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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

Discovery and characterization of a new hydrothermal field at 2°N on the slow-spreading Carlsberg Ridge

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Journal of Oceanology and Limnology 2024年第4期42卷 1106-1118页

作者： Zhongyan QIU Yejian WANG Xiqiu HAN Honglin LI Xing YU Ruyong CUI Mou LI Xuegang CHEN Jiqiang LIU key Laboratory of submarine geosciences&second institute of oceanography Ministry of Natural ResourcesHangzhou 310012China Qingdao institute of Marine Geology China Geological SurveyQingdao 266071China School of Earth Science Zhejiang UniversityHangzhou 310027China Ocean College Zhejiang UniversityZhoushan 316021China

A new hydrothermal field(Tianshi)was discovered on the rift valley wall through plume anomaly surveys and geological work conducted in 2012 and 2018 between 2°35′N and 2°43′N of the slow-spreading Carlsberg Ridge(CR).Here,the results of two expeditions conducted to detect and characterize the new hydrothermal field are *** and geochemical data,as well as 14 C ages of a sediment core collected near the field are presented to reveal the hydrothermal *** show that the Tianshi field is a basalt-hosted hydrothermal *** data of the sediments collected near the field indicate a strong hydrothermal contribution,and hydrothermal Fe and Cu fluxes range from 30 to 155 mg/(cm^(2)·ka)and 0.59 to 11.49 mg/(cm^(2)·ka),*** variations in the fluxes of hydrothermal Fe indicate that there have been at least three amplified hydrothermal venting events(H 1,H 2,and H 3)in the Tianshi field over the last 35.2 ka,in 28.6-35.2 ka BP,22.0-27.6 ka BP,and 1.2-11.4 ka BP,*** event H 2 was driven by an increased magmatic production associated with sea level fall during the Last Glacial Maximum,while event H 3 was promoted by tectonic activity associated with a rapid sea level *** study further verified the role of sea level change in modulating hydrothermal activity on mid-ocean ridges.

关键词： plume anomaly sediment core new hydrothermal field hydrothermal history Carlsberg Ridge

Numerical models of slab breakoff mechanism beneath the Java Trench

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Journal of Earth Science 2024年

作者： Dan Liang Weiwei Ding Xiongwei Niu Letian Ma Xiaodong Wei School of oceanography， Shanghai Jiao Tong University key Laboratory of submarine geosciences & second institute of oceanography， Ministry of Natural Resources

We conducted a series of numerical modelling experiments to investigate the mechanism of slab breakoff beneath the Java Trench. The subduction of seamounts， which are characterized by overthickened and buoyant crust， can be a key factor conducive to slab detachment. The modeling experiments explored a range of variable parameters， including whether seamount is involved in the subduction process， the geometry and rheological properties of the seamount， the convergence rate， and the age of subducting oceanic lithosphere. The modelling results demonstrate that the presence of seamount significantly affects the slab breakoff process. Slab breakoff typically occurs at the edges of the subducting seamount. The specific geometry and rheological strength of the seamount emerges as the internal factors in determining whether the slab breakoff will occur. Additionally， the slab age and convergence rate are the external effective controlling factors on the timing and depth of slab breakoff. The evolution of surface elevation caused by seamount subduction differs from that of general oceanic lithosphere subduction， featuring an additional uplift event related to the slab breakoff. Based on our findings， we infer that the participation of seamounts in the subduction process beneath the Java Trench (110°E) has led to the development of low-velocity zone in the mantle wedge and high-potassium volcanoes in the Java Island， which has further resulted in a compressional tectonic region in the overriding continental crust.

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Independent magma system underneath micro non-transform discontinuity: geochemical evidence of magma from Daxi area， Carlsberg Ridge

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Journal of Earth Science 2024年

作者： Hang Hu Xiqiu Han Yejian Wang Zhongyan Qiu Tong Zong Jiqiang Liu Honglin Li Xing Yu key Laboratory of submarine geosciences， & second institute of oceanography， Ministry of Natural Resources Ocean College， Zhejiang University College of Architectural Engineering， Weifang University

The discontinuities of a ridge， defined by the geophysical properties， often coincides with geochemical variations in lava， highlighting the relationship between ridge discontinuity and the underlying magmatic system. This study presents bathymetric， geophysical， and basaltic geochemical data from the Daxi-non transform discontinuity (NTD) and adjacent segments. The Daxi-NTD is a typical micro-NTD， with an offset less than 15 km. Within the NTD， a neo-volcanic ridge has emerged， with an active hydrothermal system suggesting an underlying magmatic system. The study examines mantle composition， melting degree， crystallization pressure， and melt extraction processes beneath Daxi-NTD. Comparative analysis reveals that basalts in the Daxi area undergo extensive differentiation， characterized by higher crystallization pressure and lower melting degree compared to the adjacent segments. We propose that Daxi-NTD hosts an independent magmatic system， where melt migrates vertically through the magmatic system rather than laterally from the adjacent segment center. This approach aids in understanding of the magmatism along slow-spreading ridges and provides insights into the geodynamics and tectonic evolution of younger ridge system.

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

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Acta Geologica Sinica(English Edition) 2024年第1期98卷 104-116页

作者： ZHANG Huichao CHAI Peng ZHANG Hongrui ZHOU Limin HOU Zengqian key Laboratory of submarine geosciences Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China institute of Geology Chinese Academy of Geological SciencesBeijing 100037China key Laboratory of Marine Hazards Forecasting Ministry of Natural ResourcesHohai UniversityNanjing 210024China National Research Center for Geoanalysis Beijing 100037China

Lamprophyres typically appear in hydrothermal gold *** relationship between lamprophyres and gold deposits is investigated *** 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 ***,K-feldspar veins are ideal for investigating the relationship between lamprophyres and gold *** 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 *** 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 *** 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 *** 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.

关键词： lamprophyre K-feldspar vein apatite Sr isotope gold Zhenyuan deposit Yunnan

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

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Acta Oceanologica Sinica 2024年第1期43卷 112-122页

作者： Xiaolun Chen Xiaowen Luo Ziyin Wu Xiaoming Qin Jihong Shang Huajun Xu Bin Li Mingwei Wang Hongyang Wan key Laboratory of submarine geosciences Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China Ocean College Zhejiang UniversityZhoushan 316021China key Laboratory of Ocean Space Resources Management Technology Marine Academy of ZhejiangHangzhou 310012China School of oceanography Shanghai Jiao Tong UniversityShanghai 200240China School of Civil Engineering and Architectures Zhejiang University of Science and TechnologyHangzhou 310023China National Center for Archaeology Beijing 100013China

Understanding the topographic patterns of the seafloor is a very important part of understanding our *** 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 *** this study,we introduce a pretrained visual geometry group network(VGGNet)method based on deep *** 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 *** obtaining the corrected high-precision gravity model,it is inverted to the corresponding bathymetric model by applying the gravity-depth *** 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 *** experiments show that the coefficient of determination(R~2)reaches 0.834 among the results of the four experimental groups,signifying a high *** 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 *** 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 ***,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.

关键词： gravity anomaly bathymetry inversion VGGNet multibeam sonar satellite altimetry

Preliminary Results of the Seismicity Monitoring Experiment around the 2019 Mw5.4 Earthquake Epicenter in the Central South China Sea Basin

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Journal of Earth Science 2024年第1期35卷 212-220页

作者： Wenfei Gong Aiguo Ruan Xiongwei Niu Zhenjie Wang Pingchuan Tan Xiaodong Wei Wei Wang Zhengyi Tong Liqun Cheng Fansheng Kong Shaoping Lu Jianke Fan Weiwei Ding Jinyao Gao Chunguo Yang Jiabiao Li School of oceanography Shanghai Jiaotong UniversityShanghai 200240China key Laboratory of submarine geosciences Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China Zhejiang Earthquake Administration Hangzhou 310013China School of Earth Sciences Zhejiang UniversityHangzhou 310027China Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai) Zhuhai 519082China School of Earth Sciences and Engineering Sun Yat-sen UniversityZhuhai 519082China institute of Oceanology Chinese Academy of SciencesQingdao 266071China

On September 5,2019,a moderate earthquake of Mw5.4 unexpectedly occurred in the apparently quiescent central basin of the South China *** immediately carried out a seismicity monitoring experiment around the epicenter by using broadband ocean bottom seismometers(OBS)for the following three scientific *** first is knowing the earthquake seismogenic mechanism,fault structure and further *** second is finding the role of the residual spreading ridge playing in earthquake processes and further revealing the deep structures of the ridge directional turning *** third is confirming the existence and significance of the so called“Zhongnan fault”.This paper reports the preliminary results of the first phase *** OBSs were deployed for seismicity monitoring with a duration of 288 days,but only three were ***-earthquakes were firstly detected by an automatic seismic phase picking algorithm and then were verified by analyzing their seismic phases and time-frequency characteristics in detail.A total of 21,68 and 89 microearthquakes were picked out from the three OBSs respectively within the distance of 30 *** dominant frequency of these micro-earthquakes is 12-15 Hz,indicating tectonic *** the first two months after the mainshock the seismicity was relatively stronger,and micro-earthquakes were still occurring occasionally till the end of observation,indicating the epicenter area is *** used Match&Locate method to locate 57 micro-earthquakes *** spatial distribution shows that the seismicity is developed mainly along the NE direction roughly parallel to the residual ridge with depth variations between 10-20 km.

关键词： South China Sea microseismic monitoring earthquakes fault broadband OBS

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

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Journal of Ocean University of China 2024年第3期23卷 721-730页

作者： LI Anlong WANG Panpan GUO Xijun JI Xiangkun SHEN Kunming LIN Lin YAN Zhichao YUAN Lin key Laboratory of submarine geosciences and Prospecting Techniques Ministry of Education and College of Marine GeosciencesOcean University of ChinaQingdao 266100China College of Marine Geoscience Ocean University of ChinaQingdao 266100China China Construction second Engineering Bureau Co. LTDYueyang 414000China Tianjin Research institute for Water Transport Engineering M.O.T.Tianjin 3000456China Lianyungang Xuwei Port Holding Group Co. Ltd.Lianyungang 222042China

The comprehension of sediment grain size parameters and the corresponding sedimentary environment holds paramount importance in elucidating the engineering geological attributes of the subaqueous *** 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 *** 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 *** study found four distinct sedimentary environments in the study area:coastal,transitional,shallow sea,and *** 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 ***,notable disparities in the correlation between grain size parameters and geotechnical indices emerge across different sedimentary environments.

关键词： grain size parameters cluster analysis sedimentary environment correlations geotechnical indexes

Petrology and geochemistry of cold seep carbonates from the northern Okinawa Trough,East China Sea:implications to early diagenesis

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Journal of Oceanology and Limnology 2022年第4期40卷 1388-1403页

作者： Kehong YANG Zhimin ZHU Yanhui DONG Weiyan ZHANG Fengyou CHU key Laboratory of submarine geosciences&second institute of oceanography Ministry of Natural ResourcesHangzhou 310012China

Carbonate samples were collected from the northern Okinawa Trough in the East China Sea in *** petrology,mineralogy,carbon and oxygen isotopes,and rare earth elements(REEs)of these samples were ***,high-Mg calcite,and dolomite were the main carbonate minerals,the contents of which varied greatly among the carbonate *** observations revealed the common occurrence of framboidal ***δ^(13)C values of carbonates varied from-53.7‰to-39.3‰(average of-47.3‰based on Vienna Pee Dee Belemnite(V-PDB),n=9),and theδ^(18)O values ranged from 0.6‰to 3.4‰(average of 1.9‰;V-PDB,n=9).The carbon and oxygen isotope characteristics indicated that the carbonates precipitated during the anaerobic oxidation of *** carbon source was a mixture of thermogenic methane and biogenic methane,possibly with a greater contribution from the *** oxygen isotope data showed that gas hydrate dissociation occurred during carbonate *** Ce anomalies suggested that the carbonates precipitated in an anoxic environment.A slight enrichment of middle REEs(MREEs)could be attributable to the early *** structures,minerals,oxygen isotopes,and MREEs all indicated that the carbonates experienced some degree of early ***,the infl uence of early diagenesis should be considered when using geological and geochemical proxies to reconstruct original methane seepage environments.

关键词： authigenic carbonate carbon and oxygen isotopes rare earth elements(REEs) anaerobic oxidation of methane(AOM) northern Okinawa Trough