Extraterrestrial factors and their role in the Earth’s tectonic evolution in the Early Precambrian

The paper is focused on the fundamental problem of influence of extraterrestrial factors on the Earth’s geologic and tectonic evolution. Extraterrestrial factors played a decisive role in the Earth’s genesis, the formation of the first Hadean continental crust, and the beginning of the Archean era. Their significant influence persisted in the later epochs: Even in the Phanerozoic, extraterrestrial factors might have had a considerable influence on the environment. The sialic cores of protocontinental crust (4.4-3.9 Ga) with first-generation greenstone zones (3.8-3.2 Ga) and the global system of granite-greenstone belts (3.1-2.7 Ga) formed in the rotation-plume regime, mainly in the subequatorial hot belt. The formation of these global structures was, to a large extent, influenced by asteroid impacts, which caused the impact-triggered genesis of mantle plumes. Dramatic changes in the subsequent geologic history began at 2.7-2.0 Ga; at 2.0 Ga they terminated with the Moon’s transition to an orbit similar to the present-day one (50 ± 3 Earth’s radii), accompanied by the abrupt slowdown of the Earth’s axial rotation, the termination of formation of the layer D", and the start of recent plate tectonics, which is accompanied by the plume tectonics.     

Paleoproterozoic thermotectogenesis: A rotation-plume model of the formation of the Aldan Shield

The Aldan Shield—the southern segment of the Aldan-Stanovoi sialic nuclear, 1100 km in diameter—is subdivided into an inner granulite-gneiss and an outer amphibolite-gneiss domain. This heterogeneity arose in the Paleoproterozoic as a result of thermotectogenesis, i.e., the sum of magmatism, metamorphism, and deformation superimposed on the older Archean crust. In addition to metamorphic heterogeneity, the main consequences of the Paleoproterozoic thermotectogenesis comprised the emplacement of mafic dikes of various ages and the centrifugal evolution of a radial tectonomagmatic system consisting of complementary granitoids and anorthosites. Thermotectogenesis proceeded in a pulsatory manner with alternation of extension and compression settings in the near-equatorial epi-Archean supercontinent. These consequences and the mechanism of pulsatory evolution are described by a model of plume-related underplating in combination with the change of the Earth’s rotation in the regime of oscillatory evolution of the Earth-Moon system.     

华北前寒武纪成矿系统与重大地质事件的联系

前寒武纪是指显生宙最古老的地质时代——寒武纪之前的地质时代,它占了地球演化历史的近90％.地球陆壳的80％～90％以上是在前寒武纪形成的,记录了复杂和惊心动魄的地质构造过程,还赋存着丰富的矿产资源.前寒武纪最重要的地质事件有陆壳的巨量增生、前板块机制/板块机制的构造转折、由缺氧到富氧的地球环境的剧变.华北克拉通是全球最古老陆块之一,前寒武纪各阶段全球性重大地质事件几乎都被记录下来,并表现出一些特殊性.与全球其它克拉通相比,华北陆壳生长-稳定化过程具有多阶段特征,太古宙末-古元古代环境剧变记录复杂多样,古元古代与板块体制建立和超大陆演化相关的俯冲碰撞和伸展裂解等地质记录丰富,中-新元古代经历持续伸展并接受巨量裂谷沉积.这些重大地质事件都伴随大规模成矿作用,形成了华北克拉通丰富的矿产资源和独特的优势矿种.     

http://www.sciencedirect.com/science/article/pii/S1674987112001570

The supercontinent cycle,by which Earth history is seen as having been punctuated by the episodic assembly and breakup of supercontinents,has influenced the rock record more than any other geologic phenomena,and its recognition is arguably the most important advance in Earth Science since plate tectonics.It documents fundamental aspects of the planet’s interior dynamics and has charted the course of Earth’s tectonic,climatic and biogeochemical evolution for billions of years.But while the widespread realization of the importance of supercontinents in Earth history is a relatively recent development,the supercontinent cycle was first proposed thirty years ago and episodicity in tectonic processes was recognized long before plate tectonics provided a potential explanation for its occurrence.With interest in the supercontinent cycle gaining momentum and the literature expanding rapidly,it is instructive to recall the historical context from which the concept developed.Here we examine the supercontinent cycle from this perspective by tracing its development from the early recognition of long-term episodicity in tectonic processes,through the identification of tectonic cycles following the advent of plate tectonics,to the first realization that these phenomena were the manifestation of episodic supercontinent assembly and breakup.     

Magmatism and metallogeny of the Early Earth as a reflection of its geologic evolution

The paper is focused on the evolution of the Earth starting with the planetary accretion and differentiation of the primordial material (similar in composition to CI chondrites) into the core and mantle and the formation of the Moon as a result of the impact of the Earth with a smaller cosmic body. The features of the Hadean eon (ca. 4500–4000 Ma) are described in detail. Frequent meteorite-asteroid bombardments which the Earth experienced in the Hadean could have caused the generation of mafic/ultramafic primary magmas. These magmas also differentiated to produce some granitic magmas, from which zircons crystallized. The repeated meteorite bombardments destroyed the protocrust, which submerged into the mantle to remelt, leaving refractory zircons, indicators of the Early Earth’s geologic conditions, behind.The mantle convection that started in the Archean could possibly be responsible for the Earth’s subsequent endogenous evolution. Long-living deep-seated mantle plumes could have promoted the generation of basalt-komatiitic crust, which, thickening, could have submerged into the mantle as a result of sagduction, where it remelted. Partial melting of the thick crust, leaving eclogite as a residue, could have yielded tonalite-trondhjemite-granodiorite (TTG) melts. TTG rocks are believed to compose the Earth’s protocrust. Banded iron bodies, the only mineral deposits of that time, were produced in the oceans that covered the Earth.This environment, recognized as LID tectonics combined with plume tectonics, probably existed on the Earth prior to the transitional period, which was marked by a series of new geologic processes and led to a modern-style tectonics, involving plate tectonics and plume tectonics mechanisms, by 2 Ga. The transitional period was likely to be initiated at about 3.4 Ga, with the segregation of outer and inner cores, which terminated by 3.1 Ga. Other rocks series (calc-alkaline volcanic and intrusive) rather than TTGs were produced at that time. Beginning from 3.4-3.3 Ga, mineral deposits became more diverse; noble and siderophile metal occurrences were predominant among ore deposits. Carbonatites, hosting rare-metal mineralization, could have formed only by 2.0 Ga. From 3.1 to 2.7 Ga, there was a period of “small-plate” tectonics and first subduction and spreading processes, which resulted in the first supercontinent by 2.7 Ga. Its amalgamation indicates the start of superplume-supercontinent cycles.Between 2.7 and 2.0 Ga, the D″ layer formed at the core-mantle interface. It became a kind of thermal regulator for the ascending already tholeiitic mantle plume magmas. All deep-seated layers of the Earth and large low-velocity shear provinces, called mantle hot fields, partially melted enriched EM-I and EM-II mantles, and the depleted recent asthenosphere mantle, which is parental for midocean-ridge basalts, were finally generated by 2 Ga. Therefore, an interaction of all Earth’s layers began from that time.     

早期碰撞造山过程与板块构造：前寒武纪地质研究的机遇和挑战

普遍认为修正后的板块构造模式仍适用于新太古代地质研究，但是早期板块构造过程与后期有明显差异，包括陆块规模、造山带类型、碰撞造山过程等。典型碰撞造山带在地史上的初次形成具有划时代的构造演化意义，涉及典型板块构造初始发生过程、最早超级大陆拼合、威尔逊旋回及板块碰撞造山过程等方面。华北中部保留一条近南北向的碰撞造山带（2 600~2 500 Ma BP），保留特征的巨型复式褶皱、不同层次推覆构造、蛇绿岩混杂带等。围绕华北中部造山带及其25亿年重大构造热事件的研究，对认识华北早期构造演化及其超大陆再造具有重要意义，也是早期板块构造研究的关键突破口之一，开展其不同地壳层次构造变形及其前陆盆地的研究，将深化早期板块边界及其造山过程的科学认识。     

沉积型锰矿床的形成及其与古海洋环境的协同演化

海相沉积型锰矿的成矿过程受古海洋沉积环境影响，而古海洋环境又与超大陆聚合与裂解、极端地质事件、生命演化等密切相关，因此，海相富锰地层是岩石圈、水圈、大气圈和生物圈等多圈层耦合关系与物质循环相关信息的重要载体。深层海水缺氧模型、最小氧化带模型和幕式充氧模型都显示海水中氧化还原梯度的变化是导致锰矿形成的最主要原因。全球范围内海相沉积型锰矿主要形成于古元古代、新元古代和显生宙3个地质历史时期。其中，元古宙时期，地球上发育了完善的氧化还原分层的古海洋结构；古元古代早期和新元古代，超大陆裂解引起的海平面升降变化导致古海洋氧化还原结构产生动荡，并促使大规模沉积型锰成矿作用发生；地球沉寂期（1800~800 Ma）涵盖了整个中元古代，这一时期仅在华北地台发育了少量沉积型锰矿床，反映该时期古海洋中锰的迁移受到了抑制；显生宙地球再次进入活跃期，经历了数次海洋缺氧事件，冰室-温室气候交替促使海水的化学性质剧烈变化，并在局部氧化还原分层的沉积盆地中富集形成沉积型锰矿床。总之，古海洋氧化还原环境的变化是沉积型锰矿形成的必要条件，同时，区域性沉积盆地的结构、海平面的升降、火山作用导致的物缘供给等多种因素都会影响沉积型锰矿的形成。与沉积型铁矿相比，沉积型锰矿对局部海水化学性质的变化更加敏感，综合研究铁锰矿床的共生与分异过程，将有助于更加有效的识别不同尺度的沉积过程与古海洋环境变化。     

The giant Imiter silver deposit: Neoproterozoic epithermal mineralization in the Anti-Atlas, Morocco

The world-class Imiter silver deposit, in the Anti-Atlas Mountains of Morocco, is a Neoproterozoic epithermal vein deposit genetically associated with a felsic volcanic event, and formed within a regional extensional tectonic regime. Rhyolitic volcanism related to ore formation has been dated at 550Dž Ma by ion-probe U/Pb on zircons. The economic silver mineralization is superimposed on an older, discrete base-metal assemblage associated with calc-alkaline granodioritic magmatism. The magmatism is dated at 572LJ Ma by ion-probe U/Pb dating on zircons, and by ⁴⁰Ar/³⁹Ar dating on hydrothermal muscovites. In the Anti-Atlas Mountains, the Precambrian-Cambrian transition appears as an important period for the formation of major, productive precious-metal deposits associated with volcanic events and extensional tectonics. The Imiter silver deposit constitutes a Precambrian analogue to modern epithermal deposits.     

诸广铀成矿区矿床成因探讨

本文通过对诸广地区内生铀矿床成矿地质背景分析,系统论述了矿区地质特征及矿床地球化学特征,对本区矿床成因进行了探讨,提出诸广地区存在富铀的前寒武纪结晶基底;成矿物质来源于上地幔流体与下地壳富铀前寒武纪结晶基底的混熔交代;成矿作用受晚中生代伸展裂陷构造——深源热流体演化机制控制,形成中高温热流体充填成矿的高品位脉型矿化和中低温热流体交代成矿的较低品位碎裂蚀变岩－微脉浸染型矿化。     

Mantle plumes of Central Asia (Northeast Asia) and their role in forming endogenous deposits

The Phanerozoic within-plate magmatism and the related deposits of Siberia are reviewed. The formation of post-perovskite at about 2.5 Ga in the Earth’s interior and the isotope characteristics of within-plate igneous rocks have shown that plate tectonics and deep geodynamics started to operate at about 2–2.5 Ga. The assembly and breakup of supercontinents under the effect of the superplumes formed in layer D″ is considered. Thus, the supercontinent–superplume cycles spanning about 700 Ma are recognized in the Earth’s history.The manifestations of the within-plate magmatic activity are found throughout the whole Phanerozoic. It was demonstrated earlier that between 570 and 160 Ma, the Siberian continent drifted within the African hot mantle field or large low shear velocity province (LLSVP). At least four plumes, excluding the superplume leading to the breakup of Rodinia at 750 Ma, interacted with the Siberian continent. The superplume leading to the breakup of Rodinia was also responsible for the origin of ultramafic intrusions with carbonatites hosting rare-metal (Nb, Ta, REE) mineralization as well as ultramafic–mafic intrusions with Cu–Ni–Pt mineralization localized along the rift zones.The plumes originated in other Phanerozoic cycles formed most likely at the lower-upper mantle boundary, where most of the stagnant slabs is accumulated. Those plumes were responsible for the origin of within-plate igneous rocks. The granitic batholiths formed in the centers of zonal area surrounded by rift zones containing abundant rare-metal intrusions with rare-metal mineralization. Gold, tin, base metal, and porphyry copper deposits are also related to these zonal area.The studies have shown that the formation of folded zones and related deposits which surround these zones as well as the structures of cratons and their metallogenic specialization should be considered in terms of both plate tectonics and plume tectonics.     

前寒武纪重大地质事件

本文概括性地阐述我国前寒武纪冥古宙、太古宙、元古宙三大地史阶段的重大地质事件,粗略勾绘前寒武纪地球演化的轨迹,期望了解我国与全球变化的异同,进一步突出我国前寒武纪三大地史阶段中新太古代超级地质事件及元古宙时期中国大陆块体对哥伦比亚及罗迪尼亚两个超大陆形成与破裂的地质响应。冥古宙是地球最早期的地史阶段,从太阳系形成的4 567 Ma至地球上最老的4 030 Ma的Acasta片麻杂岩。碎屑锆石保存最好的地点是西澳的Mt. Narryer和Jack Hills。目前在中国大陆至少有7个地点发现具有罕见的约4.0 Ga的碎屑锆石,这些地点并不位于克拉通区,而是赋存于造山系新元古代至古生代以碎屑岩为主的地层中。太古宙(4 030~2 420 Ma)定义为从最古老的岩石出现(4 030 Ma Acasta片麻岩)至冰碛层首次广泛分布的寒冷期之间的一段地史。最古老的岩石为英云闪长片麻岩,构成加拿大西北斯拉夫克拉通4.03~3.94 Ga Acasta片麻岩的一部分。西南格陵兰Isua带保存全球有最老的表壳岩,形成于3 810 Ma。太古宙最重大的地质事件莫过于2 780~2 420 Ma时期的新太古代超级事件。值得指出的是华北克拉通最古老、也是中国最古老的岩石出露在中国辽宁鞍山地区,约3.80 Ga英云闪长岩奧长花岗质片麻岩和3.30 Ga的表壳岩已被识别。华北克拉通太古宙有与世界各地太古宙相似的演化历史和特点,包括花岗岩绿岩带及高级变质片麻岩带、广泛的英云闪长岩奧长花岗岩花岗闪长岩(TTG)片麻岩、古陆壳的出露(略老于3.8 Ga)、广泛分布的BIF等。我国太古宙花岗岩绿岩带虽然在华北克拉通分布较广,但与南非、格陵兰、加拿大、西澳等地经典的花岗岩绿岩带相比,时代偏新,仅以新太古代为主,规模偏小,缺少大面积分布的科马提岩,且变质程度偏高,主要为角闪岩相麻粒岩相变质。演化到元古宙(2 420~541 Ma),则进入成熟的、较冷的、刚性程度较高的地球,以现代样式板块构造、超大陆旋回和更复杂的疑源类(eukaryotic)生命的发育为特征。这种变化大致出现在2 420 Ma左右,与哈默斯利型BIF的消失及地史中首次广泛出现的冰川沉积物年代相近。古元古代早期十分重要的“休伦冰川事件”、指示大氧化事件的古老红层在我国尚未被发现,与Lomagundi Jatuli (LJE) δ13C的同位素漂移有关的关门山组古元古代沉积地层的同位素年代学依据不足;古元古代磷矿和具有巨大石油潜力的2.01 Ga Shunga事件也未能鉴别。但中国最大特色是发育了与哥伦比亚和罗迪尼亚超大陆汇聚与裂解有关的良好地质记录,特别是华北克拉通保存了古元古代与哥伦比亚超大陆汇聚有关的超高温、高压麻粒岩等变质及岩浆事件,1 780 Ma以后的中元古代又保存了与哥伦比亚超大陆裂解有关的裂谷沉积及岩浆活动;而在扬子和塔里木陆块区则保存了与新元古代早期与罗迪尼亚超大陆汇聚有关的蛇绿岩、混杂岩、洋内弧、俯冲增生杂岩及大陆边缘弧,在约800 Ma以后则发育了与罗迪尼亚超大陆裂解有关的沉积及岩浆活动的地质记录,为中国和全球地质学者研究这一时期地球系统变化和成矿作用提供了客观的野外实验室和良好的范例。     

The Orosirian (1800–2050 Ma) plate tectonic episode: Key for reconstructing the Proterozoic tectonic record

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.     

塔里木西北缘阿克苏地区大陆拉斑玄武岩对新元古代裂解事件的制约

塔里木西北缘新元古界苏盖特布拉克组不整合覆盖在前寒武纪阿克苏群蓝片岩及侵入其中的基性岩墙之上,苏盖特布拉克组底部发育两层玄武岩夹层,其形成时代和成因背景对认识塔里木板块前寒武纪构造演化及有关的超大陆循环和地球动力学过程具有重要意义。本文对这两层玄武岩进行了全岩地球化学和锆石U-Pb年代学研究。结果显示,玄武岩均属于大陆拉斑玄武岩系列,微量元素地球化学特性与典型的大陆溢流玄武岩非常相似,其岩浆来源于富集地幔,并遭受了一定程度的地壳混染作用。玄武岩中锆石的LA-ICP-MS U-Pb年龄分布在1945~755Ma,这些锆石均属于玄武岩浆上升过程中从地壳岩石捕获的继承锆石,记录了塔里木北缘元古代期间多期变质和岩浆事件。这一年龄范围表明,玄武岩形成的时代应晚于755Ma。本文的研究结果表明,阿克苏大陆拉斑玄武岩形成于板内裂谷环境,可能与新元古代Rodinia超大陆之下的地幔柱活动有关,是塔里木板块从Rodinia超大陆裂解出来的直接证据。     

地球轨道参数在前寒武纪地层中的记录及研究进展

前寒武纪(4.6 Ga～541 Ma)占据约90％的地球发展历史.该时期大气成分、海洋氧化还原条件、全球气候和生命演化历程等均发生极大程度的改变,为现在的地球系统奠定了基础.地球轨道参数是描述地球系统演化过程的重要指标,对于研究日地系统、地月系统及地球本身演化具有重要意义.近年来一些学者在全球范围内2650～550 M...     

A Neoarchean–Proterozoic Supercontinent (~2.8–0.9 Ga): An Alternative to the Model of Supercontinent Cycles

The model of supercontinent cycles is revisited on the basis of reevaluation of existing ideas on the geodynamics and tectonics of granulite gneiss belts and areals. Granulite-gneiss belts and areals of a regional scale correspond to mantle–plume (superplume) activity and form the major components of intracontinental orogens. The evolution of geodynamic settings of the Earth’s crust origin can be imagined as a “spiral sequence”: (1) interaction of mantle plumes and “embryonic” microplate tectonics during the Paleo- Mesoarchean (~3.80–2.75 Ga); (2) plume-tectonics and local plume-driven plate-tectonics within supercontinent during Neoarchean and Proterozoic (~2.75–0.85 Ga); (3) plate tectonics in the Phanerozoic along with a reduced role of mantle plumes starting from ~0.85 Ga.     

Precambrian geodynamics: Concepts and models

In contrast to modern-day plate tectonics, studying Precambrian geodynamics presents a unique challenge as currently there is no agreement upon paradigm concerning the global geodynamics and lithosphere tectonics for the early Earth. This review is focused on discussing results of recent modeling studies in the context of existing concepts and constraints for Precambrian geodynamics with an emphasis placed on three critical aspects: (1) subduction and plate tectonics, (2) collision and orogeny, and (3) craton formation and stability. The three key features of Precambrian Earth evolution are outlined based on combining available observations and numerical and analogue models. These are summarized below:

• •Archean geodynamics was dominated by plume tectonics and the development of hot accretionary orogens with low topography, three-dimensional deformation and pronounced gravitational tectonics. Mantle downwellings and lithospheric delamination (dripping-off) processes are likely to have played a key role in assembling and stabilizing the hot orogens on a timescale up to hundreds of millions of years. Both oceanic-like and continental-like lithospheres were rheologically weak due to the high Moho temperature (> 800 °C) and melt percolation from hot partially molten sublithospheric mantle.
• •Wide spread development of modern-style subduction on Earth started during Mesoarchean–Neoarchean at 3.2–2.5 Ga. This is marked by the appearance of paired metamorphic complexes and oldest eclogite ages in subcontinental lithospheric mantle. Numerical models suggest that the transition occurred at mantle temperatures 175–250 °C higher than present day values, and was triggered by stabilization of rheologically strong plates of both continental and oceanic type. Due to the hot mantle temperature, slab break-off was more frequent in the Precambrian time causing more episodic subduction compared to present day.
• •Wide spread development of modern-style (cold) collision on Earth started during Neoproterozoic at 600–800 Ma and is thus decoupled from the onset of modern-style subduction. Cold collision created favorable conditions for the generation of ultrahigh-pressure (UHP) metamorphic complexes which become widespread in Phanerozoic orogens. Numerical models suggest that the transition occurred at mantle temperatures 80–150 °C higher than present day values and was associated with stabilization of the continental subduction. Frequent shallow slab break-off limited occurrence of UHP rocks in the Precambrian time.

Further progress in understanding Precambrian geodynamics requires cross-disciplinary efforts with a special emphasis placed upon quantitative testing of existing geodynamic concepts and extrapolating back in geological time, using both global and regional scale thermomechanical numerical models, which have been validated for present day Earth conditions.     

前寒武纪的超大陆旋回及其板块构造演化意义

太古代末早古生代存在４次超大陆或大陆聚合时期,超大陆的聚合与裂解造成全球性的重大构造热事件,成为全球板块构造演化的主线,威尔逊旋回在早前寒武纪已明显起作用。超大陆的聚合表现为克拉通的增生与陆块的碰撞造山作用;超大型的裂解表现为非造山岩浆活动、大规模基性岩墙群侵位及大陆裂谷的爆发等。超大陆的裂解可能与地幔柱上涌或超大陆下放射性物质积聚造成的热能积累有关,或地外物质冲击的触发有关。华北克拉通与世界古陆块的前寒武纪构造演化对比,及其在超大陆中的拼合模式成为我国大陆地质学研究面临的挑战性重大科学问题。     

Tectonic activity of the early Earth (4.56-3.4(2.7?) Ga)

The paper discusses a possible model of the ancient (Hadean-Archean) Earth’s geodynamic evolution. We believe that the early Earth was characterized by a stagnant lid regime and whole-mantle convection suggesting cells that convect through the whole mantle (from the core-mantle boundary to the lithosphere base). The lid tectonics was perturbed by asteroid-meteorite bombardments that destroyed the primary terrestrial partly granitoid crust. The destroyed crust together with the residual enriched mantle reservoirs sank into the lower mantle. In addition to the crust destruction, the bombardments led to emplacement of a huge proportion of basalt-komatiitic melts, which can be interpreted as mantle overturn events. In the Hadean, the Earth survived frequent large-scale asteroid-meteorite bombardments, which resulted in almost a complete destruction of the primary terrestrial crust. In the Early Archean, the Earth still experienced the same tectonic processes, as in the Hadean; however, meteorite impact was small-scale and the bombardments influenced only a limited area of a common, as it seems to us, subequatorial supercontinent. Those bombardments led to the sagduction of the Archean basalt-komatiiic terrestrial crust, which sank into the mantle, transforming into amphibolite-eclogite rocks giving rise to a tonalite-troondhjemite-granodiorite suite. As preserved in the zircon record, the formation of the Archean mantle-derived magmas occurred as pulses at 4.5, 4.2-4.3, 3.8-3.9, and 3.3-3.4 Ga. These peaks, most likely, correspond to the Hadean-Archean meteorite bombardments. There is evidence of formation of the subcontinental lithospheric mantle (SCLM) beneath the cratons between 3.3 and 3.5 Ga. This SCLM was markedly different from peridotites of modern ophiolites. However, the existence of ophiolitic peridotites indicates that modern style plate tectonic processes were in operation at that time, as we will discuss below. The transition from the early Earth (Hadean-Archean) tectonic style to the recent tectonics occurred between 3.4 (2.7?) and 2.0 Ga.     

Comparison of Supercontinent Cycles in the Metallogeny of Rare Earth Elements

The distribution of integrated resources of large and superlarge deposits (LSLDs) of rare earth elements (REEs) is compared to the current model of supercontinent cyclicity during Earth’s evolution. It is found that REE LSLDs are related predominantly to igneous complexes (carbonatite, nepheline syenites, syenite-alkaline granites, subalkaline granites), which are often additionally enriched in the hypergenic zone. A certain part of the resources is concentrated in independent hypergenic formations represented by placers and ion-adsorbed clays. Each supercontinent cycle—Kenoran, Columbian, Rodinian, Pangean, and Amasian—is expressed in the REE metallogeny in particular way: we revealed significant intercycle variations in the amount of REE LSLDs, the variety of their types, total accumulated resources, and some other characteristics.     

Stabilization and breakdown of Archean Cratons: Formation of sedimentary basins,mafic magmatism,and metallogenic productivity

The Kenorland supercontinent was created as a result of the ascent of the most powerful mantle plumes in the Earth’s geological history and accompanied by the formation of the continental crust and its subsequent accretion into a supercontinent 2.7 Ga ago. The geological phenomena that occurred at that time in Australia, Canada, and South Africa reflecting its features are considered in this paper. The first sedimentary basins resting upon the sialic basement give evidence for long-existing peneplanes formed in the Early Precambrian, i.e., for stabilization of the underlying cratons; this is also supported by the appearance of rapakivi granite 2.8 Ga ago. The platform regime existed as early as the Mesoarchean 3.5 Ga ago. The platform sedimentary basins developed almost continuously over a billion years. Layered mafic intrusions were frequently emplaced into sedimentary sequences. Unique gold, uranium, PGE, chrome, and other deposits are hosted in sedimentary basins and layered intrusions. The extremely high intensity of plume activity determined the origin and breakdown of the Kenorland supercontinent and the cause of transport of ore elements concentrated in unique deposits. In terms of the intensity of plume-related magmatism and ore formation, the considered period of geological history has no more recent analogues and was critical for the Earth’s evolution.