Assembly, Accretion and Break-up of the Paleo-Mesoproterozoic Columbia(Nuna) Supercontinent: Records in the North China Craton

Columbia(Nuna)is a Paleo-Mesoproterozoic supercontinent that was assembled during global 2.0–1.8Ga collisional events,underwent long-lived,subductionrelated accretion at key continental margins in the period

Petrogenesis and Rb-Sr Isotopic Characteristics of Paleo-Mesoproterozoic Mirgarani Granite Sonbhadra Uttar Pradesh India:Geodynamics Implication for Supercontinent Cycle

The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715±0.012(MSWD=0.11),showing an S-type affinity.The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh(1590±30 Ma).The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC.Petro-graphic and geochemical studies revealed that the granite is enriched in Rb(271 ppm),Pb(77 ppm),Th(25 ppm),and U(33 ppm)and depleted in Sr(95 ppm),Nb(16 ppm),Ba(399 ppm)and Zr(143 ppm)contents as compared to the normal granite.The Mirgarani granite is a peraluminous(A/CNK=1.23),high potassic(K_(2)O 6.42%),Calc-Alkalic to Alkali-Calcic{(Na_(2)O+K_(2)O)-CaO=6.29}S-Type granite,a feature supported by the presence of modal garnet and normative corundum(2.68%).The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700℃ during the Co-lumbian-Nuna Supercontinent.

The boring billion? - Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent

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.

Paleoproterozoic volcanic rocks in the southern margin of the North China Craton, central China:Implications for the Columbia supercontinent

The volcanic rocks of the Xiong’er Group are situated in the southern margin of the North China Craton(NCC).Research on the Xiong er Group is important to understand the tectonic evolution of the NCC and the Columbia supercontinent during the Paleoproterozoic.In this study,to constrain the age of the Xiong’er volcanic rocks and identify its tectonic environment,we report zircon LA-ICP-MS data with Hf isotope,whole-rock major and trace element compositions and Sr-Nd-Pb-Hf isotopes of the volcanic rocks of the Xiong’er Group.The Xiong’er volcanic rocks mainly consist of basaltic andesite,andesite.dacite and rhyolite,with minor basalt.Our new sets of data combined with those from previous studies indicate that Xiong’er volcanism should have lasted from 1827 Ma to 1746 Ma as the major phase of the volcanism.These volcanics have extremely low MgO.Cr and Ni contents,are enriched in LREEs and LILEs but depleted in HFSEs(Nb,Ta,and Ti),similar to arc-related volcanic rocks.They are characterized by negative zirconεHft values of-17.4 to 8.8,whole-rock initial 87Sr/86Sr values of 0.7023 to 0.7177 andεNd(t)values of-10.9 to 6.4.and Pb isotopes(206Pb/204Pb=14.366-16.431,207Pb/204Pb=15.106-15.371,208Pb/204Pb=32.455-37.422).The available elemental and Sr-Nd-Pb-Hf isotope data suggest that the Xiong’er volcanic rocks were sourced from a mantle contaminated by continental crust.The volcanic rocks of the Xiong’er Group might have been generated by high-degree partial melting of a lithospheric mantle that was originally modified by oceanic subduction in the Archean.Thus,we suggest that the subduction-modified lithospheric mantle occurred in an extensional setting during the breakup of the Columbia supercontinent in the Late Paleoproterozoic,rather than in an arc setting.

Voyage of the Indian subcontinent since Pangea breakup and driving force of supercontinent cycles: Insights on dynamics from numerical modeling

Recent advances in three-dimensional numerical simulations of mantle convection have aided in approximately reproducing continental movement since the Pangea breakup at 200 Ma. These have also led to a better understanding of the thermal and mechanical coupling between mantle convection and surface plate motion and predictions of the configuration of the next supercontinent. The simulations of mantle convection from 200 Ma to the present reveals that the development of large-scale cold mantle downwellings in the North Tethys Ocean at the earlier stage of the Pangea breakup triggered the northward movement of the Indian subcontinent. The model of high temperature anomaly region beneath Pangea resulting from the thermal insulation effect support the breakup of Pangea in the real Earth time scale, as also suggested in previous geological and geodynamic models. However, considering the low radioactive heat generation rate of the depleted upper mantle, the high temperature anomaly region might have been generated by upwelling plumes with contribution of deep subducted TTG(tonalite-trondhjemite-granite) materials enriched in radiogenic elements. Integrating the numerical results of mantle convection from 200 Ma to the present, and from the present to the future, it is considered that the mantle drag force acting on the base of continents may be comparable to the slab pull force, which implies that convection in the shallower part of the mantle is strongly coupled with surface plate motion.

The dominant driving force for supercontinent breakup: Plume push or subduction retreat?

Understanding the dominant force responsible for supercontinent breakup is crucial for establishing Earth＇s geodynamic evolution that includes supercontinent cycles and plate tectonics. Conventionally,two forces have been considered： the push by mantle plumes from the sub-continental mantle which is called the active force for breakup, and the dragging force from oceanic subduction retreat which is called the passive force for breakup. However, the relative importance of these two forces is unclear. Here we model the supercontinent breakup coupled with global mantle convection in order to address this question. Our global model features a spherical harmonic degree-2 structure, which includes a major subduction girdle and two large upwelling（superplume） systems. Based on this global mantle structure,we examine the distribution of extensional stress applied to the supercontinent by both subsupercontinent mantle upwellings and subduction retreat at the supercontinent peripheral. Our results show that：（1） at the center half of the supercontinent, plume push stress is ～3 times larger than the stress induced by subduction retreat;（2） an average hot anomaly of no higher than 50 K beneath the supercontinent can produce a push force strong enough to cause the initialization of supercontinent breakup;（3） the extensional stress induced by subduction retreat concentrates on a ～600 km wide zone on the boundary of the supercontinent, but has far less impact to the interior of the supercontinent. We therefore conclude that although circum-supercontinent subduction retreat assists supercontinent breakup, sub-supercontinent mantle upwelling is the essential force.

Paleoproterozoic Nb-enriched meta-gabbros in the Quanji Massif,NW China:Implications for assembly of the Columbia supercontinent

Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO^t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(^(143)Nd/^(144)Nd)_t and(^(87)Sr/^(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.

Spatio-temporal evolution of the Satpura Mountain Belt of India:A comparison with the Capricorn Orogen of Western Australia and implication for evolution of the supercontinent Columbia

Reconstruction of the Neoproterozoic supercontinent Rodinia shows near neighbour positions of the South Indian Cratons and Western Australian Cratons. These cratonic areas are characterized by extensive Paleoproterozoic tectonism. Detailed analysis of the spatio-temporal data of the Satpura Mountains of India indicates presence of at least three episodes of Proterozoic orogeny at ~ 2100-1900 Ma, ~ 1850 Ma and ~ 1650 Ma, and associated basin development and closing. A subdued imprint of the Grenville orogeny （~ 950 Ma） is also found in rock records of this Mountain Belt. The Capricorn Orogen of Western Australia also shows three episodes of orogeny： Opthalmian-Glenburgh Orogeny （2100-1950 Ma）, Capricorn Orogeny （ ~ 1800 Ma） and Mangaroon Orogeny （ ~ 1650 Ma）, and basin opening and closing related to these tectonic movements. These broad similarities suggest their joint evolution possibly in a near neighbour posi- tion during Paleoproterozoic Era. In view of juxtaposition of the Western Australia along the east coast of India, at the position of the Eastern Ghats, during Archean, it is suggested that the breaking of this Archean megacraton at - 2400 Ma led to northward movement of the broken components and formation of the Satpura-Capricorn Orogen （at - 2100 and - 1800 Ma） due to the collision of cratonic blocks with the pre- existing northern cratonic nuclei of India and Western Australia. This is also the time of formation of thesupercontinent Columbia. A phase of basin opening followed the ~ 1800 Ma event, followed by another phase of collisional event at - 1600 Ma at the site of the Satpura--Capricorn Orogen. Subsequent evolutions of the Satpura and the Capricorn Orogens differ slightly, indicating separate evolutional history.

Supercontinent tectonics and biogeochemical cycle:A matter of 'life and death'

The formation and disruption of supercontinents have significantly impacted mantle dynamics, solid earth processes, surface environments and the biogeochemical cycle. In the early history of the Earth, the collision of parallel intra-oceanic arcs was an important process in building embryonic continents. Superdownwelling along Y-shaped triple junctions might have been one of the important processes that aided in the rapid assembly of continental fragments into closely packed supercontinents. Various models have been proposed for the fragmentation of supercontinents including thermal blanket and superplume hypotheses. The reassembly of supercontinents after breakup and the ocean closure occurs through ＂introversion＂, ＂extroversion＂ or a combination of both, and is characterized by either Pacific-type or Atlantic-type ocean closure. The breakup of supercontinents and development of hydro- thermal system in rifts with granitic basement create anomalous chemical environments enriched in nutri- ents, which serve as the primary building blocks of the skeleton and bone of early modern life forms. A typical example is the rifting of the Rodinia supercontinent, which opened up an N--S oriented sea way along which nutrient enriched upwelling brought about a habitable geochemical environment. The assembly of supercontinents also had significant impact on life evolution. The role played by the Cambrian Gondwana assembly has been emphasized in many models, including the formation of ＇Trans- gondwana Mountains＇ that might have provided an effective source of rich nutrients to the equatorial waters, thus aiding the rapid increase in biodiversity. The planet has witnessed several mass extinction events during its history, mostly connected with major climatic fluctuations including global cooling and warming events, major glaciations, fluctuations in sea level, global anoxia, volcanic eruptions, asteroid impacts and gamma radiation. Some recent models speculate a relationship between superplumes, supercontinent breakup and mass extinction. Upwelling plumes cause continental rifting and formation of large igneous provinces. Subsequent volcanic emissions and resultant plume-induced ＂winter＂ have catastrophic effect on the atmosphere that lead to mass extinctions and long term oceanic anoxia. The assembly and dispersal of continents appear to have influenced the biogeochemical cycle, but whether the individual stages of organic evolution and extinction on the planet are closely linked to Solid Earth processes remains to be investigated.

Refnement of the supercontinent cycle with Hf, Nd and Sr isotopes

The combined use of Hf,Nd and Sr isotopes is more useful in understanding the supercontinent cycle than the use of only Hf isotopic data from detrital zircons.Sr and Nd seawater isotopes,although not as precise as εNd and εHf distributions,also record input from ocean ridge systems.Unlike detrital zircons where sources cannot be precisely located because of crustal recycling,both the location and tectonic setting often can be constrained for whole-rock Nd isotopic data.Furthermore,primary zircon sources may not reside on the same continent as derivative detrital zircons due to supercontinent breakup and assembly.Common to all of the isotopic studies are geographic sampling biases reflecting outcrop distributions,river system sampling,or geologists,and these may be responsible for most of the decorrelation observed between isotopic systems.Distributions between 3.5 and 2 Ga based on εHf median values of four detrital zircon databases as well as our compiled εNd database are noisy but uniformly distributed in time,whereas data between 2 and 1 Ga data are more tightly clustered with smaller variations.Grouped age peaks suggest that both isotopic systems are sampling similar types of orogens.Only after 1 Ga and before 3.5 Ga do we see wide variations and significant disagreement between databases,which may partially reflect variations in both the number of sample locations and the number of samples per location.External and internal orogens show similar patterns in εNd and εHfwith age suggesting that both juvenile and reworked crustal components are produced in both types of orogens with similar proportions.However,both types of orogens clearly produce more juvenile isotopic signatures in retreating mode than in advancing mode.Many secular changes in εHf and εNd distributions correlate with the supercontinent cycle.Although supercontinent breakup is correlated with short-lived decreasing εHf and εNd （≤ 100 Myr） for most supercontinents,there is no isotopic evidence for the breakup of the Paleoproterozoic supercontinent Nuna.Assembly of supercontinents by extroversion is recorded by decreasing εNd in granitoids and metasediments and decreasing εHf in zircons,attesting to the role of crustal reworking in external orogens in advancing mode.As expected,seawater Sr isotopes increase and seawater Nd isotopes decrease during supercontinent assembly by extroversion.Pangea is the only supercontinent that has a clear isotopic record of introversion assembly,during which median εNd and εHf rise rapidly for ≤ 100 Myr.Although expected to increase,radiogenic seawater Sr decreases （and seawater Nd increases） during assembly of Pangea,a feature that may be caused by juvenile input into the oceans from new ocean ridges and external orogens in retreating mode.The fact that a probable onset of plate tectonics around 3 Ga is not recorded in isotopic distributions may be due the existence of widespread felsic crust formed prior to the onset of plate tectonics in a stagnant lid tectonic regime,as supported by Nd and Hf model ages.

High-temperature granulites and supercontinents

The formation of continents involves a combination of magmatic and metamorphic processes. These processes become indistinguishable at the crust-mantle interface, where the pressure-temperature（P-T）conditions of（ultra） high-temperature granulites and magmatic rocks are similar. Continents grow laterally, by magmatic activity above oceanic subduction zones（high-pressure metamorphic setting）, and vertically by accumulation of mantle-derived magmas at the base of the crust（high-temperature metamorphic setting）. Both events are separated from each other in time; the vertical accretion postdating lateral growth by several tens of millions of years. Fluid inclusion data indicate that during the high-temperature metamorphic episode the granulite lower crust is invaded by large amounts of low H2O-activity fluids including high-density CO2 and concentrated saline solutions（brines）. These fluids are expelled from the lower crust to higher crustal levels at the end of the high-grade metamorphic event. The final amalgamation of supercontinents corresponds to episodes of ultra-high temperature metamorphism involving large-scale accumulation of these low-water activity fluids in the lower crust.This accumulation causes tectonic instability, which together with the heat input from the subcontinental lithospheric mantle, leads to the disruption of supercontinents. Thus, the fragmentation of a supercontinent is already programmed at the time of its amalgamation.

Precambrian supercontinents,glaciations,atmospheric oxygenation,metazoan evolution and an impact that may have changed the second half of Earth history

In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- tions, when extensive glaciations occurred, together with alternating warm periods which were accom- panied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian ＂explosion＂ of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth＇s climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break- up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic （Huronian） carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan evolution not take off after the Great Oxidation Event of the Paleoproterozoic？ The answer may lie in the huge scar left by the -2023 Ma Vredefort impact in South Africa, and in the worldwide organic carbon-rich deposits of the Shunga Event, arresting to the near-extirpation of life and possible radical alteration of the course of Earth history.

Speculations on the mechanisms for the formation and breakup of supercontinents

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.

LA-ICPMS U-Pb Ages of Zircon from Metaleucosomes, Olongbuluke Microcontinent, North Qaidam, and Implications on the Response to the Global Rodinia Supercontinent Assembly Event in NW China

U-Pb dating was conducted on different domains of zircons from metamorphosed leucosomes in Delingha （ 德令哈） complex, the lower basement rocks of the Olongbuluke （欧龙布鲁克 ） microcontinent, North Qaidam, in order to review its complex tectonothermal history. The zircon core is comprised of highly-modified magmatic zircon relicts, the zircon mantle was produced in response to anatexis of a Late Protoproterozoic thermal event; age and isotopic composition of both the zircon core and the zircon mantle have been seriously disturbed due to the thermal event related with growth of the zircon overgrowth rim. The 207 PIV 206 Pb apparent age of the overgrowth rim was estimated to be - 1 030 Ma. This Late Mesoproterozoic thermal event has been interpreted as a response to the global Rodinia supercontinent assembly event in the Olongbuluke microcontinent, Northwest China.

Origins of the supercontinent cycle

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 epi- sodicity 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 superconti- nent assembly and breakup.

Strange attractors, spiritual interlopers and lonely wanderers:The search for pre-Pangean supercontinents

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.

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 combi- nation of introversion and extroversion processes. Small-scale thermal heterogeneity dominates deep mantle convection during the supercontinent cycle, although large-scale upwelling plumes intermit- tently originate under the drifting continents and/or the supercontinent.

LA-ICP-MS U-Pb Geochronology of Detrital Zircons in Eastern Liaoning Province： An Early Paleozoic Formation Associated with the Gondwana Supercontinent Event

Objective The Liao-Ji orogenic belt is a famous Paleoproterozoic orogenic belt in the East Block of the North China Craton(NCC),which extend in NE-SW direction.The geological mass in the Paleoproterozoic Liao-Ji belt is mainly composed of the Liaoji granites and metamorphic volcanic-sedimentary rocks of the Liaohe group(and its

Mechanics of Mafic Dyke Swarms and Breakup of Supercontinent

Dyke swarms can be divided into three types:parallel dyke swarms,radiating dyke swarms and fan-shape dyke swarm,for which the mechanisms of formation are different(Fig.1).Parallel dyke swarms form in response

2.2Ga Subduction-Related Mafic Magmatic Rocks in the Kongling Complex:Evidence for the Assembly of the Columbia Supercontinent

Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,