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1.
笔者在"关于板块运动启动时间的争论"一文(陆松年等,2016)基础上,参阅公开发表的部分文章,介绍了前板块岩浆洋和停滞盖研究的新进展,并再次讨论有关板块运动启动时间的不同认识和观点。根据太阳系30个类地行星天体图像资料,硅酸盐质行星体在它的生命期由于冷却和岩石圈增厚似乎经历过多种构造样式,包括岩浆洋、多类型停滞盖以及板块构造。硅酸盐类行星由于增生、分异、撞击和放射性活动,使星体变热,发生熔融反应而形成"岩浆洋"。硅酸盐星球体早期很可能是大面积但寿命很短的岩浆洋,之后的星球可能受两种构造模型控制:停滞盖构造和板块构造。已有资料表明,停滞盖构造是类地行星的主要构造类型,而板块构造在类地行星中是十分罕见的。停滞盖构造是一个单一的、围绕天体的板块,基本由硅酸盐质岩石圈组成。停滞盖构造有三种主要变化形态——热管、滴状及柱状体、拆沉及上涌流。板块构造启动时间从>4.4Ga到0.85Ga至少有11种不同观点:认为板块构造始于冥古宙的有1种、始于始-古太古代的有3种、始于中-新太古代的有4种、始于古元古代有1种、始于新元古代的有2种。本文重点介绍了地球冥古宙-太古宙板块运动启动的地质学证据和特点。 相似文献
2.
Derek Wyman 《地学前缘(英文版)》2018,9(1):3-17
Evidence for episodic crustal growth extending back to the Hadean has recently prompted a number of numerically based geodynamic models that incorporate cyclic changes from stagnant lid to mobile lid tectonics. A large part of the geologic record is missing for the times at which several of these cycles are inferred to have taken place. The cratons, however, are likely to retain important clues relating to similar cycles developed in the Mesoarchean and Neoarchean. Widespread acceptance of a form of plate tectonics by ～3.2 Ga is not at odds with the sporadic occurrence of stagnant lid tectonics after this time. The concept of scale as applied to cratons, mantle plumes and Neoarchean volcanic arcs are likely to provide important constraints on future models of Earth's geodynamic evolution. The Superior Province will provide some of the most concrete evidence in this regard given that its constituent blocks may have been locked into a stagnant lid relatively soon after their formation and then assembled in the next global plate tectonic interval. Perceived complexities associated with inferred mantle plume — volcanic arc associations in the Superior Province and other cratons may be related to an over estimation of plume size. A possible stagnant lid episode between ～2.9 Ga and ～2.8 Ga is identified by previously unexplained lapses in volcanism on cratons, including the Kaapvaal, Yilgarn and Superior Province cratons. If real, then mantle dynamics associated with this episode likely eliminated any contemporaneous mantle plume incubation sites, which has important implications for widespread plumes developed at ～2.7 Ga and favours a shallow mantle source in the transition zone. The Superior Province provides a uniquely preserved local proxy for this global event and could serve as the basis for detailed numerical models in the future. 相似文献
3.
When Earth's tectonic style transitioned from stagnant lid (single plate) to the modern episode of plate tectonics is important but unresolved, and all lines of evidence should be considered, including the climate record. The transition should have disturbed the oceans and atmosphere by redistributing continents, increasing explosive arc volcanism, stimulating mantle plumes and disrupting climate equilibrium established by the previous balance of silicate‐weathering greenhouse gas feedbacks. Formation of subduction zones would redistribute mass sufficiently to cause true polar wander if the subducted slabs were added in the upper mantle at intermediate to high latitudes. The Neoproterozoic Snowball Earth climate crisis may reflect this transition. The transition to plate tectonics is compatible with nearly all proposed geodynamic and oceanographic triggers for Neoproterozoic Snowball Earth events, and could also have contributed to biological triggers. Only extraterrestrial triggers cannot be reconciled with the hypothesis that the Neoproterozoic climate crisis was caused by a prolonged (200–250 m.y.) transition to plate tectonics. 相似文献
4.
The evolution of Earth＇s biosphere,atmosphere and hydrosphere is tied to the formation of continental crust and its subsequent movements on tectonic plates.The supercontinent cycle posits that the continental crust is periodically amalgamated into a single landmass,subsequently breaking up and dispersing into various continental fragments.Columbia is possibly the first true supercontinent,it amalgamated during the 2.0-1.7 Ga period,and collisional orogenesis resulting from its formation peaked at 1.95-1.85 Ga.Geological and palaeomagnetic evidence indicate that Columbia remained as a quasi-integral continental lid until at least 1.3 Ga.Numerous break-up attempts are evidenced by dyke swarms with a large temporal and spatial range; however,palaeomagnetic and geologic evidence suggest these attempts remained unsuccessful.Rather than dispersing into continental fragments,the Columbia supercontinent underwent only minor modifications to form the next supercontinent （Rodinia） at 1.1 -0.9 Ga; these included the transformation of external accretionary belts into the internal Grenville and equivalent collisional belts.Although Columbia provides evidence for a form of ‘lid tectonics’,modern style plate tectonics occurred on its periphery in the form of accretionary orogens.The detrital zircon and preserved geological record are compatible with an increase in the volume of continental crust during Columbia＇s lifespan; this is a consequence of the continuous accretionary processes along its margins.The quiescence in plate tectonic movements during Columbia＇s lifespan is correlative with a long period of stability in Earth＇s atmospheric and oceanic chemistry.Increased variability starting at 1.3 Ga in the environmental record coincides with the transformation of Columbia to Rodinia; thus,the link between plate tectonics and environmental change is strengthened with this interpretation of supercontinent history. 相似文献
5.
Robert J.Stern 《地学前缘(英文版)》2016,7(4):573-580
As we continue searching for exoplanets,we wonder if life and technological species capable of communicating with us exists on any of them.As geoscientists,we can also wonder how important is the presence or absence of plate tectonics for the evolution of technological species.This essay considers this question,focusing on tectonically active rocky(silicate) planets,like Earth,Venus,and Mars.The development of technological species on Earth provides key insights for understanding evolution on exoplanets,including the likely role that plate tectonics may play.An Earth-sized silicate planet is likely to experience several tectonic styles over its lifetime,as it cools and its lithosphere thickens,strengthens,and becomes denser.These include magma ocean,various styles of stagnant lid,and perhaps plate tectonics.Abundant liquid water favors both life and plate tectonics.Ocean is required for early evolution of diverse single-celled organisms,then colonies of cells which specialized further to form guts,appendages,and sensory organisms up to the complexity of fish(central nervous system,appendages,eyes).Large expanses of dry land also begin in the ocean,today produced above subduction zones in juvenile arcs and by their coalescence to form continents,although it is not clear that plate tectonics was required to create continental crust on Earth.Dry land of continents is required for further evolution of technological species,where modification of appendages for grasping and manipulating,and improvement of eyes and central nervous system could be perfected.These bioassets allowed intelligent creatures to examine the night sky and wonder,the beginning of abstract thinking,including religion and science.Technology arises from the exigencies of daily living such as tool-making,agriculture,clothing,and weapons,but the pace of innovation accelerates once it is allied with science.Finally,the importance of plate tectonics for developing a technological species is examined via a thought experiment using two otherwise identical planets:one with plate tectonics and the other without.A planet with oceans,continents,and plate tectonics maximizes opportunities for speciation and natural selection,whereas a similar planet without plate tectonics provides fewer such opportunities.Plate tectonics exerts environmental pressures that drive evolution without being capable of extinguishing all life.Plate tectonic processes such as the redistribution of continents,growth of mountain ranges,formation of land bridges,and opening and closing of oceans provide a continuous but moderate environmental pressure that stimulates populations to adapt and evolve.Plate tectonics may not be needed in order for life to begin,but evolution of technological species is favored on planets with oceans,continents,plate tectonics,and intermittently clear night sky. 相似文献
6.
The Earth is the only body in the solar system for which significant observational constraints are accessible to such a degree that they can be used to discriminate between competing models of Earth's tectonic evolution.It is a natural tendency to use observations of the Earth to inform more general models of planetary evolution.However,our understating of Earth's evolution is far from complete.In recent years,there has been growing geodynamic and geochemical evidence that suggests that plate tectonics may not have operated on the early Earth,with both the timing of its onset and the length of its activity far from certain.Recently,the potential of tectonic bi-stability(multiple stable,energetically allowed solutions)has been shown to be dynamically viable,both from analytical analysis and through numeric experiments in two and three dimensions.This indicates that multiple tectonic modes may operate on a single planetary body at different times within its temporal evolution.It also allows for the potential that feedback mechanisms between the internal dynamics and surface processes(e.g.,surface temperature changes driven by long term climate evolution),acting at different thermal evolution times,can cause terrestrial worlds to alternate between multiple tectonic states over giga-year timescales.The implication within this framework is that terrestrial planets have the potential to migrate through tectonic regimes at similar‘thermal evolution times'(e.g.,points were they have a similar bulk mantle temperature and energies),but at very different'temporal times'(time since planetary formation).It can be further shown that identical planets at similar stages of their evolution may exhibit different tectonic regimes due to random variations.Here,we will discuss constraints on the tectonic evolution of the Earth and present a novel framework of planetary evolution that moves toward probabilistic arguments based on general physical principals,as opposed to particular rheologies,and incorporates the potential of tectonic regime transitions and multiple tectonics states being viable at equivalent physical and chemical conditions. 相似文献
7.
Mantle circulation in planets with strongly temperature‐dependent viscosity results in stagnant‐lid convection. It is fundamental to understand how this stagnant‐lid regime can change into a plate‐like convection regime as on the present‐day Earth. Here, we use 2D numerical models to study subduction initiation from an initial stagnant lid with laboratory‐consistent parameters and without pre‐existing weak zones or kinematic boundary conditions. Our results show that subduction can be initiated dynamically as a result of a thermal localization instability. The lithosphere may deform in a stagnant‐lid mode, an un‐necking mode, a symmetric‐subduction mode or an asymmetric‐subduction mode. The asymmetric‐subduction mode occurs only for relatively large friction angles and moderate thermal ages, and the presence of heterogeneities increases the parameter space of this mode. The limited parameter space might explain why only the present‐day Earth has plate tectonics, and suggests that the initiation of plate tectonics is more difficult than previously anticipated. 相似文献
8.
《地学前缘(英文版)》2023,14(3):101553
Eight lines of evidence indicate that the Orosirian Period in mid-Paleoproterozoic time was characterized by plate tectonics: ophiolites, low T/P metamorphism including eclogites, passive margin formation, tall mountains, paleomagnetic constraints, ore deposits, abundant S-type granites, and seismic images of paleo-subduction zones. This plate tectonic episode occurred about 1 billion years earlier than the present plate tectonic episode began in Neoproterozoic time. The two plate tectonic episodes bracket the ‘Boring Billion’, which may have been a protracted single lid tectonic episode that began when the supercontinent Nuna or Columbia formed. Recognition of multiple lines of evidence for Orosirian plate tectonics demonstrates that Earth’s tectonic style can be reconstructed with some confidence back to at least Early Paleoproterozoic time, and thus the absence of compelling evidence for Mesoproterozoic plate tectonics is not obvious due to poor preservation. A tectono-magmatic lull ～2.3 Ga suggests an earlier episode of single lid tectonics. Evidence for two episodes of plate tectonics and two episodes of single lid tectonics indicates that Earth switched between single lid and plate tectonics multiple times during the last 2.4 Ga. 相似文献
9.
构造体制极大地制约着地球和其他太阳系类地天体（类地行星、岩石质卫星和小行星等）的地表散热、内部温度和物质演化。现有的少量地质记录表明，地球在板块构造启动之前就存在非常活跃的"前板块构造"运动并可能对其早期壳幔分异产生了重要的影响，在这些构造体制下，物质和能量循环的规模和速率可能是后续的板块运动无法比拟的。但受限于早期地质记录的稀缺以及研究手段不成熟等因素，对前板块构造运动的研究一直被学界所忽视，人们对其的认识主要局限于停滞盖层（stagnant-lid tectonics）等。长期以来的空间探测和地基观测表明，木星系统的木卫一存在大规模的火山活动，随之形成了极高的地表热流和地表更新速率以及活跃的造山作用。这些观测事实不同寻常，颠覆了人们对类地天体构造演化模式的一些固有认识，需要新的构造模式——"热管构造"（heat-pipe tectonics）予以解释，其涵义为：类似木卫一上的大规模火山作用可使类地天体的软流圈-岩石圈-地表之间发生快速的物质和能量循环，该循环以岩浆的形成-上升-喷发-冷却和沉降-折返为主要形式，可将天体内部的热散快速散发到外太空。上述过程涉及类地天体内、外部之间物质的大规模、快速迁移和相变，其导热原理与热管相同，因而被称为"热管构造"，其散热效率远高于现今大多数类地天体单纯依赖岩石圈进行内外热传导的停滞盖层构造，以及地球上以板块的形成和俯冲过程主导内部散热的板块构造体制。尽管早期地球与木卫一在内生热机制等方面存在显著差异，但二者的内部温度和内生热率较高，导致其岩浆作用总体均较为活跃，这些关键动力学特征的相似性暗示其构造体制可能类似。因此，研究木卫一的热管构造体制对揭示地球的前板块构造的性质和演化有重要的启示意义。本文综述了近40年来人类对木卫一的主要探测成果，论述了热管构造提出的必要性和依据，总结了该构造体制的特征和发生条件，讨论了早期地球发生热管构造的可能性。早期地球可能经历了热管构造阶段，期间地球通过大规模火山作用散发了内部热量、促进了壳幔分异，并在地球内生热作用减弱、热管构造不能继续维持时被板块构造等取代。由于热管构造的垂向物质循环较为强烈，不利于保留TTG等低密度的壳幔分异产物，我们依据TTG大规模形成的时间上限推测：地球发生热管构造时间可能限于冥古宙-始太古代时期（约38亿年以前）。由于前板块构造时期地球自身的地质记录十分有限，对其热管构造体制的性质和确切的形成条件等很大程度上需要从木卫一获得答案。 相似文献
10.
板块构造理论可以被认为是构造地质学研究的基本模型和框架。传统板块构造理论认为岩石圈板块在软流圈上方随软流圈对流发生运动,软流圈对流所需要的能量则完全由地球内部能量,如重力势能和放射性衰变产生的热能提供。但是近年来的一些研究证明了气候变化会对板块构造活动,如造山带活动产生直接影响。对传统的板块构造所需能量全部由地球内部提供这一观点做出了补充和更新。本文主要从两个方面对外动力作用可能影响板块构造做出分析,一是利用傅里叶分析证明了太阳辐射变化在构造活动,如洋中脊两侧地貌和火山沉积物中均能够留下记录;二是建立了一个简单的平面力学模型,探究洋流同大陆的力学作用会如何影响大陆运动特征。虽然这一模型忽略了很多因素,定量计算的结果本身并不具有很严格的数据绝对意义。但是这一模型的结果可以证明地球所有板块构造活动中释放的能量低于地球系统每年从太阳辐射中接收的能量,而且模型得到的大陆运动特征同现今实际观测下的运动特征存在一致性,洋流向大陆岩石圈传递的能量同地震活动释放的能量处于同一量级,从侧面可以证明洋流可能对板块构造产生了较大的影响。 相似文献
11.
湖北郧县王家庄有两期脉体 ,早期为纤维状石英脉 ,总体呈北北东向分布 ,平行脉壁有一中间面使其对称分布 ,显示张性裂隙持续发育过程 ;与之垂直的横向压性裂隙将它“错开”。形貌上酷似板块构造的大洋中脊和转换断层。晚期云母脉叠置在上述两组裂隙之上 ,并使原来裂隙性质发生变化。这些特征与区域应力场分布 ,特别是与两郧断裂的演化息息相关。根据分形理论 ,将王家庄石英云母脉与板块构造进行对比 ,一方面从微观的角度证实了板块构造一些基本观点的合理性。同时从微观信息得到深入研究板块构造的一些新启示 :对板块形成机制不要局限于软流圈对流 ,而应从更深层次研究地幔物质运动规律 ;要将大陆和大洋作为一个整体研究全球应力场分布规律与构造演化历史 ,其中转换断层是联系大陆和大洋的纽带 ;加强RRR型三联点研究 ,它是研究深部 (地幔 )物质运动和上部 (地壳、岩石圈 )构造应力场相互关系的重要窗口 相似文献
12.
行星构造:寻求地球演化的踪迹 总被引：1，自引：0，他引：1
地质构造是记录地球内、外动力地质作用过程的标志。和地球相似,太阳系其他天体上也发育丰富的地质构造。以研究天体表面的地质构造及其动力学机制为目的的"行星构造学"是建立在构造地质学、遥感地质学和地球物理学等学科基础上的一门新兴前沿学科。由于天体的大小、组分和轨道位置不同,表面构造特征及其形成机制各异。对比研究地球和其他天体上的构造特征,是完善地球动力学的重要途径。水星和月球的热演化轨迹大致相同,内部持续冷却造成全球收缩,表面形成大量的挤压构造,而伸展构造仅局部发育。火星的岩石圈主要通过热传导散热,表面发育大量的挤压构造,且其形成时间可能呈单峰式分布。同时,火星表面的伸展和挤压构造和大火山群紧密相关,表明深部动力过程影响了火星上的区域构造。金星和地球的大小相似,但金星表面的最大年龄远小于地球大陆地壳的平均年龄,~80%的早期地质记录完全被后期的岩浆-构造活动抹去,表面发育大量的火山-深大裂谷系,说明"幔柱"活动对金星的构造演化至关重要,因此热传导可能也是当前金星岩石圈的主要散热方式。以上天体的岩石圈形变均以垂直运动为主。在外太阳系,一些卫星的表壳主要由冰水和其他挥发分组成,有些卫星存在下伏的液态水圈,潮汐作用可能是驱动其构造演化的主要动力。在特殊的应力来源和物质特性的共同作用下,在这些卫星上发育大量的走滑断层和疑似俯冲消减带。行星地质构造从能量和物质属性的角度探究构造运动的物理和化学过程,与地球动力学研究相辅相成,对揭示地球早期动力学过程的关键科学问题具有重要的指示意义。 相似文献
13.
地球圈层耦合扭转机制及其成因 总被引：1，自引：1，他引：0
全球扭转构造体系不仅是球面现象,而且波及整个地球.本文着重指出地球圈层耦合扭转的机制,揭示该机制对于板块构造的控制规律.赤道面与银道面的交角达62°36′,当银心从北天球移动到南天球时,在公转离心力的驱动下,塑性地幔将向南半球运移而大陆板块则向北半球漂移,从而导致南、北半球的非对称性和两半球的相对扭转.地球的大陆漂移的节律与银河系涡旋周期一致,太阳系内旋转状态相同的行(卫)星与地球同步扭转. 相似文献
14.
J.D.A.Piper 《地学前缘(英文版)》2018,9(1):61-89
Although Plate Tectonics cannot be effectively tested by palaeomagnetism in the Precambrian aeon due to the paucity of high precision poles spanning such a long time period,the possibility of Lid Tectonics is eminently testable because it seeks accordance of the wider dataset over prolonged intervals of time;deficiencies and complexities in the data merely contribute to dispersion.Accordance of palaeomagnetic poles across a quasi-integral continental crust for time periods of up to thousands of millions of years,together with recognition of very long intervals characterised by minimal polar motions(～2.6-2.0,～1.5-1.25 and～0.75-0.6 Ga)has been used to demonstrate that Lid Tectonics dominated this aeon.The new PALEOMAGIA database is used to refine a model for the Precambrian lid incorporating a large quasiintegral crescentric core running from South-Central Africa through Laurentia to Siberia with peripheral cratons subject to reorganisation at～2.1,～1.6 and～1.1 Ga.The model explains low levels of tidal friction,reduced heat balance,unique petrologic and isotopic signatures,and the prolonged crustal stability of Earth's"Middle Age",whilst density concentrations of the palaeomagnetic poles show that the centre of the continental lid was persistently focussed near Earth's rotation axis from～2.8 to 0.6 Ga.The exception was the～2.7-2.2 Ga interval defined by～90°polar movements which translated the periphery of the lid to the rotation pole for this quasi-static period,a time characterised by glaciation and low levels of magmatic activity;the～2.7 Ga shift correlates with key interval of mid-Archaean crustal growth to some 60-70%of the present volume and REE signatures whilst the～2.2 Ga shift correlates with the Lomagundiδ～(13)C and Great Oxygenation events.The palaeomagnetic signature of breakup of the lid at～0.6 Ga is recorded by the world-wide Ediacaran development of passive margins and associated environmental signatures of new ocean basins.This event defined the end of a dominant Lid Tectonic phase in the history of Earth's continental lithosphere recorded by the quasi-integral Precambrian supercontinent Palaeopangaea and the beginning of the comprehensive Plate Tectonics which has characterised the Phanerozoic aeon.Peripheral modifications to the lid achieved a symmetrical and hemispheric shape in Neoproterozoic times comparable to the familiar short-lived supercontinent(Neo)Pangaea(～350-150 Ma)and this appears to be the sole supercontinent cycle recorded by the palaeomagnetic record.Prolonged integrity of a large continental nucleus accompanied by periodic readjustments of peripheral shields can reconcile divergent tectonic analyses of Precambrian times which on the one hand propose multiple Wilson Cycles to explain some signatures of Plate Tectonics,and alternative interpretations which consider that Plate Tectonics did not commence until the end of the Neoproterozoic. 相似文献
15.
Erik Asphaug 《Chemie der Erde / Geochemistry》2010,70(3):199-219
It is assumed in models of terrestrial planet formation that colliding bodies simply merge. From this the dynamical and chemical properties (and habitability) of finished planets have been computed, and our own and other planetary systems compared to the results of these calculations. But efficient mergers may be exceptions to the rule, for the similar-sized collisions (SSCs) that dominate terrestrial planet formation, simply because moderately off-axis SSCs are grazing; their centers of mass overshoot. In a “hit and run” collision the smaller body narrowly avoids accretion and is profoundly deformed and altered by gravitational and mechanical torques, shears, tides, and impact shocks. Consequences to the larger body are minor in inverse proportion to its relative mass. Over the possible impact angles, hit-and-run is the most common outcome for impact velocities vimp between and 2.7 times the mutual escape velocity vesc between similar-sized planets. Slower collisions are usually accretionary, and faster SSCs are erosive or disruptive, and thus the prevalence of hit-and-run is sensitive to the velocity regime during epochs of accretion. Consequences of hit-and-run are diverse. If barely grazing, the target strips much of the exterior from the impactor—any atmosphere and ocean, much of the crust—and unloads its deep interior from hydrostatic pressure for about an hour. If closer to head-on a hit-and-run can cause the impactor core to plow through the target mantle, graze the target core, and emerge as a chain of diverse new planetoids on escaping trajectories. A hypothesis is developed for the diversity of next-largest bodies (NLBs) in an accreting planetary system—the bodies from which asteroids and meteorites derive. Because nearly all the NLBs eventually get accreted by the largest (Venus and Earth in our terrestrial system) or by the Sun, or otherwise lost, those we see today have survived the attrition of merger, evolving with each close call towards denser and volatile-poor bulk composition. This hypothesis would explain the observed density diversity of differentiated asteroids, and of dwarf planets beyond Neptune, in terms of episodic global-scale losses of rock or ice mantles, respectively. In an event similar to the Moon-forming giant impact, Mercury might have lost its original crust and upper mantle when it emerged from a modest velocity hit and run collision with a larger embryo or planet. In systems with super-Earths, profound diversity and diminished habitability is predicted among the unaccreted Earth-mass planets, as many of these will have be stripped of their atmospheres, oceans and crusts. 相似文献
16.
南海扩张的动力学因素及其数值模拟讨论 总被引：22，自引：6，他引：16
由于南海处于欧亚板块、太平洋板块和印度-澳大利亚板块的交汇区,演化历史十分复杂,历来存在多种成因观点的争论。本文采用数值模拟方法,在XiaBinetal.(2005)、夏斌等(2004)、崔学军等(2005)、谢建华等(2005)相关工作基础上,对南海扩张机制进行了进一步探讨,并针对南海地区“近南北向水平拉张”南海扩张的贡献大小,以及“近南北向水平拉张”与“地幔上涌”在南海扩张中作用的相互关系进行了数值模拟实验。结果表明由印度-欧亚板块碰撞和太平洋板块向欧亚板块俯冲的共同作用,所导致的“南北向构造拉张”和“地幔上涌”的共同作用能有效引起岩石圈和地壳两者很大程度的减薄。因此认为这种“南北向构造拉张”和“地幔上涌”的共同作用方式最有利于南海的扩张。 相似文献
17.
Models of the volume of continental crust through Earth history vary significantly due to a range of assumptions and data sets; estimates for 3 Ga range from <10% to >120% of present day volume. We argue that continental area and thickness varied independently and increased at different rates and over different periods, in response to different tectonic processes, through Earth history. Crustal area increased steadily on a pre-plate tectonic Earth, prior to ca. 3 Ga. By 3 Ga the area of continental crust appears to have reached a dynamic equilibrium of around 40% of the Earth's surface, and this was maintained in the plate tectonic world throughout the last 3 billion years. New continental crust was relatively thin and mafic from ca. 4–3 Ga but started to increase substantially with the inferred onset of plate tectonics at ca. 3 Ga, which also led to the sustained development of Earth's bimodal hypsometry. Integration of thickness and area data suggests continental volume increased from 4.5 Ga to 1.8 Ga, and that it remained relatively constant through Earth's middle age (1.8–0.8 Ga). Since the Neoproterozoic, the estimated crustal thickness, and by implication the volume of the continental crust, appears to have decreased by as much as 15%. This decrease indicates that crust was destroyed more rapidly than it was generated. This is perhaps associated with the commencement of cold subduction, represented by low dT/dP metamorphic assemblages, resulting in higher rates of destruction of the continental crust through increased sediment subduction and subduction erosion. 相似文献
18.
David J. Stevenson 《Comptes Rendus Geoscience》2003,335(1):99-111
Mantle convection is the method of heat elimination for silicate mantles in terrestrial bodies, provided they are not too small or too hot. Bodies that are small (～Moon or smaller, possibly even Mercury) may rely largely on conduction or melt migration, and bodies that are very hot (Io, very early Earth) may use massive melt migration (magma oceans) and heat pipes. In the standard, simple picture, we can use scaling laws to determine the secular cooling of a planet, likelihood and form of volcanism, and the possibility of a core dynamo. Contrary to popular belief, small planets do not cool faster than larger planets (provided they convect) but they do tend to have a slightly lower internal temperature at all times and thus may cease to be volcanically active at an earlier epoch. On the other hand, a larger volume fraction of a small planet may be involved in melt generation. However, our understanding of heat transfer by mantle convection is limited by three very important, largely unsolved problems: The complexities of rheology, the effects of compositional gradients, and the effects of phase transitions, especially melting. The most striking manifestation of the role of rheology lies in the difference between a mobile lid mode (plate tectonics for Earth) and a stagnant lid mode (other large terrestrial bodies). This difference may arise because of the role of water, but perhaps also because of melting, or size (gravity), or the vagaries of history. It has profound effects for the differences in history of Earth, Venus and Mars, including their surface geology, volatile reservoirs and magnetic fields. Since thermal convection is driven by small density differences, it can also be greatly altered or limited by compositional or phase effects. Melt migration introduces additional complications to the heat transport as well as being a source for the irreversible differentiation that might promote layering. Our limited understanding and ability to model these processes continues to limit the development of a predictive framework for the differences among the terrestrial planets. 相似文献
19.
The ~ 2.5 Ga Malanjkhand Cu mineralization is hosted by adakitic granitoids in central India. The mineralization represents a large Cu deposit. However, significant debate still surrounds its identification as an analogue of modern circum-Pacific style porphyry Cu deposits. The controversy is intricately linked to several first-order geological issues, such as: the onset of modern plate tectonics and ensuing supercontinent cycles, temporal evolution of the Earth's continental crust coupled with buoyancy of the sub-continental lithospheric mantle (SCLM) and oxidation state of the sub-arc mantle wedge. The petrology and geochemistry of the early Cretaceous Lower Yangtze River Belt (LYRB) adakitic granitoids, central-eastern China that hosts several porphyry Cu deposits are similar to the ~ 2.5 Ga Malanjkhand adakitic granitoids of central India, hosting Cu mineralization. The relict amphibole chemistry of both, the LYRB and Malanjkhand granitoids reveals similar “porphyry mineralizing trends” implying high concentrations of H2O and elevated fO2 conditions of the ore-bearing shallowly emplaced adakitic granitoids. Consequently, the Malanjkhand and LYRB adakitic granitoids were generated in near-identical tectonothermal regimes. The LYRB porphyry Cu deposits belong to the circum–Pacific metallogenic belt of the Eurasian active continental margin. Collectively, the mineralogical, petrological and geochemical similarities of the Malanjkhand and the LYRB adakitic granitoids imply porphyry style mineralization of the Malanjkhand Cu deposit. The identification of Malanjkhand mineralization as a truly Neoarchean porphyry Cu deposit along with coeval adakites, calc-alkaline rhyolites, high-Mg andesites (HMA), followed by rift-related tholeiites and A2-type granites helps to constrain the tectonic evolution of central India. The rarity of porphyry Cu deposits in the Earth's early history is primarily attributed to their lack of preservation. This study opens up exploration possibilities for hitherto unexplored and concealed porphyry Cu deposits in other geologically favorable Precambrian terranes comprising shallowly emplaced adakitic granitoids. 相似文献
20.
大陆岩石圈与软流圈之间的耦合关系─—大陆动力学研究的突破口 总被引：3，自引：0，他引：3
板块构造学说解释了全球构造的许多现象，但尚未满意地解释大陆构造中的一些问题，例如陆内造山带的形成、造山带和盆地形成的复杂历史和旋回性问题、大陆构造圈的不均一性等。新近提出的一些构造模式，都不约而同地指出了软流圈在大陆构造发展中的重要作用，但尚未成功解决软流圈运动的驱动力问题。本文认为，大陆岩石圈与软流圈之间相互作用关系的深入研究，是阐明大陆动力学过程的关键之一。此外，本文还对“软流体振荡作用”工作假说作了初步讨论。 相似文献