New versions of the universal Jd-Di exchange clinopyroxene barometer for peridotites,pyroxenites and eclogites,and also garnet barometer for eclogites and peridotites were developed.They were checked using large exper...New versions of the universal Jd-Di exchange clinopyroxene barometer for peridotites,pyroxenites and eclogites,and also garnet barometer for eclogites and peridotites were developed.They were checked using large experimental data sets for eciogitic(~530) and peridotitic systems(〉650).The precision of the universal Cpx barometer for peridotites based on Jd-Di exchange is close to Cr-Tschermal展开更多
The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V.Grib kimberlite pipe(Arkhangelsk Diamond Province,Russia) was studied.Based on petrographic characteristics,the perid...The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V.Grib kimberlite pipe(Arkhangelsk Diamond Province,Russia) was studied.Based on petrographic characteristics,the peridotite xenolith reflects a sheared peridotite.The sheared peridotite experienced a complex evolution with formation of three main mineral assemblages:(1) a relict harzburgite assemblage consist of olivine and orthopyroxene porphyroclasts and cores of garnet grains(Gar1) with sinusoidal rare earth elements(REE) chondrite C1 normalized patterns;(2) a neoblastic olivine and orthopyroxene assemblage;(3) the last assemblage associated with the formation of clinopyroxene and garnet marginal zones(Gar2).Major and trace element compositions of olivine,orthopyroxene,clinopyroxene and garnet indicate that both the neoblast and clinopyroxene-Gar2 mineral assemblages were in equilibrium with a high Fe-Ti carbonate-silicate metasomatic agent.The nature of the metasomatic agent was estimated based on high field strength elements(HFSE) composition of olivine neoblasts,the garnet-clinopyroxene equilibrium condition and calculated by REE-composition of Gar2 and clinopyroxene.All these evidences indicate that the agent was a high temperature carbonate-silicate melt that is geochemically linked to the formation of the protokimberlite melt.展开更多
Orogenic peridotites in the Dabie-Sulu orogenic belt are commonly subdivided into‘crustal’type and‘mantle’type.They exhibit distinct mineral textures,metamorphic evolution,and whole-rock and mineral compositions.M...Orogenic peridotites in the Dabie-Sulu orogenic belt are commonly subdivided into‘crustal’type and‘mantle’type.They exhibit distinct mineral textures,metamorphic evolution,and whole-rock and mineral compositions.Most‘mantle’type peridotites originated from the subcontinental lithospheric mantle(SCLM)of the North China Craton and thus provide direct evidence of crust-mantle interactions in the continental subduction channel.In garnet peridotites,both garnet and Cr-spinel can be equilibrated at peak pressure conditions.Their stabilities are mainly controlled by the refertilized degree of whole-rock;therefore,spinel composition cannot be used to discriminate the partial melting degree of orogenic peridotites.Refractory mantle-derived dunites contain the textures of low Mg and high Ca olivine veins that crosscut orthopyroxene porphyroblasts,which is considered as evidence for silica-undersaturated melt-rock reactions.Such reactions occurring before subduction may potentially affect Re-Os isotopic compositions.Rutile,Ti-clinohumite and zircon in mantle-derived peridotites or pyroxenites provide direct mineralogical evidence for the transport of high field strength elements(HFSEs)from the subducted crust into the mantle wedge.Based on detailed in situ element and isotope analyses,we can constrain the source of metasomatic agents,the metasomatic time and the process of mass transfer.The mantle wedge above continental subduction zones has a wide range of oxygen fugacity values(FMQ=?5.50–1.75),showing a roughly negative correlation with the subducted depths.However,the calculated results of oxygen fugacity are significantly affected by mineral assemblages,P-T conditions and dehydrogenation-oxidation of nominally anhydrous mantle olivine during exhumation.Although significant progress has been made in the study of orogenic peridotites in the Dabie-Sulu orogenic belt,many critical questions remain.With new approaches and advanced technologic applications,additional knowledge of the phase relation in the peridotite-pyroxenite complex system,the mantle geodynamic process before continental subduction,the effects of crustal metasomatism on chemical composition,the oxygen fugacity,and the physical properties of the mantle wedge is anticipated.展开更多
This study carried out a comprehensive review of mantle-derived garnet peridotites on the basis of their garnet-spinel compositional relationships. The P-T estimates of the garnet peridotites of both orogenic and xeno...This study carried out a comprehensive review of mantle-derived garnet peridotites on the basis of their garnet-spinel compositional relationships. The P-T estimates of the garnet peridotites of both orogenic and xenolithic derivations confirm previously established two garnet-spinel transition (GST) zones. Results of natural samples and experimental studies of all the garnet peridotites plot below the first GST at low P (〈2 GPa). The second GST at high P (6-10 GPa), obtained from the experimental system (MgO-Cr203-SiO2), was firstly evidenced from natural samples in this study and may imply a challenge to our understanding of Cr-rich and Al-poor mineral phase transition under ultrahigh P condition. Based on the data and our estimates, we propose the existence of another GST within the garnet peridotite discontinuous zone and a potential spinel-phase peridotite zone in the upper mantle.展开更多
基金supported by RBRF (Grant Nos.11-05-00060a,16-05-00860a)
文摘New versions of the universal Jd-Di exchange clinopyroxene barometer for peridotites,pyroxenites and eclogites,and also garnet barometer for eclogites and peridotites were developed.They were checked using large experimental data sets for eciogitic(~530) and peridotitic systems(〉650).The precision of the universal Cpx barometer for peridotites based on Jd-Di exchange is close to Cr-Tschermal
基金financially supported by the Program for Development MSUsupported by the Russian Foundation for Basic Research, project Nos.15-05-03778a and 16-05-00298a
文摘The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V.Grib kimberlite pipe(Arkhangelsk Diamond Province,Russia) was studied.Based on petrographic characteristics,the peridotite xenolith reflects a sheared peridotite.The sheared peridotite experienced a complex evolution with formation of three main mineral assemblages:(1) a relict harzburgite assemblage consist of olivine and orthopyroxene porphyroclasts and cores of garnet grains(Gar1) with sinusoidal rare earth elements(REE) chondrite C1 normalized patterns;(2) a neoblastic olivine and orthopyroxene assemblage;(3) the last assemblage associated with the formation of clinopyroxene and garnet marginal zones(Gar2).Major and trace element compositions of olivine,orthopyroxene,clinopyroxene and garnet indicate that both the neoblast and clinopyroxene-Gar2 mineral assemblages were in equilibrium with a high Fe-Ti carbonate-silicate metasomatic agent.The nature of the metasomatic agent was estimated based on high field strength elements(HFSE) composition of olivine neoblasts,the garnet-clinopyroxene equilibrium condition and calculated by REE-composition of Gar2 and clinopyroxene.All these evidences indicate that the agent was a high temperature carbonate-silicate melt that is geochemically linked to the formation of the protokimberlite melt.
基金supported by the National Basic Research Program of China(Grant No.2015CB856103)the National Natural Science Foundation of China(Grant Nos.41090371&41372078)
文摘Orogenic peridotites in the Dabie-Sulu orogenic belt are commonly subdivided into‘crustal’type and‘mantle’type.They exhibit distinct mineral textures,metamorphic evolution,and whole-rock and mineral compositions.Most‘mantle’type peridotites originated from the subcontinental lithospheric mantle(SCLM)of the North China Craton and thus provide direct evidence of crust-mantle interactions in the continental subduction channel.In garnet peridotites,both garnet and Cr-spinel can be equilibrated at peak pressure conditions.Their stabilities are mainly controlled by the refertilized degree of whole-rock;therefore,spinel composition cannot be used to discriminate the partial melting degree of orogenic peridotites.Refractory mantle-derived dunites contain the textures of low Mg and high Ca olivine veins that crosscut orthopyroxene porphyroblasts,which is considered as evidence for silica-undersaturated melt-rock reactions.Such reactions occurring before subduction may potentially affect Re-Os isotopic compositions.Rutile,Ti-clinohumite and zircon in mantle-derived peridotites or pyroxenites provide direct mineralogical evidence for the transport of high field strength elements(HFSEs)from the subducted crust into the mantle wedge.Based on detailed in situ element and isotope analyses,we can constrain the source of metasomatic agents,the metasomatic time and the process of mass transfer.The mantle wedge above continental subduction zones has a wide range of oxygen fugacity values(FMQ=?5.50–1.75),showing a roughly negative correlation with the subducted depths.However,the calculated results of oxygen fugacity are significantly affected by mineral assemblages,P-T conditions and dehydrogenation-oxidation of nominally anhydrous mantle olivine during exhumation.Although significant progress has been made in the study of orogenic peridotites in the Dabie-Sulu orogenic belt,many critical questions remain.With new approaches and advanced technologic applications,additional knowledge of the phase relation in the peridotite-pyroxenite complex system,the mantle geodynamic process before continental subduction,the effects of crustal metasomatism on chemical composition,the oxygen fugacity,and the physical properties of the mantle wedge is anticipated.
基金supported by the Special Research Project of the State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences (No. 1008)the National Natural Science Foundation of China (No. 90714008)
文摘This study carried out a comprehensive review of mantle-derived garnet peridotites on the basis of their garnet-spinel compositional relationships. The P-T estimates of the garnet peridotites of both orogenic and xenolithic derivations confirm previously established two garnet-spinel transition (GST) zones. Results of natural samples and experimental studies of all the garnet peridotites plot below the first GST at low P (〈2 GPa). The second GST at high P (6-10 GPa), obtained from the experimental system (MgO-Cr203-SiO2), was firstly evidenced from natural samples in this study and may imply a challenge to our understanding of Cr-rich and Al-poor mineral phase transition under ultrahigh P condition. Based on the data and our estimates, we propose the existence of another GST within the garnet peridotite discontinuous zone and a potential spinel-phase peridotite zone in the upper mantle.