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

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Journal of Ocean University of China 2024年第3期23卷 643-653页

作者： GUO Kun zhai shikui FAN Di ZHANG Xia ZHANG Yu ZHU Zhimin Laoshan Laboratory Qingdao 266237China Key Laboratory of Submarine Geosciences and Prospecting Techniques Ministry of EducationCollege of Marine GeosciencesOcean University of ChinaQingdao 266100China Key Laboratory of Submarine Geosciences&Second Institute of Oceanography Ministry of Natural ResourcesHangzhou 310012China

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 *** 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 *** 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 *** calculated clinopyroxene crystallization temperatures showed a narrow range of 990-1061℃,and their crystallization pressures ranged from 2.0 to 3.2 *** 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 *** 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.

关键词： trace elements clinopyroxenes southern Okinawa Trough seafloor spreading back-arc basin

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Magma Evolution Processes in the Southern Okinawa Trough:Insights from Melt Inclusions

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Journal of Ocean University of China 2021年第6期20卷 1383-1397页

作者： ZHANG Yujiao zhai shikui Key Laboratory of Submarine Geosciences and Prospection of Ministry of Education Ocean University of ChinaQingdao 266100China

The Okinawa Trough is an initial back-arc basin that is influenced by the subduction of the Philippine Sea Plate and develops on the continental *** Okinawa Trough is a natural laboratory for the study of basin evolution,magmatism,and crustmantle processes in the early stage of back-arc *** inclusions are small droplets of magma that are captured during the mineral crystallization process and can record the geochemical composition changes during magma *** this study,the geochemical compositions of melt inclusions in host plagioclases of two volcanic rock samples at Station nos.9-1 and 9-2 from the southern Okinawa Trough are systematically *** on previous studies,the origin and evolution of magma and the introduction of subducting materials in the study area are *** show that melt inclusions are characterized by the relative enrichment of large-ion lithophile elements,depletion of high-field-strength elements,and slight enrichment of rare earth ***,the subduction of the Philippine Sea Plate introduced sediment-derived melts and fluids into the magma source area of the southern Okinawa ***,4%to 5%partial melting of the hydrated mantle produces basaltic *** melt inclusions of andesite and dacite investigated in this study were formed by fractional crystallization of basaltic ***,the crystallization of plagioclase,pyroxene,and magnetite occurred during the late stage of magma *** temperature-pressure data show that the melt inclusions in plagioclase have two capture periods:one is at temperatures above 1250℃and the other is at temperatures between 1180℃and 1200℃.The capture pressure of the inclusions at temperatures between 1180℃and 1200℃is between 5.6 kPa and 6.1 kPa,corresponding to the depth of 15–17 km below the *** geochemical characteristics of major and trace elements in inclusions show that the samples from two stations(i.e.,9-1 and 9-2)have similar

关键词： melt inclusions magma evolution processes contamination of crustal materials introduction of subducting materials the southern Okinawa Trough

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Basic mathematical model for the normal black smoker system and the hydrothermal megaplume formation

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Acta Oceanologica Sinica 2007年第6期26卷 30-40页

作者： LIU Longlong zhai shikui College of Marine Geoscience Ocean University of China Qingdao 266003 China

A tube model to simulate the normal black smoker system has been built, where the Darcy flow equation, the Ergun equation and the turbulent pipe flow equation are used respectively to describe the dynamic process of different key areas in the hydrothermal circulation system. At the same time, a convection - diffuse Equation for the temperature field is used for describe the exchange of thermal energy and the law of temperature variation. Combining the above facts and using efficient mathematical algorithms and programming with the MatLab programming language, the variation curves of temperature, pressure and mass flow rate are determined, while also the dynamic heat equilibrium and pressure equilibrium within the black smoker system are analyzed. On the basis of the model of the normal black smoker system, a megaplume formation model is further built. For instance, the hydrothermal venting plume on the Juan de Fuca Ridge has been simulated and the simulation results are fairly consistent with Baker＇ s imputed data in 1986. On the basis of the above productive simulation, a series of factors for megaplume formation and the effectiveness of the main parameters of the periodicity of the megaplume formation, temperature and the maximum mass flow rate are systematically discussed. Main conclusions are as follows： The normal black smoker system can evolve into a megaplum eruption. In fact, the passageway of the hydrothermal discharge is blocked by the hydrothermal sediments during the black smoker period, which leads to a hydrothermal fluid accumulation, rise of temperature and increase of buoyancy pressure under the seabed. After a period of 2 - 3 a, the megaplume hydrothermal eruption will occur when the increasing buoyancy pressure is high enough to crack the blockage （cap）. Meanwhile, the temperature of the heat source must exceed 500 ℃, while the highest temperature of the eruption fluid may be high up to 413 ℃, which is fairly consistent with the surveying data. If

关键词： normal black smoker megaplume mathematical model simulation for hydrothermal circulation system

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Strontium Isotope Compositions of Hydrothermal Barite from the Yonaguni Ⅳ: Insight into Fluid/Sediment Interaction and Barite Crystallization Condition

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Journal of Ocean University of China 2020年第2期19卷 377-385页

作者： ZHANG Xia zhai shikui YU Zenghui Key Laboratory of Submarine Geosciences and Prospecting Techniques Ministry of Education College of Marine Geosciences Ocean University of China

Hydrothermal barite is a typical low-temperature mineral formed during the mixing of hydrothermal fluid and *** of its extremely low solubility,barite behaves as a close system after crystallization and preserves the geochemical fingerprint of hydrothermal *** this study,the elemental contents and Sr isotope compositions of hydrothermal barites from the Yonaguni IV were determined using electron microprobe and LA-MC-ICP-MS *** these bases,the fluid/sediment interaction during the hydrothermal circulation and physicochemical condition of barite crystallization were *** show that the 87 Sr/86 Sr values of hydrothermal barites from the Yonaguni IV are apparently higher than those of the seawater and associated volcanic rocks,indicating the sufficient interaction between the hydrothermal fluid and overlying *** Sr abundance shows large variations,reflecting the changes in barite growth rate during the fluid *** mineralization condition in the Yonaguni IV was *** the crystallization of barite,hydrothermal fluid and seawater mixed in varying degrees,with the pro-portions of hydrothermal fluid varied from 36%to 72%.The calculated crystallization temperatures range from 109 to 220℃.Sediment plays a critical role during the mineralization process in the Yonaguni IV and incorporation of sediment component into hydrothermal system was prior to barite crystallization and sulfide mineralization.

关键词： strontium isotope hydrothermal barite fluid/sediment interaction crystallization condition Okinawa Trough

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Changjiang River sediment delivering into the sea in response to water storage of Sanxia Reservoir in 2003

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Acta Oceanologica Sinica 2006年第2期25卷 71-79页

作者： CHU Zhongxin zhai shikui CHEN Xiufa College of Marine Geosciences Ocean University of China Qingdao 266003 China Development and Research center China Geological Survey Beijing 100083 China

The Sanxia Reservoir on the Changjiang River stored water from 1 to 10 June and from 25 October to 5 November in 2003, elevating the water level to 135 and 139 m above mean sea level at the dam, respectively. A monthly dataset of water discharge, suspended sediment concentration （SSC） and sediment load of the Changjiang River from 1953 to 2003 measured at the Datong Hydrological Gauging Station of the downstreammost Changjiang River was mainly used to examine the Changjiang River sediment delivering into the sea in 2003 in response to the Sanxia Reservoir water storages in the same year. The results show that （1） compared with those in 2002, 2001, and the multi-yearly （1953-2000） average, both annual SSC and sediment load at Datong in 2003 were markedly reduced, and they were even smaller than the multi-yearly （1953-2000） minimum, although the annual runoff in 2003 did not change largely; and （2） compared with those in the corresponding months in 2002, 2001 and the multi-monthly average from 1953 to 2000, monthly SSC and sediment load at Datong both in June and November of 2003 were also markedly reduced, and those in June 2003 were even smaller than the multi-monthly minimum from 1953 to 2000. These may indicate that sediment sedimentation in the Sanxia Reservoir resulting from the Sanxia Reservoir water storage should be the main cause of the decreased annual and monthly SSC and sediment load of the Changjiang River into the sea in 2003. Besides, it seems that the Sanxia Reservoir water storage in the early June （flood season） of 2003 had more impacts on the decreased monthly SSC into the sea than that in the late October and early November （approximately non-flood season） of 2003.

关键词： Changjiang (Yangtze) River Sanxia Reservoir water storage sediment

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Heat and mass flux estimation of modern seafloor hydrothermal activity

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Acta Oceanologica Sinica 2006年第6期25卷 43-51页

作者： zhai shikui WANG Xingtao YU Zenghui Marine Geoscience Institute Ocean University of China Qingdao 266003 China Bureau of Ocean and Fishing in Weihai Weihai 264200 China

Research on heat and mass flux yielded by modern seafloor hydrothermal activity is very important, because it is involved not only in the base of ocean environment research, but also in the historical evolution of seawater properties. Currently, estimating heat flux is based on the observation data of hydrothermal smokers, low-temperature diffusive flow and mid-ocean ridge mainly. But there are some faults, for example, there is lack of a concurrent conductive item in estimating the heat flux by smokers and the error between the half-space cooling model and the observation data is too large. So, three kinds of methods are applied to re-estimating the heat flux of hydrothermal activity resepectively, corresponding estimation is 97. 359 GW by hydrothermal smoker and diffusive flow, 84.895 GW by hydrothermal plume, and 4. 11 TW by exponential attenuation method put forward by this paper. Research on mass flux estimation is relatively rare, the main reason for this is insufficient field observation data. Mass fluxes of different elements are calculated using hydrothermal vent fluid data from the TAG hydrothermal area on the Mid-Atlantic Ridge for the first time. Difference of estimations by different methods reflects the researching extent of hydrothermal activity, and systematically in - situ observation will help to estimate the contribution of hydrothermal activity to ocean chemical environment, ocean circulation and global climate precisely.

关键词： hydrothermal activity heat flux mass flux exponential attenuation method

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Elemental geochemical records of seafloor hydrothermal activities in the sediments from the Okinawa Trough

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Acta Oceanologica Sinica 2007年第4期26卷 53-62页

作者： zhai shikui YU Zenghui DU Tongjun Department of Marine Geosciences Ocean University of China Qingdao 266003 China

The major and minor element contents in the sediment core H9 from the hydrothermal fields of the Okinawa Trough show a sharp change at the depth of 80 cm. The elements enriched in the upper 80 cm core are those enriched in the hydrothermal deposits and in the surface sediments recovered from the hydrothermal fields in the trough, which indicates the input of hydrothermal materials. Comparing with other hydrothermal sediments from Mid-ocean Ridges or the Lau Basin, the degree of the enrichment of elements iron, copper,cobah, and nickel is relatively low. However, the enrichment of elements manganese, lead, arsenic, antimony and mercury is remarkable. The average contents of these elements in the upper 80 cm core sediments are three to six times those in the lower section, and 3 - 12 times those in the surface sediments which are not influenced by hydrothermal activities. Hydrothermal activities have contributed significant manganese, lead, arsenic, antimony and mercury to the sediments, and these elements are distinct indicators for the hydrothermal activity in the Okinawa Trough. The significant enrichment of these elements in Core H9 upward from the depth 80 cm indicates the start or the significant enhancing of the hydrothermal activity in this area at about 5 740 aB. P. The average accumulation rate of manganese during this period is about 40 461μg/（ cm^2·ka） , which is similar to the hydrothermal sediments in the Lau Basin or the East Pacific Rise.

关键词： Okinawa Trough hydrothermal activity elemental geochemical record

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Geochemical characteristics of Sr isotopes in the LS33 drill core from the Qiongdongnan Basin, South China Sea, and their response to the uplift of the Tibetan Plateau

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Acta Oceanologica Sinica 2023年第5期42卷 117-129页

作者： Ke Wang shikui zhai Zenghui Yu Huaijing Zhang College of Marine Geosciences Ocean University of ChinaQingdao 266100China Sinopec Matrix Co. Ltd.Qingdao 266000China Key Lab of Submarine Geosciences and Prospecting Techniques Ministry of EducationQingdao 266100China

Making full use of modern analytical and testing techniques to explore and establish new indexes or methods for extracting paleoseawater geochemical information from sediments will help to reconstruct the sedimentary paleoenvironment in different research *** connection between the subsidence of the South China Sea basin and the uplift of the Tibetan Plateau has been a scientific concern in recent *** explore the information on the sedimentary paleoenvironment,provenance changes and uplift of Tibetan Plateau contained in core sediments(debris),we selected core samples from Well LS33 in the Qiongdongnan Basin,South China Sea,and analyzed the contents of typical elements(Al,Th,and rare earth elements)that can indicate changes in provenance and the Sr isotopic compositions,which can reveal the geochemical characteristics of the paleoseawater depending on the type of material(authigenic carbonate and terrigenous detritus).The results show the following:(1)during the late Miocene,the Red River transported a large amount of detrital sediments from the ancient continental block(South China)to the Qiongdongnan Basin.(2)The authigenic carbonates accurately record changes in the 87Sr/86Sr ratios in the South China Sea since the *** ratios reflect the semi-closed marginal sea environment of the South China Sea(relative to the ocean)and the sedimentary paleoenvironment evolution process of the deep-water area of the Qiongdongnan Basin from continental to transitional and then to bathyal.(3)Since the Neogene,the variations in the 87Sr/86Sr ratio in the authigenic carbonates have been consistent with the variations in the uplift rate of the Tibetan Plateau and the sediment accumulation rate in the Qiongdongnan *** consistent changes indicate the complex geological process of the change in the rock weathering intensity and terrigenous Sr flux caused by changes in the uplift rate of the Tibetan Plateau,which influence the Sr isotope composition of s

关键词： sediments from a drill core grouping analysis elements and Sr isotopes provenance and paleoenvironment uplift of the Tibetan Plateau and subsidence of the South China Sea basin

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Evolving patterns of the fluids within the TAG hydrothermal field

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Science China Earth Sciences 2009年第1期52卷 29-37页

作者： LI HuaiMing zhai shikui YU ZengHui TAO ChunHui CHU FengYou Department of Marine Geoscience Ocean University of ChinaQingdao 266100China Key Laboratory of Submarine Geosciences State Oceanic AdministrationHangzhou 310012China Second Institute of Oceanography State Oceanic AdministrationHangzhou 310012China

The mixing of seawater/hydrothermal fluid within the large seafloor hydrothermal sulfide deposits plays a key role in the formation processes of the sulfide deposits. Some issues attract considerable attentions in the study of seafloor hydrothermal system in recent years, such as the relationships among different types of vent fluids, the characteristics of chemical compositions and mineral assemblages of the hydrothermal deposits and their governing factors. Combined with the measured data of hydrothermal fluid in the TAG field, the thermodynamic model of mixing processes of the heated seawater at different temperatures and the hydrothermal fluid is calculated to understand the precipitation mechanism of anhydrite and the genetic relationships between the black and white smoker fluids within the TAG mound. The results indicate that the heating of seawater and the mixing of hydrothermal fluid/seawater are largely responsible for anhydrite precipitation and the temperature of the heated seawater is not higher than 150°C and the temperature of the end-member hydrothermal fluid is not lower than 400°C. Based on the simulated results, the evolving patterns of fluids within the TAG deposit are discussed. The mixed fluid of the end-member hydrothermal fluid and the seawater heated by wall rock undergoes conductive cooling during upflowing within the deposit and forms “White Smoker” eventually. In addition, the end-member hydrothermal fluid without mixed with seawater, but undergoing conductive cooling, vents out of the deposit and forms “Black Smoker”.

关键词： seafloor hydrothermal system mixing process evolving patterns of fluids TAG hydrothermal field

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Geochemical Features of Sulfides from the Deyin-1 Hydrothermal Field at the Southern Mid-Atlantic Ridge near 15?S

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Journal of Ocean University of China 2017年第6期16卷 1043-1054页

作者： WANG Shujie LI Huaiming zhai shikui YU Zenghui CAI Zongwei Key Laboratory of Submarine Geosciences and Prospecting Techniques Ministry of EducationCollege of Marine Geosciences Ocean University of China Qingdao 266100 P. R. China Key Laboratory of Submarine Geosciences Second Institute of Oceanography State Oceanic AdministrationHangzhou 310012 P. R. China

In this study, geochemical compositions of elements in sulfide samples collected from the Deyin-1 hydrothermal field near the 15?S southern Mid-Atlantic Ridge(SMAR) were analyzed by the X-ray fluorescence spectrometry(XRF) and inductively coupled plasma mass spectrometry(ICP-MS) to examine the enrichment regulations of ore-forming elements and hydrothermal mineralization. These sulfide precipitates can be classified macroscopically into three types: Fe-rich sulfide, Fe-Cu-rich sulfide and Fe-Zn-rich sulfide, and are characterized by the enrichment of base metal elements along with a sequence of Fe>Zn>Cu. Compared with sulfides from other hydrothermal fields on MAR, Zn concentrations of sulfides in the research area are significantly high, while Cu concentrations are relatively low. For all major, trace or rare-earth elements(REE), their concentrations and related characteristic parameters exhibit significant variations(up to one or two orders of magnitude), which indicates the sulfides from different hydrothermal vents or even a same station were formed at different stages of hydrothermal mineralization, and suggests the variations of chemical compositions of the hydrothermal fluid with respect to time. The hydrothermal temperatures of sulfides precipitation decreased gradually from station TVG10(***10) to ***12, and to ***11, indicating that the precipitation of hydrothermal sulfides is subjected to conditions changed from high temperature to low temperature, and that the hydrothermal activity of study area was at the late stage of a general trend of evolution from strong to weak. The abnormally low concentrations of REE in sulfides and their similar chondrite-normalized REE patterns show that REEs in all sulfides were derived from a same source, but underwent different processes of migration or enrichment, or sulfides were formed at different stages of hydrothermal mineralization. The sulfides collected from the active hydrothermal vent were mainly attrib

关键词： southern Mid-Atlantic Ridge Deyin-1 hydrothermal field hydrothermal sulfide geochemistry of element mineralization

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