大洋岛弧的前世今生

根据板块构造理论,板块的边界是地质作用最为强烈的地区,因而它们是当今固体地球科学研究的重点。依据应力性质的不同,地球上板块的边界类型有扩张的洋中脊、汇聚的俯冲带和调节板块运动差异的转换断层三种。就汇聚型板块边界而言,它又可进一步划分为洋-洋俯冲的大洋或洋内岛弧带(Intra-oceanic arc)、洋-陆俯冲的安第斯型活动大陆边缘带和陆-陆接触的大陆碰撞带三种。相对而言,大洋岛弧的研究程度最低。传统认为最典型的大洋岛弧——日本诸岛,已不再被认为是洋-洋俯冲的产物,因为已有研究显示它是从亚洲大陆裂解的碎块。根据目前的调查,现今的大洋岛弧主要集中在西太平洋地区,以太平洋与菲律宾板块间的Izu-Bonin-Mariana弧和太平洋-澳大利亚间的西南太平洋岛弧为代表。大洋岛弧研究的最重要问题是,洋洋之间如何产生了俯冲。目前多倾向于认为:大洋中的转换断层可使不同时代的大洋岩石圈相互接触,在这种情况下,较老的岩石圈由于冷却时间较长而密度相对较大,因而可下沉而俯冲到较年轻的岩石圈之下。这一模型也被誉为蛇绿岩形成的初始俯冲定律(Subduction Initial Rule,简称SIR)。但存在的问题是,目前全球还没发现有转换断层转变为俯冲带的实例。更何况,全球大洋中发育如此众多的转换断层,但为何只在西太平洋发育大洋岛弧?本文通过对资料的总结还发现,这些大洋岛弧基本都是从亚洲或者澳大利亚大陆东部边缘裂解的碎块,只是后期的弧后扩张作用使裂解的碎块发生强烈的改造,形成具有类似大洋岩石圈的特点。目前提出的洋-洋自发形成俯冲带的模型并没有理论基础,也没有实际地质事实的支持。但在加勒比海、斯科舍海和阿留申地区,大洋岛弧的出现与洋底高原诱发的俯冲带跃迁或俯冲极性反转有关。因此,板块构造理论中的洋洋初始俯冲模式需要进一步资料的验证。     

地球的层圈结构与穿越层圈构造

从1906年发现地核到20世纪60年代,地球物理学、地质学和矿物物理学的研究揭示了地球具有物理化学性质截然不同的层圈结构,并根据全球地震波速度和密度的变化建立了初始参考地球模型。1967年提出的板块构造理论假定刚性的岩石圈板块在塑性的软流圈之上发生运动,在洋中脊不断形成的洋壳逐渐在海沟俯冲,由于板块是刚性的,变形将主要集中在板块边界。板块构造理论成功地解释了大洋岩石圈的形成和消亡、火山和地震活动带的分布以及全球构造格局,给地球科学带来了一场革命。但是,经典的板块构造理论尚未解决板块运动的起源和驱动力、大陆岩石圈的弥散性变形、大陆深俯冲等问题,因此大陆动力学成为对板块构造理论的重要补充。近年来的研究表明:在板块汇聚边界,大洋岩石圈可以俯冲至地幔过渡带、下地幔,乃至核幔边界;而大陆岩石圈可以俯冲至150~300 km深度,然后相对低密度的陆壳物质快速折返形成含柯石英和微粒金刚石的超高压变质带。地幔柱活动是是俯冲板块再循环的产物,不仅可以形成大火成岩省和洋岛玄武岩,还可以把俯冲到地幔过渡带的物质带回浅部,导致蛇绿岩中保留金刚石和深地幔矿物。因此,俯冲带和地幔柱不仅提供了穿越层圈的物质和能量交换的通道,也驱动了对地球宜居性至关重要的水循环和碳循环,是研究地球物质组成和动力学演化的重要窗口。     

板块构造学说面临的挑战

板块构造学说揭示了海底扩张和板块的水平运动现象,阐明了与板块边界相联系的岩浆活动。但大量资料表明地球历史上岩石圈板块与软流圈是同步耦合运动的,而不是在软流圈上滑移。全球扩张与俯冲的不对称性现象也是不吻合于板块构造理论所期望的。安第斯弧作为洋陆俯冲的典范在地球物理和地球化学上均缺少证据。对于与俯冲带相关的弧后引张、大陆增生、地壳物质返回地幔和成矿作用方面均存在较多的问题。大火成岩省所揭示的岩浆活动现象超越了板块构造的格局,并发生在整个地质历史时期和更广泛的地域范围。大火成岩省学说所解释的大陆增长、地壳物质返回地幔和成矿作用过程完全不同于板块构造学说。驱动地幔柱的深地幔对流假说允许岩石圈板块与下伏软流圈一起运动,吻合铅同位素所揭示的岩石圈与软流圈长期耦合的规律。     

西准噶尔蛇绿岩:古大洋俯冲增生过程的记录

蛇绿岩记录了大洋岩石圈形成、演化、消亡的全过程,是刻画区域板块构造和洋 陆格局演化的关键证据。本文通过系统梳理前人相关研究,总结西准噶尔蛇绿岩最新研究成果,探讨大陆地壳增生方式、恢复古大洋演化历史,从而对西准噶尔构造体制转化提供新制约。西准噶尔地区发育多条震旦纪—石炭纪被构造肢解的蛇绿岩带,具有典型的岩块 基质结构,绝大多数蛇绿岩包括正常洋壳组分和海山/大洋高原残片,其中基性岩具有MORB和OIB的地球化学特征。基于前人研究,本文认为在西准噶尔古大洋发育过程中,发育不同时代与地幔柱有关的海山/大洋高原,同时存在增生型和侵蚀型两类汇聚板块边界。另外,大洋高原增生不仅是大陆地壳增生的有效途径之一,还可能诱发俯冲极性反转和传递。而在大洋高原形成初期,还可能存在地幔柱诱发俯冲起始机制。     

俯冲带结构演变解剖与研究展望

俯冲带作为板块构造最为重要的标志之一,是地球最大的物质循环系统,被称为“俯冲工厂”.俯冲作用是驱动和维持板块运动的重要动力引擎.一个完整的俯冲带发育海沟、增生楔、弧前盆地、岩浆弧、弧后盆地（或弧背前陆盆地）等基本构造单元.在一些特殊情况下（如洋脊俯冲、年轻洋壳俯冲、海山俯冲）,则可形成一些特殊的俯冲带结构（如平板俯冲、俯冲侵蚀）,导致岩浆弧、增生楔、弧前盆地等不发育甚至缺失.俯冲大洋板片可滞留于或穿越地幔过渡带进入下地幔甚至到达核幔边界,把地壳物质带入到地球深部,并通过地幔柱活动上升到浅部.俯冲带是构造活动强烈的区域,存在走滑、挤压、伸展等变形及其构造叠加.俯冲带海沟可向大洋或大陆方向迁移,岛弧及增生楔等也随之发生迁移,使俯冲带上盘发生周期性挤压和伸展,形成复杂的古地理格局.微陆块、岛弧、海山/洋底高原等地质体在俯冲带发生增生时,可阻塞先存的俯冲带,造成俯冲带跃迁或俯冲极性反转,在其外侧形成新的俯冲带.俯冲带深部精细结构、俯冲起始如何发生、板块俯冲与地幔柱的深部关联机制等是当前俯冲带研究中值得关注的前沿问题.开展俯冲带地球物理深部探测、古缝合带与现今俯冲带对比研究、俯冲带动力学数值模拟是解决上述科学问题的重要途径.      

蛇绿岩就位机制及时限

蛇绿岩就位机制可以划分出4种:1)碰撞仰冲型:被动大陆边缘或岛弧与洋壳碰撞时,俯冲到一定深度的硅铝质物质在浮力作用下折返,并上驮相对完整的大洋岩石圈残片到达地表;2)增生底垫型:洋底、海沟沉积物及海底较高地形的上层物质从俯冲板块上刮削下来,持续底垫到上覆板块之下,使大洋岩石圈残片逐渐被动抬高;3)俯冲剥离型:断裂发育相...     

对次点火山岩中地幔包体的研究揭示大洋岩石圈在俯冲消减前的交代作用

<正>次点火山(petit-spot volcano)是指远离大洋中脊和地幔柱的大洋板块在即将进入俯冲带之前,由于板块的弯曲引发部分熔融所导致的局部海底火山作用。次点火山有时夹带有来自深部岩石圈的包体和捕虏晶,是了解大洋岩石圈深部物质组成的重要信息载体。次点火山自从在日本外海发现以来,在智利,汤加及巽他等俯冲带外围     

地幔楔体的热结构:水注入触发的对流作用

在岛弧下面是消减的“冷”大洋岩石圈。而另一方面,消减带又是以“热”岩浆的产生为特征的,这是地球科学应当探讨的一个模糊问题。实验岩石学已经指出,在地幔楔体中需要一个高温区以便产生岛弧型玄武岩岩浆。获得这样高温的一种可能机制可以是在由大洋岩石圈的俯冲所诱导的地幔楔体进入上地幔中所产生的次级对流。由于板状次生流体的增加产生的地幔楔体的基底,是有足够低粘度的向下拖曳的含水层,可能压制大规模的建造     

构造古地理重建与动力地形

摘要：构造古地理是研究地质历史时期的构造过程和自然地理演化的科学。大数据时代的计算能力和效率的迅速提高及地球动力学模拟技术的发展,要求古地理研究应建立在全球板块构造背景下,重建“深时”、原位、原型的活动古地理。本文在综合分析国际、国内关于GPlates和CitcomS的地球动力学模拟软件平台的研究成果基础上,系统阐述了板块构造古地理重建思路、内容和方法,残余地形(动力地形)的分离技术、动力地形与板块俯冲、深部地幔流动的动力成因关系;介绍了利用地表动力地形等古地理资料进行约束,揭示板块运动过程、地幔动力学过程研究思路、方法;提出了古地理重建和地球动力学研究中应遵循的“定时、定位、定向和定型”的原则。将全球板块构造古地理模型(GPlates)与基于物理特性的地幔和岩石圈有限元模型(CitcomS)相结合,将动力地形与地幔活动过程研究相结合,对揭示4-D地球动力学具有重要理论意义。     

前寒武纪地球动力学(Ⅴ):板块构造起源

文中系统综述了板块构造启动时间的不同观点及其依据,并探讨了板块构造启动的三个必备条件:刚性岩石圈、俯冲作用、地幔对流循环的起源,进而探讨了前寒武纪俯冲作用、板块构造体制与现代俯冲作用、板块体制的差异。板块构造体制启动的三个缺一不可的条件:刚性、俯冲和地幔对流,直到27~21亿年期间才在全球不同地点同时满足。但现代板块构造体制起始的时间为10(或19)~8(或6)亿年,其标志性物质记录或识别标志依然是蛇绿岩建造、高压-超高压变质、岛弧型岩浆建造等。最后,系统描述了板块构造可能的启动机制和过程,为认识前板块构造和板块构造差异提供一个约束,也为推动地球动力学统一理论的思考和探索提供一些最新认识。     

Initiation of Subduction Zones as a Consequence of Lateral Compositional Buoyancy Contrast within the Lithosphere: a Petrological Perspective

Tonga and Mariana fore-arc peridotites, inferred to representtheir respective sub-arc mantle lithospheres, are compositionallyhighly depleted (low Fe/Mg) and thus physically buoyant relativeto abyssal peridotites representing normal oceanic lithosphere(high Fe/Mg) formed at ocean ridges. The observation that thedepletion of these fore-arc lithospheres is unrelated to, andpre-dates, the inception of present-day western Pacific subductionzones demonstrates the pre-existence of compositional buoyancycontrast at the sites of these subduction zones. These observationsallow us to suggest that lateral compositional buoyancy contrastwithin the oceanic lithosphere creates the favoured and necessarycondition for subduction initiation. Edges of buoyant oceanicplateaux, for example, mark a compositional buoyancy contrastwithin the oceanic lithosphere. These edges under deviatoriccompression (e.g. ridge push) could develop reverse faults withcombined forces in excess of the oceanic lithosphere strength,allowing the dense normal oceanic lithosphere to sink into theasthenosphere beneath the buoyant overriding oceanic plateaux,i.e. the initiation of subduction zones. We term this conceptthe ‘oceanic plateau model’. This model explainsmany other observations and offers testable hypotheses on importantgeodynamic problems on a global scale. These include (1) theorigin of the 43 Ma bend along the Hawaii–Emperor SeamountChain in the Pacific, (2) mechanisms of ophiolite emplacement,(3) continental accretion, etc. Subduction initiation is notunique to oceanic plateaux, but the plateau model well illustratesthe importance of the compositional buoyancy contrast withinthe lithosphere for subduction initiation. Most portions ofpassive continental margins, such as in the Atlantic where largecompositional buoyancy contrast exists, are the loci of futuresubduction zones. KEY WORDS: subduction initiation; compositional buoyancy contrast; oceanic lithosphere; plate tectonics; mantle plumes; hotspots; oceanic plateaux; passive continental margins; continental accretion; mantle peridotites; ophiolites     

West Pacific and North Indian Ocean Seafloor and Their Ocean-Continent Connection Zones: Evolution and Debates

The Indian Ocean and the West Pacific Ocean and their ocean-continent connection zones are the core area of "the Belt and Road". Scientific and in-depth recognition to the natural environment, disaster distribution, resources, energy potential of “the Belt and Road” development, is the cut-in point of the current Earth science community to serve urgent national needs. This paper mainly discusses the following key tectonic problems in the West Pacific and North Indian oceans and their ocean-continent connection zones (OCCZs): 1. modern marine geodynamic problems related to the two oceans. Based on the research and development needs to the two oceans and the ocean-continent transition zones, this item includes the following questions. (1) Plate origin, growth, death and evolution in the two oceans, for example, 1) The initial origin and process of the triangle Pacific Plate including causes and difference of the Galapagos and West Shatsky microplates; 2) spatial and temporal process, present status and trends of the plates within the Paleo- or Present-day Pacific Ocean to the evolution of the East Asian Continental Domain; 3) origin and evolution of the Indian Ocean and assembly and dispersal of supercontinents. (2) Latest research progress and problems of mid-oceanic ridges: 1) the ridge-hot spot interaction and ridge accretion, how to think about the relationship between vertical accretion behavior of thousands years or tens of thousands years and lateral spreading of millions years at 0 Ma mid-oceanic ridges; 2) the difference of formation mechanisms between the back-arc basin extension and the normal mid-oceanic ridge spreading; 3) the differentials between ultra-slow dian Ocean and the rapid Pacific spreading, whether there are active and passive spreading, and a push force in the mid-oceanic ridge; 4) mid-oceanic ridge jumping and termination: causes of the intra-oceanic plate reorganization, termination, and spatial jumps; 5) interaction of mantle plume and mid-oceanic ridge. (3) On the intra-oceanic subduction and tectonics: 1) the origin of intra-oceanic arc and subduction, ridge subduction and slab window on continental margins, transform faults and transform-type continental margin; 2) causes of the large igneous provinces, oceanic plateaus and seamount chains. (4) The oceanic core complex and rheology of oceanic crust in the Indian Ocean. (5) Advances on the driving force within oceanic plates, including mantle convection, negative buoyancy, trench suction and mid-oceanic ridge push, is reviewed and discussed. 2. The ocean-continent connection zones near the two oceans, including: (1) Property of continental margin basement: the crusts of the Okinawa Trough, the Okhotsk Sea, and east of New Zealand are the continental crusts or oceanic crusts, and origin of micro-continent within the oceans; (2) the ocean-continent transition and coupling process, revealing from the comparison of the major events between the West Pacific Ocean seamount chains and the continental margins, mantle exhumation and the ocean-continent transition zones, causes of transform fault within back-arc basin, formation and subduction of transform-type continental margin; (3) strike-slip faulting between the West Pacific Ocean and the East Asian Continent and its temporal and spatial range and scale; (4) connection between deep and surface processes within the two ocean and their connection zones, namely the assembly among the Eurasian, Pacific and India-Australia plates and the related effect from the deep mantle, lithosphere, to crust and surface Earth system, and some related issues within the connection zones of the two oceans under the super-convergent background. 3. On the relationship, especially their present relations and evolutionary trends, between the Paleo- or Present-day Pacific plates and the Tethyan Belt, the Eurasian Plate or the plates within the Indian Ocean. At last, this paper makes a perspective of the related marine geology, ocean-continent connection zone and in-depth geology for the two oceans and one zone.     

Plate tectonics,flood basalts and the evolution of Earth’s oceans

The chemical composition of the bulk silicate Earth (BSE) indicates that the present‐day thermal budget of Earth is likely to be characterized by a significant excess of surface heat loss over internal heat generation, indicating an important role of secular cooling in Earth’s history. When combined with petrological constraints on the degree of secular cooling, this thermal budget places a tight constraint on permissible heat‐flow scaling for mantle convection, along with implications for the operation of plate tectonics on Earth, the history of mantle plumes and flood basalt magmatism, and the origin and evolution of Earth’s oceans. In the presence of plate tectonics, hotter mantle may have convected more slowly because it generates thicker dehydrated lithosphere, which could slow down subduction. The intervals of globally synchronous orogenies are consistent with the predicted variation of plate velocity for the last 3.6 Gyr. Hotter mantle also produces thicker, buoyant basaltic crust, and the subductability of oceanic lithosphere is a critical factor regarding the emergence of plate tectonics before the Proterozoic. Moreover, sluggish convection in the past is equivalent to reduced secular cooling, thus suggesting a more minor role of mantle plumes in the early Earth. Finally, deeper ocean basins are possible with slower plate motion in the past, and Earth’s oceans in the Archean is suggested to have had about twice as much water as today, and the mantle may have started as dry and have been gradually hydrated by subduction. The global water cycle may thus be dominated by regassing, rather than degassing, pointing towards the impact origin of Earth’s oceans, which is shown to be supported by the revised composition of the BSE.     

探测大陆岩石圈的属性、相态与物质运动: 固体地球物理学的新使命

20世纪大地构造物理学取得引人瞩目的进展。本文详细评述了探测地球大陆圈层的属性、相态与物质运动取得的进展和技术路线。并且指出,大陆地壳和海洋地壳结构上的最基本区别是后者是相对均匀和整体刚性的,内部不存在明显的物质运动。前者的下地壳部分区域是不均匀和流变的,其中的物质运动使大陆板内的地壳产生比较强烈的变形和岩浆活动。因此,当前发展板块构造学说的最焦点就是对地壳不均匀性和流变岩石进行三维成像,从下到上找出大陆地壳物质运动规律。同时,一定要坚持深层油气和地震预测方面的应用基础研究,为人类社会可持续发展作出更大的贡献。     

Geological constraints on the alpine evolution of the Mediterranean Tethys

The geological data on the Mediterranean chains and basins are used to point out the constraints that they put on the location through time of oceanic versus continental lithosphere and on the successive relations between them. Emphasis is put on the rules and conventions which enable us to interpret the geological data in terms of plate tectonics and on the major disputed points for which a solution must be chosen.In the first part, the location of oceanic versus continental lithosphere is dealt with, using the data on the present-day basins, the ophiolites and the subduction processes. A Neogene age is retained for the Western Mediterranean and the surrounding continental blocks are considered to have been previously a part of Iberia. A Cretaceous age is retained for the Eastern Mediterranean; Apulia is considered as a part of the African plate except for this period. The Black Sea is considered as a back-arc basin formed mostly during the Upper Cretaceous. The ophiolites are used to locate the Mesozoic oceans; for the double ophiolitic belts of the Dinaro-Hellenides and the Taurides, the tectonic interpretations which minimise the number of oceanic basins have been retained. For the Kirsehir block of Turkey, the chosen solution locates a Jurassic ocean to the north and makes it disappear when a Cretaceous ocean opens to the south. Data on the subduction processes added to the information on these basins and led us to consider as oceanic the unknown basements of the Carpathian flysch and the Maghrebian flysch basins.The second part deals with the organisation of basins and platforms, emphasising the chronology of their formation and subsequent crushing. It furnished step by step constraints on the tectonic history of the system which is related to plate displacement.The general pattern derived from these data shows a wedge-shaped Tethyan ocean which disappeared mostly through repeated subduction below the eastern part of its northern margin. The Jurassic stage shows westward extension of the ocean between the Eurasian and African plates and ends with the Dinaro-Hellenic obduction; the Cretaceous stage shows a complete reorganisation including individual displacement of the Iberian, Apulian and Kirsehir sub-plates; the Tertiary stage shows the general collision between the renewed Eurasian and African plates and Neogene subduction of the basins which avoided collision.     

日本的综合大洋钻探计划(IODP)

对日本的IODP活动以及科学目标进行简要介绍。IODP核心技术支撑之一的立管钻探船“地球号”可在水深4 000 m的海底钻进7 000 m,钻达发震带和上地幔,实现日本的IODP科学目标。日本的IODP科学规划主要有三大科学主题和八项研究目标,三大科学主题包括地幔过程和地球系统演化,地壳作用过程和地球系统演化,俯冲带和地球系统演化过程中的动力学及物质循环。其八项研究目标为：①钻探西太平洋洋底高原,认识核—幔作用过程;②钻探太平洋白垩纪—新生代沉积物,详细研究地球温室期间的物质循环及从温室环境到冰室环境的转化过程;③钻探大洋岛弧,认识大陆地壳形成过程;④钻探扩张的弧后,认识洋壳岩石圈形成过程;⑤钻探亚洲边缘海及陆坡,认识陆壳—洋壳—大气圈关系;⑥调查增生楔中的碳循环及深部生物圈;⑦调查汇聚板块边缘大地震周期及形成机制、构造及物质循环;⑧研究生活于增生楔环境中极端微生物生物学。     

Gravity models of two-level collision of lithospheric plates in northeastern Asia

Structural forms of emplacement of crustal and mantle rigid sheets in collision zones of lithospheric plates in northeastern Asia are analyzed using formalized gravity models reflecting the rheological properties of geological media. Splitting of the lithosphere of moving plates into crustal and mantle constituents is the main feature of collision zones, which is repeated in the structural units irrespective of their location, rank, and age. Formal signs of crustal sheet thrusting over convergent plate boundaries and subduction of the lithospheric mantle beneath these boundaries have been revealed. The deep boundaries and thickness of lithospheric plates and asthenospheric lenses have been traced. A similarity in the deep structure of collision zones of second-order marginal-sea buffer plates differing in age is displayed at the boundaries with the Eurasian, North American, and Pacific plates of the first order. Collision of oceanic crustal segments with the Mesozoic continental margin in the Sikhote-Alin is characterized, as well as collision of the oceanic lithosphere with the Kamchatka composite island arc. A spatiotemporal series of deep-seated Middle Mesozoic, Late Mesosoic, and Cenozoic collision tectonic units having similar structure is displayed in the transitional zone from the Asian continent to the Pacific plate.     

Architecture and composition of ocean floor subducted beneath northern Gondwana during Neoproterozoic to Cambrian: A palinspastic reconstruction based on Ocean Plate Stratigraphy (OPS)

The Blovice accretionary complex, Bohemian Massif, hosts well-preserved basaltic blocks derived from an oceanic plate subducted beneath the northern active margin of Gondwana during late Neoproterozoic to early Cambrian. The major and trace element and Hf–Nd isotope systematics revealed two different suites, tholeiitic and alkaline, whose composition reflects different sources of melts within a back-arc basin setting. The former suite has composition similar to mid-ocean ridge basalts (MORB), yet with striking enrichment in large-ion lithophile elements (LILE) and Pb paralleled by depletion in Nb, in agreement with its derivation from depleted mantle fluxed by subduction-related fluids. In contrast, the latter suite has composition similar to ocean island basalts (OIB) with variable contribution of ancient, recycled crustal material. We argue that both suites represent volcanic members of Ocean Plate Stratigraphy (OPS) and indicate that the oceanic realm consumed by the Cadomian subduction was a complex mosaic of intra-oceanic subduction zones, volcanic island arcs, and back-arc basins with mantle plume impinging the spreading centre. Hence, the basalt geochemistry implies that two distinct domains of oceanic lithosphere may have existed off the Gondwana’s continental edge: an outboard domain, made up of old and less buoyant oceanic lithosphere (remnants of the Mirovoi Ocean surrounding former Rodinia?) that was steeply subducted and generated the back-arcs, and young, hot, and more buoyant oceanic lithosphere generated in the back-arcs and later involved in accretionary complexes as dismembered OPS. Perhaps the best recent analogy of this setting is the Izu Bonin–Mariana arc–Philippine Sea in the western Pacific.     

论全球岩石圈板块构造的动力学机制

全球板块构造的动力学机制问题是一个热门但至今尚未解决的难题。本文首先回顾了近百年来大地构造学的各种主要假说和近四十年来板块构造学说的许多新进展。在上述研究的基础上, 受Rampino和Stothers关于陨击作用可引起地表重大灾变事件思想的启发,笔者提出了一个新的假说。基于中、新生代(200 Ma以来)每隔33 Ma太阳系就会穿越一次银河系星际物质密集的银道面,诱发太阳系内部引力场的巨变,使部分小行星失稳,从而撞击地球。笔者根据用以描述中生代以来全球板块构造的七种不同的运动模式, 提出了巨大陨星在不同地点、以不同角度撞击地表岩石圈,可能诱发地幔底辟的形成,从而推动板块呈放射状或单向运移的假说,也即在200、170、100、65和0.78 Ma等时期的陨击事件基本上是垂直地表面而撞击的,从而诱发地幔底辟的形成和岩石圈板块的放射状张裂和运移;138 Ma的陨击事件可能是指向印度板块的斜向撞击;而35 Ma时期的微玻璃陨石撞击事件则是陨石以极低角度撞击地球表面的表现。陨石撞击地球,这是太阳系内部各星体之间引力作用变化的表现,因而此假说不是什么外因作用论。