Interactions between basaltic melt and orthopyroxenite(Opx)were investigated to gain a better understanding of the consequences of the residence and transport of ocean island basalts(OIBs)within the mantle.The experim...Interactions between basaltic melt and orthopyroxenite(Opx)were investigated to gain a better understanding of the consequences of the residence and transport of ocean island basalts(OIBs)within the mantle.The experiments were conducted using a DS-3600 six-anvil apparatus at 3.0–4.5 GPa and 1300–1450℃.The basaltic melt and Opx coexisted at local equilibrium at these pressures and temperatures;the initial melts dissolved Opx,which modified their chemical composition,and clinopyroxene(Cpx)precipitated with or without garnet(Grt).The trace-element contents of Grt,Cpx,and melt were measured and the mineral–melt distribution coefficients(D)of Cpx–melt and Grt–melt were calculated,which can be used to assess the distribution of trace elements between basalt and minerals in the mantle.Two types of reaction rim were found in the experimental products,Cpx,and Cpx+Grt;this result indicates that residual rocks within the mantle should be pyroxenite or garnet pyroxenite.Both rock types are found in mantle xenoliths from Hawaii,and the rare-earth-element(REE)pattern of Cpx in these mantle pyroxenites matches those of Cpx in the experimental reaction rims.Furthermore,residual melts in the experimental products plot in similar positions to Hawaiian high-SiO_(2)OIBs on major-element Harker diagrams,and their trace-element patterns show the signature of residual Grt,particularly in runs at1350℃ and 4.0–4.5 GPa.Trace-element concentrations of the experimental residual melts plot in similar positions to the Hawaiian OIBs on commonly used discrimination diagrams(Ti vs.Zr,Cr vs.Y,Cr vs.V,Zr/Y vs.Zr,and Ti/Y vs.Nb/Y).These results indicate that reaction between basaltic melt and pyroxenite might contribute to the generation of Hawaiian high-SiO2 OIBs and account for their chemical variability.展开更多
Recently, we focused on the Darbut and Karamay ophiolitic m41anges in West Junggar of the Central Asian Orogenic Belt (CAOB, SengOr et al., 1993; Windley et al., 2007; Xiao and Santosh, 2014), and made much progress...Recently, we focused on the Darbut and Karamay ophiolitic m41anges in West Junggar of the Central Asian Orogenic Belt (CAOB, SengOr et al., 1993; Windley et al., 2007; Xiao and Santosh, 2014), and made much progress. This study was supported by the National Nature Science Foundation of China (No. 41303027) and Special Fund for Basic Scientific Research of Central Colleges Project (No. 2014G1271058). The achievements are illustrated as follows.展开更多
Understanding the origin of ocean island basalts(OIB) has important bearings on Earth's deep mantle.Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes mat...Understanding the origin of ocean island basalts(OIB) has important bearings on Earth's deep mantle.Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB's formation, its exact fraction in OIB's mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. Here we show, through theoretical calculation, that unlike many known proxies, triple oxygen isotope compositions(i.e.D^(17 )O) in olivine samples are not affected by crystallization and partial melting. This unique feature, therefore, allows olivine D^(17 )O values to identify subducted oceanic crusts in OIB's mantle source. Furthermore, the fractions of subducted ocean sediments and hydrothermally altered oceanic crust in OIB's mantle source can be quantified using their characteristic D^(17 )O values. Based on published D^(17 )O data, we estimated the fraction of subducted oceanic crust to be as high as 22.3% in certain OIB, but the affected region in the respective mantle plume is likely to be limited.展开更多
The compositional variability of ocean island basalts(OIBs)is thought to reflect partial melting of a lithologicallyheterogeneous mantle source dominated by either pyroxenite or peridotite.The Pohnpei Island in Micron...The compositional variability of ocean island basalts(OIBs)is thought to reflect partial melting of a lithologicallyheterogeneous mantle source dominated by either pyroxenite or peridotite.The Pohnpei Island in Micronesia,which is associated with the Caroline hotspot,is suggested to have been generated from partial melting of a pyroxenite-rich mantle.To examine this hypothesis,we present new major-and trace-element compositions of olivine phenocrysts in basalts from the island.The olivines exhibit large systematic inter-and intra-crystalline compositional variability.In Sample DS1,olivines record compositional zonation,in which cores have relatively high Fo(77–85),Ni(550×10^(-6 )–2392×10^(-6 )),and Fe/Mn ratios(66–82),whereas rims have lower Fo(71–78),Ni(526×10^(-6 )–1537×10^(-6 )),and Fe/Mn ratios(51–62).By contrast,olivines within other samples preserve no clear compositional zonation,exhibiting similar or slightly lower Fo values(66–78),Ni contents(401×10^(-6 )–1268×10^(-6 )),and Fe/Mn ratios(53–69)as the rims of zoned crystals.The distinct chemical contrast between the two different types of olivine suggests they formed in magma chambers at different depths.Analysis using forward petrological modeling and multi-element indicators(Fe/Mn,Zn/Fe,FC3MS(FeO^(T)/CaO-(3×MgO/SiO^(2))),Mn/Zn,and Ni/(Mg/Fe))of whole-rock samples and high-Fo olivines is inconsistent with a pyroxenite-rich mantle source.We suggest these inconsistencies reflect an influence on the partition coefficients of Ni and Mn between olivine and liquid during melting at variable pressures and temperatures.In addition,magma recharge and mixing within the magmatic plumbing system can change the composition of olivine.We suggest that identification of the mantle source of OIBs in volcanic islands such as the Pohnpei Island using olivine geochemistry should be treated with caution.展开更多
The alkaline oceanic island basalts(OIBs)with under-saturated SiO2 and high contents of CaO and alkaline are usually attributed to mantle sources different from typical tholeiitic OIBs.Based on the results of high pre...The alkaline oceanic island basalts(OIBs)with under-saturated SiO2 and high contents of CaO and alkaline are usually attributed to mantle sources different from typical tholeiitic OIBs.Based on the results of high pressure and temperature experiment study,the genesis of silica under-saturated alkaline basaltic melts could be explained by the role of CO2,thus,the genetic relationship of alkaline basalts with CO2 has become a topic of relevance because it is closely related to the deep carbon cycle.The Magellan Seamount chain in the West Pacific Seamount Province has wide distribution of alkali basalts.For the first time,we collected alkaline basalt samples from the Kocebu Seamount of the Magellan Seamount chain and found that magmatic apatites widely occur in the less evolved volcanic rock samples,and the high contents of phosphorus should be a feature of the alkaline OIBs of the Magellan Seamounts.Compared with typical OIBs,these alkaline volcanic rocks have higher CaO and P2O5,lower SiO2 content,negative anomaly of high field strength elements(HFSEs),more distinctly negative anomaly of potassium(K)and the ubiquity of titanaugite,indicating a CO2-rich mantle source.Based on the relatively high K2O and TiO2 contents and La/Yb ratio and low MgO content of these alkaline rocks,we suggest that the volcanic rocks of the Magellan Seamounts are originated from carbonated eclogites derived possibly from ancient subducted altered oceanic crust.展开更多
基金Natural Science Foundations of China(Grant Nos.41502057 and 41472065)Foundations of Suzhou University(Nos.2019ZD46,2015jb01 and 2015jb07).
文摘Interactions between basaltic melt and orthopyroxenite(Opx)were investigated to gain a better understanding of the consequences of the residence and transport of ocean island basalts(OIBs)within the mantle.The experiments were conducted using a DS-3600 six-anvil apparatus at 3.0–4.5 GPa and 1300–1450℃.The basaltic melt and Opx coexisted at local equilibrium at these pressures and temperatures;the initial melts dissolved Opx,which modified their chemical composition,and clinopyroxene(Cpx)precipitated with or without garnet(Grt).The trace-element contents of Grt,Cpx,and melt were measured and the mineral–melt distribution coefficients(D)of Cpx–melt and Grt–melt were calculated,which can be used to assess the distribution of trace elements between basalt and minerals in the mantle.Two types of reaction rim were found in the experimental products,Cpx,and Cpx+Grt;this result indicates that residual rocks within the mantle should be pyroxenite or garnet pyroxenite.Both rock types are found in mantle xenoliths from Hawaii,and the rare-earth-element(REE)pattern of Cpx in these mantle pyroxenites matches those of Cpx in the experimental reaction rims.Furthermore,residual melts in the experimental products plot in similar positions to Hawaiian high-SiO_(2)OIBs on major-element Harker diagrams,and their trace-element patterns show the signature of residual Grt,particularly in runs at1350℃ and 4.0–4.5 GPa.Trace-element concentrations of the experimental residual melts plot in similar positions to the Hawaiian OIBs on commonly used discrimination diagrams(Ti vs.Zr,Cr vs.Y,Cr vs.V,Zr/Y vs.Zr,and Ti/Y vs.Nb/Y).These results indicate that reaction between basaltic melt and pyroxenite might contribute to the generation of Hawaiian high-SiO2 OIBs and account for their chemical variability.
基金supported by the National Nature Science Foundation of China(No.41303027)Special Fund for Basic Scientific Research of Central Colleges Project(No.2014G1271058)
文摘Recently, we focused on the Darbut and Karamay ophiolitic m41anges in West Junggar of the Central Asian Orogenic Belt (CAOB, SengOr et al., 1993; Windley et al., 2007; Xiao and Santosh, 2014), and made much progress. This study was supported by the National Nature Science Foundation of China (No. 41303027) and Special Fund for Basic Scientific Research of Central Colleges Project (No. 2014G1271058). The achievements are illustrated as follows.
基金funding supports from the strategic priority research program (B) of Chinese Academy ofSciences (XDB18010104) and (XDB18010100)Chinese NSF Project (41490635)
文摘Understanding the origin of ocean island basalts(OIB) has important bearings on Earth's deep mantle.Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB's formation, its exact fraction in OIB's mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. Here we show, through theoretical calculation, that unlike many known proxies, triple oxygen isotope compositions(i.e.D^(17 )O) in olivine samples are not affected by crystallization and partial melting. This unique feature, therefore, allows olivine D^(17 )O values to identify subducted oceanic crusts in OIB's mantle source. Furthermore, the fractions of subducted ocean sediments and hydrothermally altered oceanic crust in OIB's mantle source can be quantified using their characteristic D^(17 )O values. Based on published D^(17 )O data, we estimated the fraction of subducted oceanic crust to be as high as 22.3% in certain OIB, but the affected region in the respective mantle plume is likely to be limited.
基金The Resources and Environment Projects of China Ocean Mineral R&D Association under contract No.DY135-E2-2-01the Natural Science Foundation of Shandong Province under contract No.ZR2020QD076
文摘The compositional variability of ocean island basalts(OIBs)is thought to reflect partial melting of a lithologicallyheterogeneous mantle source dominated by either pyroxenite or peridotite.The Pohnpei Island in Micronesia,which is associated with the Caroline hotspot,is suggested to have been generated from partial melting of a pyroxenite-rich mantle.To examine this hypothesis,we present new major-and trace-element compositions of olivine phenocrysts in basalts from the island.The olivines exhibit large systematic inter-and intra-crystalline compositional variability.In Sample DS1,olivines record compositional zonation,in which cores have relatively high Fo(77–85),Ni(550×10^(-6 )–2392×10^(-6 )),and Fe/Mn ratios(66–82),whereas rims have lower Fo(71–78),Ni(526×10^(-6 )–1537×10^(-6 )),and Fe/Mn ratios(51–62).By contrast,olivines within other samples preserve no clear compositional zonation,exhibiting similar or slightly lower Fo values(66–78),Ni contents(401×10^(-6 )–1268×10^(-6 )),and Fe/Mn ratios(53–69)as the rims of zoned crystals.The distinct chemical contrast between the two different types of olivine suggests they formed in magma chambers at different depths.Analysis using forward petrological modeling and multi-element indicators(Fe/Mn,Zn/Fe,FC3MS(FeO^(T)/CaO-(3×MgO/SiO^(2))),Mn/Zn,and Ni/(Mg/Fe))of whole-rock samples and high-Fo olivines is inconsistent with a pyroxenite-rich mantle source.We suggest these inconsistencies reflect an influence on the partition coefficients of Ni and Mn between olivine and liquid during melting at variable pressures and temperatures.In addition,magma recharge and mixing within the magmatic plumbing system can change the composition of olivine.We suggest that identification of the mantle source of OIBs in volcanic islands such as the Pohnpei Island using olivine geochemistry should be treated with caution.
基金the National Natural Science Foundation of China(Nos.91858206,41876040)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA22050101,XDB42020302)+1 种基金the Taishan Scholars Program of Shandong Province(No.tsqn201909157),Senior User Project of R/V Kexue(No.KEXUE2018G09)the Laboratory for Marine Geology,Qingdao National Laboratory for Marine Science and Technology(No.MGQNLMTD201806)。
文摘The alkaline oceanic island basalts(OIBs)with under-saturated SiO2 and high contents of CaO and alkaline are usually attributed to mantle sources different from typical tholeiitic OIBs.Based on the results of high pressure and temperature experiment study,the genesis of silica under-saturated alkaline basaltic melts could be explained by the role of CO2,thus,the genetic relationship of alkaline basalts with CO2 has become a topic of relevance because it is closely related to the deep carbon cycle.The Magellan Seamount chain in the West Pacific Seamount Province has wide distribution of alkali basalts.For the first time,we collected alkaline basalt samples from the Kocebu Seamount of the Magellan Seamount chain and found that magmatic apatites widely occur in the less evolved volcanic rock samples,and the high contents of phosphorus should be a feature of the alkaline OIBs of the Magellan Seamounts.Compared with typical OIBs,these alkaline volcanic rocks have higher CaO and P2O5,lower SiO2 content,negative anomaly of high field strength elements(HFSEs),more distinctly negative anomaly of potassium(K)and the ubiquity of titanaugite,indicating a CO2-rich mantle source.Based on the relatively high K2O and TiO2 contents and La/Yb ratio and low MgO content of these alkaline rocks,we suggest that the volcanic rocks of the Magellan Seamounts are originated from carbonated eclogites derived possibly from ancient subducted altered oceanic crust.