Sedimentary environments in the Hangzhou Bay are introduced by a three-subregional landform pattern and a sedimentation map with six major sedimentation types. The geographic setting, sediment transportation and sedim...Sedimentary environments in the Hangzhou Bay are introduced by a three-subregional landform pattern and a sedimentation map with six major sedimentation types. The geographic setting, sediment transportation and sedimentation in different subregions are discussed with sediment grain parameters. Sedimentary basin suffering from effect of plume front can be identified by the fine sediments with median ( Mdφ ) 7φ-8φ, clay content 30% - 40% and silt 60% - 70%. Sediment transportation along the plume front seems not to be a direct effect on sedimentary formation of the shoals fringing the south coast of the Hangzhou Bay.展开更多
It is of some limitations to analyse residual currents by means of the 25 h anchored current measurements. On the basis of the drift tracking and the mooring system data, here, analyses have been done aiming at the st...It is of some limitations to analyse residual currents by means of the 25 h anchored current measurements. On the basis of the drift tracking and the mooring system data, here, analyses have been done aiming at the structural characteristics and the dynamical mechanisms of the frontal residual current field of the Hangzhou Bay. Especially a theoritical model is given focusing on the frontal density-driven currents. The results indicate that there exists obviously the upper-layer front-driven flow along the orientation of the front during neap tides in the research area of the Hangzhou Bay. But the flow is restrained by the strong vortical viscosity during spring tides. In the lower layer, the effect of the front is little and the subtidal movements are dominated by the tide-induced residual currents. In addition, the influences of wind forcing to the residual current field are also suggested to be important.展开更多
A description is given of the distribution , spacial and temporal variation , mixing and transportation processes about the plume front in the Hangzhou Bay. This front is performed as a group of interfaces among, the ...A description is given of the distribution , spacial and temporal variation , mixing and transportation processes about the plume front in the Hangzhou Bay. This front is performed as a group of interfaces among, the water masses situated in the bay. A discussion is also given of the circulation feature in the frontal zone ence of the front.展开更多
Biogeochemical character of dissolved inorganic nitrogen and phosphate at plume front is studied based on the data, which were observed in the Changjiang River Estuary in 1988. The results are as follows: The concentr...Biogeochemical character of dissolved inorganic nitrogen and phosphate at plume front is studied based on the data, which were observed in the Changjiang River Estuary in 1988. The results are as follows: The concentrations of nitrate and phosphate change abruptly -2+4at plume front and halocline. The concentrations of NO and NH are very high at 10~25 -33-4m depth. The vertical circumfluence transports NO and PO , which are released from organisms at the bottom to phytoplankton.展开更多
Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the poten...Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water jet.The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area.The experimental results showed that the optimal PAC dose was found to be 0.75 g/L.Compared with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the plume.This indicates that PAC inhibits the entire development process of the plume.The addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized flocs.The flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of plumes.Additionally,when the size of suspended particles increases,it reduces the scale at which they diffuse.Furthermore,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.展开更多
Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137....Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.展开更多
For the Pearl River plume, the supercritical, distinct plume front appears in downwelling-favorable winds, which is easily observed due to the distinct boundary between the plume water and the ambient water. In this p...For the Pearl River plume, the supercritical, distinct plume front appears in downwelling-favorable winds, which is easily observed due to the distinct boundary between the plume water and the ambient water. In this paper, in situ and satellite observations of a plume front are utilized to explore the Pearl River plume front properties under the downwelling-favorable winds. Field observations clearly show frontal structure, especially the two-layer structure in the plume water and the downward-motion of water in the frontal region. The Advanced Synthetic Aperture Radar(ASAR) images are also analyzed to unveil the plume front: there is a white stripe on the west side out of the river mouth under downwelling-favorable winds, which is identified as a supercritical plume front, and the width of the plume front is about 250 m. The normalized velocity gradient shows the intense velocity convergence in the front region. Also, analyses of ASAR images imply that the river discharge plays an important role in controlling the location and shape of the front.展开更多
Cold seeps are widely developed on the seabed of continental margins and can form gas plumes due to the upward migration of methane-rich fluids.The detection and automatic segmentation of gas plumes are of great signi...Cold seeps are widely developed on the seabed of continental margins and can form gas plumes due to the upward migration of methane-rich fluids.The detection and automatic segmentation of gas plumes are of great significance in locating and studying the cold seep system that is usually accompanied by hydrate layers in the subsurface.A multibeam echo-sounder system(MBES)can record the complete backscatter intensity of the water column,and it is one of the most effective means for detecting cold seeps.However,the gas plumes recorded in multibeam water column images(WCI)are usually blurred due to the interference of the complicated water environment and the sidelobes of the MBES,making it difficult to obtain the effective segmentation.Therefore,based on the existing UNet semantic segmentation network,this paper proposes an AP-UNet network combining the convolutional block attention module and the pyramid pooling module for the automatic segmentation and extraction of gas plumes.Comparative experiments are conducted among three traditional segmentation methods and two deep learning methods.The results show that the AP-UNet segmentation model can effectively suppress complicated water column noise interference.The segmentation precision,the Dice coefficient,and the recall rate of this model are 92.09%,92.00%,and 92.49%,respectively,which are 1.17%,2.10%,and 2.07%higher than the results of the UNet.展开更多
The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the ...The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the active age is earlier than the peak ages of the Kerguelen mantle plume.This study investigated magmatic activity of the Dingri area in the central TH which was coeval with the Kerguelen mantle plume.The intrusion in the Dingri area contains diabases and monzonites.The zircon age of diabase is 123±1 Ma,and that of monzonite is 117±1 Ma.Geochemistry and Sr-Nd isotopic analyses show that the mafic-intermediate dikes were formed in an intraplate extensional environment.The diabase is derived from the enriched lithospheric mantle and monzonite is derived from partial melting of the lower crust,with both magmatic evolutions being contaminated by crustal materials.These characteristics are similar to those of the Rajmahal-Sylhet basalt,a typical Kerguelen mantle plume product.The discovery of the Dingri mafic-intermediate dikes of the central TH suggests that the TH and Rajmahal-Sylhet Traps formed a continuous mantle plume overflow magmatic belt which was a product of the continuous eruption of the Kerguelen mantle plume.展开更多
The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks.The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prosp...The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks.The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate.Based on 2D seismic reflection,we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin(ZJNB).The results show that sixty-nine sills and fourteen forced folds have been identified.The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface.The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca.0.2 Ma.The spatial and temporal occurrences of intrusions imply that the strong post-rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core-mantle boundary.Furthermore,these forced folds could produce several types of hydrocarbon traps,due to accommodation through bending and uplift of the overlying rock and free surface,but it is critical to evaluate the effect of such emplacement when setting exploration targets.展开更多
Submarine seep plumes are a natural phenomenon in which different types of gases migrate through deep or shallow subsurface sediments and leak into seawater in pressure gradient.When detected using acoustic data,the l...Submarine seep plumes are a natural phenomenon in which different types of gases migrate through deep or shallow subsurface sediments and leak into seawater in pressure gradient.When detected using acoustic data,the leaked gases frequently exhibit a flame-like structure.We numerically modelled the relationship between the seismic response characteristic and bubble volume fraction to establish the bubble volume fraction in the submarine seep plume.Results show that our models are able to invert and predict the bubble volume fraction from field seismic oceanography data,by which synthetic seismic sections in different dominant frequencies could be numerically simulated,seismic attribute sections(e.g.,instantaneous amplitude,instantaneous frequency,and instantaneous phase)extracted,and the correlation between the seismic attributes and bubble volume fraction be quantitatively determined with functional equations.The instantaneous amplitude is positively correlated with bubble volume fraction,while the instantaneous frequency and bubble volume fraction are negatively correlated.In addition,information entropy is introduced as a proxy to quantify the relationship between the instantaneous phase and bubble volume fraction.As the bubble volume fraction increases,the information entropy of the instantaneous phase increases rapidly at the beginning,followed by a slight upward trend,and finally stabilizes.Therefore,under optimal noise conditions,the bubble volume fraction of submarine seep plumes can be inverted and predicted based on seismic response characteristics in terms of seismic attributes.展开更多
The detailed description of two granite complexes in the Olkhon subterrane is given.The Early Paleozoic Sharanur complex was formed by granitization of gneisses of the Olkhon series.It includes migmatites,granite-gnei...The detailed description of two granite complexes in the Olkhon subterrane is given.The Early Paleozoic Sharanur complex was formed by granitization of gneisses of the Olkhon series.It includes migmatites,granite-gneisses,granites and pegmatites of normal alkalinity;they belong to the type of syncollisional granites.The Middle Paleozoic Aya granite complex includes mother Aya massif of amazonite-bearing granites and several types of rare-metal pegmatites.They have elevated alkalinity,low of Ba,Sr,and high LILE and HFSE elements contents.The Aya pegmatites lie in northwest cracks of stretching and associated with the rise of the territory under the influence of the North Asian plume.These cracks and pegmatites mark the beginning of a new intraplate geodynamic setting.Two geochemical types are distinguished among the pegmatites of this complex.These are amazonite pegmatites of Li-F type with Ta mineralization and complex type pegmatite with Be-Rb-Nb-Ta and Li-F mineralization(the Ilixin vein).The Tashkiney pegmatite vein is similar to Ilixin,but lies in the gneisses of the Olkhon series.It shows high concentrations of Be,Nb,Ta,as well as W,Sn,but lacks Li and F,due to a greater depth and higher temperature of the melt crystallization of this pegmatite.展开更多
The West Congo Belt contains in its rocks of Neoproterozoic age from Nemba complex outcropping in the Moumba River. This West Congo belt is made up of a crustal segment of the Arcuaï-West Congo orogen which exten...The West Congo Belt contains in its rocks of Neoproterozoic age from Nemba complex outcropping in the Moumba River. This West Congo belt is made up of a crustal segment of the Arcuaï-West Congo orogen which extends from southwest Gabon to the northeast of Angola. This study aims to constrain the geochemical signature Nemba complex of West Congo belt from the petrograhic and geochemical study on the whole rock. The petrographic data from this study show the Moumba metabasites are made up of amphibolites, metagabbros, epidotites and greenschists interstratified in the Eburnean metasediments and affected by mesozonal to epizonal metamorphism characterized by the retromorphosis of intermediate amphibolite facies minerals into greenschist facies. Whole-rock geochemical data indicate that these metabasites are continental flood basalts (CFB) of basic nature and transitional affinity emplaced in intraplate context. These continental flood basalts are generated from magma originating from a significantly enriched shallow mantle plume and this magma then contaminated by the continental crust during their ascent. The reconstruction of tectonic signature suggests that West Congo belt would result from closure of an ocean basin with subduction phenomena. This collision would be marked by the establishment of ophiolite complex. We show that this model is incompatible with the CFB nature of metabasites and the orogenic evolution of Neoproterozoic. It does not seem that we can evoke a genetic link with a subduction of oceanic crust, because the paleogeography of Neoproterozoic (Rodinia) is marked by intracontinental rifts linked to opening of Rodinia. We therefore suggest the non-existence of ophiolitic complex in western Congo belt and reject the collisional model published by certain authors. We confirm the currently available intracontinental orogen model.展开更多
Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in ...Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterizedby relatively high abundances of MgO, total FeO and P_2O_5 and compatible elements (Cr, Ni, Sc), andrelatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and otherincompatible elements compared with the HPT. On the diagrams of trace element ratios, they areplotted on an approximately linear mixing line between depleted and enriched mantle sources,suggesting that these two types of basalts resulted from interactions of varying degrees betweenmantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole andapatite. The source region of the LPT involves a smaller proportion of lithospheric components,while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated bypartial melting of the basic igneous rocks at the base of the lower continental crust. Both the twotypes of magmas underwent certain crystal fractionation and contamination of the lower crest athigh-level magma chambers and en route to the surface.展开更多
Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction ...Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumes opens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silver concentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flow of mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineral deposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other many elements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields (Lianbaling) and further briefly analyzes the source of ore-forming material and constructs an ore-forming and -controlling model.展开更多
Abstract Greenstone belts of the eastern Dharwar Craton, India are reinterpreted as composite tecto- nostratigraphic terranes of accreted plume-derived and convergent margin-derived magmatic sequences based on new hig...Abstract Greenstone belts of the eastern Dharwar Craton, India are reinterpreted as composite tecto- nostratigraphic terranes of accreted plume-derived and convergent margin-derived magmatic sequences based on new high-precision elemental data. The former are dominated by a komatiite plus Mg-tholeiitic basalt volcanic association, with deep water siliciclastic and banded iron formation (BIF) sedimentary rocks. Plumes melted at 〈90 km under thin rifted continental lithosphere to preserve intrao- ceanic and continental margin aspects. Associated alkaline basalts record subduction-recycling of Me- soarchean oceanic crust, incubated in the asthenosphere, and erupted coevally with Mg basalts from a heterogeneous mantle plume. Together, komatiites-Mg basalts-alkaline basalts plot along the Phanero- zoic mantle array in Th/Yb versus Nb/Yb coordinate space, representing zoned plumes, establishing that these reservoirs were present in the Neoarchean mantle. Convergent margin magmatic associations are dominated by tholeiitic to calc-alkaline basalts compo- sitionally similar to recent intraoceanic arcs. As well, boninitic flows sourced in extremely depleted mantle are present, and the association of arc basalts with Mg-andesites-Nb enriched basalts-adakites documented from Cenozoic arcs characterized by subduction of young (〈20 Ma), hot, oceanic litho- sphere. Consequently, Cenozoic style "hot" subduction was operating in the Neoarchean. These diverse volcanic associations were assembled to give composite terranes in a subduction-accretion orogen at -2.7 Ga, coevally with a global accretionary orogen at -2.7 Ga, and associated orogenic gold mineralization.展开更多
In the Beishan rift in the eastern Tianshan orogen, Xinjiang Province, a N-S-trending dyke swarm is present in the Pobei area. The swarm cuts through the 270-290 Ma mafic-ultramafic intrusions associated with Ni-Cu su...In the Beishan rift in the eastern Tianshan orogen, Xinjiang Province, a N-S-trending dyke swarm is present in the Pobei area. The swarm cuts through the 270-290 Ma mafic-ultramafic intrusions associated with Ni-Cu sulphide mineralization. These mafic-ultramafic intrusions are typically found along E-W major faults in the Tianshan orogenic belts. We report SHRIMP U-Pb dating of zircons from a dyke of alkaline composition, which yielded a mean age of 252~9 Ma. Alkaline dykes of the same age are found in the Altay region of Siberia. This age is younger than the 270-290 Ma intraplate magmatic events that produced the mafic-ultramafic intrusions in the region, but in general agreement with the 250-260 Ma Permian plume event that gave rise to the Siberian traps and the Emeishan flood basalts in SW China. We suggest that there is a link between the Emeishan event and the dyke swarm in the Beishan rift and that the intraplate magmatism at 270-290 Ma reflects an early stage of mantle plume activity. The N-S trending dyke swarm in the Beishan rift may represent a later stage in the evolution of mantle plume activity in the NW and SW of China. We also speculate that in Beishan rift and possibly elsewhere in the Tianshan region, the dykes fed basaltic volcanism, whose products have since been eroded due to the strong uplift of the Tianshan orogen as a result of the IndiaEurasia collision in the Cenozoic.展开更多
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...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.展开更多
Using the occurrence characteristics of bubble plumes in the South China Sea as a reference, this paper continues to study the seismic responses produced by bubble plumes in the cold seepage active region. To make the...Using the occurrence characteristics of bubble plumes in the South China Sea as a reference, this paper continues to study the seismic responses produced by bubble plumes in the cold seepage active region. To make the plume modelling scheme more reasonable, we modified the original modelling scheme and reconstructed a plume water body model based on the variation of its radius as bubbles rise in seawater. The plume seismic records of shot gathers were obtained by forward simulation. The seismic records of single shot show obvious characteristics of a scattering wave field and the periodic characteristics of the model. Seismic records of shot gathers were processed using prestack depth migration. The boundary of its imaging section has a good convergence effect. The migration sections can be imaged distinctly with higher accuracy. The aforementioned studies once again laid a foundation for the further study of the seismic responses produced by plumes. They also gradually probed a more suitable seismic data processing method for plumes and provided a theoretical guidance for the identification of plumes.展开更多
基金This work is supported by both Grant-4860244 from the National Natural Science Foundation of China and Grant-188011 from the Zhejiang Provincial Natural Science Foundation
文摘Sedimentary environments in the Hangzhou Bay are introduced by a three-subregional landform pattern and a sedimentation map with six major sedimentation types. The geographic setting, sediment transportation and sedimentation in different subregions are discussed with sediment grain parameters. Sedimentary basin suffering from effect of plume front can be identified by the fine sediments with median ( Mdφ ) 7φ-8φ, clay content 30% - 40% and silt 60% - 70%. Sediment transportation along the plume front seems not to be a direct effect on sedimentary formation of the shoals fringing the south coast of the Hangzhou Bay.
文摘It is of some limitations to analyse residual currents by means of the 25 h anchored current measurements. On the basis of the drift tracking and the mooring system data, here, analyses have been done aiming at the structural characteristics and the dynamical mechanisms of the frontal residual current field of the Hangzhou Bay. Especially a theoritical model is given focusing on the frontal density-driven currents. The results indicate that there exists obviously the upper-layer front-driven flow along the orientation of the front during neap tides in the research area of the Hangzhou Bay. But the flow is restrained by the strong vortical viscosity during spring tides. In the lower layer, the effect of the front is little and the subtidal movements are dominated by the tide-induced residual currents. In addition, the influences of wind forcing to the residual current field are also suggested to be important.
文摘A description is given of the distribution , spacial and temporal variation , mixing and transportation processes about the plume front in the Hangzhou Bay. This front is performed as a group of interfaces among, the water masses situated in the bay. A discussion is also given of the circulation feature in the frontal zone ence of the front.
基金We wish to thank the National Natural Science Foundation of China which has offerd us the financial support for this research (No: 49736220).
文摘Biogeochemical character of dissolved inorganic nitrogen and phosphate at plume front is studied based on the data, which were observed in the Changjiang River Estuary in 1988. The results are as follows: The concentrations of nitrate and phosphate change abruptly -2+4at plume front and halocline. The concentrations of NO and NH are very high at 10~25 -33-4m depth. The vertical circumfluence transports NO and PO , which are released from organisms at the bottom to phytoplankton.
基金supported by the National Natural Science Foundation of China(Nos.52225107,U2106224,U1906234,51822904,and U1706223)the Fundamental Research Funds for the Central Universities(No.202041004)
文摘Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water jet.The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area.The experimental results showed that the optimal PAC dose was found to be 0.75 g/L.Compared with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the plume.This indicates that PAC inhibits the entire development process of the plume.The addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized flocs.The flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of plumes.Additionally,when the size of suspended particles increases,it reduces the scale at which they diffuse.Furthermore,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.
基金supported by National Science Foundation of China(42102059 and 92055202)the China Geological Survey(DD20221817 and DD20190057)+1 种基金the basic scientific research funding in CAGS(J2204)the Second Tibetan Plateau Scientific Expedition and Research(2019QZKK0702).
文摘Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.
基金supported by the National Natural Science Foundation of China(Grant Nos.41476002 and 41206164)the Natural Science Foundation of Shandong Province(Grant No.ZR2014DQ013)+1 种基金State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,Chinese Academy of Sciences(Grant No.LTO1409)China Postdoctoral Science Foundation(Grant No.2014M560574)
文摘For the Pearl River plume, the supercritical, distinct plume front appears in downwelling-favorable winds, which is easily observed due to the distinct boundary between the plume water and the ambient water. In this paper, in situ and satellite observations of a plume front are utilized to explore the Pearl River plume front properties under the downwelling-favorable winds. Field observations clearly show frontal structure, especially the two-layer structure in the plume water and the downward-motion of water in the frontal region. The Advanced Synthetic Aperture Radar(ASAR) images are also analyzed to unveil the plume front: there is a white stripe on the west side out of the river mouth under downwelling-favorable winds, which is identified as a supercritical plume front, and the width of the plume front is about 250 m. The normalized velocity gradient shows the intense velocity convergence in the front region. Also, analyses of ASAR images imply that the river discharge plays an important role in controlling the location and shape of the front.
基金Supported by the National Natural Science Foundation of China (Nos.41930535,41906165)the High-level Foreign Expert Introduction Program (No.G2021025006L)the SDUST Research Fund (No.2019TDJH103)。
文摘Cold seeps are widely developed on the seabed of continental margins and can form gas plumes due to the upward migration of methane-rich fluids.The detection and automatic segmentation of gas plumes are of great significance in locating and studying the cold seep system that is usually accompanied by hydrate layers in the subsurface.A multibeam echo-sounder system(MBES)can record the complete backscatter intensity of the water column,and it is one of the most effective means for detecting cold seeps.However,the gas plumes recorded in multibeam water column images(WCI)are usually blurred due to the interference of the complicated water environment and the sidelobes of the MBES,making it difficult to obtain the effective segmentation.Therefore,based on the existing UNet semantic segmentation network,this paper proposes an AP-UNet network combining the convolutional block attention module and the pyramid pooling module for the automatic segmentation and extraction of gas plumes.Comparative experiments are conducted among three traditional segmentation methods and two deep learning methods.The results show that the AP-UNet segmentation model can effectively suppress complicated water column noise interference.The segmentation precision,the Dice coefficient,and the recall rate of this model are 92.09%,92.00%,and 92.49%,respectively,which are 1.17%,2.10%,and 2.07%higher than the results of the UNet.
基金supported by the Geological Survey Project of China Geological Survey(Grant No.DD20211547)the Basic Survey Project of Command Center of Natural Resources Comprehensive Survey(Grant No.ZD20220508)。
文摘The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the active age is earlier than the peak ages of the Kerguelen mantle plume.This study investigated magmatic activity of the Dingri area in the central TH which was coeval with the Kerguelen mantle plume.The intrusion in the Dingri area contains diabases and monzonites.The zircon age of diabase is 123±1 Ma,and that of monzonite is 117±1 Ma.Geochemistry and Sr-Nd isotopic analyses show that the mafic-intermediate dikes were formed in an intraplate extensional environment.The diabase is derived from the enriched lithospheric mantle and monzonite is derived from partial melting of the lower crust,with both magmatic evolutions being contaminated by crustal materials.These characteristics are similar to those of the Rajmahal-Sylhet basalt,a typical Kerguelen mantle plume product.The discovery of the Dingri mafic-intermediate dikes of the central TH suggests that the TH and Rajmahal-Sylhet Traps formed a continuous mantle plume overflow magmatic belt which was a product of the continuous eruption of the Kerguelen mantle plume.
基金supported by the National Key Research and Development Project(2019YFA0708500)the National Natural Science Foundation of China(No.42202170 and U20B6001)。
文摘The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks.The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate.Based on 2D seismic reflection,we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin(ZJNB).The results show that sixty-nine sills and fourteen forced folds have been identified.The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface.The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca.0.2 Ma.The spatial and temporal occurrences of intrusions imply that the strong post-rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core-mantle boundary.Furthermore,these forced folds could produce several types of hydrocarbon traps,due to accommodation through bending and uplift of the overlying rock and free surface,but it is critical to evaluate the effect of such emplacement when setting exploration targets.
基金Supported by the Natural Science Foundation of Shandong Province(No.ZR2022MD074)the Laboratory for Marine Mineral Resources+3 种基金Qingdao National Laboratory for Marine Science and Technology(No.MMRKF201810)the National Natural Science Foundation of China(No.41606077)the National Key R&D Program of China:HighPrecision Characterization Technology of Gas Hydrate Reservoir(No.2017YFC0307406-03)supported by the Shandong Province Taishan Scholar Construction Project。
文摘Submarine seep plumes are a natural phenomenon in which different types of gases migrate through deep or shallow subsurface sediments and leak into seawater in pressure gradient.When detected using acoustic data,the leaked gases frequently exhibit a flame-like structure.We numerically modelled the relationship between the seismic response characteristic and bubble volume fraction to establish the bubble volume fraction in the submarine seep plume.Results show that our models are able to invert and predict the bubble volume fraction from field seismic oceanography data,by which synthetic seismic sections in different dominant frequencies could be numerically simulated,seismic attribute sections(e.g.,instantaneous amplitude,instantaneous frequency,and instantaneous phase)extracted,and the correlation between the seismic attributes and bubble volume fraction be quantitatively determined with functional equations.The instantaneous amplitude is positively correlated with bubble volume fraction,while the instantaneous frequency and bubble volume fraction are negatively correlated.In addition,information entropy is introduced as a proxy to quantify the relationship between the instantaneous phase and bubble volume fraction.As the bubble volume fraction increases,the information entropy of the instantaneous phase increases rapidly at the beginning,followed by a slight upward trend,and finally stabilizes.Therefore,under optimal noise conditions,the bubble volume fraction of submarine seep plumes can be inverted and predicted based on seismic response characteristics in terms of seismic attributes.
基金The study was conducted within the framework of the state task(topic ID 0350-2019-0007)and supported by grant 20-55-44002-Mong_a of the Russian Foundation for Basic Research.
文摘The detailed description of two granite complexes in the Olkhon subterrane is given.The Early Paleozoic Sharanur complex was formed by granitization of gneisses of the Olkhon series.It includes migmatites,granite-gneisses,granites and pegmatites of normal alkalinity;they belong to the type of syncollisional granites.The Middle Paleozoic Aya granite complex includes mother Aya massif of amazonite-bearing granites and several types of rare-metal pegmatites.They have elevated alkalinity,low of Ba,Sr,and high LILE and HFSE elements contents.The Aya pegmatites lie in northwest cracks of stretching and associated with the rise of the territory under the influence of the North Asian plume.These cracks and pegmatites mark the beginning of a new intraplate geodynamic setting.Two geochemical types are distinguished among the pegmatites of this complex.These are amazonite pegmatites of Li-F type with Ta mineralization and complex type pegmatite with Be-Rb-Nb-Ta and Li-F mineralization(the Ilixin vein).The Tashkiney pegmatite vein is similar to Ilixin,but lies in the gneisses of the Olkhon series.It shows high concentrations of Be,Nb,Ta,as well as W,Sn,but lacks Li and F,due to a greater depth and higher temperature of the melt crystallization of this pegmatite.
文摘The West Congo Belt contains in its rocks of Neoproterozoic age from Nemba complex outcropping in the Moumba River. This West Congo belt is made up of a crustal segment of the Arcuaï-West Congo orogen which extends from southwest Gabon to the northeast of Angola. This study aims to constrain the geochemical signature Nemba complex of West Congo belt from the petrograhic and geochemical study on the whole rock. The petrographic data from this study show the Moumba metabasites are made up of amphibolites, metagabbros, epidotites and greenschists interstratified in the Eburnean metasediments and affected by mesozonal to epizonal metamorphism characterized by the retromorphosis of intermediate amphibolite facies minerals into greenschist facies. Whole-rock geochemical data indicate that these metabasites are continental flood basalts (CFB) of basic nature and transitional affinity emplaced in intraplate context. These continental flood basalts are generated from magma originating from a significantly enriched shallow mantle plume and this magma then contaminated by the continental crust during their ascent. The reconstruction of tectonic signature suggests that West Congo belt would result from closure of an ocean basin with subduction phenomena. This collision would be marked by the establishment of ophiolite complex. We show that this model is incompatible with the CFB nature of metabasites and the orogenic evolution of Neoproterozoic. It does not seem that we can evoke a genetic link with a subduction of oceanic crust, because the paleogeography of Neoproterozoic (Rodinia) is marked by intracontinental rifts linked to opening of Rodinia. We therefore suggest the non-existence of ophiolitic complex in western Congo belt and reject the collisional model published by certain authors. We confirm the currently available intracontinental orogen model.
文摘Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterizedby relatively high abundances of MgO, total FeO and P_2O_5 and compatible elements (Cr, Ni, Sc), andrelatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and otherincompatible elements compared with the HPT. On the diagrams of trace element ratios, they areplotted on an approximately linear mixing line between depleted and enriched mantle sources,suggesting that these two types of basalts resulted from interactions of varying degrees betweenmantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole andapatite. The source region of the LPT involves a smaller proportion of lithospheric components,while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated bypartial melting of the basic igneous rocks at the base of the lower continental crust. Both the twotypes of magmas underwent certain crystal fractionation and contamination of the lower crest athigh-level magma chambers and en route to the surface.
基金This research was performed as part of the project supported by the National Natural Science Foundation of China(grant 40272088)Knowledge Innovation Project of the Chinese Academy of Sciences(KZCX1-07)the Program of Financially Aiding Backbone Teachers Working in Colleges and Universities(J-00-25).
文摘Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumes opens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silver concentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flow of mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineral deposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other many elements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields (Lianbaling) and further briefly analyzes the source of ore-forming material and constructs an ore-forming and -controlling model.
基金Department of Science and Technology(DST) for funding the Projects on Dharwar Craton
文摘Abstract Greenstone belts of the eastern Dharwar Craton, India are reinterpreted as composite tecto- nostratigraphic terranes of accreted plume-derived and convergent margin-derived magmatic sequences based on new high-precision elemental data. The former are dominated by a komatiite plus Mg-tholeiitic basalt volcanic association, with deep water siliciclastic and banded iron formation (BIF) sedimentary rocks. Plumes melted at 〈90 km under thin rifted continental lithosphere to preserve intrao- ceanic and continental margin aspects. Associated alkaline basalts record subduction-recycling of Me- soarchean oceanic crust, incubated in the asthenosphere, and erupted coevally with Mg basalts from a heterogeneous mantle plume. Together, komatiites-Mg basalts-alkaline basalts plot along the Phanero- zoic mantle array in Th/Yb versus Nb/Yb coordinate space, representing zoned plumes, establishing that these reservoirs were present in the Neoarchean mantle. Convergent margin magmatic associations are dominated by tholeiitic to calc-alkaline basalts compo- sitionally similar to recent intraoceanic arcs. As well, boninitic flows sourced in extremely depleted mantle are present, and the association of arc basalts with Mg-andesites-Nb enriched basalts-adakites documented from Cenozoic arcs characterized by subduction of young (〈20 Ma), hot, oceanic litho- sphere. Consequently, Cenozoic style "hot" subduction was operating in the Neoarchean. These diverse volcanic associations were assembled to give composite terranes in a subduction-accretion orogen at -2.7 Ga, coevally with a global accretionary orogen at -2.7 Ga, and associated orogenic gold mineralization.
基金supported by National Natural Science Foundation of China(No.40973028)Geological Survey Project(No.1212011085060)
文摘In the Beishan rift in the eastern Tianshan orogen, Xinjiang Province, a N-S-trending dyke swarm is present in the Pobei area. The swarm cuts through the 270-290 Ma mafic-ultramafic intrusions associated with Ni-Cu sulphide mineralization. These mafic-ultramafic intrusions are typically found along E-W major faults in the Tianshan orogenic belts. We report SHRIMP U-Pb dating of zircons from a dyke of alkaline composition, which yielded a mean age of 252~9 Ma. Alkaline dykes of the same age are found in the Altay region of Siberia. This age is younger than the 270-290 Ma intraplate magmatic events that produced the mafic-ultramafic intrusions in the region, but in general agreement with the 250-260 Ma Permian plume event that gave rise to the Siberian traps and the Emeishan flood basalts in SW China. We suggest that there is a link between the Emeishan event and the dyke swarm in the Beishan rift and that the intraplate magmatism at 270-290 Ma reflects an early stage of mantle plume activity. The N-S trending dyke swarm in the Beishan rift may represent a later stage in the evolution of mantle plume activity in the NW and SW of China. We also speculate that in Beishan rift and possibly elsewhere in the Tianshan region, the dykes fed basaltic volcanism, whose products have since been eroded due to the strong uplift of the Tianshan orogen as a result of the IndiaEurasia collision in the Cenozoic.
基金supported by Australian Research Council Australian Laureate Fellowship grant to ZXL (FL150100133)by China’s Thousand Talents Plan (2015)+2 种基金NSFC41674098 to NZsupported by resources provided by the High-performance Computing Platform of Peking Universitythe Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia
文摘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.
基金The National Natural Science Foundation under contract No.41306050the Science and Technology Project of Guangdong Province under contract No.2014A010103030+1 种基金the Natural Science Foundation of Guangdong Province under contract No.2015A030313617the National Marine Important Charity Special Foundation under contract No.201305019
文摘Using the occurrence characteristics of bubble plumes in the South China Sea as a reference, this paper continues to study the seismic responses produced by bubble plumes in the cold seepage active region. To make the plume modelling scheme more reasonable, we modified the original modelling scheme and reconstructed a plume water body model based on the variation of its radius as bubbles rise in seawater. The plume seismic records of shot gathers were obtained by forward simulation. The seismic records of single shot show obvious characteristics of a scattering wave field and the periodic characteristics of the model. Seismic records of shot gathers were processed using prestack depth migration. The boundary of its imaging section has a good convergence effect. The migration sections can be imaged distinctly with higher accuracy. The aforementioned studies once again laid a foundation for the further study of the seismic responses produced by plumes. They also gradually probed a more suitable seismic data processing method for plumes and provided a theoretical guidance for the identification of plumes.