Volcanic rocks both from the northern East China Sea （NECS） shelf margin and the northern Okinawa Trough are subalkaline less aluminous,and lower in High Field Strength Elements （HFSE）.These rocks are higher in La...Volcanic rocks both from the northern East China Sea （NECS） shelf margin and the northern Okinawa Trough are subalkaline less aluminous,and lower in High Field Strength Elements （HFSE）.These rocks are higher in Large Ion Lithophile Elements （LILE）,thorium and uranium contents,positive lead anomalies,negative Nb-Ta anomalies,and enrichment in Light Rare Earth Elements （LREE）.Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt （MORB）,and rhyolites from the northern Okinawa Trough have the highest 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios.The NECS shelf margin basalts have lower 87 Sr/ 86 Sr ratios,ε N d and σ 18 O than the northern Okinawa Trough silicic rocks.According to 40 K– 40 Ar isotopic ages of basalts from the NECS shelf margin,rifting of the Okinawa Trough may have been active since at least 3.65–3.86 Ma.The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere.The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough,and the formation of basaltic magmas closely relates to the thinning of continental crust.The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough,which could have been generated by the interaction of basaltic melt with an enriched crustal component.From the Ryukyu island arc to East China,the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements （HREE）,suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate,and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.展开更多
Mid-ocean ridge basalts （MORBs） from East Pacific Rise （EPR） 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationship...Mid-ocean ridge basalts （MORBs） from East Pacific Rise （EPR） 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenoerysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a “clinopyroxene paradox”. The highest magnesium-bearing MORB sample E13-3B （MGO=9.52%） is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13-3B only by fractional crystallization at pressure 〉4±1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber （at pressure -1 kbar）. The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization （PEC）. The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at 〉4±1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene＋plagioclase＋olivine crystallization at 〉4±1 kbar to mainly olivine＋plagioclase crystallization at 〈1 kbar, which contributes to the explanation of the “clinopyroxene paradox”.展开更多
To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprob...To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprobe, and in suit Sr and Ba contents of plagioclase analysed by LA-ICPMS were chosen for fingerprinting plagioclases of different provenances. Results indicate an overall homogeneous composition for each of the mineral phases except for plagioclase phenocrysts which have a wide range of composition(An=39~88). Plagioclase crystals characterized by An contents of >70 are not in equilibrium with their whole-rock compositions, and coarse-sieved plagioclase phenocryst interiors record high An contents(>70) and Sr/Ba ratios(>7), which are similar to the those of plagioclase crystals in basalt. Therefore, these crystals must have been introduced to the rhyolitic magma from a more mafic source. Equilibrium temperatures estimated using orthopyroxene-liquid, iron–titanium oxide, titanium-in-quartz and amphibole geothermometers show consistent values ranging from 792 to 869℃. The equilibrium pressure calculated using amphibole compositions is close to 121 MPa which corresponds to an approximate depth of 4 km. The fO_2 conditions estimated from Fe-Ti oxides and amphiboles plot slightly above the NNO buffer, which indicates that the rock formed under more oxidized conditions. Our results suggests that petrogenesis of the rhyolite due to basaltic magma ascend with the high An and Sr/Ba plaigoclases from deep magma chamber into the shallow chamber where the fractional crystallization and crustal assimilation happened. It also indicates that a two-layer magma chamber structure may occur under the southwestern Okinawa Trough.展开更多
In 2008-2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R＆D Association （COMRA）. Samples were ana- lyzed by gas c...In 2008-2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R＆D Association （COMRA）. Samples were ana- lyzed by gas chromatography-mass spectrometer （GC-MS）, revealing the main organic constituents of hy- drothermal barnacle and sediment to be fatty acids and alkylbenzenes. N-alkanes which possessed obvious even carbon advantage were also detected in hydrothermal sediment. The high concentrations of aromatic compounds might be the result of macromolecular thermal alteration. Microorganism in the submarine hydrothermal ecosystem, especially those related to sulfur metabolism, might be the source of the high con- centrations of fatty acids detected in these samples. In high temperature and high pressure hydrothermal environments, n-alkanes which possessed obvious even carbon advantage might originate from thermal alteration of carboxylic acids and other lipid compounds.展开更多
Sediment samples obtained from the South Mid-Atlantic Ridge were studies by gas chromatography-mass spectrometer （GC-MS） for the abundance and distributions of total fatty acids （TFAs）. Approximately 34 fatty acid...Sediment samples obtained from the South Mid-Atlantic Ridge were studies by gas chromatography-mass spectrometer （GC-MS） for the abundance and distributions of total fatty acids （TFAs）. Approximately 34 fatty acids were identified, with the chain-lengths ranging from C12 to C30. The total concentrations of TFAs （∑TFA） ranged from 7.15 to 30.09 μgg-l dry sediment, and ∑TFA was weakly correlated with bitumen content （R2=0.69）. The ∑TFA of samples around hydrothermal areas were significantly higher than that of samples away from hydrothermal areas, indicating intense primary production and large biomass in the hydro- thermal areas, and suggesting a close relationship between hydrothermal activity and ∑TFA of samples. The characteristics of the TFA composition in the present study are rich in monounsaturated fatty acids and lacking in polyunsaturated fatty acids, and the ra- tios between the concentrations of monounsaturated fatty acids and ∑TFAs in samples close to the hydrothermal areas, are about 0.8, but for samples far from the hydrothermal areas, they are only about 0.5. Several fatty acids （e.g., a/iC15：0 and C16：1co7）, which are signature biomarkers for sulfur-metabolizing bacteria, show the same distribution trend as ∑TFA of samples, further highlighting the close relationship between fatty acid content and hydrothermal activity and/or hydrothermal communities. The metabolic activities of hydrothermal communities, especially those of microorganisms, are likely the main source of fatty acids in samples.展开更多
A 43 cm long E271 sediment core collected near the East Pacific Rise（EPR） at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material af...A 43 cm long E271 sediment core collected near the East Pacific Rise（EPR） at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition.E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal,and Fe-Mn oxide by a series of chemical procedures, clay minerals（〈2 μm） were investigated by X-ray diffraction,chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils（diatoms or radiolarians）, hydrothermal fluids, or detrital mineral phases. And their δ30 Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios（a proxy for overall REE/Fe ratio） in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE.展开更多
There has been much recent interest in the origin of intermediate lava and several hypotheses are: 1) direct melting of the mantle under water-saturated conditions, 2) partial melting of altered crust, 3) fractional c...There has been much recent interest in the origin of intermediate lava and several hypotheses are: 1) direct melting of the mantle under water-saturated conditions, 2) partial melting of altered crust, 3) fractional crystallization of parent magma, and 4) magma mixing of mafic magmas with dacitic/rhyolitic magmas. Volcanic rocks series ranging from basaltic andesite to dacite(SiO_2 ranges from 53.8 to 63.0 wt.%) from the eastern Manus Basin were detected for major and trace element compositions to understand their origin. Low H_2O contents, positive correlations of La-SiO_2 and Yb-SiO_2, oxygen isotope data and the indistinct change of trace element concentrations in oscillatory zoning of plagioclase phenocrysts rule out the models in which silicic lava results from direct melting of hydrous mantle, partial melting of altered oceanic crust or gabbros, and magma mixing, respectively. Besides, the geochemical data of whole rock and melt inclusions indicate that fractional crystallization plays a dominant role in generating the intermediate lava with subduction features.展开更多
10 samples of sediments obtained from the South Mid-Atlantic Ridge were measured for the abundances and distributions of polycyclic aromatic compounds（PAHs）. The total concentrations of PAHs（∑PAHs） ranged from 2....10 samples of sediments obtained from the South Mid-Atlantic Ridge were measured for the abundances and distributions of polycyclic aromatic compounds（PAHs）. The total concentrations of PAHs（∑PAHs） ranged from 2.768 to 9.826 μg/g dry sediment. The ∑PAHs was higher in sample 22V-TVG10 and sample 26V-TVG05 which were close to hydrothermal fields, with the lowest value in sample 22V-TVG14 which was farthest from hydrothermal fields, suggesting a probable hydrothermal origin of ∑PAHs of samples. Approximately nine kinds of PAHs were identified, and low molecular mass tricyclic and tetracyclic aromatic compounds were predominant in the samples. The concentrations of fluoranthene which were typical as hydrothermal alteration compounds were the highest among PAHs with dry weight between 0.913–3.157 μg/g. The phenanthrene homologue was most abundant in the samples, and the ratios between parent phenanthrene and methylphenanthrene which probably reflected the degree of hydrothermal alteration ranged from 0.097 to 1.602. The sample 22V-TVG10 possessing a maximum ratio value showed the intense influence of the hydrothermal alteration on this sample, which might further imply that PAHs in sediments were mainly derived from the hydrothermal alteration.展开更多
The East Pacific Rise(EPR)is a typical fast spreading ridge.To gain a better understanding of the magmatism under ridges,Mid Ocean Ridge Basalts(MORBs)with remarkably heterogeneous compositions are obtained from(EPR)1...The East Pacific Rise(EPR)is a typical fast spreading ridge.To gain a better understanding of the magmatism under ridges,Mid Ocean Ridge Basalts(MORBs)with remarkably heterogeneous compositions are obtained from(EPR)1?–2?S and multielement geochemical and radioisotope analyses are conducted.Results show that these MORBs have wide variation ranges in trace element concentrations and isotopic ratios.Sample 07 has low concentrations of incompatible elements,and very low ^(87)Sr/^(86)Sr,and high ^(143)Nd/^(144)Nd from 0.70213 to 0.702289 and 0.513234 to 0.513289,respectively.However,other samples show enrichment in incompatible elements to varying degrees,and medium values of ^(87)Sr/^(86)Sr and ^(143)Nd/^(144)Nd from 0.702440 to 0.702680 and 0.513086to 0.513200,respectively.This study proposes that one depleted source and two enriched sources contribute to the formation of MORBs from EPR 1?–2?S.Samples 02 and 10 are formed by mixing between one enriched source and one depleted source,while sample 07 is crystallized from the depleted source with no mixing process involved.However,the formation of samples 06 and 11are different,and thus further research is required to determine genesis.展开更多
Fe-Si-Mn-oxyhydroxide encrustations at the East Pacific Rise （EPR） near 13°N were analyzed using the scanning electron microscope （SEM） with an energy dispersive spectrometer （EDS）. These encrustations are ...Fe-Si-Mn-oxyhydroxide encrustations at the East Pacific Rise （EPR） near 13°N were analyzed using the scanning electron microscope （SEM） with an energy dispersive spectrometer （EDS）. These encrustations are mainly composed of amorphous Fe- Si-Mn-oxyhydroxides forming laminated, spherical, porous aggregates with some biodetritus, anhydrite, nontronite, and feldspar particles. Anhydrite particles and nontronite crystals in the Fe-Si-Mn-oxyhydroxide encrustations imply that the Fe-Si-Mn-oxyhy- droxide may have formed under relatively low- to high-temperature hydrothermal conditions. The Fe-Si-Mn-oxyhydroxide encrusta- tions on pillow basalts are 1-2mm thick. The growth rate of ferromanganese crusts in the survey area suggests that these encrusta- tions are an unlikely result of hydrogenic deposition alone having a hydrothermal and （Fe/Mn ratio up to 7.7 and Fe/（Fe＋Mn＋A1） ratio exceeding 0.78） hydrogenic origin （0.22 Fe/Mn ratio close to the mean value of 0.7 for open-ocean seamount crusts）. The varying Fe/Mn ratios indicate that the Fe-Si-Mn-oxyhydroxide encrustations have formed through several stages of seafloor hydrother- malism. It is suggested that, at the initial formation stage, dense Fe-Si-oxyhydroxides with low Mn content deposit from a relatively reducing hydrothermal fluid, and then the loose Fe-Si-Mn-oxyhydroxides deposit on the Fe-Si-oxyhydroxides. As the oxidation degree of hydrothermal fluid increases and Si-oxide is inhibited, Mn-oxide will precipitate with Fe-oxyhydroxides.展开更多
This paper reports silicon and oxygen isotopes of 20 kinds of igneous rocks and their major elements from the eastern Manus Basin. Combining silicon and oxygen isotopic data from other studies, we suppose that both δ...This paper reports silicon and oxygen isotopes of 20 kinds of igneous rocks and their major elements from the eastern Manus Basin. Combining silicon and oxygen isotopic data from other studies, we suppose that both δ30Si and δ18O values increase with the increasing of SiO2 content. It means that the fractionation of silicon and oxygen isotopes are affected by the silica content. The positive correlation between CaO/Al2O3 ratios and MgO and that between Si/Al and SiO2 content indicate that clinopyroxene is the predominant mineral phase in our samples. We suppose that the fractionation of silicon and oxygen isotopes are influenced by mineral fractional crystallization. Probably, it is due to their different silicon and oxygen bridges. In this study, the δ30Simean value=-0.17‰±0.17‰ and δ18Omean value= +6.07‰±0.57‰ are higher than normal δ30Si and δ18O values of mantle, and we propose that these igneous rocks in the eastern Manus Basin are affected by hydrothermal alteration.展开更多
Utilizing Si, Fe and Mn concentrations within the end-member PACMANUS hydrothermal fluid, Si-Fe-Mn-H2O Pourbaix diagrams were constructed at 300℃and 25℃. ThePourbaix diagrams show that the main Si, Fe and Mn oxides ...Utilizing Si, Fe and Mn concentrations within the end-member PACMANUS hydrothermal fluid, Si-Fe-Mn-H2O Pourbaix diagrams were constructed at 300℃and 25℃. ThePourbaix diagrams show that the main Si, Fe and Mn oxides species precipitating from the hydrothermal fluid were SiO2, Fe（OH）3, Fe3（OH）8, Mn3O4, and Mn2O3at 25℃. During mixing of hydrothermal fluid with seawater, SiO2 precipitated earlier than Fe-Mn-oxyhydroxides because of the lower stability boundary. Then Fe（OH）2 precipitated first, followed by Fe3（OH）8 and Fe（OH）3, and last, small amounts of Mn3O4 and Mn2O3 precipitated. Fe（OH）3was readily de-posited in alkaline solution with little influence by Eh. There were many Si-Fe-Mn-concentric particles in the polished sections of the massive precipitates collected from PACMANUS. In the concentric nucleus and ellipsoid, Si oxides precipitated first before the hydrothermal fluid had mixed with seawater. In the concen-tric nucleus, after the precipitation of Si oxides, the increase of pH and Eh promoted the precipitation of Mn oxides around the Si oxides. In the large ellipsoid, the precipitation of Fe was divided into two periods. In the early period, increase of pH value of hydrothermal fluid produced by low-temperature convection and an input of a small volume of seawater promoted a small amount of Fe（OH）3 to precipitate in the Si-rich core. In the late period, after complete mixing with seawater and the resultant fluid was close to neutral or slightly alkaline in pH, Fe（OH）3was easily precipitated from the solution and distributed around the Si-rich core.展开更多
In this study, 13 groups of silicon and oxygen isotopes and major elements of the basalts near the East Pacific Rise 13°N are used to study the fractionation of silicon and oxygen isotopes. Among these data, δ30...In this study, 13 groups of silicon and oxygen isotopes and major elements of the basalts near the East Pacific Rise 13°N are used to study the fractionation of silicon and oxygen isotopes. Among these data, δ30Si values of basalts vary from -0.4%o to 0.2%o with a mean value of δ30Si of （-0.18±0.22）%o. The δ180 values range from 4.1%o to 6.4%o with a mean δ180 value of （＋5.35±0.73） %0. Since the δ30Si values increase in the series of basalt-basaltic andesite- andesite, and δ180 values display a positive correlation with the SiO2 content, we propose that the fractionation of silicon and oxygen isotopes is influenced by the SiO2 content in igneous rocks. Compared with the igneous rocks from Manus Basin with clinopyroxene as their dominant mineral phase, MORBs in this study containing olivine and plagioclase as primary minerals have lower δ180 and δ30Si values, indicating that the fractionation of silicon and oxygen isotopes is also affected by different Si-O bridges in silicate minerals. Furthermore, our samples from the EPR are defined as E-MORB based on K/Ti ratios. Probably, the difference in δ30Si and δ30O between our samples and a normal MORB are cause by the enriched components in E-MORBs.展开更多
The Okinawa Trough（OT） is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic gla...The Okinawa Trough（OT） is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic glass in the OT and discussed the effects of different magmatic sources, evolution, and subducted components in basalts. Our results showed that the middle and southern regions of the OT exhibit characteristics consistent with an iron-rich tholeiite series. Trace element proportions conform to the typical spider diagram pattern characteristic of back-arc basin basalts, rich in large ion lithophile elements（LILEs） including Rb, Ba, Pb, U, and Th, while depleted in high field-strength elements（HFSEs） including Nb, Ta, Zr, Hf, and Ti. The distribution of rare earth elements（REEs） is also consistent with enrichment by right-leaning light rare earth elements（LREEs）.The addition of enriched mantle type I（EMI） materials as well as mantle heterogeneity may have led to variable degrees of enrichment in different regions. The magma source of the middle trough has undergone crystallization towards pyroxene, while development of plagioclase was restricted partly, and the crystallization of spinel and olivine ceased altogether. At the same time, crystallization of the southern OT magma source was dominated by olivine and including the formation of plagioclase, pyroxene, and magnetite（or titanomagnetite）. Finally, the results of this study showed that 90% Th, 95% Ba in the southern basalt, 50%–70% Th and 70%–90% Ba in the middle basalt originated from subducted component. Different subducted component influence may be due to different subduction zone structural feature.展开更多
基金The Pilot Project of Knowledge Innovation Project,Chinese Academy of Sciences under contract Nos KZCX2- YW-211 and KZCX3-SW-223the National Natural Science Foundation of China under contract Nos 40830849 and 40976027+1 种基金Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract No.JQ200913the National Major Fundamental Research and Development Project under contract No.G2000046701
文摘Volcanic rocks both from the northern East China Sea （NECS） shelf margin and the northern Okinawa Trough are subalkaline less aluminous,and lower in High Field Strength Elements （HFSE）.These rocks are higher in Large Ion Lithophile Elements （LILE）,thorium and uranium contents,positive lead anomalies,negative Nb-Ta anomalies,and enrichment in Light Rare Earth Elements （LREE）.Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt （MORB）,and rhyolites from the northern Okinawa Trough have the highest 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios.The NECS shelf margin basalts have lower 87 Sr/ 86 Sr ratios,ε N d and σ 18 O than the northern Okinawa Trough silicic rocks.According to 40 K– 40 Ar isotopic ages of basalts from the NECS shelf margin,rifting of the Okinawa Trough may have been active since at least 3.65–3.86 Ma.The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere.The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough,and the formation of basaltic magmas closely relates to the thinning of continental crust.The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough,which could have been generated by the interaction of basaltic melt with an enriched crustal component.From the Ryukyu island arc to East China,the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements （HREE）,suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate,and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.
基金supported in part by the Pilot Project of Knowledge Innovation Project,Chinese Academy of Sciences(n.:KZCX3-SW-223 and KZCX2-YW-211)the Special Foundation for the Eleventh Five Plan of COMRA(no.:DYXM-115-02-1-03).
文摘Mid-ocean ridge basalts （MORBs） from East Pacific Rise （EPR） 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenoerysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a “clinopyroxene paradox”. The highest magnesium-bearing MORB sample E13-3B （MGO=9.52%） is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13-3B only by fractional crystallization at pressure 〉4±1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber （at pressure -1 kbar）. The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization （PEC）. The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at 〉4±1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene＋plagioclase＋olivine crystallization at 〉4±1 kbar to mainly olivine＋plagioclase crystallization at 〈1 kbar, which contributes to the explanation of the “clinopyroxene paradox”.
基金supported by the National Key Basic Research Program of China(No.2013CB429700)the National Natural Science Foundation of China(Nos.41325021 and 41306053)+8 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA11030302)the Special Fund for the Taishan Scholar Program of Shandong Province(No.ts201511061)the AoShan Talents Program Supported by Qingdao National Laboratory for Marine Science and Technology(No.2015ASTP-0S17)the Innovative Talent Promotion Program(No.2012RA2191)the Science and Technology Development Program of Shandong Province(No.2013GRC31502)the Scientific and Technological Innovation Project Financially Supported by Qingdao National Laboratory for Marine Science and Technology(No.2015ASKJ03)the National High Level Talent Special Support Programthe CAS/SAFEA International Partnership Program for Creative Research Teamsthe Qingdao Collaborative Innovation Center of Marine Science and Technology
文摘To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprobe, and in suit Sr and Ba contents of plagioclase analysed by LA-ICPMS were chosen for fingerprinting plagioclases of different provenances. Results indicate an overall homogeneous composition for each of the mineral phases except for plagioclase phenocrysts which have a wide range of composition(An=39~88). Plagioclase crystals characterized by An contents of >70 are not in equilibrium with their whole-rock compositions, and coarse-sieved plagioclase phenocryst interiors record high An contents(>70) and Sr/Ba ratios(>7), which are similar to the those of plagioclase crystals in basalt. Therefore, these crystals must have been introduced to the rhyolitic magma from a more mafic source. Equilibrium temperatures estimated using orthopyroxene-liquid, iron–titanium oxide, titanium-in-quartz and amphibole geothermometers show consistent values ranging from 792 to 869℃. The equilibrium pressure calculated using amphibole compositions is close to 121 MPa which corresponds to an approximate depth of 4 km. The fO_2 conditions estimated from Fe-Ti oxides and amphiboles plot slightly above the NNO buffer, which indicates that the rock formed under more oxidized conditions. Our results suggests that petrogenesis of the rhyolite due to basaltic magma ascend with the high An and Sr/Ba plaigoclases from deep magma chamber into the shallow chamber where the fractional crystallization and crustal assimilation happened. It also indicates that a two-layer magma chamber structure may occur under the southwestern Okinawa Trough.
基金The National Key Basic Research Program of China under contract No.2013CB429700National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02 and DY125-11-R-05+1 种基金Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract No.JQ200913the National Natural Science Foundation of China under contract Nos 40830849,40976027and 40906029
文摘In 2008-2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R＆D Association （COMRA）. Samples were ana- lyzed by gas chromatography-mass spectrometer （GC-MS）, revealing the main organic constituents of hy- drothermal barnacle and sediment to be fatty acids and alkylbenzenes. N-alkanes which possessed obvious even carbon advantage were also detected in hydrothermal sediment. The high concentrations of aromatic compounds might be the result of macromolecular thermal alteration. Microorganism in the submarine hydrothermal ecosystem, especially those related to sulfur metabolism, might be the source of the high con- centrations of fatty acids detected in these samples. In high temperature and high pressure hydrothermal environments, n-alkanes which possessed obvious even carbon advantage might originate from thermal alteration of carboxylic acids and other lipid compounds.
基金supported by the National Key Basic Research Program of China (Grant No. 2013CB429700)National Special Fund for the 12th Five Year Plan of COMRA (Grant Nos. DY125-12-R-02, DY125-12-R-05, DY125- 11-R-05)+2 种基金National Natural Science Foundation of China (Grant Nos. 41325021, 40830849, 40976027)Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA11030302)the Shandong Province Natural Science Foundation of China for Distinguished Young Scholars (Grant No. JQ200913)
文摘Sediment samples obtained from the South Mid-Atlantic Ridge were studies by gas chromatography-mass spectrometer （GC-MS） for the abundance and distributions of total fatty acids （TFAs）. Approximately 34 fatty acids were identified, with the chain-lengths ranging from C12 to C30. The total concentrations of TFAs （∑TFA） ranged from 7.15 to 30.09 μgg-l dry sediment, and ∑TFA was weakly correlated with bitumen content （R2=0.69）. The ∑TFA of samples around hydrothermal areas were significantly higher than that of samples away from hydrothermal areas, indicating intense primary production and large biomass in the hydro- thermal areas, and suggesting a close relationship between hydrothermal activity and ∑TFA of samples. The characteristics of the TFA composition in the present study are rich in monounsaturated fatty acids and lacking in polyunsaturated fatty acids, and the ra- tios between the concentrations of monounsaturated fatty acids and ∑TFAs in samples close to the hydrothermal areas, are about 0.8, but for samples far from the hydrothermal areas, they are only about 0.5. Several fatty acids （e.g., a/iC15：0 and C16：1co7）, which are signature biomarkers for sulfur-metabolizing bacteria, show the same distribution trend as ∑TFA of samples, further highlighting the close relationship between fatty acid content and hydrothermal activity and/or hydrothermal communities. The metabolic activities of hydrothermal communities, especially those of microorganisms, are likely the main source of fatty acids in samples.
基金The National Natural Science Foundation of China under contract No.41325021the National Basic Research Program(973 Program)of China under contract No.2013CB429700+2 种基金the National Special Fund for the 12th Five-Year Plan of COMRA under contract No.DY125-12-R-02the Special Fund for the Taishan Scholar Program of Shandong Province under contract No.ts201511061the Ao Shan Talents Program Supported by Qingdao National Laboratory for Marine Science and Technology under contract No.2015ASTP-0S17
文摘A 43 cm long E271 sediment core collected near the East Pacific Rise（EPR） at 13°N were studied to investigate the origin of smectite for understanding better the geochemical behavior of hydrothermal material after deposition.E271 sediments are typical metalliferous sediments. After removal of organic matter, carbonate, biogenic opal,and Fe-Mn oxide by a series of chemical procedures, clay minerals（〈2 μm） were investigated by X-ray diffraction,chemical analysis and Si isotope analysis. Due to the influence of seafloor hydrothermal activity and close to continent, the sources of clay minerals are complex. Illite, chlorite and kaolinite are suggested to be transported from either North or Central America by rivers or winds, but smectite is authigenic. It is enriched in iron, and its contents are highest in clay minerals. Data show that smectite is most likely formed by the reaction of hydrothermal Fe-oxyhydroxide with silica and seawater in metalliferous sediments. The Si that participates in this reaction may be derived from siliceous microfossils（diatoms or radiolarians）, hydrothermal fluids, or detrital mineral phases. And their δ30 Si values are higher than those of authigenic smectites, which implies that a Si isotope fractionation occurs during the formation because of the selective absorption of light Si isotopes onto Feoxyhydroxides. Sm/Fe mass ratios（a proxy for overall REE/Fe ratio） in E271 clay minerals are lower than those in metalliferous sediments, as well as distal hydrothermal plume particles and terrigenous clay minerals. This result suggests that some REE are lost during the smectite formation, perhaps because their large ionic radii of REE scavenged by Fe-oxyhydroxides preclude substitution in either tetrahedral or octahedral lattice sites of this mineral structure, which decreases the value of metalliferous sediments as a potential resource for REE.
基金supported by the National Key Basic Research Program of China (No. 2013CB429700)the National Natural Science Foundation of China (Nos. 4132 5021, 41306053, 40476044)+8 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (No XDA11030302)the Special Fund for the Taishan Scholar Program of Shandong Province (No. ts201511061)the AoShan Talents Program Supported by Qingdao Nationa Laboratory for Marine Science and Technology (No. 2015 ASTP-0S17)the Innovative Talent Promotion Program (No. 2012RA2191)the Science and Technology Devel opment Program of Shandong Province (No. 2013GRC 31502)the Scientific and Technological Innovation Project Financially Supported by Qingdao National Labora tory for Marine Science and Technology (No. 2015ASKJ 03)the National High Level Talent Special Support Programthe CAS/SAFEA International Partnership Program for Creative Research Teamsthe Qingdao Collaborative Innovation Center of Marine Science and Technology
文摘There has been much recent interest in the origin of intermediate lava and several hypotheses are: 1) direct melting of the mantle under water-saturated conditions, 2) partial melting of altered crust, 3) fractional crystallization of parent magma, and 4) magma mixing of mafic magmas with dacitic/rhyolitic magmas. Volcanic rocks series ranging from basaltic andesite to dacite(SiO_2 ranges from 53.8 to 63.0 wt.%) from the eastern Manus Basin were detected for major and trace element compositions to understand their origin. Low H_2O contents, positive correlations of La-SiO_2 and Yb-SiO_2, oxygen isotope data and the indistinct change of trace element concentrations in oscillatory zoning of plagioclase phenocrysts rule out the models in which silicic lava results from direct melting of hydrous mantle, partial melting of altered oceanic crust or gabbros, and magma mixing, respectively. Besides, the geochemical data of whole rock and melt inclusions indicate that fractional crystallization plays a dominant role in generating the intermediate lava with subduction features.
基金The National Key Basic Research Program of China under contract No.2013CB429700the National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02,DY125-12-R-05 and DY125-11-R-05+2 种基金the National Natural Science Foundation of China under contract Nos 41325021,40830849 and 40976027the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11030302the Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract No.JQ200913
文摘10 samples of sediments obtained from the South Mid-Atlantic Ridge were measured for the abundances and distributions of polycyclic aromatic compounds（PAHs）. The total concentrations of PAHs（∑PAHs） ranged from 2.768 to 9.826 μg/g dry sediment. The ∑PAHs was higher in sample 22V-TVG10 and sample 26V-TVG05 which were close to hydrothermal fields, with the lowest value in sample 22V-TVG14 which was farthest from hydrothermal fields, suggesting a probable hydrothermal origin of ∑PAHs of samples. Approximately nine kinds of PAHs were identified, and low molecular mass tricyclic and tetracyclic aromatic compounds were predominant in the samples. The concentrations of fluoranthene which were typical as hydrothermal alteration compounds were the highest among PAHs with dry weight between 0.913–3.157 μg/g. The phenanthrene homologue was most abundant in the samples, and the ratios between parent phenanthrene and methylphenanthrene which probably reflected the degree of hydrothermal alteration ranged from 0.097 to 1.602. The sample 22V-TVG10 possessing a maximum ratio value showed the intense influence of the hydrothermal alteration on this sample, which might further imply that PAHs in sediments were mainly derived from the hydrothermal alteration.
基金supported by the Special and Frontier Foundation for the Twelve Five Plan of the China Ocean Mineral Resources Research and Development Association (Nos.DY125-22-QY-21 and DY125-12-R-02)
文摘The East Pacific Rise(EPR)is a typical fast spreading ridge.To gain a better understanding of the magmatism under ridges,Mid Ocean Ridge Basalts(MORBs)with remarkably heterogeneous compositions are obtained from(EPR)1?–2?S and multielement geochemical and radioisotope analyses are conducted.Results show that these MORBs have wide variation ranges in trace element concentrations and isotopic ratios.Sample 07 has low concentrations of incompatible elements,and very low ^(87)Sr/^(86)Sr,and high ^(143)Nd/^(144)Nd from 0.70213 to 0.702289 and 0.513234 to 0.513289,respectively.However,other samples show enrichment in incompatible elements to varying degrees,and medium values of ^(87)Sr/^(86)Sr and ^(143)Nd/^(144)Nd from 0.702440 to 0.702680 and 0.513086to 0.513200,respectively.This study proposes that one depleted source and two enriched sources contribute to the formation of MORBs from EPR 1?–2?S.Samples 02 and 10 are formed by mixing between one enriched source and one depleted source,while sample 07 is crystallized from the depleted source with no mixing process involved.However,the formation of samples 06 and 11are different,and thus further research is required to determine genesis.
基金supported by the National Key Basic Research Program of China (2013CB429700)the Shandong Province Natural Science Foundation for Distinguished Young Scholars (JQ200913)+1 种基金the National Natural Science Foundation of China (40830849)the National Special Fund for the Eleventh Five-Year Plan of COMRA (DY125-12-R-02 and DY125-11-R-05)
文摘Fe-Si-Mn-oxyhydroxide encrustations at the East Pacific Rise （EPR） near 13°N were analyzed using the scanning electron microscope （SEM） with an energy dispersive spectrometer （EDS）. These encrustations are mainly composed of amorphous Fe- Si-Mn-oxyhydroxides forming laminated, spherical, porous aggregates with some biodetritus, anhydrite, nontronite, and feldspar particles. Anhydrite particles and nontronite crystals in the Fe-Si-Mn-oxyhydroxide encrustations imply that the Fe-Si-Mn-oxyhy- droxide may have formed under relatively low- to high-temperature hydrothermal conditions. The Fe-Si-Mn-oxyhydroxide encrusta- tions on pillow basalts are 1-2mm thick. The growth rate of ferromanganese crusts in the survey area suggests that these encrusta- tions are an unlikely result of hydrogenic deposition alone having a hydrothermal and （Fe/Mn ratio up to 7.7 and Fe/（Fe＋Mn＋A1） ratio exceeding 0.78） hydrogenic origin （0.22 Fe/Mn ratio close to the mean value of 0.7 for open-ocean seamount crusts）. The varying Fe/Mn ratios indicate that the Fe-Si-Mn-oxyhydroxide encrustations have formed through several stages of seafloor hydrother- malism. It is suggested that, at the initial formation stage, dense Fe-Si-oxyhydroxides with low Mn content deposit from a relatively reducing hydrothermal fluid, and then the loose Fe-Si-Mn-oxyhydroxides deposit on the Fe-Si-oxyhydroxides. As the oxidation degree of hydrothermal fluid increases and Si-oxide is inhibited, Mn-oxide will precipitate with Fe-oxyhydroxides.
基金supported by the National Key Basic Research Program of China (Grant No. 2013CB429700)National Natural Science Foundation of China (Grant Nos. 40976027, 40830849 and 40906029)Shandong Province Natural Science Foundation for Distinguished Young Scholars (Grant No. JQ200913)
文摘This paper reports silicon and oxygen isotopes of 20 kinds of igneous rocks and their major elements from the eastern Manus Basin. Combining silicon and oxygen isotopic data from other studies, we suppose that both δ30Si and δ18O values increase with the increasing of SiO2 content. It means that the fractionation of silicon and oxygen isotopes are affected by the silica content. The positive correlation between CaO/Al2O3 ratios and MgO and that between Si/Al and SiO2 content indicate that clinopyroxene is the predominant mineral phase in our samples. We suppose that the fractionation of silicon and oxygen isotopes are influenced by mineral fractional crystallization. Probably, it is due to their different silicon and oxygen bridges. In this study, the δ30Simean value=-0.17‰±0.17‰ and δ18Omean value= +6.07‰±0.57‰ are higher than normal δ30Si and δ18O values of mantle, and we propose that these igneous rocks in the eastern Manus Basin are affected by hydrothermal alteration.
基金The National Key Basic Research Program of China under contract Nos 2013CB429700the National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02 and DY125-12-R-05+3 种基金the National Natural Science Foundation of China under contract Nos 41325021,40830849,40976027 and 41476044the Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract Nos JQ200913the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11030302the CAS/SAFEA International Partnership Program for Creative Research Teams
文摘Utilizing Si, Fe and Mn concentrations within the end-member PACMANUS hydrothermal fluid, Si-Fe-Mn-H2O Pourbaix diagrams were constructed at 300℃and 25℃. ThePourbaix diagrams show that the main Si, Fe and Mn oxides species precipitating from the hydrothermal fluid were SiO2, Fe（OH）3, Fe3（OH）8, Mn3O4, and Mn2O3at 25℃. During mixing of hydrothermal fluid with seawater, SiO2 precipitated earlier than Fe-Mn-oxyhydroxides because of the lower stability boundary. Then Fe（OH）2 precipitated first, followed by Fe3（OH）8 and Fe（OH）3, and last, small amounts of Mn3O4 and Mn2O3 precipitated. Fe（OH）3was readily de-posited in alkaline solution with little influence by Eh. There were many Si-Fe-Mn-concentric particles in the polished sections of the massive precipitates collected from PACMANUS. In the concentric nucleus and ellipsoid, Si oxides precipitated first before the hydrothermal fluid had mixed with seawater. In the concen-tric nucleus, after the precipitation of Si oxides, the increase of pH and Eh promoted the precipitation of Mn oxides around the Si oxides. In the large ellipsoid, the precipitation of Fe was divided into two periods. In the early period, increase of pH value of hydrothermal fluid produced by low-temperature convection and an input of a small volume of seawater promoted a small amount of Fe（OH）3 to precipitate in the Si-rich core. In the late period, after complete mixing with seawater and the resultant fluid was close to neutral or slightly alkaline in pH, Fe（OH）3was easily precipitated from the solution and distributed around the Si-rich core.
基金The National Key Basic Research Program of China under contract No.2013CB429700National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02 and DY125-11-R-05+1 种基金Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract No.JQ200913the National Natural Science Foundation of China under contract Nos 40830849,40976027 and 40906029
文摘In this study, 13 groups of silicon and oxygen isotopes and major elements of the basalts near the East Pacific Rise 13°N are used to study the fractionation of silicon and oxygen isotopes. Among these data, δ30Si values of basalts vary from -0.4%o to 0.2%o with a mean value of δ30Si of （-0.18±0.22）%o. The δ180 values range from 4.1%o to 6.4%o with a mean δ180 value of （＋5.35±0.73） %0. Since the δ30Si values increase in the series of basalt-basaltic andesite- andesite, and δ180 values display a positive correlation with the SiO2 content, we propose that the fractionation of silicon and oxygen isotopes is influenced by the SiO2 content in igneous rocks. Compared with the igneous rocks from Manus Basin with clinopyroxene as their dominant mineral phase, MORBs in this study containing olivine and plagioclase as primary minerals have lower δ180 and δ30Si values, indicating that the fractionation of silicon and oxygen isotopes is also affected by different Si-O bridges in silicate minerals. Furthermore, our samples from the EPR are defined as E-MORB based on K/Ti ratios. Probably, the difference in δ30Si and δ30O between our samples and a normal MORB are cause by the enriched components in E-MORBs.
基金The National Basic Research Program of China under contract No.2013CB429702the open fund project supported by the Laboratory for Marine Geology,Qingdao National Laboratory for Marine Science and Technology under contract No.MGQNLM-KF201707+4 种基金the National Natural Science Foundation of China under contract Nos 41476044,41325021 and 41306053the Special Fund for the Taishan Scholar Program of Shandong Province under contract No.ts201511061the AoShan Talents Program supported by Qingdao National Laboratory for Marine Science and Technology under contract No.2015ASTP-0S17the Innovative Talent Promotion Program under contract No.2012RA2191the Science and Technology Development Program of Shandong Province under contract No.2013GRC31502
文摘The Okinawa Trough（OT） is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic glass in the OT and discussed the effects of different magmatic sources, evolution, and subducted components in basalts. Our results showed that the middle and southern regions of the OT exhibit characteristics consistent with an iron-rich tholeiite series. Trace element proportions conform to the typical spider diagram pattern characteristic of back-arc basin basalts, rich in large ion lithophile elements（LILEs） including Rb, Ba, Pb, U, and Th, while depleted in high field-strength elements（HFSEs） including Nb, Ta, Zr, Hf, and Ti. The distribution of rare earth elements（REEs） is also consistent with enrichment by right-leaning light rare earth elements（LREEs）.The addition of enriched mantle type I（EMI） materials as well as mantle heterogeneity may have led to variable degrees of enrichment in different regions. The magma source of the middle trough has undergone crystallization towards pyroxene, while development of plagioclase was restricted partly, and the crystallization of spinel and olivine ceased altogether. At the same time, crystallization of the southern OT magma source was dominated by olivine and including the formation of plagioclase, pyroxene, and magnetite（or titanomagnetite）. Finally, the results of this study showed that 90% Th, 95% Ba in the southern basalt, 50%–70% Th and 70%–90% Ba in the middle basalt originated from subducted component. Different subducted component influence may be due to different subduction zone structural feature.
