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1.
《Earth》2006,77(3-4):191-233
A Cenozoic tectonic reconstruction is presented for the Southwest Pacific region located east of Australia. The reconstruction is constrained by large geological and geophysical datasets and recalculated rotation parameters for Pacific–Australia and Lord Howe Rise–Pacific relative plate motion. The reconstruction is based on a conceptual tectonic model in which the large-scale structures of the region are manifestations of slab rollback and backarc extension processes. The current paradigm proclaims that the southwestern Pacific plate boundary was a west-dipping subduction boundary only since the Middle Eocene. The new reconstruction provides kinematic evidence that this configuration was already established in the Late Cretaceous and Early Paleogene. From ∼ 82 to ∼ 52 Ma, subduction was primarily accomplished by east and northeast-directed rollback of the Pacific slab, accommodating opening of the New Caledonia, South Loyalty, Coral Sea and Pocklington backarc basins and partly accommodating spreading in the Tasman Sea. The total amount of east-directed rollback of the Pacific slab that took place from ∼ 82 Ma to ∼ 52 Ma is estimated to be at least 1200 km. A large percentage of this rollback accommodated opening of the South Loyalty Basin, a north–south trending backarc basin. It is estimated from kinematic and geological constraints that the east–west width of the basin was at least ∼ 750 km. The South Loyalty and Pocklington backarc basins were subducted in the Eocene to earliest Miocene along the newly formed New Caledonia and Pocklington subduction zones. This culminated in southwestward and southward obduction of ophiolites in New Caledonia, Northland and New Guinea in the latest Eocene to earliest Miocene. It is suggested that the formation of these new subduction zones was triggered by a change in Pacific–Australia relative motion at ∼ 50 Ma. Two additional phases of eastward rollback of the Pacific slab followed, one during opening of the South Fiji Basin and Norfolk Basin in the Oligocene to Early Miocene (up to ∼ 650 km of rollback), and one during opening of the Lau Basin in the latest Miocene to Present (up to ∼ 400 km of rollback). Two new subduction zones formed in the Miocene, the south-dipping Trobriand subduction zone along which the Solomon Sea backarc Basin subducted and the north-dipping New Britain–San Cristobal–New Hebrides subduction zone, along which the Solomon Sea backarc Basin subducted in the west and the North Loyalty–South Fiji backarc Basin and remnants of the South Loyalty–Santa Cruz backarc Basin subducted in the east. Clockwise rollback of the New Hebrides section resulted in formation of the North Fiji Basin. The reconstruction provides explanations for the formation of new subduction zones and for the initiation and termination of opening of the marginal basins by either initiation of subduction of buoyant lithosphere, a change in plate kinematics or slab–mantle interaction. 相似文献
2.
Hudson Bay conceals several fundamental tectonic elements of the North American continent, including most of the ca. 1.9–1.8 Ga Trans-Hudson orogen (THO) and the Paleozoic Hudson Bay basin. Formed due to a collision between two cratons, the THO is similar in scale and tectonic style to the modern Himalayan–Karakorum orogen. During collision, the lobate shape of the indentor (Superior craton) formed an orogenic template that, along with the smaller Sask craton, exerted a persistent influence on the tectonic evolution of the region resulting in anomalous preservation of juvenile Proterozoic crust. Extensive products of 2.72–2.68 Ga and 1.9–1.8 Ga episodes of subduction are preserved, but the spatial scale of corresponding domains increases by roughly an order-of-magnitude (to 1000 km, comparable to modern subduction environments) from the Archean to the Proterozoic. Based on analysis of gravity and magnetic data and published field evidence, we propose a new tectonic model in which Proterozoic crust in the southeastern third of Hudson Bay formed within an oceanic or marginal-basin setting proximal to the Superior craton, whereas the northwestern third is underlain by Archean crust. An intervening central belt truncates the southeastern domains and is interpreted to be a continental magmatic arc.Thick, cold and refractory lithosphere that underlies the Bay is well imaged by surface-wave studies and comprises a large component of the cratonic mantle keel beneath North America. The existence of an unusually thick mantle root indicates that subduction and plate collision during the Trans-Hudson orogeny were ‘root-preserving’ (if not ‘root-forming’) processes. Although the Hudson Bay basin is the largest by surface area of four major intracratonic basins in North America, it is also the shallowest. Available evidence suggests that basin subsidence may have been triggered by eclogitization of lower-crustal material. Compared to other basins of similar age in North America, the relatively stiff lithospheric root may have inhibited subsidence of the Hudson Bay basin. 相似文献
3.
The eastern Coral Sea is a poorly explored area at the north-eastern corner of the Australian Tectonic Plate, where interaction between the Pacific and Australian plate boundaries, and accretion of the world's largest submarine plateau – the Ontong Java Plateau – has resulted in a complex assemblage of back-arc basins, island arcs, continental plateaus and volcanic products. This study combines new and existing magnetic anomaly profiles, seafloor fabric from swath bathymetry data, Ar–Ar dating of E-MORB basalts, palaeontological dating of carbonate sediments, and plate modelling from the eastern Coral Sea. Our results constrain commencement of the opening of the Santa Cruz Basin and South Rennell Trough to c. 48 Ma and termination at 25–28 Ma. Simultaneous opening of the Melanesian Basin/Solomon Sea further north suggests that a single > 2000 km long back-arc basin, with at least one triple junction existed landward of the Melanesian subduction zone from Eocene–Oligocene times. The cessation of spreading corresponds with a reorganisation of the plate boundaries in the area and the proposed initial soft collision of the Ontong Java Plateau. The correlation between back-arc basin cessation and a widespread plate reorganisation event suggests that back-arc basins may be used as markers for both local and global plate boundary changes. 相似文献
4.
《Journal of Asian Earth Sciences》2010,39(6):289-306
A large volcanic area (∼7600 km2), the Galatean Volcanic Province (GVP), developed in northwest Central Anatolia during the Miocene along the Neo-Tethys Ocean suture zone possibly by post-collisional processes. The GVP mainly comprises 20–14 My old acid to intermediate volcanites with a geochemical signature indicating a mantle source modified by earlier (Late Cretaceous) subduction-related events. 100 km south of the GVP, near Polatlı, Ankara, basaltic rocks that cover large areas are intercalated with the Miocene deposits of the Beypazarı basin, an intra-continental subsidence zone at the southwest of the GVP. Field observations, geochemistry and K–Ar age dating of the Polatlı volcanites show that they are Early (19.9 Ma) to mid (14.1 Ma) Miocene in age, covering an area as large as 215 km2. Variations in lava thickness and the thickness of the underlying silicified/baked zones suggest that the basaltic lavas erupted from a southern source, possibly from the Eskişehir fault zone, and flowed northwards. Most Polatlı samples have chemical compositions that indicate derivation from a mantle source with crustal contamination during ascent. They do not display any characteristic to suggest a subductional component. Although the GVP and Polatlı lavas formed close in time and space, they were derived from different mantle sources. Considering the positions of these two magmatic regions with regard to the Tethyan suture zone, we propose that the mantle beneath the GVP and near the suture zone memorised the earlier subduction while the mantle beneath Polatlı that is located about 100 km further from the suture zone remained apparently unchanged. After a significant volume of magma was consumed in the GVP, a later (∼10 My) and last activity (Güvem activity) has produced quantitatively much less basaltic rocks where this subductional signature seems to completely disappear. Considering that the western Anatolian crust is proposed to undergo extension since the Late Oligocene–Early Miocene times, the Early Miocene intra-plate Polatlı activity may have developed within this extensional tectonic regime. Combined with regional data, Polatlı data also provide broad estimations on how long a subductional event continues to modify the mantle after the subduction ceased (at least ∼20 My), how long the subductional signature is preserved during significant magmatism (between 6 and 10 My) and how far the subductional effect disappears laterally on the mantle with respect to the collision zone (<100 km). 相似文献
5.
《Gondwana Research》2014,26(4):1644-1659
The formation of a series of intermountain basins is likely to indicate a geodynamic transition, especially in the case of such basins within the central South China Block (CSCB). Determining whether or not these numerous intermountain basins represent a division of the Cretaceous Pan-Yangtze Basin by exhumation of Xuefeng Mountains, is key to understanding the late Mesozoic to early Cenozoic tectonics of the South China Block (SCB). Here we present apatite fission track (AFT) data and time–temperature modeling in order to reconstruct the evolution history of the Pan-Yangtze Basin. Fourteen rock samples were taken from a NE–SW-trending mountain–basin system within the CSCB, including, from west to east, the Wuling Mountains (Wuling Shan), the south and north Mayang basins, the Xuefeng Mountains (Xuefeng Shan) and the Hengyang Basin. Cretaceous lacustrine sequences are well preserved in the south and north Mayang and Hengyang basins, and sporadically crop out in the Xuefeng Mountains, whereas Paleogene piedmont proluvial–lacustrine sequences are only found in the south Mayang and Hengyang basins. AFT results indicate that the Wuling and Xuefeng mountains underwent rapid denudation post-84 Ma, whereas the south and north Mayang basins were more slowly uplifted from 67 and 84 Ma, respectively. Following a quiescent period from 32 to 19 Ma, both the mountains and basins have been rapidly denuded since 19 Ma. Both the AFT data and sedimentary facies changes suggest that the Cretaceous deposits that cover the south–north Mayang and Hengyang basins through to the Xuefeng Mountains define the Cretaceous Pan-Yangtze Basin. Integrating our results with tectonic background for the SCB, we propose that rollback subduction of the paleo-Pacific Plate produced the Pan-Yangtze Basin, which was divided into the south–north Mayang and Hengyang basins by the abrupt uplift and exhumation of the Xuefeng Mountains from 84 Ma to present, apart from a period of tectonic inactivity from 32 to 19 Ma. This late Late Cretaceous to Paleogene denudation resulted from movement on the Ziluo strike–slip fault, which formed due to intra-continental compression most likely associated with the Eurasia–Indian plate subduction and collision. Sinistral transpression along the Ailao Shan–Red River Fault at 34–17 Ma probably transformed this compression to the extrusion of the Indochina Block, and produced the quiescent window period from 32 to 19 Ma for the mountain–basin system in the CSCB. Therefore, the initiation of exhumation of the Xuefeng Mountains at 84 Ma indicates a switch in tectonic regime from Cretaceous extension to late Late Cretaceous and Cenozoic compression. 相似文献
6.
《Precambrian Research》2006,144(1-2):19-38
The magmatic and tectonic history of the Yangtze Block and its possible affinity with other Neoproterozoic arc terranes are important elements in the reconstruction of Neoproterozoic plate tectonics. The Yanbian Terrane in the western margin of the Yangtze Block is a typical arc assemblage composed of a flysch-type sedimentary sequence intruded by gabbroic and granodioritic plutons. The sedimentary sequence consists chiefly of tuffaceous material with interlayered chert, sandstone, and pillow basalts. Laser ablation ICP-MS U–Pb dating of detrital zircons from the sandstones yield ages as young as 840 Ma. The Gaojiacun and Lengshuiqing mafic intrusions are dated at 812 ± 3 Ma and 806 ± 4 Ma, respectively, using the SHRIMP zircon U–Pb technique. Geochemical data show that both the Gaojiacun and Lengshuiqing intrusions have arc signatures, with ɛNd(t) values of +1.5 to +6.0, initial 87Sr/86Sr ratios of 0.705–0.706 and pronounced negative Nb–Ta and Zr–Hf anomalies. Their geochemical variations are best explained by fractional crystallization without major crustal contamination. The Yanbian Terrane represents a typical arc assemblage formed on the western edge of the Yangtze Block during Neoproterozoic time. The sedimentary sequence was deposited in an oceanic setting, probably in a back arc basin environment. The depleted, subduction-modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized. This scenario suggests subduction of oceanic lithosphere eastward (present-day orientation) underneath the Yangtze Block. 相似文献
7.
Carlo Doglioni 《Tectonophysics》2009,463(1-4):208-213
The Schellart's [Schellart, W.P., 2007, The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle. Tectonophysics, 445, 363–372.] paper uses slab dip and upper plate extension for testing the westward drift. His analysis and discussion are misleading for the study of the net rotation of the lithosphere since the first 125 km of subduction zones are sensitive also to other parameters such upper plate thickness, geometry and obliquity of the subduction zone with respect to the convergence direction. The deeper (> 125 km) part cannot easily be compared as well because E- or NE-directed subduction zones have seismic gaps between 270–630 km. Moreover the velocity of subduction hinge cannot be precisely estimated and it does not equal to backarc spreading due to accretionary prism growth and asthenospheric intrusion at the subduction hinge. It is shown here that hinge migration in the upper plate or lower plate reference frames supports a general global polarization of the lithosphere in agreement with the westward drift of the lithosphere. The W-directed subduction zones appear controlled by the slab–mantle interaction with slab retreat imposed by the eastward mantle flow. The opposite E-NE-directed subduction zones seem rather mainly controlled by the convergence rate, plus density, thickness and viscosity of the upper and lower plates. Finally, the geological and geophysical asymmetries recorded along subduction and rift zones as a function of their polarity with respect to the tectonic mainstream are not questioned in the Schellart's paper, but they rather represent the basic evidence for the westward drift of the lithosphere. 相似文献
8.
《Precambrian Research》2006,144(1-2):92-125
This paper presents a plate tectonic model for the evolution of the Australian continent between ca. 1800 and 1100 Ma. Between ca. 1800 and 1600 Ma episodic orogenesis occurred along the southern margin of the continent above a north-dipping subduction system. During this interval multiple orogenic events occurred. The West Australian Craton collided with the North Australian Craton (ca. 1790–1770 Ma), the Archaean nucleus of the Gawler Craton amalgamated with the North Australian Craton (ca. 1740–1690 Ma), and numerous smaller terranes accreted along the western Gawler Craton and the southern Arunta Inlier (ca. 1690–1640 Ma). The pattern of accretion suggests southward migration of the plate margin, which occurred due to a combination of slab rollback and back stepping of a subduction system behind the accreted continental blocks. Coeval with subduction a series of continental back-arc basins formed in the interior of the North Australian Craton and parts of the South Australian Craton, which were attached to the North Australian Craton prior to 1500 Ma. Extension of the North Australian Craton led to the opening of an oceanic basin along the eastern margin of the continent at ca. 1660 Ma. Continuing divergence was accommodated by oceanic spreading whereas the continental basins thermally subsided resulting in the development of sag-phase basins throughout the North Australian Craton. This oceanic basin was subsequently consumed during convergence, which ultimately led to development of a ca. 1600–1500 Ma orogenic belt along the eastern margin of Proterozoic Australia. Between ca. 1470 and 1100 Ma, the South Australian Craton, consisting of the Curnamona Province and the Gawler Craton rifted from the North Australian Craton and was re-attached in its present configuration during episodic ca. 1330–1100 Ma orogenesis, which is preserved in the Albany-Fraser Belt and the Musgrave Block. 相似文献
9.
Bo Wang Liangshu Shu Michel Faure Bor-ming Jahn Dominique Cluzel Jacques Charvet Sun-lin Chung Sébastien Meffre 《Tectonophysics》2011,497(1-4):85-104
In the southern Chinese Tianshan, the southernmost part of the Central Asian Orogenic Belt (CAOB), widespread ophiolitic mélanges form distinct tectonic units that are crucial for understanding the formation of the CAOB. However, the timing of tectonic events and the subduction polarity are still in controversy. In order to better understand these geological problems, a comprehensive study was conducted on the Heiyingshan ophiolitic mélange in the SW Chinese Tianshan. Detailed structural analysis reveals that the ophiolitic mélange is tectonically underlain by sheared and weakly metamorphosed pre-Middle Devonian rocks, and unconformably overlain by non-metamorphic and undeformed lower Carboniferous (Serpukhovian) to Permian strata. The igneous assemblage of the mélange comprises OIB-like alkali basalt and andesite, N-MORB-like tholeiitic basalt, sheeted diabase dikes, cumulate gabbro and peridotite. Mafic rocks display supra-subduction signatures, and some bear evidence of contamination with the continental crust, suggesting a continental marginal (back-arc) basin setting. Zircons of a gabbro were dated at 392 ± 5 Ma by the U–Pb LA-ICP-MS method. Famennian–Visean radiolarian microfossils were found in the siliceous matrix of the ophiolitic mélange. Mylonitic phyllite which displays northward-directed kinematic evidence yielded muscovite 40Ar/39Ar plateau ages of 359 ± 2 Ma and 356 ± 2 Ma.These new data, combined with previously published results, suggest that the mafic protoliths originally formed in a back-arc basin in the Chinese southern Tianshan during the late Silurian to Middle Devonian and were subsequently incorporated into the ophiolitic mélange and thrust northward during the Late Devonian to early Carboniferous. Opening of the back-arc basin was probably induced by south-dipping subduction of the Paleo-Tianshan Ocean in the early Paleozoic, and the Central Tianshan block was rifted away from the Tarim block. Closure of the back-arc basin in the early Carboniferous formed the South Tianshan Suture Zone and re-amalgamated the two blocks. 相似文献
10.
Comparing the early Earth to the present day, geological–geochemical evidence points towards higher mantle potential temperature and a different type of tectonics. In order to investigate possible changes in Precambrian tectonic styles, we conduct 3D high-resolution petrological–thermomechanical numerical modelling experiments for oceanic plate subduction under an active continental margin at a wide range of mantle potential temperature TP (∆ TP = 0 − 250 K, compared to present day conditions). At present day mantle temperatures (∆ TP = 0 K), results of numerical experiments correspond to modern-style subduction, whereas at higher temperature conditions important systematic changes in the styles of both lithospheric deformation and mantle convection occur. For ∆ TP = 50 − 100 K a regime of dripping subduction emerges which is still very similar to present day subduction but is characterised by frequent dripping from the slab tip and a loss of coherence of the slab, which suggests a close relationship between dripping subduction and episodic subduction. At further increasing ∆ TP = 150 − 200 K dripping subduction is observed together with unstable dripping lithosphere, which corresponds to a transitional regime. For ∆ TP = 250 K, presumably equivalent to early Archean, the dominating tectonic style is characterised by small-scale mantle convection, unstable dripping lithosphere, thick basaltic crust and small plates. Even though the initial setup is still defined by present day subduction, this final regime shows many characteristics of plume-lid tectonics. Transition between the two end-members, plume-lid tectonics and plate tectonics, happens gradually and at intermediate temperatures elements of both tectonic regimes are present. We conclude, therefore, that most likely no abrupt geodynamic regime transition point can be specified in the Earth's history and its global geodynamic regime gradually evolved over time from plume-lid tectonics into modern style plate tectonics. 相似文献
11.
《Gondwana Research》2013,24(4):1378-1401
The Qilian Orogen at the northern margin of the Tibetan Plateau is a type suture zone that recorded a complete history from continental breakup to ocean basin evolution, and to the ultimate continental collision in the time period from the Neoproterozoic to the Paleozoic. The Qilian Ocean, often interpreted as representing the “Proto-Tethyan Ocean”, may actually be an eastern branch of the worldwide “Iapetus Ocean” between the two continents of Baltica and Laurentia, opened at ≥ 710 Ma as a consequence of breakup of supercontinent Rodinia.Initiation of the subduction in the Qilian Ocean probably occurred at ~ 520 Ma with the development of an Andean-type active continental margin represented by infant arc magmatism of ~ 517–490 Ma. In the beginning of Ordovician (~ 490 Ma), part of the active margin was split from the continental Alashan block and the Andean-type active margin had thus evolved to western Pacific-type trench–arc–back-arc system represented by the MORB-like crust (i.e., SSZ-type ophiolite belt) formed in a back-arc basin setting in the time period of ~ 490–445 Ma. During this time, the subducting oceanic lithosphere underwent LT-HP metamorphism along a cold geotherm of ~ 6–7 °C/km.The Qilian Ocean was closed at the end of the Ordovician (~ 445 Ma). Continental blocks started to collide and the northern edge of the Qilian–Qaidam block was underthrust/dragged beneath the Alashan block by the downgoing oceanic lithosphere to depths of ~ 100–200 km at about 435–420 Ma. Intensive orogenic activities occurred in the late Silurian and early Devonian in response to the exhumation of the subducted crustal materials.Briefly, the Qilian Orogen is conceptually a type example of the workings of plate tectonics from continental breakup to the development and evolution of an ocean basin, to the initiation of oceanic subduction and formation of arc and back-arc system, and to the final continental collision/subduction and exhumation. 相似文献
12.
The Xinan Cu–Mo deposit, newly-discovered in the Zijinshan Au–Cu–Mo Orefield (the largest porphyry–epithermal system in SE China), is featured by the presence of abundant multi-phase granitoids, which reflects the complex Mesozoic tectono-magmatic evolution in the region.New and published LA-ICP-MS zircon U–Pb age data reveal that the Mesozoic Zijinshan magmatism occurred in two major phases: (1) Middle to Late Jurassic (ca. 169–150 Ma), forming the Zijinshan complex granite and the Xinan monzogranite; (2) late Early Cretaceous to earliest Late Cretaceous (ca. 112–98 Ma), forming the Shimaoshan volcanic rocks, Sifang granodiorite, and the Xinan (fine-grained) granodiorite porphyry, porphyritic granodiorite and late aplite dykes. Additionally, a possible earliest Cretaceous magmatism (ca. 141 Ma) may have occurred based on inherited zircon evidence. Major and trace element geochemistry indicates that all the Zijinshan igneous rocks show subduction-related geochemical affinities. Zircon Ce4 +/Ce3 + values of the late Early Cretaceous to earliest Late Cretaceous granitoids (Ce4 +/Ce3 + = 190–1706) are distinctly higher than the Middle to Late Jurassic ones (Ce4 +/Ce3 + = 27–457), suggesting that the former were derived from more oxidized parental magma. The Middle to Late Jurassic Zijinshan complex granite and monzogranite have εHf (t) values of − 8.02 to − 10.00, with the two-stage Hf model ages (TDM2) of 1.72 to 1.84 Ga (similar to the Paleoproterozoic metamorphosed Cathaysia Block basement), suggesting that they were derived from partial melting of the basement. The late Early Cretaceous to earliest Late Cretaceous Sifang granodiorite and Xinan (fine-grained) granodiorite porphyry, porphyritic granodiorite and aplite dykes contain higher and wider range of εHf (t) values (0.66 to − 6.05), with TDM2 of 1.12 to 1.56 Ga, indicating that they were also partial melting product of the Cathaysia basement but with more mantle and/or juvenile mafic lower crustal input. We propose that the Zijinshan Orefield was in a compressive, Pacific subduction-related tectonic setting during the Middle to Late Jurassic. The regional tectonic regime may have changed to extensional in the late Early Cretaceous to earliest Late Cretaceous, during which the Pacific plate subduction direction change and the accompanying subduction roll-back and slab window-opening occurred. The tectonic regime transition, high oxygen fugacity and mantle/mafic lower crustal materials involvement in the late Early Cretaceous to earliest Late Cretaceous may have generated the Zijinshan porphyry-related Au–Cu–Mo mineralization. 相似文献
13.
《Gondwana Research》2014,25(2):842-858
The northern margin of the Alxa block (NMAB), located in the southernmost part of the Altaids, is important for understanding the tectonic processes associated with the closure of the Paleo-Asian ocean. In this study, we report results from our studies on two ophiolitic belts (the Enger Us and Quagan Qulu ophiolitic belts) to constrain the tectonic evolution of the Altaids. The tectonic blocks in the Enger Us ophiolite are mainly composed of ultramafic and mafic rocks, with a matrix comprising highly deformed Carboniferous clastic rocks and tuffs. Zircons from a pillow lava sample yielded SHRIMP zircon U–Pb age of 302 ± 14 Ma. Massive and pillow basalts in the Enger Us ophiolite exhibit N-MORB geochemical affinities, displaying high TiO2 and low K2O contents with tholeiitic signatures. They are characterized by depletion of light rare earth elements (LREEs) without fractionation of high field strength elements (HFSEs) and negative Nb–Ta anomalies. It is inferred that the magmas of these rocks were derived from a depleted mantle source in a mid-ocean ridge setting. The Quagan Qulu ophiolite is composed of tectonic blocks, including ultramafic, gabbros and siliceous rocks, and matrix, including deformed clastic rocks and limestones. Zircons in a gabbro sample from the Quagan Qulu ophiolite yielded SHRIMP zircon U–Pb age of 275 ± 3 Ma. The gabbros show high MgO contents, compatible elements (Ni, Co, Sc, and V), and Al2O3/TiO2 ratios, but low TiO2 and SiO2 contents. They are enriched in large-ion lithophile elements (LILEs) and depleted in LREEs and HFSEs, indicating that they were derived from an extremely depleted mantle source which was infiltrated by a subduction-derived fluid or melt. Our geochemical data suggest that gabbros in the Quagan Qulu ophiolite were formed in a back-arc basin setting. A synthesis of evidence from geochemistry, regional geology, and paleobiogeography support the notion that the Enger Us ophiolitic belt represents the major suture of the Paleo-Asian Ocean in the NMAB and the Quagan Qulu ophiolitic belt represents a back-arc basin. These two ophiolitic belts, together with the Zongnaishan–Shalazhashan arc have been suggested to be a late Paleozoic ocean-arc–back-arc basin system in the southernmost part of the Altaids. The geochronological data suggest that the subduction process occurred even in the early Permian, indicating that the final closure of the Paleo-Asian Ocean might have taken place later than the early Permian. 相似文献
14.
North-eastern China and surrounding regions host some of the best examples of Phanerozoic juvenile crust on the globe. However, the Mesozoic tectonic setting and geodynamic processes in this region remain debated. Here we attempt a systematic analysis of the spatio-temporal distribution patterns of ore deposits in NE China and surrounding regions to constrain the geodynamic milieu. From an evaluation of the available geochronological data, we identify five distinct stages of ore formation: 240–205 Ma, 190–165 Ma, 155–145 Ma, 140–120 Ma, and 115–100 Ma. The Triassic (240–205 Ma) magmatism and associated mineralisation occurred during in a post-collisional tectonic setting involving the closure of the Paleo-Asian Ocean. The Early-Mid Jurassic (190–165 Ma) events are related to the subduction of the Paleo-Pacific Ocean in the eastern Asian continental margin, whereas in the Erguna block, these are associated with the subduction of the Mongol–Okhotsk Ocean. From 155 to 120 Ma, large-scale continental extension occurred in NE China and surrounding regions. However, the Late Jurassic magmatism and mineralisation events in these areas evolved in a post-orogenic extensional environment of the Mongol–Okhotsk Ocean subduction system. The early stage of the Early Cretaceous events occurred under the combined effects of the closure of the Mongol–Okhotsk Ocean and the subduction of the Paleo-Pacific Ocean. The widespread extension ceased during the late phase of Early Cretaceous (115–100 Ma), following the rapid tectonic changes resulting from the Paleo-Pacific Oceanic plate reconfiguration. 相似文献
15.
Pillow lavas in Bompoka island of the Andaman–Nicobar islands, forming a part of Sunda–Burmese forearc, are composed of plagioclase and clinopyroxene microphenocrysts in a fine-grained ferruginous groundmass along with glass. They are also characterized by several quench plagioclase and clinopyroxene morphologies. Zr/TiO2 versus Nb/Y relationship of these pillow lavas show that these are tholeiitic basalts in composition. These basalts have low MgO (5.19–6.12 wt%), Ni (84–118 ppm), and Cr (144–175 ppm) abundance and high FeO(T)/MgO (1.71–1.92) ratios, reflecting their fractionated nature. In Th/Yb versus Nb/Yb and Ti/Yb versus Nb/Yb binary diagrams, they show N-MORB affinity. However, La/Nb–Y and Ce/Nb–Th/Nb relationships along with a slight LREE depleted (LaN/YbN = 0.75–0.82) pattern and high Ba/Zr (0.28–0.40) ratios and LILE (K, Rb, Ba, Sr and Th) enrichment relative to N-MORB, suggest their back-arc basin basalt affinity. It is inferred that these pillow basalts have been derived from a metasomatised N-MORB-like mantle source in a trench-distal (wider) back-arc basin, probably near the leading edge of the Eurasian continent during Early to Late Cretaceous times, prior to the currently active Andaman–Java subduction system. 相似文献
16.
The Pyrenees at the Iberia–Europe collision zone contain sediments showing Albian–Cenomanian high-temperature metamorphism, and coeval alkaline magmatic rocks. Stemming from different views on Jurassic–Cretaceous Iberian microplate kinematics, two schools of thought exist on the trigger of this thermal pulse: one invoking hyperextension of the Iberian and Eurasian margins, the other suggesting slab break-off. Competing scenarios for Mesozoic Iberian motion compatible with Pyrenean geology, comprise (1) transtensional eastward motion of Iberia versus Eurasia, or (2) strike-slip motion followed by orthogonal extension, both favoring hyperextension-related heating, and (3) scissor-style opening of the Bay of Biscay coupled with subduction in the Pyrenean realm, favoring the slab break-off hypothesis. We test these kinematic scenarios for Iberia against a newly compiled paleomagnetic dataset and conclude that the scissor-type scenario is the only one consistent with a well-defined ~ 35° counterclockwise rotation of Iberia during the Early Aptian. We proceed to show that when taking absolute plate motions into account, Aptian oceanic subduction in the Pyrenees followed by Late Aptian–Early Albian slab break-off should leave a slab remnant in the present-day mid-mantle below NW Africa. Mantle tomography shows the Reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500 km depth below southern Algeria. Mantle tomography is therefore consistent with the scissor-type opening of the Bay of Biscay coupled with subduction in the Pyrenean realm. Slab break-off may thus explain high-temperature metamorphism and alkaline magmatism during the Albian–Cenomanian in the Pyrenees, whereas hyperextension that exhumed Pyrenean mantle bodies occurred much earlier, in the Jurassic. 相似文献
17.
Along the western Tethyan and Andean subduction zones the distribution of Cretaceous and Cenozoic porphyry Cu deposits is not random and shows that they were emplaced in distinct regional clusters. To understand the appearance of these clusters within their geodynamical contexts and identify kinematic features which would favor the genesis of porphyry-type ore bodies, we use a paleotectonic approach. Two clusters in the Aegean-Balkan-Carpathian area, which were emplaced in upper Cretaceous and Oligo-Miocene, and two others in the Andes, which were emplaced in late Eocene and Miocene, are sufficiently well constrained to be studied in detail. It appears that they are associated with a specific polyphased kinematic context related to the convergence of tectonic plates. This context is characterized by: 1) a relatively fast convergence rate shortly followed by 2) a drastic decrease of this rate. From these observations, and assuming that the major part of plate convergence is accommodated along subduction zones, we propose a two-phase geodynamic model favoring emplacement of porphyry Cu deposits: 1) a high melt production in the mantle wedge, followed by 2) an extensional regime (or at least relaxation of the compressional stress) in the upper plate, promoting ascension of fertile magmas to the upper crust. Melt production at depth and the following extensional regime, which would be related to variations in convergence rate, are thus associated with variations in plate and trench velocities, themselves being controlled by both plate kinematics at the surface and slab dynamics in the upper mantle. In particular, along-strike folding behavior of the subducting slab may strongly influence trench velocity changes and the location of porphyry Cu deposits. Metallogenic data suggest that periods of slab retreat, which would favor mineralization processes during ~ 40 Myrs, would be separated by barren periods lasting ~ 10 to 20 Myrs, corresponding to shorter episodes of trench advance, as observed in laboratory experiments. These results confirm the control of the geodynamic context, and especially subduction dynamics, on the genesis of porphyry Cu deposits. This study also shows that the paleotectonic approach is a promising tool that could help identify geodynamic and tectonic criteria favoring the genesis of various ore deposits. 相似文献
18.
《Gondwana Research》2014,26(4):1690-1699
The continental collision between the Indian and Asian plates plays a key role in the geologic and tectonic evolution of the Tibetan plateau. In this article we present high-resolution tomographic images of the crust and upper mantle derived from a large number of high-quality seismic data from the ANTILOPE project in western Tibet. Both local and distant earthquakes were used in this study and 35,115 P-wave arrival times were manually picked from the original seismograms. Geological and geochemical results suggested that the subducting Indian plate has reached northward to the Lhasa terrane, whereas our new tomography shows that the Indian plate is currently sub-horizontal and underthrusting to the Jinsha river suture at depths of ~ 100 to ~ 250 km, suggesting that the subduction process has evolved over time. The Asian plate is also imaged clearly from the surface to a depth of ~ 100 km by our tomography, and it is located under the Tarim Basin north of the Altyn Tagh Fault. There is no obvious evidence to show that the Asian plate has subducted beneath western Tibet. The Indian and Asian plates are separated by a prominent low-velocity zone under northern Tibet. We attribute the low-velocity zone to mantle upwelling, which may account for the warm crust and upper mantle beneath that region, and thus explain the different features of magmatism between southern and northern Tibet. But the upwelling may not penetrate through the whole crust. We propose a revised geodynamic model and suggest that the high-velocity zones under Lhasa terrane may reflect a cold crust which has interrupted the crustal flow under the westernmost Tibetan plateau. 相似文献
19.
The tectonic evolution of the Indian plate, which started in Late Jurassic about 167 million years ago (~ 167 Ma) with the breakup of Gondwana, presents an exceptional and intricate case history against which a variety of plate tectonic events such as: continental breakup, sea-floor spreading, birth of new oceans, flood basalt volcanism, hotspot tracks, transform faults, subduction, obduction, continental collision, accretion, and mountain building can be investigated. Plate tectonic maps are presented here illustrating the repeated rifting of the Indian plate from surrounding Gondwana continents, its northward migration, and its collision first with the Kohistan–Ladakh Arc at the Indus Suture Zone, and then with Tibet at the Shyok–Tsangpo Suture. The associations between flood basalts and the recurrent separation of the Indian plate from Gondwana are assessed. The breakup of India from Gondwana and the opening of the Indian Ocean is thought to have been caused by plate tectonic forces (i.e., slab pull emanating from the subduction of the Tethyan ocean floor beneath Eurasia) which were localized along zones of weakness caused by mantle plumes (Bouvet, Marion, Kerguelen, and Reunion plumes). The sequential spreading of the Southwest Indian Ridge/Davie Ridge, Southeast Indian Ridge, Central Indian Ridge, Palitana Ridge, and Carlsberg Ridge in the Indian Ocean were responsible for the fragmentation of the Indian plate during the Late Jurassic and Cretaceous times. The Réunion and the Kerguelen plumes left two spectacular hotspot tracks on either side of the Indian plate. With the breakup of Gondwana, India remained isolated as an island continent, but reestablished its biotic links with Africa during the Late Cretaceous during its collision with the Kohistan–Ladakh Arc (~ 85 Ma) along the Indus Suture. Soon after the Deccan eruption, India drifted northward as an island continent by rapid motion carrying Gondwana biota, about 20 cm/year, between 67 Ma to 50 Ma; it slowed down dramatically to 5 cm/year during its collision with Asia in Early Eocene (~ 50 Ma). A northern corridor was established between India and Asia soon after the collision allowing faunal interchange. This is reflected by mixed Gondwana and Eurasian elements in the fossil record preserved in several continental Eocene formations of India. A revised India–Asia collision model suggests that the Indus Suture represents the obduction zone between India and the Kohistan–Ladakh Arc, whereas the Shyok-Suture represents the collision between the Kohistan–Ladakh arc and Tibet. Eventually, the Indus–Tsangpo Zone became the locus of the final India–Asia collision, which probably began in Early Eocene (~ 50 Ma) with the closure of Neotethys Ocean. The post-collisional tectonics for the last 50 million years is best expressed in the evolution of the Himalaya–Tibetan orogen. The great thickness of crust beneath Tibet and Himalaya and a series of north vergent thrust zones in the Himalaya and the south-vergent subduction zones in Tibetan Plateau suggest the progressive convergence between India and Asia of about 2500 km since the time of collision. In the early Eohimalayan phase (~ 50 to 25 Ma) of Himalayan orogeny (Middle Eocene–Late Oligocene), thick sediments on the leading edge of the Indian plate were squeezed, folded, and faulted to form the Tethyan Himalaya. With continuing convergence of India, the architecture of the Himalayan–Tibetan orogen is dominated by deformational structures developed in the Neogene Period during the Neohimalayan phase (~ 21 Ma to present), creating a series of north-vergent thrust belt systems such as the Main Central Thrust, the Main Boundary Thrust, and the Main Frontal Thrust to accommodate crustal shortening. Neogene molassic sediment shed from the rise of the Himalaya was deposited in a nearly continuous foreland trough in the Siwalik Group containing rich vertebrate assemblages. Tomographic imaging of the India–Asia orogen reveals that Indian lithospheric slab has been subducted subhorizontally beneath the entire Tibetan Plateau that has played a key role in the uplift of the Tibetan Plateau. The low-viscosity channel flow in response to topographic loading of Tibet provides a mechanism to explain the Himalayan–Tibetan orogen. From the start of its voyage in Southern Hemisphere, to its final impact with the Asia, the Indian plate has experienced changes in climatic conditions both short-term and long-term. We present a series of paleoclimatic maps illustrating the temperature and precipitation conditions based on estimates of Fast Ocean Atmospheric Model (FOAM), a coupled global climate model. The uplift of the Himalaya–Tibetan Plateau above the snow line created two most important global climate phenomena—the birth of the Asian monsoon and the onset of Pleistocene glaciation. As the mountains rose, and the monsoon rains intensified, increasing erosional sediments from the Himalaya were carried down by the Ganga River in the east and the Indus River in the west, and were deposited in two great deep-sea fans, the Bengal and the Indus. Vertebrate fossils provide additional resolution for the timing of three crucial tectonic events: India–KL Arc collision during the Late Cretaceous, India–Asia collision during the Early Eocene, and the rise of the Himalaya during the Early Miocene. 相似文献
20.
《Chemie der Erde / Geochemistry》2016,76(4):605-620
We discuss here the mineralogical and geochemical characteristics of mafic intrusive rocks from the Nagaland-Manipur Ophiolites (NMO) of Indo-Myanmar Orogenic Belt, northeast India to define their mantle source and tectonic environment. Mafic intrusive sequence in the NMO is characterized by hornblende-free (type-I) and hornblende-bearing (type-II) rocks. The type-I is further categorized as mafic dykes (type-Ia) of tholeiitic N-MORB composition, having TiO2 (0.72–1.93 wt.%) and flat REE patterns (LaN/YbN = 0.76–1.51) and as massive gabbros (type-Ib) that show alkaline E-MORB affinity, having moderate to high Ti content (TiO2 = 1.18 to 1.45 wt.%) with strong LREE-HREE fractionations (LaN/YbN = 4.54–7.47). Such geochemical enrichment from N-MORB to E-MORB composition indicates mixing of melts derived from a depleted mantle and a fertile mantle/plume source at the spreading center. On the other hand, type-II mafic intrusives are hornblende bearing gabbros of SSZ-type tholeiitic composition with low Ti content (TiO2 = 0.54 wt.%–0.86 wt.%) and depleted LREE pattern with respect to HREE (LaN/YbN = 0.37–0.49). They also have high Ba/Zr (1.13–2.82), Ba/Nb (45.56–151.66) and Ba/Th (84.58–744.19) and U/Th ratios (0.37–0.67) relative to the primitive mantle, which strongly represents the melt composition generated by partial melting of depleted lithospheric mantle wedge contaminated by hydrous fluids derived from subducting oceanic lithosphere in a forearc setting. Their subduction related origin is also supported by presence of calcium-rich plagioclase (An16.6–32.3). Geothermometry calculation shows that the hornblende bearing (type-II) mafic rocks crystallized at temperature in range of 565°–625 °C ± 50 (at 10 kbar). Based on these available mineralogical and geochemical evidences, we conclude that mid ocean ridge (MOR) type mafic intrusive rocks from the NMO represent the section of older oceanic crust which was generated during the divergent process of the Indian plate from the Australian plate during Cretaceous period. Conversely, the hornblende-bearing gabbros (type-II) represent the younger oceanic crust which was formed at the forearc region by partial melting of the depleted mantle wedge slightly modified by the hydrous fluids released from the subducting oceanic slab during the initial stage of subduction of Indian plate beneath the Myanmar plate. 相似文献