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Subduction erosion, which occurs at all convergent plate boundaries associated with magmatic arcs formed on crystalline forearc basement, is an important process for chemical recycling, responsible globally for the transport of ~1.7 Armstrong Units (1 AU = 1 km3/yr) of continental crust back into the mantle. Along the central Andean convergent plate margin, where there is very little terrigenous sediment being supplied to the trench as a result of the arid conditions, the occurrence of mantle-derived olivine basalts with distinctive crustal isotopic characteristics (87Sr/86Sr ≥ 0.7050; εNd ≤ −2; εHf ≤ +2) correlates spatially and/or temporally with regions and/or episodes of high rates of subduction erosion, and a strong case can be made for the formation of these basalts to be due to incorporation into the subarc mantle wedge of tectonically eroded and subducted forearc continental crust. In other convergent plate boundary magmatic arcs, such as the South Sandwich and Aleutian Islands intra-oceanic arcs and the Central American and Trans-Mexican continental margin volcanic arcs, similar correlations have been demonstrated between regions and/or episodes of relatively rapid subduction erosion and the genesis of mafic arc magmas containing enhanced proportions of tectonically eroded and subducted crustal components that are chemically distinct from pelagic and/or terrigenous trench sediments. It has also been suggested that larger amounts of melts derived from tectonically eroded and subducted continental crust, rising as diapirs of buoyant low density subduction mélanges, react with mantle peridotite to form pyroxenite metasomatites that than melt to form andesites. The process of subduction erosion and mantle source region contamination with crustal components, which is supported by both isotopic and U-Pb zircon age data implying a fast and efficient connectivity between subduction inputs and magmatic outputs, is a powerful alternative to intra-crustal assimilation in the generation of andesites, and it negates the need for large amounts of mafic cumulates to form within and then be delaminated from the lower crust, as required by the basalt-input model of continental crustal growth. However, overall, some significant amount of subducted crust and sediment is neither underplated below the forearc wedge nor incorporated into convergent plate boundary arc magmas, but instead transported deeper into the mantle where it plays a role in the formation of isotopically enriched mantle reservoirs. To ignore or underestimate the significance of the recycling of tectonically eroded and subducted continental crust in the genesis of convergent plate boundary arc magmas, including andesites, and for the evolution of both the continental crust and mantle, is to be on the wrong side of history in the understanding of these topics. 相似文献
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俯冲带部分熔融 总被引：3，自引：3，他引：0
俯冲带是地幔对流环的下沉翼,是地球内部的重要物理与化学系统。俯冲带具有比周围地幔更低的温度,因此,一般认为俯冲板片并不会发生部分熔融,而是脱水导致上覆地幔楔发生部分熔融。但是,也有研究认为,在水化的洋壳俯冲过程中可以发生部分熔融。特别是在下列情况下,俯冲洋壳的部分熔融是俯冲带岩浆作用的重要方式。年轻的大洋岩石圈发生低角度缓慢俯冲时,洋壳物质可以发生饱和水或脱水熔融,基性岩部分熔融形成埃达克岩。太古代的俯冲带很可能具有与年轻大洋岩石圈俯冲带类似的热结构,俯冲的洋壳板片部分熔融可以形成英云闪长岩-奥长花岗岩-花岗闪长岩。平俯冲大洋高原中的基性岩可以发生部分熔融产生埃达克岩。扩张洋中脊俯冲可以导致板片窗边缘的洋壳部分熔融形成埃达克岩。与俯冲洋壳相比,俯冲的大陆地壳具有很低的水含量,较难发生部分熔融,但在超高压变质陆壳岩石的折返过程中可以经历广泛的脱水熔融。超高压变质岩在地幔深部熔融形成的熔体与地幔相互作用是碰撞造山带富钾岩浆岩的可能成因机制。碰撞造山带的加厚下地壳可经历长期的高温与高压变质和脱水熔融,形成S型花岗岩和埃达克质岩石。 相似文献
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It has been thought that granitic crust,having been formed on the surface,must have survived through the Earth’s evolution because of its buoyancy.At subduction zones continental crust is predominantly created by arc magmatism and is returned to the mantle via sediment subduction,subduction erosion, and continental subduction.Granitic rocks,the major constituent of the continental crust,are lighter than the mantle at depths shallower than 270 km,but we show here,based on first principles calculations, that beneath 270 km they have negative buoyancy compared to the surrounding material in the upper mantle and transition zone,and thus can be subducted in the depth range of 270-660 km.This suggests that there can be two reservoirs of granitic material in the Earth,one on the surface and the other at the base of the mantle transition zone(MTZ).The accumulated volume of subducted granitic material at the base of the MTZ might amount to about six times the present volume of the continental crust.Our calculations also show that the seismic velocities of granitic material in the depth range from 270 to 660 km are faster than those of the surrounding mantle.This could explain the anomalous seismic-wave velocities observed around 660 km depth.The observed seismic scatterers and reported splitting of the 660 km discontinuity could be due to jadeite dissociation,chemical discontinuities between granitic material and the surrounding mantle,or a combination thereof. 相似文献
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位于青藏高原南部的冈底斯岩浆弧形成于中生代新特提斯大洋岩石圈的长期俯冲过程中,而且在印度与亚洲大陆碰撞过程中叠加了强烈的新生代岩浆作用,是世界上典型的复合型大陆岩浆弧,已经成为研究汇聚板块边缘岩浆作用和大陆地壳生长与再造的天然实验室。基于对现有研究成果的总结,我们将冈底斯岩浆弧的岩浆构造演化划分为5个阶段：第1阶段发生在晚白垩世之前,以新特提斯洋岩石圈长期正常俯冲和钙碱性弧岩浆岩的发育为特征;第2阶段发生在晚白垩世时期,以活动的新特提斯洋中脊发生俯冲和强烈的岩浆作用与显著的新生地壳生长为特征;第3阶段发生在晚白垩世晚期,以残余的新特提斯大洋岩石圈俯冲和正常弧型岩浆作用为特征;第4阶段发生在古新世至中始新世,以印度与亚洲大陆碰撞、俯冲的新特提斯洋岩石圈回转和断离,及其诱发的幔源岩浆作用、新生和古老地壳的强烈再造为特征;第5阶段为发生在晚渐新世到中中新世的后碰撞阶段,深俯冲印度岩石圈的回转和断离,或加厚岩石圈地幔的对流移去导致了加厚下地壳的部分熔融和埃达克质岩石的广泛发育,同时伴随幔源钾质超钾质岩浆作用。冈底斯弧岩浆作用与岩浆成分的系统时空变化很好地记录了从新特提斯洋俯冲到印度亚洲大陆碰撞的完整构造演化过程。 相似文献
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大陆深俯冲的最大深度——来自数值模拟实验的结果 总被引：1，自引：0，他引：1
采用粘弹性材料8块体有限元模型并设定温度场后进行的大陆深俯冲二维数值模拟表明,在组合载荷(负浮力、洋中脊推力从上到下10～30MPa 和地幔对流拖曳力100MPa)作用下,陆壳俯冲实际垂向位移可达117km,最终俯冲深度达到147km,而洋壳实际垂向位移约162km,最终俯冲深度达到231km;在洋壳、陆壳俯冲到一定深度以前,它们的俯冲速度基本保持不变,表现为洋壳、陆壳底端的位移-时间曲线近似为直线;当俯冲时间超过9Ma,洋壳、陆壳分别达到167km、96km 深度后,俯冲速度会越来越慢。 相似文献
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Cheng-Horng Lin 《地学学报》2002,14(4):281-287
ABSTRACT A tectonic model of active continental subduction followed by crustal exhumation is proposed to explain the orogeny in Taiwan. The subducted crust is represented by a low-velocity zone dipping eastwards beneath the major part of Taiwan, while the exhumed crust is marked by a high-velocity bulge, high heat flow and absence of seismicity beneath the eastern Central Range. The boundary between the subducted and exhumed crust has been identified from surface geology and analyses of thermal history across the Central Range. The dynamic force that has been driving the exhumed crust is identified by results from focal mechanisms, structural geology and geodetic survey in the eastern Central Range. Such a tectonic model may provide a good explanation for the evolution of the Taiwan Orogeny, as well as an active case for studying other long-extinct systems of continental subduction and exhumation. 相似文献
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地幔氧逸度与俯冲带深部碳循环 总被引：2，自引：2，他引：0
地幔氧逸度通过改变含碳相的存在形式和迁移方式来影响深部碳循环。本文结合最新的地幔氧逸度实验模拟和岩石学研究成果,探讨了地幔氧逸度时空分布对深部碳循环的影响。文章重点结合地幔减压熔融形成洋壳、新生洋壳蚀变、洋壳俯冲变质、深俯冲洋壳熔融以及俯冲洋壳物质(流体和固体)通过岩浆(岛弧和地幔柱)作用循环出地表等重要地质过程,探讨了伴随洋壳俯冲作用的深部碳循环过程。由于地幔氧逸度的时空变化,俯冲带含碳相表现出不同的存在形式和迁移能力。通过对西南天山俯冲带碳循环的岩石学和实验研究,我们认为应当进一步深入研究俯冲带氧化还原状态及其对俯冲带深部碳循环的影响。 相似文献
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《International Geology Review》2012,54(9):1051-1071
Asia is the world’s largest but youngest continent, in which Pacific-type (P-type) and collision-type (C-type) orogenic belts coexist with numerous amalgamated continental blocks. P-type orogens represent major sites of continental growth through tonalite-trondhjemite-granodiorite type (TTG-type) juvenile granitoid magmatism and accretion of oceanic crust and intra-oceanic arcs. The Asian continent includes several P-type orogenic belts, of which the largest are the Central Asian and Western Pacific. The Central Asian Orogenic Belt is dominated by P-type fossil orogens arranged with a regular northward subduction polarity. The Western Pacific is characterized by ongoing P-type orogeny related to the westward subduction of the Pacific plate. Asia has a multi-cratonic structure and its post-Palaeozoic history has witnessed amalgamation of the Laurasia composite continent and Pangaea supercontinent. Nowadays, Asia is surrounded by double-sided subduction zones, which generate new TTG-type crust and supply oceanic crust and microcontinents to its active margins. The TTG-crust can be tectonically eroded and subducted down to the mantle transition zone to form a ‘second’ continent, which may generate mantle upwelling, plumes, and extensive intra-plate volcanism. Moreover, recent plate movements around Asia are dominated by northward directions, which resulted in the India–Eurasia and Arabia–Eurasia collisions beginning at 50–45 and 23–20 Ma, respectively, and will result in Africa–Eurasia collision in the near future. Therefore, Asia is the best candidate to serve as the nucleus for a future supercontinent ‘Amasia’, likely to form 200–250 Ma in the future. In this paper we unravel a puzzle of continental growth in Asia through P-type orogeny by discussing its tectonic history and geological structure, subduction polarity in P-type orogens, tectonic erosion of TTG-type crust and arc subduction at convergent margins, generation of mantle plumes, and prospects of Asia growth and overgrowth. 相似文献
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《Gondwana Research》2010,17(3-4):572-580
The Izu-Bonin intra-oceanic arc with 20–35 km thick continental crust is being subducted under the Honshu, presumably since 17 Ma. Tomographic image clearly demonstrates that the whole Izu-Bonin arc is subducting under the Honshu arc. Geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 Ma. 相似文献
13.
Izu-Bonin arc subduction under the Honshu island, Japan: Evidence from geological and seismological aspect 总被引：1，自引：1，他引：0
Shinji Yamamoto Junichi Nakajima Akira Hasegawa Shigenori Maruyama 《Gondwana Research》2009,16(3-4):572-580
The Izu-Bonin intra-oceanic arc with 20–35 km thick continental crust is being subducted under the Honshu, presumably since 17 Ma. Tomographic image clearly demonstrates that the whole Izu-Bonin arc is subducting under the Honshu arc. Geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 Ma. 相似文献
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Role of tonalite-trodhjemite-granite (TTG) crust subduction on the mechanism of supercontinent breakup 总被引：1，自引：0，他引：1
The tonalite-trondhjemite-granite (TTG) crust has been considered to be buoyant and hence impossible to be subducted into the deep mantle. However, recent studies on the juvenile arc in the western Pacific region indicate that immature island arcs subduct into the deep mantle in most cases, except in the case of parallel arc collision. Moreover, sediment trapped subduction and tectonic erosion are also common. This has important implications in evaluating the role of TTG crust in the deep mantle and probably on the bottom of the mantle. Because the TTG crust is enriched in K, U and Th, ca. 20 times more than that of CI chondrite, the accumulated TTG on the Core Mantle Boundary (CMB) would have played a critical role to initiate plumes or superplumes radiating from the thermal boundary layer, particularly after 2.0 Ga, related to the origin of superplume-supercontinent cycle. This is because selective subduction of oceanic lithosphere including sediment-trapped subduction, tectonic erosion and arc- and microcontinent-subduction proceeded under the supercontinent before the final amalgamation ca. 200-300 million years after the formation of the nuclei. We speculate the mechanism of superplume evolution through the subduction of TTG-crust and propose that this process might have played a dominant role in supercontinent breakup. 相似文献
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Based on petrological and geochemical arguments, it is possible that arc magma is derived from subducted oceanic crust. In this paper, regional thermal models have been constructed to study the feasibility of melting cold subducted oceanic crusts at shallow depth (i.e. at depths of about 100 km) by a dynamic mantle. Calculated results suggest that plate subduction will generate an induced flow in the wedge above the subducting slab. This current continuously feeds hot mantle material into the corner and onto the slab surface. A high temperature thermal environment can be maintained in the vicinity of the wedge corner, immediately beneath the over-riding plate. Our regional models further demonstrate quantitatively that production of local melting is possible just about 30 km down dip from the asthenosphere wedge corner. Additional geological processes such as reasonable amounts of shear heating and minor dehydration (which will lower the local melting temperature) will further increase the probability of melting a cold subducted oceanic crust at shallow depth. 相似文献
16.
WANG Zhimin XU Bei ZHOU Yaoqi XU Hehua HUANG Shaoying The Key Laboratory of Orogenic Belts Crustal Evolution 《《地质学报》英文版》2004,78(1):313-319
Continent subduction is one of the hot research problems in geoscience. New models presented here have been set up and two-dimensional numerical modeling research on the possibility of continental subduction has been made with the finite element software, ANSYS, based on documentary evidence and reasonable assumptions that the subduction of oceanic crust has occurred, the subduction of continental crust can take place and the process can be simplified to a discontinuous plane strain theory model. The modeling results show that it is completely possible for continental crust to be subducted to a depth of 120 km under certain circumstances and conditions. At the same time, the simulations of continental subduction under a single dynamical factor have also been made, including the pull force of the subducted oceanic lithosphere, the drag force connected with mantle convection and the push force of the mid-ocean ridge. These experiments show that the drag force connected with mantle convection is critical fo 相似文献
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Insights from trace element geochemistry as to the roles of subduction zone geometry and subduction input on the chemistry of arc magmas 总被引：2，自引：0，他引：2
Heidi Wehrmann Kaj Hoernle Dieter Garbe-Schönberg Guillaume Jacques Julia Mahlke Kai Schumann 《International Journal of Earth Sciences》2014,103(7):1929-1944
Subduction zones of continental, transitional, and oceanic settings, relative to the nature of the overriding plate, are compared in terms of trace element compositions of mafic to intermediate arc rocks, in order to evaluate the relationship between subduction parameters and the presence of subduction fluids. The continental Chilean Southern Volcanic Zone (SVZ) and the transitional to oceanic Central American Volcanic Arc (CAVA) show increasing degrees of melting with increasing involvement of slab fluids, as is typical for hydrous flux melting beneath arc volcanoes. At the SVZ, the central segment with the thinnest continental crust/lithosphere erupted the highest-degree melts from the most depleted sources, similar to the oceanic-like Nicaraguan segment of the CAVA. The northern part of the SVZ, located on the thickest continental crust/lithosphere, exhibits features more similar to Costa Rica situated on the Caribbean Large Igneous Province, with lower degrees of melting from more enriched source materials. The composition of the slab fluids is characteristic for each arc system, with a particularly pronounced enrichment in Pb at the SVZ and in Ba at the CAVA. A direct compositional relationship between the arc rocks and the corresponding marine sediments that are subducted at the trenches clearly shows that the compositional signature of the lavas erupted in the different arcs carries an inherited signal from the subducted sediments. 相似文献
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Renjie Zhao Quanshu Yan Haitao Zhang Yili Guan Zhenmin Ge Long Yuan Shishuai Yan 《地球科学进展》1986,35(8):789-803
Subducted sediments play an important role in crust-mantle interaction and deep mantle processes, especially for subduction zone magmatism and mantle geochemistry. The current rate of Global Subducting Sediments (GLOSS) is 0.5~0.7 km3/a. The GLOSS are composed of terrigenous material(76 wt.%), calcium carbonate(7 wt.%), opal(10 wt.%) and mineral-bound H2O+(7 wt.%). The chemical compositions of GLOSS are similar to those of upper continental crust which is mainly controlled by the terrigenous materials, and yet the materials formed by marine processes will dilute the terrigenous materials. The components of subducted sediments are different among trenches. In the accretionary margin, the components of subducted sediments are similar to those of the upper crust, while in the non-accretionary margin the components are terrigenous materials plus those produced by marine processes. During subduction, subducted sediments will released fluids, melt or supercritical fluid to affect island arc/back-arc basin magmatism by means of aqueous fluid or sediment melt. In addition, a part of subducted sediments, together with underlying altered oceanic crust/lithosphere, recycle into the mantle and contribute to the mantle heterogeneity. Geochemical tracers indicate that subducted sediments play variable contributions to the magmatic processes in different tectonic setting. Thus, subducted sediments play an important role in two relatively independent dynamics systems (plate tectonics and mantle plume), as well as related mantle evolution models. As a result, by accurately calculating the compositions of subduction sediments and using various geochemical indicators, we can further limit the input and output fluxes of various elements or isotopes, and then obtain more accurately residual subducted components, which can provide us some important clues for geodynamic process. 相似文献
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五十年前板块构造理论的诞生是地球科学领域的一场革命,它为理解地球如何运作构建了基本框架。过去五十年对该理论的进一步研究告诉我们地质过程最终都是地球热损失的结果。例如,大洋岩石圈板块在洋中脊形成,其运动和增生以及最终通过俯冲带进入地幔导致地幔冷却降温,从而导致大规模的地幔对流。亦即,板块构造的直接驱动力是俯冲大洋岩石圈板块的下沉力。因此,没有俯冲带就没有板块构造,但是俯冲带如何开始仍然有争议。对俯冲起始的研究从未中断,有数值模拟也有地质推断。2014年在西太平洋用三个IODP航次(350、351和352)来检验“自发”和“诱发”俯冲开始的想法。所有这些努力都值得肯定,但这些是无法检验的想法。无法检验意味着没有结果。本文介绍至今唯一可用地质学方法检验的假说,亦即“岩石圈内横向物质组成差异导致的浮力差是俯冲带形成的起因”。这种浮力差位于海底高原的边部和被动大陆边缘,因此这些部位是未来俯冲带起始的必然轨迹。在远离这些部位的正常洋盆内因缺乏浮力差而俯冲带不可能起始。换句话说,“所有岛弧一定有大陆(或海底高原)基底”,这可以通过采集和研究岛弧基底岩石来验证。 相似文献
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K. M. Haase C. Beier S. Fretzdorff J. L. Smellie D. Garbe-Schönberg 《Contributions to Mineralogy and Petrology》2012,163(6):1103-1119
Lavas from the South Shetland Islands volcanic arc (northern Antarctic Peninsula) have been investigated in order to determine the age, petrogenesis and compositional evolution of a long-lived volcanic arc constructed on 32-km-thick crust, a thickness comparable with average continental crust. New 40Ar–39Ar ages for the volcanism range between 135 and 47 Ma and, together with published younger ages, confirm a broad geographical trend of decreasing ages for the volcanism from southwest to northeast. The migration pattern breaks down in Palaeogene time, with Eocene magmatism present on both Livingston and King George islands, which may be due to a change in both subduction direction and velocity after c. 60 Ma. The lavas range from tholeiitic to calc-alkaline, but there is no systematic change with age or geographic location. The compositions of lavas from the north-eastern islands indicate magma generation in a depleted mantle wedge with relatively low Sr and high Nd isotopic compositions and low U/Nb, Th/Nd and Ba/Nb ratios that was metasomatized by hydrous fluids from subducted basaltic oceanic crust. Lavas from the south-western islands show an additional sedimentary influence most likely due to fluid release from subducted sediments into the mantle wedge. Although magmatic activity in the South Shetland arc extended over c. 100 m.y., there is no evolution towards more enriched or evolved magmas with time. Few South Shetland arc lavas are sufficiently enriched with incompatible elements to provide a potential protolith for the generation of average continental crust. We conclude that even long-established subduction zones with magmatic systems founded on relatively thick crust do not necessarily form continental crustal building blocks. They probably represent only the juvenile stages of continental crust formation, and additional re-working, for example during subsequent arc-continental margin collision, is required before they can evolve into average continental crust. 相似文献