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1.
http://www.sciencedirect.com/science/article/pii/S1674987114000061   总被引：7，自引：3，他引：4  
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2.
Prolonged intraplate volcanism along the 4000 km-long East Australian margin for ca 100 Ma raises many genetic questions. Studies of the age-progressive pulses embedded in general basaltic activity have spawned a host of models. Zircon U–Pb dating of inland Queensland central volcanoes gives a stronger database to consider the structure and origin of Australian age-progressive volcanic chains. This assists appraisal of this volcanism in relation to plate motion and plate margin tectonic models. Inland Queensland central volcanoes progressed south-southeast from 34 to 31 Ma (～5.4 cm/yr) until a surge in activity led to irregular southerly progression 31 to 28 Ma. A new inland southeastern Queensland central volcano line (25 to 22 Ma), from Bunya Mountains to North Main Range, followed 3 Ma behind the adjacent coastal progression. The Australian and Tasman Sea age-progressive chains are compared against recent plate motion modelling (Indian Ocean hotspots). The chain lines differ from general vector traces owing to west-facing swells and cessations in activity. Tectonic processes on the eastern plate margin may regulate these irregularities. These include subduction, rapid roll-back and progressive detachment of the Loyalty slab (43 to 15 Ma). West-flowing Pacific-type asthenosphere, related to perturbed mantle convection, may explain the west-facing volcanic surges. Such westward Pacific flow for over 28 Ma is known at the Australian–Antarctic Discordance, southeast of the present Australian plume sites under Bass Strait–West Tasman Sea. Most basaltic activity along eastern Australia marks asthenospheric melt injections into Tasman rift zone mantle and not lithospheric plate speed. The young (post-10 Ma) fields (Queensland, Victoria–South Australia) reflect new plate couplings, which altered mantle convection and stress regimes. These areas receive asthenospheric inputs from deep thermal zones off northeast Queensland and under Bass Strait.  相似文献   

3.
Subduction is a fundamental mechanism of material exchange between the planetary interior and the surface. Despite its significance, our current understanding of fluctuating subducting plate area and slab volume flux has been limited to a range of proxy estimates. Here we present a new detailed quantification of subduction zone parameters from the Late Triassic to present day (230–0 Ma). We use a community plate motion model with evolving plate topologies to extract trench-normal convergence rates through time to compute subducting plate areas, and we use seafloor paleo-age grids to estimate the thickness of subducting lithosphere to derive the slab flux through time. Our results imply that slab flux doubled to values greater than 500 km3/yr from 180 Ma in the Jurassic to 130 Ma in the mid-Cretaceous, subsequently halving again towards the Cretaceous-Paleogene boundary, largely driven by subduction zones rimming the Pacific ocean basin. The 130 Ma spike can be attributed to a two-fold increase in mid-ocean ridge lengths following the break-up of Pangea, and a coincident increase in convergence rates, with average speeds exceeding 10 cm/yr. With one third of the total 230 - 0 Ma subducted volume entering the mantle during this short ∼50 Myr period, we suggest this slab superflux drove a surge in slab penetration into the lower mantle and an associated increase in the vigour of mantle return flow. This mid-Cretaceous event may have triggered, or at least contributed to, the formation of the Darwin Rise mantle superswell, dynamic uplift of the South African Plateau and the plume pulse that produced the Ontong-Java-Hikurangi-Manihiki and Kerguelen plateaus, among others.The models presented here contribute to an improved understanding of the time-evolving flux of material consumed by subduction, and suggest that slab superflux may be a general feature of continental dispersal following supercontinent breakup. These insights may be useful for better understanding how supercontinent cycles are related to transient episodes of Large Igneous Province and superswell formation, and the associated deep cycling of minerals and volatiles, as well as leading to a better understanding of tectonic drivers of long-term climate and icehouse-to-greenhouse transitions.  相似文献   

4.
The Central Asian Orogenic Belt(CAOB) resulted from accretion during the Paleozoic subduction of the PaleoAsian Ocean. The Xilinhot area in Inner Mongolia is located in the northern subduction zone of the central-eastern CAOB and outcropped a large number of late Paleozoic mafic intrusions. The characteristics of magma source and tectonic setting of the mafic intrusions and their response to the closure process of the Paleo-Asian Ocean are still controversial. This study presents LA-ICPMS zircon U-Pb ages and geochemical features of mafic intrusions in the Xilinhot area to constrain the northward subduction of the Paleo-Asian Ocean. The mafic intrusions consist of gabbro, hornblende gabbro, and diabase. Their intrusion times can be divided into three stages of 326–321 Ma, 276 Ma and 254 Ma by zircon U-Pb ages. The first two stages of the 326–276 Ma intrusions mostly originated from subduction-modified continental lithospheric mantle sources that underwent a variable degree partial melting(5–30%), recording the subduction of oceanic crust. The third stage of the 254 Ma mafic rocks also show arc-related features. The primary magma compositions calculated by PRIMELT2 modeling on three samples of ～326 Ma and two samples of ～254 Ma show that these mafic samples are characterized by a variable range in SiO_2(47.51–51.47 wt%), Al_2O_3(11.46–15.55 wt%), ΣFeO(8.27–9.61 wt%), MgO(13.01–15.18 wt%) and CaO(9.13–11.67 wt%), consisting with the features between enriched mantle and lower continental crust. The source mantle melting of mafic intrusions occurred under temperatures of 1302–1351°C and pressures of 0.92–1.30 GPa. The magmatic processes occurred near the crust-mantle boundary at about 33–45 km underground. Combined with previous studies, it is concluded that Carboniferous to early Permian(～326–275 Ma) northward subduction of the Paleo-Asian oceanic crust led to the formation of the mafic magmatism in the Baolidao arc zone. The whole region had entered the collision environment at ～254 Ma, but with subduction-related environments locally. The final collision between the North China craton and the South Mongolian microcontinent may have lasted until ca. 230 Ma.  相似文献   

5.
The estimated rates of upper mantle sublithospheric flows in the Hawaii–Emperor Range and Ethiopia–Arabia–Caucasus systems are reported. In the Hawaii–Emperor Range system, calculation is based on motion of the asthenospheric flow and the plate moved by it over the branch of the Central Pacific plume. The travel rate has been determined based on the position of variably aged volcanoes (up to 76 Ma) with respect to the active Kilauea Volcano. As for the Ethiopia–Arabia–Caucasus system, the age of volcanic eruptions (55–2.8 Ma) has been used to estimate the asthenospheric flow from the Ethiopian–Afar superplume in the northern bearing lines. Both systems are characterized by variations in a rate of the upper mantle flows in different epochs from 4 to 12 cm/yr, about 8 cm/yr on average. Analysis of the global seismic tomographic data has made it possible to reveal rock volumes with higher seismic wave velocities under ancient cratons; rocks reach a depth of more than 2000 km and are interpreted as detached fragments of the thickened continental lithosphere. Such volumes on both sides of the Atlantic Ocean were submerged at an average velocity of 0.9–1.0 cm/yr along with its opening. The estimated rates of the mantle flows clarify the deformation properties of the mantle and regulate the numerical models of mantle convection.  相似文献   

6.
The discovery of Permian, Mesozoic and Palaeocene palynomorphs from the Nindam forearc basin, exposed along the Indus Suture Zone in Ladakh, is reported. The palynomorphs are from volcanogenic sandstones and are poorly preserved, distorted and show the effects of abrasion (striation marks). The frequent occurrence of Proxapertites indicates the assemblage is at least Palaeocene in age. The Palaeocene palynomorphs and sediments were transported to the Nindam trough from nearby elevated landward regions (islands). These Palaeocene provenance areas were characterized by an estuarine, nearshore, tropical, warm‐humid environment and were situated at equatorial palaeolatitudes. However, the occurrence of Permian and Mesozoic palynomorphs in the assemblage indicates that the Late Palaeozoic and Mesozoic Tethyan sedimentary rocks exposed along the northern margin of the Indian plate were redeposited into the tectonically active Cretaceous–Palaeocene trench–subduction complex that existed between the Indian and the Asian plates until the collision took place at ～50–60 Ma.  相似文献   

7.
云县-景谷火山弧带大中河地区新识别出一套晚志留世中基性-中酸性火山岩组合,其LA-ICPMS锆石U-Pb年龄为421.2±1.2Ma和417.6±5.1Ma。该套火山岩具有富铝(12.73%～16.63%)、富钠(K2O/Na2O=0.56～0.99)和高Mg#(46.0～50.0)的特征,属于钙碱性系列岩石;同时富集轻稀土,Eu具有不同程度的弱亏损,亏损高场强元素(Nb、Ta、Ti),具有正εNd(t)值(3.86～4.39)和较高的Th/Ta比值(15～17),显示与活动大陆边缘岛弧型火山岩相似的地球化学性质。大中河晚志留世火山岩很可能是俯冲沉积物流体交代地幔楔物质部分熔融的产物,并在岩浆上升过程中经历了一定的分离结晶作用和浅部地壳物质的同化混染;结合区域同期(410～420Ma)岩浆活动及相关的高压变质事件分析,应为原-古特提斯洋在早古生代末期向东俯冲消减作用的产物,从而为扬子陆块西部边缘晚古生代"三江"多岛弧盆系的形成演化提供了前锋弧发育的岩石学证据及其动力学机制。  相似文献   

8.
《Gondwana Research》2010,17(3-4):414-430
The East Asian continental margin is underlain by stagnant slabs resulting from subduction of the Pacific plate from the east and the Philippine Sea plate from the south. We classify the upper mantle in this region into three major domains: (a) metasomatic–metamorphic factory (MMF), subduction zone magma factory (SZMF), and the ‘big mantle wedge’ (BMW). Whereas the convection pattern is anticlockwise in the MMF domain, it is predominantly clockwise in the SZMF and BMW, along a cross section from the south. Here we define the MMF as a small wedge corner which is driven by the subducting Pacific plate and dominated by H2O-rich fluids derived by dehydration reactions, and enriched in large ion lithophile elements (LILE) which cause the metasomatism. The SZMF is a zone intermediate between MMF and BMW domains and constitutes the main region of continental crust production by partial melting through wedge counter-corner flow. Large hydrous plume generated at about 200 km depth causes extensive reduction in viscosity and the smaller scale hydrous plumes between 60 km and 200 km also bring about an overall reduction in the viscosity of SZMF. More fertile and high temperature peridotites are supplied from the entrance to this domain. The domain extends obliquely to the volcanic front and then swings back to the deep mantle together with the subducting slab. The BMW occupies the major portion of upper mantle in the western Pacific and convects largely with a clockwise sense removing the eastern trench oceanward. Sporadic formation of hydrous plume at the depth of around 410 km and the curtain flow adjacent to the trench cause back arc spreading. We envisage that the heat source in BMW could be the accumulated TTG (tonalite–trondhjemite–granodiorite) crust on the bottom of the mantle transition zone. The ongoing process of transportation of granitic crust into the mantle transition zone is evident from the deep subduction of five intra-oceanic arcs on the subducting Philippine Sea plate from the south, in addition to the sediment trapped subduction by the Pacific plate and Philippine Sea plate. The dynamics of MMF, SZMF and BMW domains are controlled by the angle of subduction; a wide zone of MMF in SW Japan is caused by shallow angle subduction of the Philippine Sea plate and the markedly small MMF domain in the Mariana trench is due to the high angle subduction of Pacific plate. The domains in NE Japan and Kyushu region are intermediate between these two. During the Tertiary, a series of marginal basins were formed because of the nearly 2000 km northward shift of the subduction zone along the southern margin of Tethyan Asia, which may be related to the collision of India with Asia and the indentation. The volume of upper mantle under Asia was reduced extensively on the southern margin with a resultant oceanward trench retreat along the eastern margin of Asia, leading to the formation of a series of marginal basins. The western Pacific domain in general is characterized by double-sided subduction; from the east by the oldest Pacific plate and from the south by the oldest Indo-Australian plate. The old plates are hence hydrated extensively even in their central domains and therefore of low temperature. The cracks have allowed the transport of water into the deeper portions of the slab and these domains supply hydrous fluids even to the bottom of the upper mantle. Thus, a fluid dominated upper mantle in the western Pacific drives a number of microplates and promote the plate boundary processes.  相似文献   

9.
兴凯湖花岗杂岩体的锆石U——Pb 年龄及其地质意义   总被引：3，自引：0，他引：3  
佳木斯地块东南缘的兴凯湖花岗杂岩体主要由花岗闪长岩、二长花岗岩和正长花岗岩组成,其锆石的LA-ICP-MS U-Pb 测年结果显示,杨田寨南山岩体形成于257 ± 2 Ma,双子山岩体形成于215 ～212 Ma; 花岗岩的时空展布表明,两期花岗质岩浆的就位可能分别与古亚洲洋板块的俯冲作用和后造山伸展进程密切相关。结合本区和黑龙江东部其他花岗质岩石的年龄,揭示了佳木斯地块和兴凯地块在早古生代、二叠纪及三叠纪共同经历了三期大规模岩浆活动,暗示两者具有相同的构造属性,共同组成了同一陆块。  相似文献   

10.
The tectonic evolution of the southwestern margin of Pangea supercontinent is represented by the extensive late Paleozoic–Triassic magmatism along the southwestern margin of South America, including the Chilean Frontal Andes batholiths as part of the Choiyoi province. Several models have proposed cessation of subduction as the reason behind the vast amounts of felsic magmatism and apparent lack of typical arc magmas. Here, new U-Pb in zircon ages, and geochemical and isotope analyses (Rb-Sr, Sm-Nd, Re-Os) indicate that mid Permian–Triassic granitic magmatism originated in a subduction-related extensional setting (slab rollback). Subduction and anatexis of lower continental crust were the main magma-generation mechanisms, the latter caused by asthenospheric upwelling, decompression and subsequent accumulation of underplated basalts. A comparison with coeval igneous units along the Chilean-Argentine border allows extension of this model from at least 21° to 40°S. The key elements triggering slab rollback are low subduction plate velocities and convergence rates, which can be attributed to the assembly of Pangea supercontinent (mid Permian–Triassic). Therefore, subduction of the oceanic plate beneath South America has been a continuous process from early Paleozoic times onwards—rather than having a period without subduction before the onset of the Andean cycle as previous models have invoked. New geochronological constraints indicate that the peak of the voluminous crustal-derived magmatism and related explosive volcanism (Choiyoi province) was contemporaneous with the emplacement of the Emeishan and Siberian Traps LIPs, potentially conditioning the Earth system for the environmental collapse and biotic crises related to those LIPs. The observed tectonic changes, magmatism and related environmental implications could potentially be linked to the assembly of Pangea supercontinent.  相似文献   

11.
W.P. Schellart  D.R. Stegman  J. Freeman   《Earth》2008,88(1-2):118-144
Since the advent of plate tectonics different global reference frames have been used to describe the motion of plates and trenches. The difference in plate motion and trench migration between different reference frames can be substantial (up to 4 cm/yr). This study presents an overview of trench migration velocities for all the mature and incipient subduction zones on Earth as calculated in eight different global reference frames. Calculations show that, irrespective of the reference frame: (1) trench retreat always dominates over trench advance, with 62–78% of the 244 trench segments retreating; (2) the mean and median trench velocity are always positive (retreating) and within the range 1.3–1.5 cm/yr and 0.9–1.3 cm/yr, respectively; (3) rapid trench retreat is only observed close to lateral slab edges (< 1500 km); and (4) trench retreat is always slow far from slab edges (> 2000 km). These calculations are predicted by geodynamic models with a varying slab width, in which plate motion, trench motion and mantle flow result from subduction of dense slabs, suggesting that trench motion is indeed primarily driven by slab buoyancy forces and that proximity to a lateral slab edge exerts a dominant control on the trench migration velocity. Despite these four general conclusions, significant differences in velocities between such reference frames remain. It is therefore important to determine which reference frame most likely describes the true absolute velocities to get an understanding of the forces driving plate tectonics and mantle convection. It is here proposed that, based on fluid dynamic considerations and predictions from geodynamic modelling, the best candidate is the one, which optimises the number of trench segments that retreat, minimizes the trench–perpendicular trench migration velocity (vT) in the centre of wide (> 4000 km) subduction zones, maximizes the number of retreating trench segments located within 2000 km of the closest lateral slab edge, minimizes the average of the absolute of the trench–perpendicular trench migration velocity (|vT|) for all subduction zones on Earth, and minimizes the global upper mantle toroidal volume flux (To) that results from trench migration and associated lateral slab migration (i.e. slab rollback or slab roll-forward). Calculations show that these conditions are best met in one particular Indo-Atlantic hotspot reference frame, where 75% of the subduction zones retreat, vT in the centre of wide subduction zones ranges between − 3.5 and 1.8 cm/yr, 83% of the trench segments located within 2000 km of the closest lateral slab edge retreat, the average of |vT| is 2.1 cm/yr, and To = 456 km3/yr (lower limit) and 539 km3/yr (upper limit). Inclusion of all the incipient subduction zones on Earth results in slightly greater fluxes of 465 km3/yr (lower limit) and 569 km3/yr (upper limit). It is also found that this reference frame is close to minimizing the total sub-lithospheric upper mantle volume flux (K) associated with motion of continental keels located below the major cratons. It is stressed, however, that K is an order of magnitude smaller than To, and thus of subordinate importance. In conclusion, the Indo-Atlantic hotspot reference frame appears preferable for calculating plate velocities and plate boundary velocities.  相似文献   

12.
The Langshan area is located in the west of Inner Mongolia, southwest of the Solonker ophiolite belt, which is the ideal workplace to study tectonic-magmatic evolution and geodynamics background in Late Paleozoic because of the intense magmatism. LA-ICP-MS Zircon U-Pb ages yielded the formation time of granodiorite of Sharichulu and Moruogu granitic pluton (278.07±0.66) Ma and (278.05±0.69) Ma, respectively, forming in the latest early Permian. Geochemical characteristics showed that the Zhalashan granites were high-K calc-alkaline (SiO2：63.76%～67.88%;K2O：2.74%～4.02%) and weak peraluminous rocks (A/CNK：0.94～1.07) with moderate Mg# values (38.98～47.53). In addition,it exhibited LILE and LREEs enriched, HFSE and HREEs depleted with slight Eu anomaly, and all of the above-mentioned indicated the characteristics of I-type granites and arc-related. Zircon Hf isotope showed that the scatter εHf（t）values varied from -0.6～-7.5, which suggests a mixed magma source of old continental crust with a small involvement of mantle components. Together with regional geological background,the authors hold that the Latest early Permian granodiorite of Langshan area formed in an active continental margin setting under the background of southward subduction of the Paleo-Asian Ocean which were not close at that time.  相似文献   

13.
       古地磁学是进行古板块运动演化过程和古地理重建研究最有效的定量方法之一。在统计全球古地磁数据库（GPMDB） 和前人发表数据的基础上,根据国际上通用的古地磁数据可靠性判别标准--Van der Voo （1990）判据,本文对波罗的板 块（Baltica）和西伯利亚板块（Siberia）古生代古地磁数据进行了重新分析和筛选,利用GMAP 软件重建了两个板块古生代 视极移曲线和古地理方位,对它们的构造演化和运动学特征进行对比分析,获得了几点新认识,即两板块在古生代期间发 生的三次汇聚（晚奥陶世、早石炭世和晚二叠世）过程符合牛顿运动学原则（板块之下是具有很大粘度的地幔软流圈,非 理想条件下不可能完全遵守牛顿运动学原则）,且具有三种不同类型的运动学现象：晚奥陶世（~450 Ma）,波罗的和西伯利 亚板块同向北漂移并汇聚,纬向速度较快的板块波罗的将动能传给了纬向速度较慢的西伯利亚板块;早石炭世（~360 Ma）, 波罗的和西伯利亚板块相向漂移并汇聚,西伯利亚板块向南的板块纬向速度转为向北,波罗的板块向北的纬向速度逐渐减 小并转为向南;晚二叠世（~255 Ma）,波罗的和西伯利亚板块再次相向漂移并汇聚,动能抵消,纬向漂移速率都变为零。  相似文献   

14.
Accurately mapping plate boundary types and locations through time is essential for understanding the evolution of the plate-mantle system and the exchange of material between the solid Earth and surface environments.However,the complexity of the Earth system and the cryptic nature of the geological record make it difficult to discriminate tectonic environments through deep time.Here we present a new method for identifying tectonic paleo-environments on Earth through a data mining approach using global geochemical data.We first fingerprint a variety of present-day tectonic environments utilising up to 136 geochemical data attributes in any available combination.A total of 38301 geochemical analyses from basalts aged from 5-0 Ma together with a well-established plate reconstruction model are used to construct a suite of discriminatory models for the first order tectonic environments of subduction and mid-ocean ridge as distinct from intraplate hotspot oceanic environments,identifying 41,35,and 39 key discriminatory geochemical attributes,respectively.After training and validation,our model is applied to a global geochemical database of 1547 basalt samples of unknown tectonic origin aged between 1000-410 Ma,a relatively ill-constrained period of Earth’s evolution following the breakup of the Rodinia supercontinent,producing 56 unique global tectonic environment predictions throughout the Neoproterozoic and Early Paleozoic.Predictions are used to discriminate between three alternative published Rodinia configuration models,identifying the model demonstrating the closest spatio-temporal consistency with the basalt record,and emphasizing the importance of integrating geochemical data into plate reconstructions.Our approach offers an extensible framework for constructing full-plate,deeptime reconstructions capable of assimilating a broad range of geochemical and geological observations,enabling next generation Earth system models.  相似文献   

15.
The shapes and orientations of Benioff zones beneath island arcs, interpreted as marking the location of subducted lithosphere, provide the best presently available constraints on the global convective flow pattern associated with plate motions. This global flow influences the dynamics of subduction. Subduction zone phenomena therefore provide powerful tests for models of mantle flow. We compute global flow models which, while simple, include those features which are best constrained, namely the observed plate velocities, applied as boundary conditions, and the density contrasts given by thermal models of the lithosphere and subducted slabs. Two viscosity structures are used; for one, flow is confined to the upper mantle, while for the other, flow extends throughout the mantle.Instantaneous flow velocity vectors match observed Benioff zone dips and shapes for the model which allows mantle-wide flow but not for the upper mantle model, which has a highly contorted flow pattern. The effect of trench migration on particle trajectories is calculated; it is not important if subduction velocities are greater than migration rates. Two-dimensional finite element models show that including a coherent high viscosity slab does not change these conclusions. A coherent high viscosity slab extending deep into the upper mantle would significantly slow subduction if flow were confined to the upper mantle. The maximum earthquake magnitude, Mw, for island arcs correlates well with the age of the subducted slab and pressure gradient between the trench and back-arc region for the whole mantle, but not the upper mantle, flow model. The correlations with orientations of Benioff zones and seismic coupling strongly suggest that the global return flow associated with plate motions extends below 700 km. For both models, regions of back-arc spreading have asthenospheric shear pulling the back-arc toward the trench; regions without back-arc spreading have the opposite sense of shear, suggesting global flow strongly influences back-arc spreading.  相似文献   

16.
Central Asian Orogenic Belt(CAOB) is one of the largest accretionary orogenic belts in the world. The eastern segment of CAOB is dominated by Paleozoic Paleo Asian Ocean tectonic regime, Mesozoic Paleo-Pacific tectonic regime and Mongolian-Okhotsk tectonic regime. The Songliao and Jiamusi blocks are located in the easternmost part of the CAOB and are the key region to solve the problem about overprinting processes of multiple tectonic regimes. It is generally believed that the Mudanjiang Ocean between the two blocks was finally closed in the Mesozoic, but the Paleozoic magmatism also developed along the Mudanjiang suture zone, while on both sides of the suture zone, there were comparable Paleozoic strata, indicating that the two blocks had converged during the Paleozoic, and the evolution history of the two blocks in the Late Paleozoic remains controversial. The Carboniferous-Permian terrestrial strata mainly developed in Binxian, Wuchang and Tieli on Songliao Block, Baoqing and Mishan on Jiamusi Block. Samples from the Songliao and Jiamusi blocks in the Late Carboniferous-Early Permian and Late Permian are collected for comparative analysis. The LAICP-MS zircon U-Pb dating results show that the maximum depositional age of Middle Permian Tumenling Formation and Late Permian Hongshan Formation in Songliao Block is ～260 Ma, while that of Tatouhe Formation and Carboniferous strata in Jiamusi Block are ～290 Ma and ～300 Ma, respectively, which supports the previous stratigraphic division scheme. The age peaks of ～290–300 Ma, ～400 Ma, ～500 Ma appeared in the Late Carboniferous to Early Permian strata of Jiamusi Block and the Middle Permian strata of Songliao Block. The age peak of ～500 Ma in the Middle Permian strata of Songliao Block may come from the Cambrian basement, Mashan Complex, of Jiamusi Block, while the age peaks of ～420–440 Ma in the Carboniferous strata of Jiamusi Block may come from the Silurian magmatic arc in Zhangguangcai Range in the eastern margin of Songliao Block, reflects the history that they had been potential sources of each other, indicating that they may have combined in the Paleozoic. The Hongshan Formation of Songliao Block in the Late Permian lacks the age peak of ～500 Ma, which indicate that Jiamusi Block was not the provenance of Songliao Block in the Late Permian, that is, there was a palaeogeographic isolation between the two blocks. Combined with the ～210 Ma bimodal volcanic rocks developed along the Mudanjiang suture zone reported previously, we believe that the oceanic basin between the Songliao and Jiamusi blocks should have been connected in Late Permian and reopened during Late Permian to Late Triassic.  相似文献   

17.
The gneisses and metabasites of the Sierra de Limón Verde were investigated by P–T–t determinations. The rocks are unique in the Central Andes because of their high pressure metamorphic conditions with P≈13±1 kbar at T≈660–720°C. Their age of metamorphism is ≈270 Ma, based on Sm–Nd mineral isochrons. Final uplift of the isolated basement block occurred in the Triassic with a K–Ar age of biotite at ca 235 Ma. In our interpretation, the protolith of the Permian metamorphic rocks is the crust that formed and stabilized during Early Paleozoic. The Sierra de Limón Verde rocks give insight into the lowermost part of the crust in Early Mesozoic. Its Sm–Nd isotopic composition is indistinguishable from the composition of the crust that formed in the Early Paleozoic metamorphic–magmatic cycle (ca 500 Ma) in northern Chile and NW Argentina. The tectonic-geodynamic setting that triggered the high P (∼45 km depth) metamorphism and the locally restricted exhumation of the rocks remains speculative. Continental collision or a subduction related accretionary complex is unlikely considering the regional geological situation. Transpression–transtension in a strike slip system along the continental margin is suggested as a hypothesis for future investigations.  相似文献   

18.
王雷  刘俊来  滕超  常玉巧 《地质论评》2021,67(1):251-264
晚古生代—早中生代古亚洲洋板块俯冲华北板块在辽北法库地区形成大型产状近水平的韧性剪切带。剪切带发展伴随着多期幔源及壳源的岩浆侵入,侵入岩在韧性剪切作用下发生韧性变形,记录了韧性剪切带变形历史。详细的野外地质调查结合岩石的宏观变形、显微构造及石英c轴组构特征分析,揭示了法库韧性剪切带内五龙山杂岩、高丽沟杂岩、早期十间房超单元变形处于上盘向北的剪切作用之下,晚期十间房超单元岩石变形指示构造运动转变为上盘向南剪切。LA-ICP-MS锆石U-Pb分析结果显示高丽沟杂岩变形时间为264.7±3.6 Ma(MSWD=1.3),早期十间房超单变形时间为253.9±4.3 Ma(MSWD=3.3),晚期十间房超单元244.0±3.0 Ma(MSWD=1.9)。岩石地球化学特征表明早期十间房超单元及小房申岩体中部分岩石来源于部分熔融的岩石圈地幔。结合前人研究成果,我们认为华北板块北缘东段(辽北地区)晚二叠世(264.7~253.9 Ma)处于古亚洲洋板块俯冲华北板块作用之下;晚二叠世至早三叠世(253.9~244.0 Ma)构造体制转变为碰撞后伸展且逐渐停止,244.0±3.0 Ma碰撞后伸展逐渐结束;构造体制转变并逐渐结束的过程是壳幔共同作用的结果,暗示了古亚洲洋板块的俯冲板片断离、重力失衡,这标志着辽北地区古亚洲洋构造域演化结束。  相似文献   

19.
With the aim of constraining the influence of the surrounding plates on the Late Paleozoic–Mesozoic paleogeographic and tectonic evolution of the southern North China Craton (NCC), we undertook new U–Pb and Hf isotope data for detrital zircons obtained from ten samples of upper Paleozoic to Mesozoic sediments in the Luoyang Basin and Dengfeng area. Samples of upper Paleozoic to Mesozoic strata were obtained from the Taiyuan, Xiashihezi, Shangshihezi, Shiqianfeng, Ermaying, Shangyoufangzhuang, Upper Jurassic unnamed, and Lower Cretaceous unnamed formations (from oldest to youngest). On the basis of the youngest zircon ages, combined with the age-diagnostic fossils, and volcanic interlayer, we propose that the Taiyuan Formation (youngest zircon age of 439 Ma) formed during the Late Carboniferous and Early Permian, the Xiashihezi Formation (276 Ma) during the Early Permian, the Shangshihezi (376 Ma) and Shiqianfeng (279 Ma) formations during the Middle–Late Permian, the Ermaying Group (232 Ma) and Shangyoufangzhuang Formation (230 and 210 Ma) during the Late Triassic, the Jurassic unnamed formation (154 Ma) during the Late Jurassic, and the Cretaceous unnamed formation (158 Ma) during the Early Cretaceous. These results, together with previously published data, indicate that: (1) Upper Carboniferous–Lower Permian sandstones were sourced from the Northern Qinling Orogen (NQO); (2) Lower Permian sandstones were formed mainly from material derived from the Yinshan–Yanshan Orogenic Belt (YYOB) on the northern margin of the NCC with only minor material from the NQO; (3) Middle–Upper Permian sandstones were derived primarily from the NQO, with only a small contribution from the YYOB; (4) Upper Triassic sandstones were sourced mainly from the YYOB and contain only minor amounts of material from the NQO; (5) Upper Jurassic sandstones were derived from material sourced from the NQO; and (6) Lower Cretaceous conglomerate was formed mainly from recycled earlier detritus.The provenance shift in the Upper Carboniferous–Mesozoic sediments within the study area indicates that the YYOB was strongly uplifted twice, first in relation to subduction of the Paleo-Asian Ocean Plate beneath the northern margin of the NCC during the Early Permian, and subsequently in relation to collision between the southern Mongolian Plate and the northern margin of the NCC during the Late Triassic. The three episodes of tectonic uplift of the NQO were probably related to collision between the North and South Qinling terranes, northward subduction of the Mianlue Ocean Plate, and collision between the Yangtze Craton and the southern margin of the NCC during the Late Carboniferous–Early Permian, Middle–Late Permian, and Late Jurassic, respectively. The southern margin of the central NCC was rapidly uplifted and eroded during the Early Cretaceous.  相似文献   

20.
本文对延边开山屯地区二叠纪侵入岩和地层中的(碎屑)锆石进行了LA-ICP-MS和SIMS U-Pb年代学及Hf同位素的研究,同时对侵入岩进行了全岩地球化学特征的研究,以便制约开山屯地区的构造属性以及延边地区晚古生代-早中生代演化历史。延边开山屯地区大蒜沟组复成分砾岩和岩屑杂砂岩中锆石最年轻峰值年龄为298Ma和293Ma,此外还存在330Ma、366Ma、438Ma、454Ma、479Ma峰值年龄。这些古生代碎屑锆石的ε_(Hf)(t)值介于-1.14～+15.17之间;开山屯组长石杂砂岩和长石砂岩中的锆石最年轻年龄峰值分别为259Ma和253Ma,此外还存在279Ma、456Ma、476Ma、500Ma、529Ma以及新元古代-古元古代(891～1765Ma)的峰值年龄。其中古生代碎屑锆石的ε_(Hf)(t)值介于-5.22～+10.15之间。开山屯地区中二叠世闪长岩和晚二叠世辉长闪长岩的形成时代分别为261Ma和256Ma,属于低钾拉斑-中钾钙碱性系列,相对富集轻稀土和大离子亲石元素,亏损重稀土和高场强元素,主要来源于受俯冲流体/熔体交代的亏损地幔楔的部分熔融。综合研究认为,开山屯地区与兴凯地块具有亲缘性;大蒜沟组的沉积时限为早-中二叠世,形成于兴凯地块西部活动大陆边缘的弧前盆地或增生楔环境;开山屯组形成于早-中三叠世,具有双向物源的特点(华北板块和兴凯地块)。早-中二叠世延边地区处于活动大陆边缘的构造背景。延边地区的古亚洲洋于早-中三叠世最终闭合。  相似文献   

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