http://www.sciencedirect.com/science/article/pii/S167498711200103X

The supercontinent cycle has had a profound effect on the Earth's evolution since the Late Archean but our understanding of the forces responsible for its operation remains elusive. Supercontinents appear to form by two end-member processes: extroversion, in which the oceanic lithosphere surrounding the supercontinent (exterior ocean) is preferentially subducted (e.g. Pannotia), and introversion in which the oceanic lithosphere formed between dispersing fragments of the previous supercontinent (interior ocean) is preferentially subducted (e.g. Pangea). Extroversion can be explained by “top–down” geodynamics, in which a supercontinent breaks up over a geoid high and amalgamates above a geoid low. Introversion, on the other hand, requires that the combined forces of slab-pull and ridge push (which operate in concert after supercontinent break-up) must be overcome in order to enable the previously dispersing continents to turn inward. Introversion may begin when subduction zones are initiated along boundaries between the interior and exterior oceans and become trapped within the interior ocean. We speculate that the reversal in continental motion required for introversion may be induced by slab avalanche events that trigger the rise of superplumes from the core-mantle boundary.     

A comparison of the evolution of arc complexes in Paleozoic interior and peripheral orogens: Speculations on geodynamic correlations

We discuss the potential geodynamic connections between Paleozoic arc development along the flanks of the interior (e.g. the Iapetus and Rheic) oceans and the exterior Paleopacific Ocean. Paleozoic arcs in the Iapetus and Rheic oceanic realms are preserved in the Appalachian–Caledonide and Variscan orogens, and in the Paleopacific Ocean realm they are preserved in the Terra Australis Orogen. Potential geodynamic connections are suggested by paleocontinental reconstructions showing Cambrian–Early Ordovician contraction of the exterior ocean as the interior oceans expanded, and subsequent Paleozoic expansion of the exterior oceans while the interior oceans contracted. Subduction initiated in the eastern segment of Iapetus at ca. 515 Ma and Early to Middle Ordovician orogenesis along the flanks of this ocean is highlighted by arc–continent collisions and ophiolite obductions. Over a similar time interval, subduction and orogenesis took place in the exterior ocean and included formation of the Macquarie arc in the Tasmanides of Eastern Australia and the Famatina arc and correlatives in the periphery of the proto-Andean margin of Gondwana. Major changes in the style of subduction (from retreating to advancing) in interior oceans occurred during the Silurian, following accretion of the peri-Gondwanan terranes and Baltica, and closure of the northeastern segment of Iapetus. During the same time interval, subduction in the Paleopacific Ocean was predominantly in a retreating mode, although intermittent episodes of contraction closed major marginal basins. In addition, however, there were major disturbances in the Earth tectonic systems during the Ordovician, including an unprecedented rise in marine life diversity, as well as significant fluctuations in sea level, atmospheric CO₂, and ⁸⁷Sr/⁸⁶Sr and ¹³C in marine strata carbonates. Stable and radiogenic isotopic data provide evidence for the addition of abundant mantle-derived magma, fluids and large mineral deposits that have a significant mantle-derived component. When considered together, the coeval, profound changes in the style of tectonic activity and the disturbances recorded in Earth Systems are consistent with the emergence of a superplume during the Ordovician. We speculate that the emergence of a superplume triggered by slab avalanche events within the Iapetus and Paleopacific oceans was associated with the establishment of a new geoid high within the Paleopacific regime, the closure of the interior Rheic Ocean and the amalgamation of Laurussia and Gondwana, which was a key event in the Late Carboniferous amalgamation of Pangea.     

The contemporary North Pangea supercontinent and the geodynamic causes of its formation

The supercontinental status of the contemporary aggregation of continents called North Pangea is substantiated. This supercontinent comprises all continents with the probable exception of Antarctica. In addition to the spatial contiguity of continents, the supercontinent is characterized by the prevalence of the continental crust that combines North America and Eurasia, Eurasia and Africa, and Eurasia and Australia. Over the course of the 300–250-Ma evolution from Wegener’s Pangea to contemporary North Pangea, the aggregation of continents has not lost its supercontinental status, despite modification of the supercontinent shape and opening and closure of the newly formed Paleotethys, Tethys, Atlantic, and Indian oceans. Over the last 250–300 Ma, all movements of the lithospheric plates have most likely occurred within the Indo-Atlantic segment of the Earth, whereas the Pacific segment has remained oceanic. In short, the formation of the North Pangea supercontinent can be outlined in the following terms. The long and deep subduction of the lithospheric plates beneath Eurasia and North America gave rise to the stabilization of the continents and accumulation of huge bodies of the cold lithosphere commensurable in volume with the upper mantle at the deeper mantle levels. This brought about compensation ascent of hot mantle (mantle plumes) near the convergent plate boundaries and far from them. A special geodynamic setting develops beneath the supercontinent. Due to encircling subduction of the lithospheric plates and related squeezing of the hot mantle, an ascending flow, or plume (superplume) formed beneath the central part of the supercontinent. In our view, the African superplume broke up Wegener’s Pangea in the Atlantic region, caused the opening of the Atlantic and Indian oceans, and migrated to the Arctic Region 53 Ma ago.     

Heat flow and destabilized cratons: a comparative study of the North China,Siberian, and Wyoming cratons

Heat has a close relation to cratonic stability. We reconstructed the thermal history of the eastern North China, Wyoming, and Siberian cratons by using xenolith and thermal indicator data, and then the thermal lithospheric thickness in geological time was calculated by combining the crustal structural and thermal parameters. Researches from three cratons demonstrate that heat-flow values of the eastern North China Craton (eNCC) and Wyoming Craton (WC) have increased exceeding 20 mW/m² in the Meso-Cenozoic and the thermal lithospheric thickness has decreased by >100 km because of the cratonic destabilization. However, the thermal history variation of the Siberian Craton (SC) is small, ~5 mW/m², the lithosphere has remained stable and it has experienced relatively little lithospheric thinning <100 km. The differences of the cratonic thermal regime are related to the breakup of the Pangea supercontinent. Destabilized cratons on active continental margin are directly affected by plate subduction. Stable cratons in the interior of the supercontinents are directly affected by the upwelling of superplumes and that may result in lithospheric thinning. Differences in the thermal evolutions of cratons provide new geothermal evidence for the different thermal regimes associated with the breakup of the Pangea supercontinent.     

Geodynamic setting of recent volcanism in North Eurasia

A GIS layout of the map of recent volcanism in North Eurasia is used to estimate the geodynamic setting of this volcanism. The fields of recent volcanic activity surround the Russian and Siberian platforms—the largest ancient tectonic blocks of Eurasia—from the arctic part of North Eurasia to the Russian Northeast and Far East and then via Central Asia to the Caucasus and West Europe. Asymmetry in the spatial distribution of recent volcanics of North Eurasia is emphasized by compositional variations and corresponding geodynamic settings. Recent volcanic rocks in the arctic part of North Eurasia comprise the within-plate alkaline and subalkaline basic rocks on the islands of the Arctic Ocean and tholeiitic basalts of the mid-ocean Gakkel Ridge. The southern, eastern, and western volcanic fields are characterized by a combination of within-plate alkaline and subalkaline basic rocks, including carbonatites in Afghanistan, and island-arc or collision basalt-andesite-rhyolite associations. The spatial distribution of recent volcanism is controlled by the thermal state of the mantle beneath North Eurasia. The enormous mass of the oceanic lithosphere was subducted during the formation of the Pangea supercontinent primarily beneath Eurasia (cold superplume) and cooled its mantle, having retained the North Pangea supercontinent almost unchanged for 200 Ma. Volcanic activity was related to the development of various shallow-seated geodynamic settings and deep-seated within-plate processes. Within-plate volcanism in eastern and southern North Eurasia is controlled, as a rule, by upper mantle plumes, which appeared in zones of convergence of lithospheric plates in connection with ascending hot flows compensating submergence of cold lithospheric slabs. After the breakdown of Pangea, which affected the northern hemisphere of the Earth insignificantly, marine basins with oceanic crust started to form in the Cretaceous and Cenozoic in response to the subsequent breakdown of the supercontinent in the northern hemisphere. In our opinion, the young Arctic Ocean that arose before the growth of the Gakkel Ridge and, probably, the oceanic portion of the Amerasia Basin should be regarded as a typical intracontinental basin within the supercontinent [48]. Most likely, this basin was formed under the effect of mantle plumes in the course of their propagation (expansion, after Yu.M. Pushcharovsky) to the north of the Central Atlantic, including an inferred plume of the North Pole (HALIP).     

Recent volcanism in relation to plate interaction and deep-level geodynamics

The spatial distribution of recent (under 2 Ma) volcanism has been studied in relation to mantle hotspots and the evolution of the present-day supercontinent which we named Northern Pangea. Recent volcanism is observed in Eurasia, North and South America, Africa, Greenland, the Arctic, and the Atlantic, Indian, and Pacific Oceans. Several types of volcanism are distinguished: mid-ocean ridge (MOR) volcanism; subduction volcanism of island arcs and active continental margins (IA + ACM); continental collision (CC) volcanism; intraplate (IP) volcanism related to mantle hotspots, continental rifts, and transcontinental belts. Continental volcanism is obviously related to the evolution of Northern Pangea, which comprises Eurasia, North and South America, India, Australia, and Africa. The supercontinent is large, with predominant continental crust. The geodynamic setting and recent volcanism of Northern Pangea are determined by two opposite processes. On one hand, subduction from the Pacific Ocean, India, the Arabian Peninsula, and Africa consolidates the supercontinent. On the other hand, the spreading of oceanic plates from the Atlantic splits Northern Pangea, changes its shape as compared with Wegener’s Pangea, and causes the Atlantic geodynamics to spread to the Arctic. The long-lasting steady subduction beneath Eurasia and North America favored intense IA + ACM volcanism. Also, it caused cold lithosphere to accumulate in the deep mantle in northern Northern Pangea and replace the hot deep mantle, which was pressed to the supercontinental margins. Later on, this mantle rose as plumes (IP mafic magma sources), which were the ascending currents of global mantle convection and minor convection systems at convergent plate boundaries. Wegener’s Pangea broke up because of the African superplume, which occupied consecutively the Central Atlantic, the South Atlantic, and the Indian Ocean and expanded toward the Arctic. Intraplate plume magmatism in Eurasia and North America was accompanied by surface collisional or subduction magmatism. In the Atlantic, Arctic, Indian, and Pacific Oceans, deep-level plume magmatism (high-alkali mafic rocks) was accompanied by surface spreading magmatism (tholeiitic basalts).     

Mantle convection modeling of the supercontinent cycle： Introversion,extroversion, or a combination？

The periodic assembly and dispersal of continental fragments,referred to as the supercontinent cycle,bear close relation to the evolution of mantle convection and plate tectonics.Supercontinent formation involves complex processes of"introversion"(closure of interior oceans),"extroversion"(closure of exterior oceans),or a combination of these processes in uniting dispersed continental fragments.Recent developments in numerical modeling and advancements in computation techniques enable us to simulate Earth’s mantle convection with drifting continents under realistic convection vigor and rheology in Earth-like geometry(i.e.,3D spherical-shell).We report a numerical simulation of 3D mantle convection,incorporating drifting deformable continents,to evaluate supercontinent processes in a realistic mantle convection regime.Our results show that supercontinents are assembled by a combination of introversion and extroversion processes.Small-scale thermal heterogeneity dominates deep mantle convection during the supercontinent cycle,although large-scale upwelling plumes intermittently originate under the drifting continents and/or the supercontinent.     

Highly depleted oceanic lithosphere in the Rheic Ocean: Implications for Paleozoic plate reconstructions

The Rheic Ocean formed at ca. 500 Ma, when several peri-Gondwanan terranes (e.g. Avalonia and Carolinia) drifted from the northern margin of Gondwana, and were consumed during the Late Carboniferous collision between Laurussia and Gondwana, a key event in the formation of Pangea. Several mafic complexes ranging in age from ca. 400–330 Ma preserve many of the lithotectonic and/or chemical characteristics of ophiolites. They are characterized by anomalously high εNd values that are typically either between or above the widely accepted model depleted mantle curves. These data indicate derivation from a highly depleted (HD) mantle and imply that (i) the mantle source of these complexes displays time-integrated depletion in Nd relative to Sm, and (ii) depletion is the result of an earlier melting event in the mantle from which basalt was extracted. The extent of mantle depletion indicates that this melting event occurred in the Neoproterozoic, possibly up to 500 million years before the Rheic Ocean formed. If so, the mantle lithosphere that gave rise to the Rheic Ocean mafic complexes must have been captured from an adjacent, older oceanic tract. The transfer of this captured lithosphere to the upper plate enabled it to become preferentially preserved. Possible Mesozoic–Cenozoic analogues include the capture of the Caribbean plate or the Scotia plate from the Pacific to the Atlantic oceanic realm. Our model implies that virtually all of the oceanic lithosphere generated during the opening phase of the Rheic Ocean was consumed by subduction during Laurentia–Gondwana convergence.     

http://www.sciencedirect.com/science/article/pii/S1674987113001576

The observation is made that there are very strong similarities between the supercontinents Columbia, Rodinia and Pangea. If plate tectonics was operating over the past 2.5 billion years of Earth history, and dominated by extroversion and introversion of ocean basins, it would be unusual for three superconti-nents to resemble one another so closely. The term＇strange attractor＇ is applied to landmasses that form a coherent geometry in all three supercontinents. Baltica, Laurentia and Siberia form a group of＇strange attractors＇ as do the elements of East Gondwana （India, Australia, Antarctica, Madagascar）. The elements of ＂West Gondwana＂ are positioned as a slightly looser amalgam of cratonic blocks in all three super-continents and are referred to as ＇spiritual interlopers＇. Relatively few landmasses （the South China, North China, Kalahari and perhaps Tarim cratons） are positioned in distinct locations within each of the three supercontinents and these are referred to as＇lonely wanderers＇. 〈br〉 There may be several explanations for why these supercontinents show such remarkable similarities. One possibility is that modern-style plate tectonics did not begin until the late Neoproterozoic and horizontal motions were restricted and a vertical style of ＇lid tectonics＇ dominated. If motions were limited for most of the Proterozoic, it would explain the remarkable similarities seen in the Columbia and Rodinia supercontinents, but would still require the strange attractors to rift, drift and return to approximately the same geometry within Pangea. 〈br〉 A second possibility is that our views of older supercontinents are shaped by well-known connections documented for the most recent supercontinent, Pangea. It is intriguing that three of the four ＇lonely wanderers＇ （Tarim, North China, South China） did not unite until just before, or slightly after the breakup of Pangea. The fourth＇lonely wanderer＇, the Kalahari （and core Kaapvaal） craton has a somewhat unique Archean-age geology compared to its nearest neighbors in Gondwana, but very similar to that in western Australia.     

俯冲带部分熔融

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。     

Tectonic evolution of the southwestern margin of Pangea and its global implications: Evidence from the mid Permian–Triassic magmatism along the Chilean-Argentine border

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

The Open of the Paleo‐Tethys Ocean: Inferred from the Early Paleozoic Ophiolite in the Qiangtang Area,Northern Tibetan Plateau

The Paleo‐Tethys Ocean was a Paleozoic ocean located between the Gondwana and Laurasia supercontinents. It was usually consider to opening in the early Paleozoic with the rifting of the Hun superterrane from Gondwana following the subduction of the Rheic Ocean/proto‐Tethys Ocean. However, the opening time and detailed evolutionary history of the Paleo‐Tethys Ocean are still unclear. The Paleozoic ophiolites have recently been documented in the middle of the Qiangtang terrane, northern Tibetan Plateau, and they mainly occur in the Gangma Co area. These ophiolites are composed of serpentinite, pyroxenite, isotropic and cumulate gabbros, basalt, hornblendite and plagiogranite. Whole‐rock geochemical data suggest that all mafic rocks were formed in an oceanic‐ridge setting. Furthermore, positive whole‐rock εNd(t) and zircon εHf(t) values suggest that these rocks were derived from a long‐term depleted mantle source. The data allow us to conform that these rocks represent an ophiolite suite. Zircon U‐Pb dating of gabbros and plagiogranites yielded weighted mean ages of 437‐501 Ma. The occurrence of the ophiolite suite suggests that a Paleozoic Ocean basin (Paleo‐Tethys) existed in middle of the Qiangtang terrane. We hypothesize that the ophiolite in the middle of the Qiangtang terrane represents the western extension of the Sanjiang Paleo‐Tethys ophiolite in the east margin of the Tibetan Plateau, and they mark the main Paleo‐Tethys Ocean. This is the oldest ophiolite from the Paleo‐Tethyan suture zones and the Paleo‐Tethys Ocean basin probably opened in the Middle Cambrian, and continued to grow throughout the Paleozoic. The ocean was finally closed in the Middle to Late Triassic as inferred from the metamorphic ages of eclogite and blueschist that occur nearby. The Paleo‐Tethys Ocean was probably formed by the breakup of the northern margin of Gondwana, with southward subduction of the proto‐Tethys oceanic lithosphere along the northern margin of the supercontinent.     

Abyssal and hydrated mantle wedge serpentinised peridotites: a comparison of the 15$$^\circ$$20$$'$$′N fracture zone and New Caledonia serpentinites

Subduction of serpentinised mantle transfers oxidised and hydrated mantle lithosphere into the Earth, with consequences for the oxidation state of sub-arc mantle and the genesis of arc-related ore deposits. The role of subducted serpentinised mantle lithosphere in earth system processes is uncertain because subduction fluxes are poorly constrained. Most subducted serpentinised mantle is serpentinised on the ocean floor settings. Yet this material is poorly represented in the literature because it is difficult to access. Large volumes of accessible serpentinite are available in ophiolite complexes, and most interpretations of subduction fluxes associated with ultramafic rocks are based on ophiolite studies. Seafloor and ophiolite serpentinisation can occur under different conditions, so it is necessary to assess if ophiolite serpentinites are a good proxy for seafloor serpentinites. Serpentinites sampled during ODP cruise 209 were compared with serpentinites from New Caledonia. The ODP209 serpentinites were serpentinised by modified seawater in a shallow hydrothermal seafloor setting. The New Caledonia serpentinites were serpentinised in a mantle wedge setting by slab-derived fluids, with possible contributions from oceanic serpentinisation and post-obduction serpentinisation. Petrological, whole rock and mineralogical analyses were combined to compare the two sample sets. Petrologically, the evolution of serpentinisation was close to identical in the two environments. However, more oxidised iron, Cl, S and C is present in serpentine from the ODP209 serpentinites relative to the New Caledonia serpentinites. Given these observations, the use of serpentinites from different geodynamic settings as a proxy for abyssal serpentinites from spreading settings must be undertaken with caution.     

变质作用、板块构造及超级大陆旋回

麻粒岩相超高温变质作用（GUHTM）主要发育于新太古代至寒武纪岩石中;推测在深部较年轻的,特别是新生代造山带岩石中也会有GUHTM存在。岩石中最初出现GUHTM记录意味着产生瞬时极高热流处的地球动力学发生了改变。许多GUHTM带可能发育于类似现代大陆弧后的构造背景中。在较热的地球上,超大陆及其裂解形成的循环组合,尤其是经岩石圈减薄的洋盆卷入到其外翻过程中可能产生比现代太平洋边缘更热的大陆弧后。中温榴辉岩 高压麻粒岩相变质作用（EHPGM）也是最先发现于新太古代岩石记录中,并发育于从元古宙至古生代岩石中。EHPGM带是对GUHTM带的补充,并经常认为是记录了从俯冲至碰撞造山作用的过程。在元古宙岩石记录中的蓝片岩明显记录了与现代俯冲作用相关的低热流梯度。以发育柯石英(±硬柱石)或金刚石为特征的硬柱石蓝片岩和榴辉岩（高压变质作用,HPM）及超高压变质岩（UHPM）主要是在显生宙形成。HPMUHPM记录了显生宙俯冲碰撞造山带早期碰撞过程中的低热流梯度及陆壳的深俯冲作用。尽管与直觉不同,在超级大陆聚敛期（Wilson旋回洋盆打开和关闭）的大陆地块增生过程,许多HPMUHPM带看来确实是通过小洋盆关闭而发育起来的,反映双重热体制的双重变质带仅发育于新太古代以来的岩石记录中。双重热体制是现代板块构造的特点,而双重变质作用则是板块构造在岩石记录中的特征性标志。尽管构造样式很可能不同,新太古代以来GUHTM和EHPGM带的发育证明“元古宙板块构造体制”的开始。以冷俯冲和大陆地壳深俯冲至地幔,以及其中的部分又从深达300 km处发生折返为标志,“元古宙板块构造体制”在新元古代进化为“现代板块构造体制”,这个转变可由岩石中的HPMUHPM证明。记录这种极端条件的变质带年龄是不一致的,而变质作用发生时间与各大陆岩石圈聚合到超级克拉通（如Superia/Sclavia）或超级大陆（如Nuna (Columbia), Rodinia, Gondwana, 和Pangea）的时间却是一致的。     

Contemporaneous assembly of Western Gondwana and final Rodinia break-up: Implications for the supercontinent cycle

Geological, geochronological and isotopic data are integrated in order to present a revised model for the Neoproterozoic evolution of Western Gondwana. Although the classical geodynamic scenario assumed for the period 800–700 Ma is related to Rodinia break-up and the consequent opening of major oceanic basins, a significantly different tectonic evolution can be inferred for most Western Gondwana cratons. These cratons occupied a marginal position in the southern hemisphere with respect to Rodinia and recorded subduction with back-arc extension, island arc development and limited formation of oceanic crust in internal oceans. This period was thus characterized by increased crustal growth in Western Gondwana, resulting from addition of juvenile continental crust along convergent margins. In contrast, crustal reworking and metacratonization were dominant during the subsequent assembly of Gondwana. The Río de la Plata, Congo-São Francisco, West African and Amazonian cratons collided at ca. 630–600 Ma along the West Gondwana Orogen. These events overlap in time with the onset of the opening of the Iapetus Ocean at ca. 610–600 Ma, which gave rise to the separation of Baltica, Laurentia and Amazonia and resulted from the final Rodinia break-up. The East African/Antarctic Orogen recorded the subsequent amalgamation of Western and Eastern Gondwana after ca. 580 Ma, contemporaneously with the beginning of subduction in the Terra Australis Orogen along the southern Gondwana margin. However, the Kalahari Craton was lately incorporated during the Late Ediacaran–Early Cambrian. The proposed Gondwana evolution rules out the existence of Pannotia, as the final Gondwana amalgamation postdates latest connections between Laurentia and Amazonia. Additionally, a combination of introversion and extroversion is proposed for the assembly of Gondwana. The contemporaneous record of final Rodinia break-up and Gondwana assembly has major implications for the supercontinent cycle, as supercontinent amalgamation and break-up do not necessarily represent alternating episodic processes but overlap in time.     

冈底斯弧的岩浆作用：从新特提斯俯冲到印度亚洲碰撞

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。     

Supercontinent formation from stochastic collision and mantle convection models

The large-scale tectonics in the last billion years (Ga) are predominated by the assembly and breakup of supercontinents Rodinia and Pangea. The mechanisms controlling the assembly of supercontinents are not clear. Here, we investigate the assembly of a supercontinent with 1) stochastic models of randomly-moving continental blocks and 2) 3-D spherical models of mantle convection with continental blocks. For the stochastic models, we determined the time required for all the blocks to assemble into a single supercontinent on a spherical surface. We found that the assembly time from our stochastic models is significantly longer than inferred for Pangea and Rodinia. However, our study also suggests that the assembly time from stochastic models is sensitive to the rules for randomly assigning continental motion in the models. In our dynamic models of mantle convection, continental blocks are modeled as deformable and compositionally distinct materials from the mantle. We found that mantle convective planform has significant effects on supercontinent assembly. For models with moderately strong lithosphere and the lower mantle relative to the upper mantle that lead to degree-1 mantle convection, continental blocks always assemble to a supercontinent in  250 million years (Ma) and this assembly time is consistent with inferred for Pangea and Rodinia. However, for models with intrinsically small-scale mantle flows, we found that even when continental blocks merge to form a supercontinent, the assembly times are too long and the convective structures outside of supercontinent regions are of too small wavelengths, compared with observed.     

Subduction zone stresses: Constraints from mechanics and from topographic and geoid anomalies

There are, in principle, direct relations between several important phenomena associated with subduction zones: the depth of oceanic trenches, the magnitude of the net force from trenches acting on subducting plates, the distribution and fault plane orientations of earthquakes, the magnitude of stresses on subduction faults, the bathymetry of back-arc regions, and the magnitudes of gravity and geoid anomalies. These phenomena are related through the stresses transmitted through surface and subducted lithosphere, and are associated with the mass anomaly of the subducted lithosphere. Quantitative estimates suggest that observed trench depths imply a trench pull force on subducting plates which is comparable to the ridge push force but much less than the excess weight of the subducted lithospheric slab. It is further suggested that either the mass anomaly of subducted lithosphere is much less than would be expected on the basis of conventional thermal and compositional models or that (a) a large resistance acts on the upper part of slabs due to high-stress corner flow, and (b) the mass anomaly of the slab is 70–90% compensated either by a broad 1 km-deep back-arc depression or a low density mantle wedge above the slab or both.     

克拉通演化的超大陆背景与克拉通盆地的成因机制

研究表明克拉通的形成与超大陆的汇聚和裂解有着重要关系。本文对近年来超大陆重建的研究进行了分析对比,对克拉通发展与超大陆事件的关系做出了总结。前人对超大陆的研究表明,其形成与地幔动力有直接联系,地幔柱重组的旋回导致了超大陆的旋回。Phillips and Bunge（2007）在前人三维球体地幔对流模型的基础上加入大陆进行了模拟实验,结果显示周期性的超大陆旋回只发生在理想模型中,而Senshu et al.（2009）对代表陆壳的英云闪长岩-奥长花岗岩-花岗岩（TTG）地壳进行了研究,提出随着俯冲的TTG地壳产热速率的下降,超大陆旋回的周期随之变长;更有许多学者指出,历史上哥伦比亚超大陆存在时间明显较长,因此超大陆的旋回并不具有周期性。对近年来不同学者提出的哥伦比亚、 罗迪尼亚、 冈瓦纳、 潘基亚4个超大陆新的重建证据进行分析,大致确定出上述4个超大陆的形成时间、 格局及演化过程。此外,对华北、 东欧、 西伯利亚、 亚马孙、 刚果、 西非6个克拉通各自的演化进行分析,也显示出克拉通演化与超大陆汇聚及裂解在时间与空间上有对应关系。通过分析得出克拉通演化与超大陆旋回有关,且确定出克拉通演化的4个超大陆旋回。本文最后讨论了克拉通盆地的成因机制以及3种端元类型,并将盆地的发育与超大陆演化的巨旋回相联系。     

Geological records of the pacific plate subduction in the northeast asian continental margin; An overview北大核心CSCD

The Paleo-Pacific Ocean was originated from the Panthalassa, which was a vast global ocean surrounding the Pangea Supercontinent. With the breakup of the Pangea and the closure of the Paleo-Tethyan Ocean, the Paleo-Pacific, Atlantic, Arctic and Indian Oceanic plates were in turn formed. About 190 Ma, the Pacific Plate was initially generated at the junction of the oceanic rift among the Izanagi, Karallon and Pheonix plates. Although most geologists considered a coherent genetic relationship between Meso-Cenozoic tectonic evolution of NE Asian continental margin and subduction of the Pacific Plate, there still exist some key problems. The main issues include; ( I ) the formation, motion trait and evolution paths of the Pacific Plate, especially the Izanagi Plate which subducted beneath the NE Asian continental margin at least since early Jurassic; ( 2) the beginning time of the Pacific Plate subduction; (3) the identification of subduction-related magmatisni; and(4) physical conditions of subduction processes. Based on the recent research progress of the above issues, this paper synthesizes that the subduction of the Paleo-Pacific Plate( or Izanagi Plate) beneath the NE Asian continent started in the early Jurassic. The subduction zone was gradually migrated eastward and constituted anarchipelagic oceanic framework with the involvement of old microblocks or foreign massifs.