉雅造山带。因此,拉萨地体是揭示青藏高原形成与演化历史的关键之一。拉萨地体中的中、高级变质岩以前被认为是拉萨地体的前寒武纪变质基底。但新近的研究表明,拉萨地体经历了多期和不同类型的变质作用,包括在洋壳俯冲构造体制下发生的新元古代和晚古生代高压变质作用,在陆-陆碰撞环境下发生的早古生代和早中生代中压型变质作用,在洋中脊俯冲过程中发生的晚白垩纪高温/中压变质作用,以及在大陆俯冲带上盘加厚大陆地壳深部发生的两期新生代中压型变质作用。这些变质作用和伴生的岩浆作用表明,拉萨地体经历了从新元古代至新生代的复杂演化过程。(1)北拉萨地体的结晶基底包括新元古代的洋壳岩石,它们很可能是在Rodinia超大陆裂解过程中形成的莫桑比克洋的残余。(2)随着莫桑比克洋的俯冲和东、西冈瓦纳大陆的汇聚,拉萨地体洋壳基底经历了晚新元古代的(～650Ma)的高压变质作用和早古代的(～485Ma)中压型变质作用。这很可能表明北拉萨地体起源于东非造山带的北端。(3)在古特提斯洋向冈瓦纳大陆北缘的俯冲过程中,拉萨地体和羌塘地体经历了中古生代的(～360Ma)岩浆作用。(4)古特提斯洋盆的闭合和南、北拉萨地体的碰撞,导致了晚二叠纪(～260Ma)高压变质带和三叠纪(～220Ma)中压变质带的形成。(5)在新特提斯洋中脊向北的俯冲过程中,拉萨地体经历了晚白垩纪(～90Ma)安第斯型造山作用,形成了高温/中压型变质带和高温的紫苏花岗岩。(6)在早新生代(55～45Ma),印度与欧亚板块的碰撞,导致拉萨地体地壳加厚,形成了中压角闪岩相变质作用和同碰撞岩浆作用。(7)在晚始新世(40～30Ma),随着大陆的继续汇聚,南拉萨地体经历了另一期角闪岩相至麻粒岩相变质作用和深熔作用。拉萨地体的构造演化过程是研究汇聚板块边缘变质作用与动力学的最佳实例。 相似文献
16.
Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth 总被引：50，自引：0，他引：50
Ping Jian Dunyi Liu Alfred Krner Brian F. Windley Yuruo Shi Fuqin Zhang Guanghai Shi Laicheng Miao Wei Zhang Qi Zhang Liqao Zhang Jishun Ren 《Lithos》2008,101(3-4):233-259
We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth. 相似文献
17.
《Gondwana Research》2014,25(1):170-189
The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during Late Eocene (40–30 Ma). (10) During Mesozoic and Cenozoic, two different stages of paired metamorphic belts were formed in the oceanic or continental subduction zones and the middle and lower crust of the hanging wall of the subduction zone. The tectonic imprints from the Lhasa terrane provide excellent examples for understanding metamorphic processes and geodynamics at convergent plate boundaries. 相似文献
18.
Victor A. Ramos 《Geological Journal》2010,45(1):2-25
The analyses of the main parameters controlling the present Chile‐type and Marianas‐type tectonic settings developed along the eastern Pacific region show four different tectonic regimes: (1) a nearly neutral regime in the Oregon subduction zone; (2) major extensional regimes as the Nicaragua subduction zone developed in continental crust; (3) a Marianas setting in the Sandwich subduction zone with ocean floored back‐arc basin with a unique west‐dipping subduction zone and (4) the classic and dominant Chile‐type under compression. The magmatic, structural and sedimentary behaviours of these four settings are discussed to understand the past tectonic regimes in the Mesozoic Andes based on their present geological and tectonic characteristics. The evaluation of the different parameters that governed the past and present tectonic regimes indicates that absolute motion of the upper plate relative to the hotspot frame and the consequent trench roll‐back velocity are the first order parameters that control the deformation. Locally, the influences of the trench fill, linked to the dominant climate in the forearc, and the age of the subducted oceanic crust, have secondary roles. Ridge collisions of seismic and seismic oceanic ridges as well as fracture zone collisions have also a local outcome, and may produce an increase in coupling that reinforces compressional deformation. Local strain variations in the past and present Andes are not related with changes in the relative convergence rate, which is less important than the absolute motion relative to the Pacific hotspot frame, or changes in the thermal state of the upper plate. Changes in the slab dip, mainly those linked to steepening subduction zones, produce significant variations in the thermal state, that are important to generate extreme deformation in the foreland. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
The Stonyford Volcanic Complex: a Forearc Seamount in the Northern California Coast Ranges 总被引：2，自引：0，他引：2
SHERVAIS JOHN W.; SCHUMAN MARCHELL M. ZOGLMAN; HANAN BARRY B. 《Journal of Petrology》2005,46(10):2091-2128
Jurassic age volcanic rocks of the Stonyford volcanic complex(SFVC) comprise three distinct petrological groups based ontheir whole-rock geochemistry: (1) oceanic tholeiites; (2) transitionalalkali basalts and glasses; (3) high-Al, low-Ti tholeiites.Major and trace element, and Sr–Nd–Pb isotopic dataindicate that the oceanic tholeiites formed as low-degree partialmelts of normal mid-ocean ridge basalt (N-MORB)-source asthenospheresimilar in isotope composition to the East Pacific Rise today;the alkalic lavas were derived from an enriched source similarto that of E-MORB. The high-Al, low-Ti lavas resemble second-stagemelts of a depleted MORB-source asthenosphere that formed bymelting spinel lherzolite at low pressures. Trace element systematicsof the high-Al, low-Ti basalts show the influence of an enrichedcomponent, which overprints generally depleted trace elementcharacteristics. Tectonic discrimination diagrams show thatthe oceanic tholeiite and alkali suites are similar to present-daybasalts generated at mid-oceanic ridges. The high-Al, low-Tisuite resembles primitive arc basalts with an enriched, alkalibasalt-like overprint. Isotopic data show the influence of recycledcomponents in all three suites. The SFVC was constructed ona substrate of normal Coast Range ophiolite in an extensionalforearc setting. The close juxtaposition of the MORB-like olivinetholeiites with alkali and high-Al, low-Ti basalts suggestsderivation from a hybrid mantle source region that includedMORB-source asthenosphere, enriched oceanic asthenosphere, andthe depleted supra-subduction zone mantle wedge. We proposethat the SFVC formed in response to collision of a mid-oceanridge spreading center with the Coast Range ophiolite subductionzone. Formation of a slab window beneath the forearc duringcollision allowed the influx of ridge-derived magmas or themantle source of these magmas. Continued melting of the previouslydepleted mantle wedge above the now defunct subduction zoneproduced strongly depleted high-Al, low-Ti basalts that werepartially fertilized with enriched, alkali basalt-type meltsand slab-derived fluids. KEY WORDS: CRO; oceanic basalts; California 相似文献
20.
Early Palaeozoic subduction of the palaeo-Pacific plate and terrane accretion along the palaeomargin of the East Antarctic Craton is well-documented in North Victoria Land, where the Tonalite Belt is a complex of synkinematic intrusions emplaced within the Lanterman–Murchison Shear Zone at the boundary between the Wilson Terrane and the allochthonous Bowers Terrane. Stepwise leaching Pb/Pb and U–Pb studies of titanite separates carried out on two well-foliated samples of tonalites yielded ages of deformation bracketed between 490 and 480 Ma with an isochron age of 480 ±13 Myr. Ar/Ar and K–Ar ages of 477 Myr in the metamorphic rocks of accreted terranes point to fast cooling and uplift after accretion. The new titanite ages, compared with a regional distribution of magmatic and metamorphic ages, indicate an early Ordovician age for terrane collision and amalgamation. As a consequence of collision, subduction shifted to an outward position along the palaeomargin of the East Antarctic Craton. 相似文献