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Geochemistry and age of seamounts in the West Pacific: mantle processes and petrogenetic implications

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Acta Oceanologica Sinica 2019年第1期38卷 71-77页

作者： Limei Tang Yanhui Dong Fengyou Chu Ling Chen Weilin Ma Yonggang Liu Key laboratory of Submarine geosciences Ministry of Natural Resources Second Institute of Oceanography Ministry of Natural Resources Guangzhou Marine Geological Survey Ministry of Natural Resources

Research on seamounts provides some of the best constraints for understanding intraplate volcanism, and samples from seamounts reveal crucial evidence about the geochemical makeup of the oceanic mantle. There are still many seamounts in the West Pacific Seamount Province(WPSP) that have not been studied, meaning their ages and geochemistry remain unknown. A better understanding of these seamount trails and their evolutionary history, investigated with age and geochemistry data, will enable better understanding of the geological processes operating underneath the Pacific Ocean Plate. Here, new ^(40)Ar/^(39) Ar ages and trace element and Sr-Nd-Pb isotopic data for seven basalt rocks from four seamounts in the WPSP are provided. Chemically, these rocks are all Oceanic Island Alkali basalt(OIA type); analysis of olivine phenocrysts shows that the magmas experienced strong olivine fractionation and changed from olivine + plagioclase to olivine + plagioclase + clinopyroxene cotectic during their evolution. Rare earth element(REE) patterns and a spider diagram of the samples in this study show OIB(Ocean Island Basalt) like behavior. The range of ^(87)Sr/^(86) Sr values is from 0.704 60 to 0.706 24, the range of ^(206)Pb/^(204) Pb values is from 18.241 to 18.599, and the range of ^(143)Nd/^(144) Nd values is from 0.512 646 to 0.512 826; together, these values indicate magma sources ranging from EMI to EMII. Finally, new ^(40)Ar/^(39) Ar age data show that these seamounts formed at ～97 and ～106 Ma, indicating that some may have undergone the same formation processes as seamounts in the eastern part of the Magellan Seamount Trail, but other seamounts likely have different origins.

关键词： ^40Ar/^39Ar ages geochemistry magmatic evolution basalts West Pacific

Ice sheet controls on fine-grained deposition at the southern Mendeleev Ridge since the penultimate interglacial

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Acta Oceanologica Sinica 2020年第9期39卷 86-95页

作者： Liming Ye Xiaoguo Yu Weiyan Zhang Rong Wang Key laboratory of Submarine geosciences Ministry of Natural ResourcesHangzhou 310012China Second Institute of Oceanography Ministry of Natural ResourcesHangzhou 310012China

Clay minerals deposited at the southern Mendeleev Ridge in the Arctic Ocean have a unique provenance,which can be used to reconstruct changes in the local sedimentary *** show that sediments in core ARC7-E23 record high-frequency changes in clay minerals since the penultimate *** clay minerals,grain size,and ice-rafted debris indicate the extent of the East Siberia Ice Sheet(ESIS).During the glacial periods of Marine Isotope Stage 2(MIS2)and MIS4,the southern Mendeleev Ridge was likely covered by an ESIS-extended ice shelf,blocking almost all sediment input from the Canadian Arctic and Laptev Sea,but allowing transport of fine-grained sediments from the East Siberian and Chukchi Sea *** ESIS retreat,the Beaufort Gyre and Transpolar Drift became the primary transport mechanism for the distally sourced *** conditions in MIS3 enhanced both the oceanic circulation and sediment transport.

关键词： Arctic Ocean Mendeleev Ridge East Siberian Ice Sheet clay minerals

Chemical composition and petrogenesis of plagioclases in plagioclase-phyric basalts from the Southwest Indian Ridge(51°E)

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Acta Oceanologica Sinica 2020年第7期39卷 42-49页

作者： Jie Li Jihao Zhu Fengyou Chu Xiaohu Li Zhimin Zhu Hao Wang Key laboratory of Submarine geosciences Ministry of Natural ResourcesHangzhou 310012China Second Institute of Oceanography Ministry of Natural ResourcesHangzhou 310012China

Electron microprobe analysis was conducted on plagioclase from the plagioclase ultraphyric basalts(PUBs)erupted on the Southwest Indian Ridge(SWIR)(51°E)to investigate the geochemical changes in order to better understand the magmatic processes occurring under ultraslow spreading ridges and to provide insights into the thermal and dynamic regimes of the magmatic reservoirs and conduit *** phenocryst cores are generally calcic(An74–82)and are depleted in FeO and *** the phenocryst rims(An67–71)and the plagioclase in the groundmass(An58–63)are more sodic and have higher FeO and MgO contents than the phenocryst *** crystallization temperatures of the phenocryst cores and the calculation of the equilibrium between the phenocrysts and the matrix suggest that the plagioclase cores are unlikely to have crystallized from the host basaltic melt,but are likely to have crystallized from a more calcic *** enrichment in incompatible elements(FeO and MgO),as well as the higher FeO/MgO ratios of the outermost phenocryst rims and the groundmass,are the result of plagioclase-melt disequilibrium diffusion during the short residence time in which the plagioclase *** results indicate that an evolved melt replenishing under the SWIR(51°E)drives the eruption over a short period of time.

关键词： plagioclase–phyric basalt plagioclase phenocrysts magmatic evolution SWIR

Geochemical characteristics of platinum-group elements in polymetallic nodules from the Northwest Pacific Ocean

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Acta Oceanologica Sinica 2020年第8期39卷 34-42页

作者： Zhongrong Qiu Yanhui Dong Weilin Ma Weiyan Zhang Kehong Yang Hongqiao Zhao Key laboratory of Submarine geosciences Ministry of Natural ResourcesHangzhou 310012China Second Institute of Oceanography Ministry of Natural ResourcesHangzhou 310012China

Polymetallic nodules and cobalt (Co)-rich crusts are enriched in platinum-group elements (PGEs),especially platinum (Pt) and may be important sinks of *** present,little information is available on PGEs in polymetallic nodules,and their geochemical characteristics and the causes of PGEs enrichment are *** PGEs of polymetallic nodules from abyssal basin in the Marcus-Wake Seamount area of the Northwest Pacific Ocean are reported and compared with the published PGEs data of polymetallic nodules and Co-rich crusts in the *** total PGEs (ΣPGE) content of polymetallic nodules in study area is 258×10^–9) in average,markedly higher than that of Clarion-Clipperton Zone (CCZ) nodules (ΣPGE=127×10^–9) and lower than that of Co-rich crusts in the Marcus-Wake Seamount (ΣPGE=653×10^–9),similar to that of Co-rich crusts in the South China Sea(ΣPGE=252×10^~–9).The CI chondrite-normalized PGEs patterns in different regions of polymetallic nodules and cobalt-rich crusts are highly consistent,with all being characterized by positive Pt and negative Pd anomalies These results,together with those of previous studies,indicate that PGEs in polymetallic nodules and Co-rich crusts are mainly derived directly from *** contents of polymetallic nodules from the study area are negatively correlated with water depth,and Pt/ΣPGE ratios in nodules there are also lower than those of the Corich crusts in the adjacent area,indicating that sedimentary water depth and oxygen fugacity of ambient seawater are the possible important controlling factors for Pt accumulation in crusts and nodules.

关键词： platinum-group elements polymetallic nodules Co-rich crusts Marcus-Wake Seamount

Evolution and diagenetic implications of framboids in the methane-related carbonates of the northern Okinawa Trough

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Acta Oceanologica Sinica 2021年第12期40卷 114-124页

作者： Kehong Yang Zhimin Zhu Yanhui Dong Fengyou Chu Weiyan Zhang Key laboratory of Submarine geosciences Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China

Authigenic carbonate samples were collected from the northern Okinawa *** on their carbon and oxygen isotopes,these samples were found to be methane-related carbonates precipitated by the anaerobic oxidation of methane(AOM).Petrological analysis revealed numerous framboidal pyrites that had been partly *** order to trace the variation and diagenetic information of these framboidal pyrites,their diameters and geochemical components were studied using an electron *** results showed that their diameters varied from 4μm to 17μm(n=60;geometric mean of 9.9μm)and were of a normal *** diameters of single pyrite that formed the framboidal pyrites varied from 1μm to 2μ*** framboidal pyrites with diameters of 6–14μm accounted for~80%of the *** geometric mean of 9.9μm indicates that they are probably diagenetic pyrites that were precipitated in a lower dysoxic environment(weakly oxygenated bottom waters).The S/Fe ratio of the framboidal minerals ranged from 0 to 1.67,and the pyrite content of single framboid varied between 0%and 86.4%.Therefore,numerous pyrites were oxygenated to iron oxides or oxyhydroxides,and were retained as pseudomorphism *** size of framboidal pyrites precipitated in cold seeps can be used to trace the redox environment;however,acquisition of additional data via investigation of different cold seeps is necessary to obtain more persuasive results.

关键词： framboidal pyrite grain size S/Fe ratio methane-related carbonate

Geochemical speciation and spatial distributions of phosphorus in surface sediments from the basin of the Marcus-Wake seamounts in the western Pacific Ocean

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Acta Oceanologica Sinica 2022年第4期41卷 80-90页

作者： Chao Yuan Fansheng Meng Xuying Yao Jianyu Ni Key laboratory of Submarine geosciences Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China

The concentrations of five forms of phosphorus(P)including exchangeable or loosely adsorbed P(Ex-P),Febound P(Fe-P),authigenic P(Auth-P),detrital P(Det-P),and organic P(Org-P)from the basin among the Marcus-Wake seamounts(19.4°–24°N,156.5°–161.5°E)in the western Pacific Ocean were quantified using a sequential extraction method(SEDEX)to investigate the distribution and sources of different P *** of total P(TP)varied from 14.0μmol/g to 44.1μmol/g,with an average of(32.4±7.7)μmol/*** phosphorus,which was the major chemical form of sedimentary P,ranged from 12.6μmol/g to 40.6μmol/g,while the concentration of Org-P varied between 1.38μmol/g and 5.18μmol/g,accounting for 83.4%–93.4%and 6.6%–16.6%of the TP,*** relative proportions of the five P species followed the order of Det-P>Auth-P>Org-P>Fe-P>*** average,Det-P was the major P sink resulted from the atmospheric input and accounted for approximately 58.9%±12.4%of the ***-P and Org-P comprised 22.8%±11.4%and11.5%±3.0%of the TP,respectively,while Fe-P accounted for 5.1%±2.6%.Lastly,Ex-P comprised 1.6%±0.3%of the ***-P exhibited a negative correlation with Fe-P and Auth-P,while Fe-P showed a positive correlation with *** indicated that the formation of Fe-P and Auth-P was at the expense of the regeneration or remineralization of Org-P during early *** concentrations of Det-P and Auth-P as well as a low ratio of total organic C to reactive P(TOC/Rea-P)suggested that the aeolian input may play a significant role in sedimentary P budget in the study ***,well-oxygenated bottom water and low sedimentation rate could be responsible for the low TOC/Org-P ratio in the sediment.

关键词： phosphorus speciation SEDEX sediments western Pacific Ocean

Growth structures and growth strata of the Qianjiadian Basin in the western Yanshan fold and thrust belt, North China

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Science China Earth Sciences 2019年第7期62卷 1092-1109页

作者： Xiaofei SHI Shaofeng LIU Chengfa LIN State Key laboratory of Geological Processes and Mineral resources and School of geosciences and resources China University of Geosciences (Beijing)

The northwestward subduction of the Izanagi Plate beneath the eastern Eurasian Plate during the Late Mesozoic caused a series of compressional deformation events in the Yanshan fold and thrust belt(YFTB), but the tectonic deformation timing, tectonic properties and relationship between tectonic uplift and sediment accumulation in the intermontane basins continue to be debated. For this reason, the sedimentology, sediment provenance, and basin structure of the Qianjiadian Basin(QJB) in the northern Beijing region during the Late Jurassic and Early Cretaceous were studied in detail. The results suggest that a fault-propagation fold-type(FPFT) growth structure and growth strata developed on the western edge of the QJB and that the top part of Member 2 and Member 3 of the Tuchengzi Formation are growth strata controlled by the limb rotation mechanism. In two small thrust faults in the QJB, the Mesoproterozoic Xiamaling Formation is thrust over the Tuchengzi Formation, and these faults may have controlled the development of the fault-bend fold-type growth strata. An analysis of the "source-to-sink" process suggests that the hanging wall succession of the Shangyi-Pingquan fault(SPF) was the main source area of the Late Jurassic to early Early Cretaceous strata in the QJB. A zircon206 Pb/238 U age of 140.8±2.4 Ma for the volcanic rocks at the bottom of the FPFT growth strata represents the timing of the initiation of FPFT growth structure development. The discovery of the FPFT growth structure and growth strata in the QJB indicate that the QJB was an intermontane flexural basin controlled by fold and thrust structures during the early Early Cretaceous. Near the E-W-trending SPF, the NE-SW-trending Qianjiadian thrust fault(QJTF) and two small intrabasinal thrust faults may constitute a unified right-lateral strike-slip system that formed in response to the northwestward flat subduction of the Izanagi Plate beneath the East Asian continent during the Jurassic-Early Cretaceou

关键词： Yanshan fold and thrust belt Qianjiadian Basin Tuchengzi Formation Growth structure Growth strata Izanagi Plate

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

Characteristics of particle fluxes in the Prydz Bay polynya, Eastern Antarctica

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Science China Earth Sciences 2019年第4期62卷 657-670页

作者： Zhengbing HAN Chuanyu HU Weiping SUN Jun ZHAO Jianming PAN Gaojing FAN Haisheng ZHANG Second Institute of Oceanography Ministry of Natural Resources Key laboratory of Marine Ecosystem and Biogeochemistry State Oceanic Administration China University of geosciences

The settling of particulate carbon in seawater is a key component of the ocean carbon cycle. We deployed a set of sediment trap in the polynya of Prydz Bay from December 2010 to December 2011 to investigate the seasonal variations in particle fluxes. There was a clear seasonal variation in the particle fluxes, with maximum and minimum fluxes recorded during the summer and winter, respectively. The average total flux over the sampling period was 193.58 mg m^(-2)d^(-1), and the average fluxes of organic carbon(C_(org)), inorganic carbon(C_(inorg)), and biogenic silica(Si_(bio)) were 721.78, 28.67, and 2382.80 μmol m^(-2) d^(-1), respectively. Si_(bio)was the main contributor to the total mass flux, and strongly correlated with C_(org). The high Si_(bio)/C_(org)molar ratios(>1) suggest that C_(org)was transported to deep sea in association with Si_(bio). By comparing remote sensing data of sea ice and chlorophyll in the upper water column, we found that the dynamics of carbon fluxes were closely related to changes in sea ice. Algae in sea ice may have a key role in biological pump processes in early summer. Apart from the ice algae bloom period, variations in carbon fluxes generally corresponded with phytoplankton blooms in the upper water. The ballast effect controlled the particle settling velocity and the efficiency of the biological pump. Sea ice rafts initiated the first particle export event and enhanced the particle settling efficiency during melting period. As diatoms might become less dominant in the ice-free area, sea ice loss may cause the efficiency of the biological pump efficiency to decrease over the long term.

关键词： Prydz Bay Particle fluxes Polynya Ballast effect Biological pump efficiency