The deep structure,material circulation,and dynamic processes in the Southeast Asia have long been an elusive scientific puzzle due to the lack of systematic scientific observations and recognized theoretical models.B...The deep structure,material circulation,and dynamic processes in the Southeast Asia have long been an elusive scientific puzzle due to the lack of systematic scientific observations and recognized theoretical models.Based on the deep seismic tomography using long-period natural earthquake data,in this study,the deep structure and material circulation of the curved subduction system in Southeast Asia was studied,and the dynamic processes since 100 million years ago was reconstructed.It is pointed out that challenges still exist in the precise reconstruction of deep mantle structures of the study area,the influence of multi-stage subduction on deep material exchange and shallow magma activity,as well as the spatiotemporal evolution and coupling mechanism of multi-plate convergence.Future work should focus on high-resolution land-sea joint 3-D seismic tomography imaging of the curved subduction system in the Southeast Asia,combined with geochemical analysis and geodynamic modelling works.展开更多
Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate s...Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.展开更多
The Papua New Guinea-Solomon(PN-SL)arc is one of the regions with active crustal motions and strong geological actions.Thus,its complex subduction system makes it an ideal laboratory for studying the initiation mechan...The Papua New Guinea-Solomon(PN-SL)arc is one of the regions with active crustal motions and strong geological actions.Thus,its complex subduction system makes it an ideal laboratory for studying the initiation mechanism of plate subduction.However,the PN-SL subduction system has not yet been sufficiently studied,and its density structure has yet to be revealed.In this paper,we used the free-air gravity data,Parker-Oldenburg density surface inversion method,and the genetic algorithm density inversion method to obtain the density structure of an approximately 1000-km-long northwest-southeast line crossing the PN-SL subduction system under the constraints of the CRUST1.0 global crustal model,onshore seismic data,and the LLNL-G3Dv3 global P-wave velocity model.The density structure shows that density differences between the plates on the two sides of the trench could play a significant role in plate subduction.展开更多
Talc is a layered hydrous silicate mineral that plays a vital role in transporting water into Earth’s interior and is crucial for explaining geophysical observations in subduction zone settings.In this study,we explo...Talc is a layered hydrous silicate mineral that plays a vital role in transporting water into Earth’s interior and is crucial for explaining geophysical observations in subduction zone settings.In this study,we explored the structure,equation of state,and elasticity of both triclinic and monoclinic talc under high pressures up to 18 GPa using first principles simulations based on density functional theory corrected for dispersive forces.Our results indicate that principal components of the full elastic constant tensor C_(11) and C_(22),shear components C_(66),and several off-diagonal components show anomalous pressure dependence.This non-monotonic pressure dependence of elastic constant components is likely related to the structural changes and is often manifested in a polytypic transition from a low-pressure polytype talc-I to a high-pressure polytype talc-Ⅱ.The polytypic transition of talc occurs at pressures within its thermodynamic stability.However,the bulk and shear elastic moduli show no anomalous softening.Our study also shows that talc has low velocity,extremely high anisotropy,and anomalously high V_(P)/V_(S) ratio,thus making it a potential candidate mineral phase that could readily explain unusually high V_(P)/V_(S) ratio and large shear wave splitting delays as observed from seismological studies in many subduction systems.展开更多
The bidirectional subduction system,island arc magmatic activities,and thermal structure of the forearc basin in the Molucca Sea are taken into consideration in this study.The active volcanic arcs on both sides of the...The bidirectional subduction system,island arc magmatic activities,and thermal structure of the forearc basin in the Molucca Sea are taken into consideration in this study.The active volcanic arcs on both sides of the bidirectional subduction zone in the Molucca Sea are undergoing arc-arc collisions.We applied a finite element thermal simulation method to reconstruct the thermal evolution history of the Molucca Sea Plate based on geophysical data.Then,we analyzed the thermodynamic characteristics of island arc volcanism on both sides of the bidirectional subduction zone.The results showed that at 10Myr,the oceanic ridge of the Molucca Sea Plate was asymmetrically biased to the west,causing this bidirectional subduction to be deeper in the west than in the east.Furthermore,the oceanic ridge subducted under the Sangihe arc at 5.5Myr,causing intermittent cessation of volcanic activities.Due to the convergence of bidirectional subduction,the geothermal gradient in the top 3km depth of the forearc area between the Sangihe and Halmahera arcs decreased from about 60℃km^(−1) at 4Myr to about 38℃km^(−1) today.Finally,within the 45–100 km depth range of the sliding surface of the subduction,anomalously high-temperature zones formed due to shear friction during the bidirectional subduction.展开更多
Based on structural deformation analysis in the oblique Sumatra subduction system, we review uplift mechanisms of the forearc high and formation of the forearc basin. The development of the forearc high has been attri...Based on structural deformation analysis in the oblique Sumatra subduction system, we review uplift mechanisms of the forearc high and formation of the forearc basin. The development of the forearc high has been attributed to the flexural uplift, basin inversion, uplift of older accretion wedge, and backthrust in the landward margin of the accretion wedge. Observation of recently acquired seismic reflection data shows that the interplay between trenchward-vergent thrusts and arcward-vergent backthrusts has played a major role in the uplift of forearc high. The uplifted sediments on the forearc high were previously formed in a forearc basin environment. The present-day morphology of the forearc high and forearc basin is related to the uplift of the accretionary wedge and the overlying forearc basin sediments during Pliocene. Regardless of obliquity in the subduction system, the Sumatran forearc region is dominated by compression that plays an important role in forming Neogene basin depocenters that elongated parallel to the trench.展开更多
The research paper"Geodynamic processes of the southeastern Neo-Tethys Ocean and the formation mechanism of the curved subduction system in Southeast Asia"(Sci China Earth Sci,2023,66:703-717)contained error...The research paper"Geodynamic processes of the southeastern Neo-Tethys Ocean and the formation mechanism of the curved subduction system in Southeast Asia"(Sci China Earth Sci,2023,66:703-717)contained errors.The corrections in an erratum do not change or affect the result or conclusion of the paper.展开更多
The dependence of the subduction regime on three-dimensional slab geometry poses a challenge for accurately estimating the evolving thermal structure of megathrusts globally. Although slab dips and ages have gained at...The dependence of the subduction regime on three-dimensional slab geometry poses a challenge for accurately estimating the evolving thermal structure of megathrusts globally. Although slab dips and ages have gained attention, the specific impacts of oblique subduction remain unmeasured. Here, we present an integrated thermal model that quantifies how slab morphology can shape the thermal state of megathrusts, such as those in the Makran Subduction Zone. The model considers both slab obliquity and depth variations along the trench. We find a considerable match between the slab petrological dehydration zone and the distribution of great crustal earthquakes. We suggest that the accumulation of fluids along megathrusts by slab metamorphism can foster more polarized conditions for decreasing plate coupling and increasing interplate ruptures. It is thus imperative to improve model representation and more realistically represent how drivers of slab geometry affect metamorphic transitions and the occurrence of earthquakes at megathrusts.展开更多
Southeast Asia is located at the intersection of the Tethys and Pacific domains. The superimposed effects of the two tectonic domains have resulted in complicated deep structure, surface magma responses, and dynamic p...Southeast Asia is located at the intersection of the Tethys and Pacific domains. The superimposed effects of the two tectonic domains have resulted in complicated deep structure, surface magma responses, and dynamic processes of Southeast Asia. Based on the latest long-term passive seismic experiment and numerical modeling, this study reconstructs the dynamic processes of the closure of the Neo-Tethys Ocean and the formation of the curved subduction system in Southeast Asia since the Late Mesozoic. P-wave velocity structure shows a remnant of the Neo-Tethys subducted slab in the lower mantle beneath Southeast Asia at a depth of approximately 1500 km. On the Java-East Timor subduction zone, the remnant slab is coupled with the Indo-Australian subducting slab in the upper mantle with the same direction, while on the Sumatra subduction zone, the remnant slab is decoupled from the Indo-Australian subducting slab in different directions. The formation of the curved subduction system in Southeast Asia is resulted from the northward subdcutions of previous Neo-Tethys and current IndoAustralian Plate, and the westward subduction of the Pacific Plate since Mesozoic. The former is characterized by continuous subduction and subsequent continental block collision, forming the current continental lithosphere in Southeast Asia and the curve-shaped Sumatra-Java subduction zone;the latter is characterized by subduction retreat and back-arc spreading, forming the eastern Philippine subduction zone and a series of marginal sea basins. Since the Early Cretaceous, the opening of the North Australian Sea resulted in stagnation of the Australian Block in the high latitude area of the southern hemisphere for a long time.The North Australian Sea was dominated by out-dipping double subduction from 45 Ma, which resulted in rapid northward drifting of the Australian Block and final collision with the Sundaland.展开更多
This study focuses on the geology,geochemistry,Sr-Nd isotopes and their tectonic settings of three types of basalts in Diyanmiao ophiolite in the Xar Moron area located on the eastern margin of the Central Asian Oroge...This study focuses on the geology,geochemistry,Sr-Nd isotopes and their tectonic settings of three types of basalts in Diyanmiao ophiolite in the Xar Moron area located on the eastern margin of the Central Asian Orogenic Belt.Type I basalts are oceanic tholeiites with a depleted light rare earth element(LREE)pattern,which are similar to the typical N-mid-oceanic ridge basalt(MORB)and suggests that they were formed at a mid-oceanic ridge.The initial 87Sr/86Sr ratios of Type I basalts range from 0.703966 to 0.705276 and theεNd(t)values are from 16.49 to 17.15,indicating that they were derived from a depleted mantle source.Type II basalts belong to the medium-potassium calc-akaline series and have the geochem-ical characteristics of Nb-enriched basalt(NEB)with high Nb content(14.5 ppm)and strong enrichment in LREEs,implying that they were created by the partial melting of mantle wedge peridotite that previously metasomatized by slab melts.Type III basalts are high-Al basalt(HAB)with high-Al contents(Al_(2)0_(3)=16.75 wt.%-18.00 wt.%),distinct Nb depletion and high Th/Yb ratios.Thus they were likely gen-erated in a normal island-arc setting.Therefore,the association of MORB,NEB,and HAB in the study area may be due to the subduction of a mid-oceanic ridge,and the Diyanmiao ophiolite is proposed to be formed in the forearc setting of a mid-oceanic ridge subduction system.展开更多
A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented fo...A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories： （i） Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and （ii） morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma （convection, turbulence, degassing, etc.）. Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.展开更多
The Paleoproterozoic was a critical time in whether modern-style plate tectonics had become globally dominant(e.g.,Wan et al.,2020).The Capricorn Orogen witnessed the assembly of the Pilbara and Yilgarn Cratons and an...The Paleoproterozoic was a critical time in whether modern-style plate tectonics had become globally dominant(e.g.,Wan et al.,2020).The Capricorn Orogen witnessed the assembly of the Pilbara and Yilgarn Cratons and an exotic microcontinent,the Glenburgh Terrane,to form the West Australia Craton(WAC)through two collisional orogenic events,the 2215–2145 Ma Ophthalmian and 2005–1950 Ma Glenburgh Orogenies(Johnson et al.,2013;Fig.1).Compared to other Proterozoic orogenic belts in Australia,the Capricorn Orogen preserves‘complete'opposing continental margin successions,together with intervening arc fragments associated with oceanic closure and foreland basins associated with collisional loading(Cawood et al.,2009).展开更多
Three M_(W)>7.0 earthquakes in 2020-2021 occurred in the Shumagin seismic gap and its adjacent area of the Alaska-Aleutian subduction zone,including the Mw7.8 Simeonof thrust earthquake on July 22,2020,the M_(W)7.6...Three M_(W)>7.0 earthquakes in 2020-2021 occurred in the Shumagin seismic gap and its adjacent area of the Alaska-Aleutian subduction zone,including the Mw7.8 Simeonof thrust earthquake on July 22,2020,the M_(W)7.6 Sand Point strike-slip earthquake on October 19,2020,and the M_(W)8.2 Chignik thrust earthquake on July 29,2021.The spatial and temporal proximity of these three earthquakes prompts us to probe stress-triggering effects among them.Here we examine the coseismic Coulomb stress change imparted by the three earthquakes and their influence on the subduction interface.Our results show that:(1)The Simeonof earthquake has strong loading effects on the subsequent Sand Point and Chignik earthquakes,with the Coulomb stress changes of 3.95 bars and 2.89 bars,respectively.The Coulomb stress change caused by the Sand Point earthquake at the hypocenter of the Chignik earthquake is merely around 0.01 bars,suggesting the negligible triggering effect on the latter earthquake;(2)The triggering effects of the Simeonof,Sand Point,and Chignik earthquakes on aftershocks within three months are not well pronounced because of the triggering rates of 38%,14%,and 43%respectively.Other factors may have played an important role in promoting the occurrence of these aftershocks,such as the roughness of the subduction interface,the complicated velocity structure of the lithosphere,and the heterogeneous prestress therein;(3)The three earthquakes caused remarkable coseismic Coulomb stress changes at the subduction interface nearby these mainshocks,with an average Coulomb stress change of 3.2 bars in the shallow region directly inwards the trench.展开更多
The Sumatra subduction zone is located in the southwest of the Suna plate,between the Euro-Asia Plate and Indo-Austrilian Plates.With the obliquely subducting of the Indo-Austrilian Plate toward the the Euro-Asia Plat...The Sumatra subduction zone is located in the southwest of the Suna plate,between the Euro-Asia Plate and Indo-Austrilian Plates.With the obliquely subducting of the Indo-Austrilian Plate toward the the Euro-Asia Plate,complex tectonics,strong earthquakes and volcanoes have been observed in this area which has become a well experimental field used to study the subduction zone.In this work,we employed receiver function method to evaluate the S-wave velocity structure beneath 5 broadband seismic stations along the Sumatra subduction zone.We selected 332 receiver function waveforms with intelligent software and manual picking methods,including 130,34,42,29 and 97 receiver function waveforms corresponding to BKNI,GSI,LHMI,MNAI,and PMBI sta-tions,respectively.These stacked receiver function waveforms were applied to inversion to estimate Swave structure beneath each station based on a Neighborhood Algorithm(NA).Our results indicate that the sediment layers for GSI,LHMI and MNAI stations are more than 3 km thick,two stations of which are thicker than 6 km(e.g.GSI and LHMI).The difference of receiver function waveforms for NE,SW and W orientation at station GSI where is accompanied with strong thrust earthquakes suggests that there is a complicated structure beneath this station.Station BKNI and PMBI are located on the eastern side of the Sumatra fault and the thickness of their sediment layers is only~1 km.The crustal thickness for back-arc basin is within 30-36 km.However,the crustal thickness of forearc area varies from~26 km of the forearc ridge to 26-30 km of the forearc basin toward continent and its,which suggests that the down dip limit(slab-Moho intersection)of seismogenic zone is within 29-36 km in forearc and explains why the shallow-focus earthquakes play a dominant role in this area.The stable state for the inner wedge of forearc within a seismogenic circle provides a favorable environment for storing stress.Meanwhile,these faults caused by the subducting of Indo-Austrilian Plate constructed a condition(e.g.cracking of intact rocks and frictional sliding)in which it would trigger shallow-focus seismic activities(releasing stress).展开更多
The Mariana subduction structure is a hot topic in ocean-ocean subduction zone research,and its subduction mechanism has attracted wide attention from experts and scholars in China and abroad.Based on the multi-channe...The Mariana subduction structure is a hot topic in ocean-ocean subduction zone research,and its subduction mechanism has attracted wide attention from experts and scholars in China and abroad.Based on the multi-channel seismic data of survey line MGL1204 in the Mariana fore-arc and DSDP ocean drilling data,this paper studies the development and evolution characteristics of the structure and strata in the Cenozoic Mariana fore-arc sedimentary basin.The Cenozoic strata are divided into six seismic sequences,with the possible era of each seismic sequence discerned,and the relationship between fault development and earthquakes analyzed.The episodic activity of the volcanic chain of the Mariana island arc is thought to control the tectonic and stratigraphic development pattern of the Cenozoic sedimentary basin in the fore-arc.Between 16°N-19°N and 146°E-151°E,the maximum thickness of the sedimentary center of the Cenozoic fore-arc sedimentary basin in Mariana is about 2360 m.Normal faults are developed in the area and some broke to the seabed,indicating that the Mariana island arc is still in the post-arc expansion stage.The application of multi-channel seismic sections in structural and stratigraphic evolution study is an important means to elucidating the Mariana subduction mechanism.展开更多
We report new SHRIMP zircon U-Pb ages,zircon Lu-Hf isotopic and whole rock geochemical data from Permian granitoids located in the Alxa area of Inner Mongolia,China.In combination with published geochronological and g...We report new SHRIMP zircon U-Pb ages,zircon Lu-Hf isotopic and whole rock geochemical data from Permian granitoids located in the Alxa area of Inner Mongolia,China.In combination with published geochronological and geochemical data,the granitoids in the region can be divided into two age groups:ca.285 Ma and ca.269 Ma.The granitoids of the first group are mainly composed of calc-alkaline to high-K calc-alkaline,weakly peraluminous Ⅰ-type granodiorites with ε_(Hf)(t)values of-19.6 to-4.3,which demonstrates evidence of crustal reworking;the granitoids of the second group,however,mainly consist of A-type granites that are high-K calc-alkaline to shoshonite,metaluminous to weakly peraluminous,and have high 10,000×Ga/Al ratios(2.59-3.12)and ε_(Hf)(t)values ranging from-11.3 to-2.7,all of which demonstrates a mixed crust-mantle source.We interpret the granitoids of the first group to have formed during the subduction of Central Asian oceanic crust and the second group to have formed by the asthenospheric upwelling caused by the formation of slab windows during late ocean ridge subduction.展开更多
Crustal recycling at convergent plate boundaries is essential to mantle heterogeneity.However,crustal signatures in the mantle source of basaltic rocks above subduction zones were primarily incorporated in the form of...Crustal recycling at convergent plate boundaries is essential to mantle heterogeneity.However,crustal signatures in the mantle source of basaltic rocks above subduction zones were primarily incorporated in the form of liquid rather than solid phases.The physicochemical property of liquid phases is determined by the dehydration behavior of crustal rocks at the slab-mantle interface in subduction channels.Because of the significant fractionation in incompatible trace elements but the full inheritance in radiogenic isotopes relative to their crustal sources,the production of liquid phases is crucial to the geochemical transfer from the subducting crust into the mantle.In this process,the stability of specific minerals in subducting crustal rocks exerts a primary control on the enrichment of given trace elements in the liquid phases.For this reason,geochemically enriched oceanic basalts can be categorized into two types in terms of their trace element distribution patterns in the primitive mantle-normalized diagram.One is island arc basalts(IAB),showing enrichment in LILE,Pb and LREE but depletion in HFSE such as Nb and Ta relative to HREE,The other is ocean island basalts(OIB),exhibiting enrichment in LILE and LREE,enrichment or non-depletion in HFSE but depletion in Pb relative to HREE.In either types,these basalts show the enhanced enrichment of LILE and LREE with increasing their incompatibility relative to normal mid-ocean ridge basalts(MORB).The thermal regime of subduction zones can be categorized into two stages in both time and space,The first stage is characterized by compressional tectonism at low thermal gradients.As a consequence,metamorphic dehydration of the subducting crust prevails at forearc to subarc depths due to the breakdown of hydrous minerals such as mica and amphibole in the stability field of garnet and rutile,resulting in the liberation of aqueous solutions with the trace element composition that is considerably enriched in LILE,Pb and LREE but depleted in HFSE and HREE relative to normal MORB.This provides the crustal signature for the mantle sources of IAB.The second stage is indicated by extensional tectonism at high thermal gradients,leading to the partial melting of metamorphically dehydrated crustal rocks at subarc to postarc depths.This involves not only the breakdown of hydrous minerals such as amphibole,phengite and allanite in the stability field of garnet but also the dissolution of rutile into hydrous melts.As such,the hydrous melts can acquire the trace element composition that is significantly enriched in LILE,HFSE and LREE but depleted in Pb and HREE relative to normal MORB,providing the crustal signature for the mantle sources of OIB.In either case,these liquid phases would metasomatize the overlying mantle wedge peridotite at different depths,generating ultramafic metasomatites such as serpentinized and chloritized peridotites,and olivine-poor pyroxenites and hornblendites.As a consequence,the crustal signatures are transferred by the liquid phases from the subducting slab into the mantle.展开更多
Plate subduction is the largest natural factory that processes elements,which controls recycling and mineralization of a variety of elements.There are three major ore deposit belts in the world:the circumPacific,the c...Plate subduction is the largest natural factory that processes elements,which controls recycling and mineralization of a variety of elements.There are three major ore deposit belts in the world:the circumPacific,the centralAsian,and the Tethys belts.All the three belts are closely associated with plate subductions,the mechanism remains obscure.We approached this problem from systematic studies on the behaviours of elements during geologic processes.This contribution summaries the recent progress of our research group.Our results suggest that porphyry Cu deposits form through partial melting of subducted young oceanic crust under oxygen fugacities higher than AFMQ^+1.5,which is promoted after the elevation of atmospheric oxygen at ca.550 Ma.Tin deposits are associated with reducing magmatic rocks formed as a consequence of slab rollback.The Neo-Tethys tectonic regime hosts more than 60%of the world's total Sn reserves.This is due to the reducing environment formed during the subduction of organic rich sediments.For the same reason,porphyry Cu deposits formed in the late stages during the closure of the Neo-Tethys Ocean.Tungsten deposits are also controlled by slab rollback,but is not so sensitive to oxygen fugacity.Subduction related W/Sn deposits are mostly accompanied by abundant accessory fluorites due to the breakdown of phengite and apatite.Decomposition of phengite is also significant for hard rock lithium deposits,whereas orogenic belt resulted from plate subduction promote the formation of Li brine deposits.Cretaceous red bed basins near the Nanling region are favorable for Li brines.Both Mo and Re are enriched in the oxidationreduction cycle during surface processes,and may get further enriched once Mo-,Re-enriched sediments are subducted and involved in magmatism.During plate subduction,Mo and Re fractionate from each other.Molybdenum is mainly hosted in porphyry Mo deposits and to a less extent,porphyry Cu-Mo deposits,whereas Re is predominantly hosted in porphyry Cu-Mo deposits and sedimentary sulfide deposits.展开更多
Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of n...Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of numerical models of mantle dynamics pre-and post-Pangea timeframes requires global kinematic descriptions with full plate reconstructions extending into the Paleozoic(410 Ma). Current plate models that cover Paleozoic times are characterised by large plate speeds and trench migration rates because they assume that lowermost mantle structures are rigid and fixed through time. When used as a surface boundary constraint in geodynamic models, these plate reconstructions do not accurately reproduce the present-day structure of the lowermost mantle. Building upon previous work, we present a global plate motion model with continuously closing plate boundaries ranging from the early Devonian at 410 Ma to present day.We analyse the model in terms of surface kinematics and predicted lower mantle structure. The magnitude of global plate speeds has been greatly reduced in our reconstruction by modifying the evolution of the synthetic Panthalassa oceanic plates, implementing a Paleozoic reference frame independent of any geodynamic assumptions, and implementing revised models for the Paleozoic evolution of North and South China and the closure of the Rheic Ocean. Paleozoic(410-250 Ma) RMS plate speeds are on average ～8 cm/yr, which is comparable to Mesozoic-Cenozoic rates of ～6 cm/yr on average.Paleozoic global median values of trench migration trend from higher speeds(～2.5 cm/yr) in the late Devonian to rates closer to 0 cm/yr at the end of the Permian(～250 Ma), and during the Mesozoic-Cenozoic(250-0 Ma) generally cluster tightly around ～1.1 cm/yr. Plate motions are best constrained over the past 130 Myr and calculations of global trench convergence rates over this period indicate median rates range between 3.2 cm/yr and 12.4 cm/yr with a present day median rate estimated at～5 cm/yr. For Paleozoic times(410-251 Ma) our model results in median convergence rates largely～5 cm/yr. Globally,～90% of subduction zones modelled in our reconstruction are determined to be in a convergent regime for the period of 120-0 Ma. Over the full span of the model, from 410 Ma to 0 Ma,～93% of subduction zones are calculated to be convergent, and at least 85% of subduction zones are converging for 97% of modelled times. Our changes improve global plate and trench kinematics since the late Paleozoic and our reconstructions of the lowermost mantle structure challenge the proposed fixity of lower mantle structures, suggesting that the eastern margin of the African LLSVP margin has moved by as much as ～1450 km since late Permian times(260 Ma). The model of the plate-mantle system we present suggests that during the Permian Period, South China was proximal to the eastern margin of the African LLSVP and not the western margin of the Pacific LLSVP as previous thought.展开更多
Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphi...Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited （detrital） and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence （CL） imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones （domains） to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure （HP） metamorphic conditions of T = 571-668℃ and P =1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782-849℃ and P 〉 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600- 710℃ and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10-11 Ma and exhumation of the rocks occurred over a period of 19-20 Ma. Thus, subduction from - 55 km to 〉 160 km deep mantle depth took place at rates of approximately 9.5-10.5 km/Ma and exhumation from depths 〉160 km to the base of the crust at -30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin lithosphere followed by ultrafast exhumation driven by buoyancy forces after break-off of the UHP slab deep within the mantle.展开更多
基金Support by the National Natural Science Foundation of China(No.92258303)the Project of Donghai Laboratory(No.DH-2022ZY0005)。
文摘The deep structure,material circulation,and dynamic processes in the Southeast Asia have long been an elusive scientific puzzle due to the lack of systematic scientific observations and recognized theoretical models.Based on the deep seismic tomography using long-period natural earthquake data,in this study,the deep structure and material circulation of the curved subduction system in Southeast Asia was studied,and the dynamic processes since 100 million years ago was reconstructed.It is pointed out that challenges still exist in the precise reconstruction of deep mantle structures of the study area,the influence of multi-stage subduction on deep material exchange and shallow magma activity,as well as the spatiotemporal evolution and coupling mechanism of multi-plate convergence.Future work should focus on high-resolution land-sea joint 3-D seismic tomography imaging of the curved subduction system in the Southeast Asia,combined with geochemical analysis and geodynamic modelling works.
文摘Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.
基金the National Natural Science Foundation of China(Nos.91858215,42076224)。
文摘The Papua New Guinea-Solomon(PN-SL)arc is one of the regions with active crustal motions and strong geological actions.Thus,its complex subduction system makes it an ideal laboratory for studying the initiation mechanism of plate subduction.However,the PN-SL subduction system has not yet been sufficiently studied,and its density structure has yet to be revealed.In this paper,we used the free-air gravity data,Parker-Oldenburg density surface inversion method,and the genetic algorithm density inversion method to obtain the density structure of an approximately 1000-km-long northwest-southeast line crossing the PN-SL subduction system under the constraints of the CRUST1.0 global crustal model,onshore seismic data,and the LLNL-G3Dv3 global P-wave velocity model.The density structure shows that density differences between the plates on the two sides of the trench could play a significant role in plate subduction.
基金supported by the US National Science Foundation grant EAR 1763215 and EAR 1753125XSEDE facilities(GEO170003)+4 种基金the High-Performance Computing,Research Computing Center,Florida State Universitythe UK’s National Supercomputer Service through the UK CarParrinello Consortium(EPSRC Grant No.EP/P022561/1)and project ID d56"Planetary Interiors"funding from the INSU-CNRSthe French Government Laboratory of Excellence initiative n°ANR-10-LABX-0006,the Région Auvergnethe European Regional Development Fund(Cler Volc contribution number 530).
文摘Talc is a layered hydrous silicate mineral that plays a vital role in transporting water into Earth’s interior and is crucial for explaining geophysical observations in subduction zone settings.In this study,we explored the structure,equation of state,and elasticity of both triclinic and monoclinic talc under high pressures up to 18 GPa using first principles simulations based on density functional theory corrected for dispersive forces.Our results indicate that principal components of the full elastic constant tensor C_(11) and C_(22),shear components C_(66),and several off-diagonal components show anomalous pressure dependence.This non-monotonic pressure dependence of elastic constant components is likely related to the structural changes and is often manifested in a polytypic transition from a low-pressure polytype talc-I to a high-pressure polytype talc-Ⅱ.The polytypic transition of talc occurs at pressures within its thermodynamic stability.However,the bulk and shear elastic moduli show no anomalous softening.Our study also shows that talc has low velocity,extremely high anisotropy,and anomalously high V_(P)/V_(S) ratio,thus making it a potential candidate mineral phase that could readily explain unusually high V_(P)/V_(S) ratio and large shear wave splitting delays as observed from seismological studies in many subduction systems.
基金supported by the Natural Science Foundation of Shandong Province(No.ZR2021MD069)the Strategic Pioneer Science and Technology Special Project of the Chinese Academy of Sciences(No.XDB42020104)+1 种基金the National Natural Science Foundation of China(No.42176052)the Project of Introducing and Cultivating Young Talents in the Universities of Shandong Province(No.LUJIAOKEHAN-2021-51).
文摘The bidirectional subduction system,island arc magmatic activities,and thermal structure of the forearc basin in the Molucca Sea are taken into consideration in this study.The active volcanic arcs on both sides of the bidirectional subduction zone in the Molucca Sea are undergoing arc-arc collisions.We applied a finite element thermal simulation method to reconstruct the thermal evolution history of the Molucca Sea Plate based on geophysical data.Then,we analyzed the thermodynamic characteristics of island arc volcanism on both sides of the bidirectional subduction zone.The results showed that at 10Myr,the oceanic ridge of the Molucca Sea Plate was asymmetrically biased to the west,causing this bidirectional subduction to be deeper in the west than in the east.Furthermore,the oceanic ridge subducted under the Sangihe arc at 5.5Myr,causing intermittent cessation of volcanic activities.Due to the convergence of bidirectional subduction,the geothermal gradient in the top 3km depth of the forearc area between the Sangihe and Halmahera arcs decreased from about 60℃km^(−1) at 4Myr to about 38℃km^(−1) today.Finally,within the 45–100 km depth range of the sliding surface of the subduction,anomalously high-temperature zones formed due to shear friction during the bidirectional subduction.
文摘Based on structural deformation analysis in the oblique Sumatra subduction system, we review uplift mechanisms of the forearc high and formation of the forearc basin. The development of the forearc high has been attributed to the flexural uplift, basin inversion, uplift of older accretion wedge, and backthrust in the landward margin of the accretion wedge. Observation of recently acquired seismic reflection data shows that the interplay between trenchward-vergent thrusts and arcward-vergent backthrusts has played a major role in the uplift of forearc high. The uplifted sediments on the forearc high were previously formed in a forearc basin environment. The present-day morphology of the forearc high and forearc basin is related to the uplift of the accretionary wedge and the overlying forearc basin sediments during Pliocene. Regardless of obliquity in the subduction system, the Sumatran forearc region is dominated by compression that plays an important role in forming Neogene basin depocenters that elongated parallel to the trench.
文摘The research paper"Geodynamic processes of the southeastern Neo-Tethys Ocean and the formation mechanism of the curved subduction system in Southeast Asia"(Sci China Earth Sci,2023,66:703-717)contained errors.The corrections in an erratum do not change or affect the result or conclusion of the paper.
基金benefited from the financial support of the Chinese Academy of Sciences Pioneer Hundred Talents Programthe Second Tibetan Plateau Scientific Expedition and Research Program (Grant No. 2019QZKK0708)+2 种基金the MEXT KAKENHI grant (Grant No. 21H05203)the Kobe University Strategic International Collaborative Research Grant (Type B Fostering Joint Research)the “Science of Slowto-Fast Earthquakes” project。
文摘The dependence of the subduction regime on three-dimensional slab geometry poses a challenge for accurately estimating the evolving thermal structure of megathrusts globally. Although slab dips and ages have gained attention, the specific impacts of oblique subduction remain unmeasured. Here, we present an integrated thermal model that quantifies how slab morphology can shape the thermal state of megathrusts, such as those in the Makran Subduction Zone. The model considers both slab obliquity and depth variations along the trench. We find a considerable match between the slab petrological dehydration zone and the distribution of great crustal earthquakes. We suggest that the accumulation of fluids along megathrusts by slab metamorphism can foster more polarized conditions for decreasing plate coupling and increasing interplate ruptures. It is thus imperative to improve model representation and more realistically represent how drivers of slab geometry affect metamorphic transitions and the occurrence of earthquakes at megathrusts.
基金supported by the National Natural Science Foundation of China(Grant Nos.42025601,41890811&92155203)。
文摘Southeast Asia is located at the intersection of the Tethys and Pacific domains. The superimposed effects of the two tectonic domains have resulted in complicated deep structure, surface magma responses, and dynamic processes of Southeast Asia. Based on the latest long-term passive seismic experiment and numerical modeling, this study reconstructs the dynamic processes of the closure of the Neo-Tethys Ocean and the formation of the curved subduction system in Southeast Asia since the Late Mesozoic. P-wave velocity structure shows a remnant of the Neo-Tethys subducted slab in the lower mantle beneath Southeast Asia at a depth of approximately 1500 km. On the Java-East Timor subduction zone, the remnant slab is coupled with the Indo-Australian subducting slab in the upper mantle with the same direction, while on the Sumatra subduction zone, the remnant slab is decoupled from the Indo-Australian subducting slab in different directions. The formation of the curved subduction system in Southeast Asia is resulted from the northward subdcutions of previous Neo-Tethys and current IndoAustralian Plate, and the westward subduction of the Pacific Plate since Mesozoic. The former is characterized by continuous subduction and subsequent continental block collision, forming the current continental lithosphere in Southeast Asia and the curve-shaped Sumatra-Java subduction zone;the latter is characterized by subduction retreat and back-arc spreading, forming the eastern Philippine subduction zone and a series of marginal sea basins. Since the Early Cretaceous, the opening of the North Australian Sea resulted in stagnation of the Australian Block in the high latitude area of the southern hemisphere for a long time.The North Australian Sea was dominated by out-dipping double subduction from 45 Ma, which resulted in rapid northward drifting of the Australian Block and final collision with the Sundaland.
基金This study was financially supported by Inner Mongolia Autonomous Region Geological and Mineral Exploration Fund(Nos.2017-YS01 and 2020-YS01)the Project of the Institute of Mineral Resources,China Metallurgical Geology Bureau(No.CMGB202002).
文摘This study focuses on the geology,geochemistry,Sr-Nd isotopes and their tectonic settings of three types of basalts in Diyanmiao ophiolite in the Xar Moron area located on the eastern margin of the Central Asian Orogenic Belt.Type I basalts are oceanic tholeiites with a depleted light rare earth element(LREE)pattern,which are similar to the typical N-mid-oceanic ridge basalt(MORB)and suggests that they were formed at a mid-oceanic ridge.The initial 87Sr/86Sr ratios of Type I basalts range from 0.703966 to 0.705276 and theεNd(t)values are from 16.49 to 17.15,indicating that they were derived from a depleted mantle source.Type II basalts belong to the medium-potassium calc-akaline series and have the geochem-ical characteristics of Nb-enriched basalt(NEB)with high Nb content(14.5 ppm)and strong enrichment in LREEs,implying that they were created by the partial melting of mantle wedge peridotite that previously metasomatized by slab melts.Type III basalts are high-Al basalt(HAB)with high-Al contents(Al_(2)0_(3)=16.75 wt.%-18.00 wt.%),distinct Nb depletion and high Th/Yb ratios.Thus they were likely gen-erated in a normal island-arc setting.Therefore,the association of MORB,NEB,and HAB in the study area may be due to the subduction of a mid-oceanic ridge,and the Diyanmiao ophiolite is proposed to be formed in the forearc setting of a mid-oceanic ridge subduction system.
文摘A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories： （i） Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and （ii） morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma （convection, turbulence, degassing, etc.）. Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.
文摘The Paleoproterozoic was a critical time in whether modern-style plate tectonics had become globally dominant(e.g.,Wan et al.,2020).The Capricorn Orogen witnessed the assembly of the Pilbara and Yilgarn Cratons and an exotic microcontinent,the Glenburgh Terrane,to form the West Australia Craton(WAC)through two collisional orogenic events,the 2215–2145 Ma Ophthalmian and 2005–1950 Ma Glenburgh Orogenies(Johnson et al.,2013;Fig.1).Compared to other Proterozoic orogenic belts in Australia,the Capricorn Orogen preserves‘complete'opposing continental margin successions,together with intervening arc fragments associated with oceanic closure and foreland basins associated with collisional loading(Cawood et al.,2009).
基金supported by grants from the National Natural Science Foundation of China(Grant No.sU2139205,41774011,41874011)the National Key Research and Development Program of China(Grant No.2018YFC1503605)。
文摘Three M_(W)>7.0 earthquakes in 2020-2021 occurred in the Shumagin seismic gap and its adjacent area of the Alaska-Aleutian subduction zone,including the Mw7.8 Simeonof thrust earthquake on July 22,2020,the M_(W)7.6 Sand Point strike-slip earthquake on October 19,2020,and the M_(W)8.2 Chignik thrust earthquake on July 29,2021.The spatial and temporal proximity of these three earthquakes prompts us to probe stress-triggering effects among them.Here we examine the coseismic Coulomb stress change imparted by the three earthquakes and their influence on the subduction interface.Our results show that:(1)The Simeonof earthquake has strong loading effects on the subsequent Sand Point and Chignik earthquakes,with the Coulomb stress changes of 3.95 bars and 2.89 bars,respectively.The Coulomb stress change caused by the Sand Point earthquake at the hypocenter of the Chignik earthquake is merely around 0.01 bars,suggesting the negligible triggering effect on the latter earthquake;(2)The triggering effects of the Simeonof,Sand Point,and Chignik earthquakes on aftershocks within three months are not well pronounced because of the triggering rates of 38%,14%,and 43%respectively.Other factors may have played an important role in promoting the occurrence of these aftershocks,such as the roughness of the subduction interface,the complicated velocity structure of the lithosphere,and the heterogeneous prestress therein;(3)The three earthquakes caused remarkable coseismic Coulomb stress changes at the subduction interface nearby these mainshocks,with an average Coulomb stress change of 3.2 bars in the shallow region directly inwards the trench.
基金supported by NSFC(42306084)Hunan Provincial Natural Science Foundation of China(2023JJ40223)Scientific Research Fund of Hunan Provincial Education Department(21B0566).
文摘The Sumatra subduction zone is located in the southwest of the Suna plate,between the Euro-Asia Plate and Indo-Austrilian Plates.With the obliquely subducting of the Indo-Austrilian Plate toward the the Euro-Asia Plate,complex tectonics,strong earthquakes and volcanoes have been observed in this area which has become a well experimental field used to study the subduction zone.In this work,we employed receiver function method to evaluate the S-wave velocity structure beneath 5 broadband seismic stations along the Sumatra subduction zone.We selected 332 receiver function waveforms with intelligent software and manual picking methods,including 130,34,42,29 and 97 receiver function waveforms corresponding to BKNI,GSI,LHMI,MNAI,and PMBI sta-tions,respectively.These stacked receiver function waveforms were applied to inversion to estimate Swave structure beneath each station based on a Neighborhood Algorithm(NA).Our results indicate that the sediment layers for GSI,LHMI and MNAI stations are more than 3 km thick,two stations of which are thicker than 6 km(e.g.GSI and LHMI).The difference of receiver function waveforms for NE,SW and W orientation at station GSI where is accompanied with strong thrust earthquakes suggests that there is a complicated structure beneath this station.Station BKNI and PMBI are located on the eastern side of the Sumatra fault and the thickness of their sediment layers is only~1 km.The crustal thickness for back-arc basin is within 30-36 km.However,the crustal thickness of forearc area varies from~26 km of the forearc ridge to 26-30 km of the forearc basin toward continent and its,which suggests that the down dip limit(slab-Moho intersection)of seismogenic zone is within 29-36 km in forearc and explains why the shallow-focus earthquakes play a dominant role in this area.The stable state for the inner wedge of forearc within a seismogenic circle provides a favorable environment for storing stress.Meanwhile,these faults caused by the subducting of Indo-Austrilian Plate constructed a condition(e.g.cracking of intact rocks and frictional sliding)in which it would trigger shallow-focus seismic activities(releasing stress).
基金supported by the National Natural Science Foundation of China(Grant Nos.91858215 and 91958206)the National Key Research and Development Program of China(Grant No.2018YFC1405901)the Key Research and Development Program of Shandong Province(Grant No.2019GHY112019)。
文摘The Mariana subduction structure is a hot topic in ocean-ocean subduction zone research,and its subduction mechanism has attracted wide attention from experts and scholars in China and abroad.Based on the multi-channel seismic data of survey line MGL1204 in the Mariana fore-arc and DSDP ocean drilling data,this paper studies the development and evolution characteristics of the structure and strata in the Cenozoic Mariana fore-arc sedimentary basin.The Cenozoic strata are divided into six seismic sequences,with the possible era of each seismic sequence discerned,and the relationship between fault development and earthquakes analyzed.The episodic activity of the volcanic chain of the Mariana island arc is thought to control the tectonic and stratigraphic development pattern of the Cenozoic sedimentary basin in the fore-arc.Between 16°N-19°N and 146°E-151°E,the maximum thickness of the sedimentary center of the Cenozoic fore-arc sedimentary basin in Mariana is about 2360 m.Normal faults are developed in the area and some broke to the seabed,indicating that the Mariana island arc is still in the post-arc expansion stage.The application of multi-channel seismic sections in structural and stratigraphic evolution study is an important means to elucidating the Mariana subduction mechanism.
基金financially supported by the Geological Survey of China(Grant Nos.DD20240075,and DD20243516)the National Natural Science Foundation of China(Grant No.41872209)Basic Scientific Research Fund of the Institute of Geology,Chinese Academy of Geological Sciences(Grant No.J2314)。
文摘We report new SHRIMP zircon U-Pb ages,zircon Lu-Hf isotopic and whole rock geochemical data from Permian granitoids located in the Alxa area of Inner Mongolia,China.In combination with published geochronological and geochemical data,the granitoids in the region can be divided into two age groups:ca.285 Ma and ca.269 Ma.The granitoids of the first group are mainly composed of calc-alkaline to high-K calc-alkaline,weakly peraluminous Ⅰ-type granodiorites with ε_(Hf)(t)values of-19.6 to-4.3,which demonstrates evidence of crustal reworking;the granitoids of the second group,however,mainly consist of A-type granites that are high-K calc-alkaline to shoshonite,metaluminous to weakly peraluminous,and have high 10,000×Ga/Al ratios(2.59-3.12)and ε_(Hf)(t)values ranging from-11.3 to-2.7,all of which demonstrates a mixed crust-mantle source.We interpret the granitoids of the first group to have formed during the subduction of Central Asian oceanic crust and the second group to have formed by the asthenospheric upwelling caused by the formation of slab windows during late ocean ridge subduction.
基金supported by funds from the Chinese Academy of Sciences(XDB18020303)the Chinese Ministry of Science and Technology(2015CB856100)the National Natural ScienceFoundation of China(41590620)
文摘Crustal recycling at convergent plate boundaries is essential to mantle heterogeneity.However,crustal signatures in the mantle source of basaltic rocks above subduction zones were primarily incorporated in the form of liquid rather than solid phases.The physicochemical property of liquid phases is determined by the dehydration behavior of crustal rocks at the slab-mantle interface in subduction channels.Because of the significant fractionation in incompatible trace elements but the full inheritance in radiogenic isotopes relative to their crustal sources,the production of liquid phases is crucial to the geochemical transfer from the subducting crust into the mantle.In this process,the stability of specific minerals in subducting crustal rocks exerts a primary control on the enrichment of given trace elements in the liquid phases.For this reason,geochemically enriched oceanic basalts can be categorized into two types in terms of their trace element distribution patterns in the primitive mantle-normalized diagram.One is island arc basalts(IAB),showing enrichment in LILE,Pb and LREE but depletion in HFSE such as Nb and Ta relative to HREE,The other is ocean island basalts(OIB),exhibiting enrichment in LILE and LREE,enrichment or non-depletion in HFSE but depletion in Pb relative to HREE.In either types,these basalts show the enhanced enrichment of LILE and LREE with increasing their incompatibility relative to normal mid-ocean ridge basalts(MORB).The thermal regime of subduction zones can be categorized into two stages in both time and space,The first stage is characterized by compressional tectonism at low thermal gradients.As a consequence,metamorphic dehydration of the subducting crust prevails at forearc to subarc depths due to the breakdown of hydrous minerals such as mica and amphibole in the stability field of garnet and rutile,resulting in the liberation of aqueous solutions with the trace element composition that is considerably enriched in LILE,Pb and LREE but depleted in HFSE and HREE relative to normal MORB.This provides the crustal signature for the mantle sources of IAB.The second stage is indicated by extensional tectonism at high thermal gradients,leading to the partial melting of metamorphically dehydrated crustal rocks at subarc to postarc depths.This involves not only the breakdown of hydrous minerals such as amphibole,phengite and allanite in the stability field of garnet but also the dissolution of rutile into hydrous melts.As such,the hydrous melts can acquire the trace element composition that is significantly enriched in LILE,HFSE and LREE but depleted in Pb and HREE relative to normal MORB,providing the crustal signature for the mantle sources of OIB.In either case,these liquid phases would metasomatize the overlying mantle wedge peridotite at different depths,generating ultramafic metasomatites such as serpentinized and chloritized peridotites,and olivine-poor pyroxenites and hornblendites.As a consequence,the crustal signatures are transferred by the liquid phases from the subducting slab into the mantle.
基金Supported by the National Key R&D Program of China(No.2016YFC0600408)
文摘Plate subduction is the largest natural factory that processes elements,which controls recycling and mineralization of a variety of elements.There are three major ore deposit belts in the world:the circumPacific,the centralAsian,and the Tethys belts.All the three belts are closely associated with plate subductions,the mechanism remains obscure.We approached this problem from systematic studies on the behaviours of elements during geologic processes.This contribution summaries the recent progress of our research group.Our results suggest that porphyry Cu deposits form through partial melting of subducted young oceanic crust under oxygen fugacities higher than AFMQ^+1.5,which is promoted after the elevation of atmospheric oxygen at ca.550 Ma.Tin deposits are associated with reducing magmatic rocks formed as a consequence of slab rollback.The Neo-Tethys tectonic regime hosts more than 60%of the world's total Sn reserves.This is due to the reducing environment formed during the subduction of organic rich sediments.For the same reason,porphyry Cu deposits formed in the late stages during the closure of the Neo-Tethys Ocean.Tungsten deposits are also controlled by slab rollback,but is not so sensitive to oxygen fugacity.Subduction related W/Sn deposits are mostly accompanied by abundant accessory fluorites due to the breakdown of phengite and apatite.Decomposition of phengite is also significant for hard rock lithium deposits,whereas orogenic belt resulted from plate subduction promote the formation of Li brine deposits.Cretaceous red bed basins near the Nanling region are favorable for Li brines.Both Mo and Re are enriched in the oxidationreduction cycle during surface processes,and may get further enriched once Mo-,Re-enriched sediments are subducted and involved in magmatism.During plate subduction,Mo and Re fractionate from each other.Molybdenum is mainly hosted in porphyry Mo deposits and to a less extent,porphyry Cu-Mo deposits,whereas Re is predominantly hosted in porphyry Cu-Mo deposits and sedimentary sulfide deposits.
基金supported by the Australian Governmentsupport of the Australian Government Research Training Program Scholarship+1 种基金supported by Australian Research Council grant DE160101020supported by Australian Research Council grant IH130200012 and DP130101946
文摘Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of numerical models of mantle dynamics pre-and post-Pangea timeframes requires global kinematic descriptions with full plate reconstructions extending into the Paleozoic(410 Ma). Current plate models that cover Paleozoic times are characterised by large plate speeds and trench migration rates because they assume that lowermost mantle structures are rigid and fixed through time. When used as a surface boundary constraint in geodynamic models, these plate reconstructions do not accurately reproduce the present-day structure of the lowermost mantle. Building upon previous work, we present a global plate motion model with continuously closing plate boundaries ranging from the early Devonian at 410 Ma to present day.We analyse the model in terms of surface kinematics and predicted lower mantle structure. The magnitude of global plate speeds has been greatly reduced in our reconstruction by modifying the evolution of the synthetic Panthalassa oceanic plates, implementing a Paleozoic reference frame independent of any geodynamic assumptions, and implementing revised models for the Paleozoic evolution of North and South China and the closure of the Rheic Ocean. Paleozoic(410-250 Ma) RMS plate speeds are on average ～8 cm/yr, which is comparable to Mesozoic-Cenozoic rates of ～6 cm/yr on average.Paleozoic global median values of trench migration trend from higher speeds(～2.5 cm/yr) in the late Devonian to rates closer to 0 cm/yr at the end of the Permian(～250 Ma), and during the Mesozoic-Cenozoic(250-0 Ma) generally cluster tightly around ～1.1 cm/yr. Plate motions are best constrained over the past 130 Myr and calculations of global trench convergence rates over this period indicate median rates range between 3.2 cm/yr and 12.4 cm/yr with a present day median rate estimated at～5 cm/yr. For Paleozoic times(410-251 Ma) our model results in median convergence rates largely～5 cm/yr. Globally,～90% of subduction zones modelled in our reconstruction are determined to be in a convergent regime for the period of 120-0 Ma. Over the full span of the model, from 410 Ma to 0 Ma,～93% of subduction zones are calculated to be convergent, and at least 85% of subduction zones are converging for 97% of modelled times. Our changes improve global plate and trench kinematics since the late Paleozoic and our reconstructions of the lowermost mantle structure challenge the proposed fixity of lower mantle structures, suggesting that the eastern margin of the African LLSVP margin has moved by as much as ～1450 km since late Permian times(260 Ma). The model of the plate-mantle system we present suggests that during the Permian Period, South China was proximal to the eastern margin of the African LLSVP and not the western margin of the Pacific LLSVP as previous thought.
基金the National 973 Project of Chinese Ministry of Science and Technology （Grant No. 2003CB716502） the Natural Science Foundation of China （Grant No. 40399143） +1 种基金 the German Science Foundation （DFG grant No. GE 1152/2-2 , WE2850/3- 1）.
文摘Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited （detrital） and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence （CL） imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones （domains） to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure （HP） metamorphic conditions of T = 571-668℃ and P =1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782-849℃ and P 〉 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600- 710℃ and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10-11 Ma and exhumation of the rocks occurred over a period of 19-20 Ma. Thus, subduction from - 55 km to 〉 160 km deep mantle depth took place at rates of approximately 9.5-10.5 km/Ma and exhumation from depths 〉160 km to the base of the crust at -30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin lithosphere followed by ultrafast exhumation driven by buoyancy forces after break-off of the UHP slab deep within the mantle.
