Constraints on Characteristics and Distribution of Gas Hydrate and Free Gas Using Broad-Band Processing of Three-Dimensional Seismic Data

Gas hydrate drilling expeditions in the Pearl River Mouth Basin,South China Sea,have identified concentrated gas hydrates with variable thickness.Moreover,free gas and the coexistence of gas hydrate and free gas have been confirmed by logging,coring,and production tests in the foraminifera-rich silty sediments with complex bottom-simulating reflectors(BSRs).The broad-band processing is conducted on conventional three-dimensional(3D)seismic data to improve the image and detection accuracy of gas hydratebearing layers and delineate the saturation and thickness of gas hydrate-and free gas-bearing sediments.Several geophysical attributes extracted along the base of the gas hydrate stability zone are used to demonstrate the variable distribution and the controlling factors for the differential enrichment of gas hydrate.The inverted gas hydrate saturation at the production zone is over 40% with a thickness of 90 m,showing the interbedded distribution with different boundaries between gas hydrate-and free gas-bearing layers.However,the gas hydrate saturation value at the adjacent canyon is 70%,with 30-m-thick patches and linear features.The lithological and fault controls on gas hydrate and free gas distributions are demonstrated by tracing each gas hydrate-bearing layer.Moreover,the BSR depths based on broad-band reprocessed 3D seismic data not only exhibit variations due to small-scale topographic changes caused by seafloor sedimentation and erosion but also show the upward shift of BSR and the blocky distribution of the coexistence of gas hydrate and free gas in the Pearl River Mouth Basin.

Geology and Geochemistry of K-feldspar Veins in Lamprophyre at the Zhenyuan Gold Deposit,Yunnan,Southwest China:Implications for Gold Mineralization

Lamprophyres typically appear in hydrothermal gold deposits.The relationship between lamprophyres and gold deposits is investigated widely.Some researchers suggest that the emplacement of lamprophyres triggers gold mineralization,whereas others hypothesize that the formation of lamprophyres increases the fertility of mantle sources and ore-forming fluids.K-feldspar veins,with ages between those of lamprophyres and gold deposits,appear in lamprophyres in Zhenyuan.Therefore,K-feldspar veins are ideal for investigating the relationship between lamprophyres and gold deposits.Phlogopite in K-feldspar veins has lower Mg#,Ni,and Cr contents and higher TiO2,Li,Ba,Sr,Sc,Zr,Nb,and Cs contents than phlogopite in lamprophyres.The in-situ Sr isotopic values of apatites(0.7063–0.7066)in K-feldspar veins are within the range for apatites(0.7064–0.7078)from lamprophyres.High large-ion lithophile element concentrations and low Nb and Ta concentrations in phlogopite from lamprophyres,in addition to high(87Sr/86Sr)i values of apatite(0.7064–0.7078),indicate that the magma parental to these phlogopite and apatite crystals is derived from an enriched mantle.Kfeldspar veins are genetically correlated with lamprophyres,whereas sulfide mineral assemblage and trace element compositions of pyrite in K-feldspar veins suggest that K-feldspar veins in lamprophyres are not directly related to gold mineralization of the Zhenyuan deposit.

Inversion of Seabed Geotechnical Properties in the Arctic Chukchi Deep Sea Basin Based on Time Domain Adaptive Search Matching Algorithm

The chirp sub-bottom profiler,for its high resolution,easy accessibility and cost-effectiveness,has been widely used in acoustic detection.In this paper,the acoustic impedance and grain size compositions were obtained based on the chirp sub-bottom profiler data collected in the Chukchi Plateau area during the 11th Arctic Expedition of China.The time-domain adaptive search matching algorithm was used and validated on our established theoretical model.The misfit between the inversion result and the theoretical model is less than 0.067%.The grain size was calculated according to the empirical relationship between the acoustic impedance and the grain size of the sediment.The average acoustic impedance of sub-seafloor strata is 2.5026×10^(6) kg(s m^(2))^(-1)and the average grain size(θvalue)of the seafloor surface sediment is 7.1498,indicating the predominant occurrence of very fine silt sediment in the study area.Comparison of the inversion results and the laboratory measurements of nearby borehole samples shows that they are in general agreement.

Elemental Compositions of Clinopyroxenes from Southern Okinawa Trough Basalt:Implications for Magmatism and Structural Environment in an Initial Back-Arc Basin

The major and trace elemental compositions of clinopyroxene from basalt were used to characterize the nature of the primitive magma and structural environment beneath the southern Okinawa Trough(SOT),which is an initial back-arc basin at a continental margin.The clinopyroxenes in the basalt were augite with variable Mg^(#)contents(73.37-78.22).The regular variations in major oxide contents(i.e.,CaO,FeO,TiO_(2),and Cr)with decreasing Mg#implied that the clinopyroxenes evolved from being enriched in Mg,Ca,and Cr to being enriched in Fe and Ti.The clinopyroxenes had relatively low rare earth element concentrations(7.51×10^(-6) to 12.68×10^(-6))and negative Eu anomalies(δEu=0.67-0.95).The Kd_(cpx) values of clinopyroxenes(0.2-0.26),which were used to examine whether the clinopyroxene was equilibrated with its host basalt,demonstrate that these clinopyroxene phenocrysts were not captured crystals but were instead produced by crystallization differentiation of the magma.The calculated clinopyroxene crystallization temperatures showed a narrow range of 990-1061℃,and their crystallization pressures ranged from 2.0 to 3.2 kbar.The geochemistry features of these clinopyroxenes indicated that the parent magma belonged to the subalkaline tholeiitic magma series and suggested that the magma experienced crystallization differentiation of olivine,plagioclase,and clinopyroxene,where the crystallization of plagioclase occurred earlier than that of clinopyroxene.Combined with geophysical data,this research on primitive magma and its crystallization differentiation from clinopyroxene indicates that the SOT is in the stage of‘seafloor spreading’and that basaltic rocks produced from tholeiitic magma represent the generation of oceanic crust.

Geochronology and Geochemistry of the Xingxingxia Triassic A-type Granites in Central Tianshan,NW China:Petrogenesis and Tectonic Implications

The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt.In this study,we present SHRIMP zircon U-Pb ages,Hf isotopic and geochemical data on the Xingxingxia biotite granite,amazonite granite and granitic pegmatite in Central Tianshan,NW China.Zircon U-Pb dating yielded formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite.These granitoid rocks have high K_(2)O with low MgO and CaO contents.They are enriched in Nb,Ta,Hf and Y,while being depleted in Ba and Sr,showing flat HREE patterns and negative Eu anomalies.They have typical A-type granite geochemical signatures with high Ga/A_(1)(8–13)and TFeO/(TFeO+MgO)ratios,showing an A_(2) affinity for biotite granite and an A_(1) affinity for amazonite granite and granitic pegmatite.Zircon ε_(Hf)(t)values of the granitoids are 0.45–2.66,with Hf model ages of 0.99–1.17 Ga.This suggests that these A-type granites originated from partial melting of the lower crust.We propose that Xingxingxia Triassic A-type granites formed under lithospheric extension from post-orogenic to anorogenic intraplate settings and NE-trending regional strike-slip fault-controlled magma emplacement in the upper crust.

Acoustic Velocity-Based Inversion of the Physical Properties of Sea Ice in the Central Arctic Region

Studying the Arctic sea ice contributes to a comprehensive understanding of the climate system in polar regions and offers valuable insights into the interplay between polar climate change and the global climate and environment.One of the key research aspects is the investigation of the temperature,salinity,and density parameters of sea ice to obtain essential insights.During the 11th Chinese National Arctic Research Expedition,acoustic velocity was measured on an ice core at a short-term ice station,however,temperature,salinity,and density were not measured.In the present work,we utilized a genetic algorithm to invert these obtained acoustic velocity data to sea ice temperature,salinity,and density parameters on the basis of the relationship between acoustic velocity and the physical properties of Arctic summer sea ice.We validated the effectiveness of this inversion procedure by comparing its findings with those of other researchers.The results indicate that within the normalized depth range of 0.43-0.94,the ranges for temperature,salinity,and density are -0.48--0.29℃,1.63-3.35,and 793.1-904.1 kg m^(-3),respectively.

Correlation Study on Grain Size Characteristics and Geotechnical Properties of Surface Sediments in Qingdao Offshore Area

The comprehension of sediment grain size parameters and the corresponding sedimentary environment holds paramount importance in elucidating the engineering geological attributes of the subaqueous seabed.This study delineated the sedimentary environment zoning in the northern sea area of Qingdao through cluster analysis of grain size parameters derived from 123 surface sediment samples.The study analyzed the correlation between sediment geotechnical indices and grain size parameters across diverse sedimentary environments.A correlation equation was established for samples exhibiting a strong correlation.The study found four distinct sedimentary environments in the study area:coastal,transitional,shallow sea,and residual.Within the same sedimentary environment,the average grain size and sorting coefficient exhibit significant correlations with geotechnical indices such as water content,density,shear strength,plastic limit,liquid limit,and plastic index.However,notable disparities in the correlation between grain size parameters and geotechnical indices emerge across different sedimentary environments.

Effect of particle composition and consolidation degree on the wave-induced liquefaction of soil beds

The wave-induced liquefaction of seabed is responsible for causing damage to marine structures.Particle composition and consolidation degree are the key factors affecting the pore water pressure response and liquefaction behavior of the seabed under wave action.The present study conducted wave flume experiments on silt and silty fine sand beds with varying particle compositions.Furthermore,a comprehensive analysis of the differences and underlying reasons for liquefaction behavior in two different types of soil was conducted from both macroscopic and microscopic perspectives.The experimental results indicate that the silt bed necessitates a lower wave load intensity to attain the liquefaction state in comparison to the silty fine sand bed.Additionally,the duration and development depth of liquefaction are greater in the silt bed.The dissimilarity in liquefaction behavior between the two types of soil can be attributed to the variation in their permeability and plastic deformation capacity.The permeability coefficient and compression modulus of silt are lower than those of silty fine sand.Consequently,silt is more prone to the accumulation of pore pressure and subsequent liquefaction under external loading.Prior research has demonstrated that silt beds with varying consolidation degrees exhibit distinct initial failure modes.Specifically,a dense bed undergoes shear failure,whereas a loose bed experiences initial liquefaction failure.This study utilized discrete element simulation to examine the microscopic mechanisms that underlie this phenomenon.

Storm Liquefaction Deposits:A Possibility of Time Reversal in Sedimentary Strata of an Estuarial Coastal Area

In the sedimentary strata dating of estuarial coastal areas,it is often found that there is phenomenon of time-reversal in strata.The seabed sediments could be liquefied under storm waves.A laboratory wave flume experiment demonstrated that storm-induced liquefaction deposits are formed by the oscillations of liquefied sediments.In this paper,the particle size distribution and ^(210)Pb_(ex) specific activity of the sediment samples from the liquefaction disturbed zone and adjacent stable zone of the Yellow River Delta were tested.The stratigraphic divisions based on storm liquefaction deposit sequence can effectively explain the vertical changes in particle size and ^(210)Pb_(ex) specific activity.Due to the differentiation of particles during the storm induced liquefaction,coarse and fine particles regrouped,which could explain the phenomenon of time-reversal in dating data.

Three-dimensional constrained gravity inversion of Moho depth and crustal structural characteristics at Mozambique continental margin

Mozambique's continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary(COB) in Mozambique's continental margin is considered of great significance to rebuild Gondwana land and understand its movement mode. Along these lines, in this work, the initial Moho was fit using the known Moho depth from reflection seismic profiles, and a 3D multi-point constrained gravity inversion was carried out. Thus, highaccuracy Moho depth and crustal thickness in the study area were acquired. According to the crustal structure distribution based on the inversion results, the continental crust at the narrowest position of the Mozambique Channel was detected. According to the analysis of the crustal thickness, the Mozambique ridge is generally oceanic crust and the COB of the whole Mozambique continental margin is divided.

A VGGNet-based correction for satellite altimetry-derived gravity anomalies to improve the accuracy of bathymetry to depths of 6500 m

Understanding the topographic patterns of the seafloor is a very important part of understanding our planet.Although the science involved in bathymetric surveying has advanced much over the decades,less than 20%of the seafloor has been precisely modeled to date,and there is an urgent need to improve the accuracy and reduce the uncertainty of underwater survey data.In this study,we introduce a pretrained visual geometry group network(VGGNet)method based on deep learning.To apply this method,we input gravity anomaly data derived from ship measurements and satellite altimetry into the model and correct the latter,which has a larger spatial coverage,based on the former,which is considered the true value and is more accurate.After obtaining the corrected high-precision gravity model,it is inverted to the corresponding bathymetric model by applying the gravity-depth correlation.We choose four data pairs collected from different environments,i.e.,the Southern Ocean,Pacific Ocean,Atlantic Ocean and Caribbean Sea,to evaluate the topographic correction results of the model.The experiments show that the coefficient of determination(R~2)reaches 0.834 among the results of the four experimental groups,signifying a high correlation.The standard deviation and normalized root mean square error are also evaluated,and the accuracy of their performance improved by up to 24.2%compared with similar research done in recent years.The evaluation of the R^(2) values at different water depths shows that our model can achieve performance results above 0.90 at certain water depths and can also significantly improve results from mid-water depths when compared to previous research.Finally,the bathymetry corrected by our model is able to show an accuracy improvement level of more than 21%within 1%of the total water depths,which is sufficient to prove that the VGGNet-based method has the ability to perform a gravity-bathymetry correction and achieve outstanding results.

Implementation of a particle-in-cell method for the energy solver in 3D spherical geodynamic modeling

The thermal evolution of the Earth’s interior and its dynamic effects are the focus of Earth sciences.However,the commonly adopted grid-based temperature solver is usually prone to numerical oscillations,especially in the presence of sharp thermal gradients,such as when modeling subducting slabs and rising plumes.This phenomenon prohibits the correct representation of thermal evolution and may cause incorrect implications of geodynamic processes.After examining several approaches for removing these numerical oscillations,we show that the Lagrangian method provides an ideal way to solve this problem.In this study,we propose a particle-in-cell method as a strategy for improving the solution to the energy equation and demonstrate its effectiveness in both one-dimensional and three-dimensional thermal problems,as well as in a global spherical simulation with data assimilation.We have implemented this method in the open-source finite-element code CitcomS,which features a spherical coordinate system,distributed memory parallel computing,and data assimilation algorithms.

Distribution Characteristics of Cobalt-rich Ferromanganese Crust Resources on Submarine Seamounts in the Western Pacific

Based on the survey data of five submarine seamount provinces （chains） in the Western Pacific, the distribution characteristics of cobalt-rich ferromanganese crust resources have been researched in this paper by using the relative reference data and applying the theories of hotspot and seafloor spreading. The main research results obtained are as follows： The Co-rich crust thickness in the study area is gradually increasing from east to west and from south to north having a negative correlation （r = -0.59） with longitude and a positive correlation （r = 0.48） with latitude. The crust thickness varying along longitude and latitude is influenced by the hotspot and seafloor spreading. The oceanic crusts and seamounts in the northwest part of the study area are older, and the crust resources are superior to those in the southeast part. In the depth of 〈1500 m, 1500-2000 m, 2000-2500 m in the study area, the cobalt crust thickness is respectively 5.45 cm, 4.34 cm and 3.55 cm, and in the depth of 2500-3000 m and 3000-3500 m, it drops respectively to 2.84 cm and 3.37 cm. The Co-rich crust resources are mainly concentrated in the seamount summit margins and the upper flanks in the depth of 〈2500 m. There is a strong negative correlation （r = -0.67） between the cobalt crust abundance and the slope of the seamount, 75 kg/m^2 and 50 kg/mz at the slopes of 0°-20° and 20°-34° respectively. Cobalt crusts are mainly distributed in the parts whose slopes are less than 20°. It is consistent with the fractal result that the slope threshold of cobalt crust distribution is 19°, and slopes over 20° are not conducive to the crust growth. The cobalt crusts of high grade are mainly enriched in the region within 150°E-140°W and 30°S-30°N in the Pacific, where there are about 587 seamounts at the depth of 3500- 6000 m and over 30 Ma of the oceanic crusts. The perspective area rich in cobalt crust resources is about 41×104 km^2 and the resource quantity is approximately 27 billion tons.

Mineralogical and Geochemical Constraints on the Mantle Source Characteristics of Basaltic Lavas from the Central Mariana Trough

The composition of mantle-derived basalts reflects the nature of their mantle source regions,which constrain magma generation and composition.Here we present a new whole rock major and trace elements and phenocryst composition of the basaltic lava in the central Mariana Trough.These data provide insights into the mantle source characteristics affected by subduction components.The rocks range from basalts to basaltic andesites,which have high subduction-mobile element contents(e.g.,K,U,Th,LREE)related to N-MORB.The calculated temperature and depth of magma generation are about 1300℃and 30 km,respectively.Although the results above suggest that the addition of hydrous fluid and/or a melt derived from a slab decreases the temperature of mantle partial melting and mildly modifies the composition of a mantle source,the mantle source lithology from which primary magma is generated remains to be peridotite.

Seabed Physical Parameter Research Based on Active-Source OBS Data in the Chukchi Sea Shelf of the Arctic

The acquisition of seabed physical parameters is one of the focuses of marine acoustic researches.However,the activesource ocean bottom seismometer(OBS)detection method in the marine geophysical research is rarely used to acquire seabed physical parameters,and less work is performed in the Arctic.In this study,two active-source OBS data collected from the 9th and 11th Chinese National Arctic Research Expedition(CHINARE)are selected to obtain the physical parameters of seabed sediments.Two kinds of energy spark are used as the active sources,while the cost function inversion method is used based on the arrival time difference between the reflected and direct waves.The thickness and sound velocity of the sediment layers are obtained by inversion,and the empirical formula is used to calculate the physical parameters of the seabed sediment,which are compared with the measured results.The cost function inversion method based on the time difference of arrival of the reflected and direct waves is tested to be effective and feasible in the inversion of seabed parameters from active-source OBS data.The method is further applied to obtain the physical parameters of Chukchi seabed sediments,which provides the idea and reference for the application of marine geophysical activesource OBS detection technology in the inversion of polar seabed physical parameters.

Distribution Characteristics and Controlling Factors of Heavy Metals in Surface Sediments from the Bay-Island-Estuary System(BIES):A Case Study in Coastal Waters of Fujian Province,China

Based on the contents of six heavy metal elements in surface sediments from coastal areas of Fujian Province,the distribution characteristics and controlling factors of six heavy metals in a bay-island-estuary system(BIES)were studied.This paper focuses on the influence of the hydrodynamic environment,and systematically discusses how grain size compositions,chemical environment,tidal current,ocean circulation and human activities influence the distribution and transportation of the heavy metals.The results indicated that the distribution and migration of Cu,Pb,Zn and Cr elements were mainly controlled by natural factors such as regional geological background,grain size compositions,and tidal residual currents.In contrast,As and Hg was mainly affected by human factors such as agriculture and industrial manufacturing.In the BIES,where the chemical environment exerted limited influence,the accumulation and migration of heavy metals are mainly influenced by human activities and enhanced by estuary processes as well as the complex sedimentary dynamic environment caused by many bays and islands.

Tectonics of the Solomon Sea Basin from Vertical Gravity Gradient and Seismic Data

The Solomon Sea Basin is a Cenozoic back-arc spreading basin within the convergence system of the Pacific and Indo-Australian plates.Against the background of subduction polarity reversal,the current Solomon Sea Basin gradually formed a rhombic morphology with the subduction of the basin along the New Britain Trench and the Trobriand Trough.By analyzing the vertical gravity gradient,natural earthquake and seismic reflection data,this study determines the structural characteristics of the Solomon Sea Basin.It was found that the tectonics of the basin are characterized by the original expansion structure within the central part in addition to the structure induced by the latest subduction along the basin margin.The original spreading structure of the basin presented an east–west linear graben and horst controlled by normal faults during the basin expansion period.As a result of the subduction and slab-pull of the Solomon Sea Basin,extensional structure belts parallel to the New Britain Trench formed along the basin margin.

Density Structure of the Papua New Guinea-Solomon Arc Subduction System

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.

Two Kinds of Waves Causing the Resuspension of Deep-Sea Sediments:Excitation and Internal Solitary Waves

The resuspension of marine sediments plays a key role in the biogeochemical cycle and marine ecology system.Internal solitary waves are considered to be important driving forces of the resuspension of bottom sediments.In this paper,the movement of turbidity currents,the generation and the effects on the bottom bed of internal solitary waves and excitation waves are studied by flume tests and numerical simulations,and the sediment resuspension are analyzed.The results show that the excitation wave can lead to the resuspension of the bottom sediments under all the conditions,while the internal solitary wave can lead to the resuspension of the sediment only under some special conditions,such as high amplitude or large underwater slope.Under the experimental conditions,the change in the near-bottom velocity caused by the excitation wave is close to three times that of the internal solitary wave.

Record of hydrothermal activity in the Yuhuang hydrothermal field and its implications for the Southwest Indian Ridge:evidence from sulfide chronology

The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits.However,the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained.In this study,mineralogical analyses and 230Th/U dating were performed.Hydrothermal activity may start about(35.9±2.3)ka from the southwest part of the YHF and may cease about(708±81)a ago from the northeast part of the YHF.The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR.Hydrothermal activity in the SWIR has been relatively active over the past20 ka.In contrast,between 40 ka and 100 ka,hydrothermal activity was relatively infrequently and short in duration.The maximum activity occurred at 15–11 ka,9–7 ka,6–0.2 ka.There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage.The minimum mass accumulation rate of YHF is about 278 t/a,which is higher than most HFs related to ultramafic systems.The ultraslow spreading SWIR has the greatest potential to form large-scale seafloor massive sulfides(SMS)deposits.The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.