The New Caledonia ophiolite(Peridotite Nappe)consists primarily of harzburgites,locally overlain by mafic-ultramafic cumulates,and minor spinel and plagioclase lherzolites.In this study,a comprehensive geochemical dat...The New Caledonia ophiolite(Peridotite Nappe)consists primarily of harzburgites,locally overlain by mafic-ultramafic cumulates,and minor spinel and plagioclase lherzolites.In this study,a comprehensive geochemical data set(major and trace element,Sr-Nd-Pb isotopes)has been obtained on a new set of fresh harzburgites in order to track the processes recorded by this mantle section and its evolution.The studied harzburgites are low-strain tectonites showing porphyroclastic textures,locally grading into protomylonitic textures.They exhibit a refractory nature,as attested by the notable absence of primary clinopyroxene,very high Fo content of olivine(91-93 mol.%),high Mg#of orthopyroxene(0.91-0.93)and high Cr#of spinel(0.44-0.71).The harzburgites are characterised by remarkably low REE concentrations(<0.1 chondritic values)and display"U-shaped"profiles,with steeply sloping HREE(DyN/YbN=0.07-0.16)and fractionated LREE-MREE segments(LaN/SmN=2.1-8.3),in the range of modern fore-arc peridotites.Geochemical modelling shows that the HREE composition of the harzburgites can be reproduced by multi-stage melting including a first phase of melt depletion in dry conditions(15%fractional melting),followed by hydrous melting in a subduction zone setting(up to 15%-18%).However,melting models fail to explain the enrichments observed for some FME(i.e.Ba,Sr,Pb),LREE-MREE and Zr-Hf.These enrichments,coupled with the frequent occurrence of thin,undeformed films of Al2 O3,and CaO-poor orthopyroxene(Al2O3=0.88-1.53 wt.%,CaO=0.31-0.56 wt.%)and clinopyroxene with low Na2 O(0.03-0.16 wt.%),Al2 O3(0.66-1.35 wt.%)and TiO2(0.04-0.10 wt.%)contents,point to FME addition during fluid-assisted melting followed by late stage metasomatism most likely operated by subductionrelated melts with a depleted trace element signature.Nd isotopic ratios range from unradiogenic to radiogenic(-0.80<εNdi≤+13.32)and negatively correlate with Sr isotopes(0.70257≤87Sr/86Sr≤0.70770).Pb isotopes cover a wide range,trending from DMM toward enriched,sediment-like,compositions.We interpret the geochemical signature displayed by the New Caledonia harzburgites as reflecting the evolution of a highly depleted fore-arc mantle wedge variably modified by different fluid and melt inputs during Eocene subduction.展开更多
The ultramafic massif of Feragen,which belongs to the eastern ophiolitic belt of Norway,has abundant amounts of chromite ores.Recent studies have revealed a complex melt evolution in a supra-subduction zone(SSZ)enviro...The ultramafic massif of Feragen,which belongs to the eastern ophiolitic belt of Norway,has abundant amounts of chromite ores.Recent studies have revealed a complex melt evolution in a supra-subduction zone(SSZ)environment.This study presents new whole-rock major element,trace element,and platinum-group element chemistry to evaluate their petrogenesis and tectonic evolution.Harzburgites have high CaO,Al_(2)O_(3),TiO_(2),MgO,and REE contents corresponding to abyssal peridotites,whereas dunites have low CaO,Al_(2)O_(3),TiO_(2),MgO,and REE contents corresponding to SSZ peridotites.The Cr^(#)and TiO_(2) of chromian spinels in the harzburgites suggest as much as about 15%–20%melting and the dunites are more depleted with>40%melting.The harzburgites and the dunites and high-Cr chromitites represent,respectively,the products of low-degree partial melting in a back-arc setting,and the products of melt-rock interaction in a SSZ environment.The calculated fO_(2) values for dunites and high-Cr chromitites(-0.17–+0.23 and+2.78–+5.65,respectively and generally above the FMQ buffer)are also consistent with the interaction between back-arc ophiolites with oxidized boninitic melts in a SSZ setting.展开更多
Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus...Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus.The results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing pressure.By combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic ages.The present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.展开更多
本文报道了柴北缘大陆型超高压变质带沙柳河地区发现的蛇绿岩型地幔橄榄岩,其原始矿物组合为橄榄石+斜方辉石+铬铁矿。方辉橄榄岩中识别出两个世代的橄榄石,第一世代橄榄石(OI^1)残晶发育扭折带,化学成分与现代大洋地幔橄榄岩的橄榄石一...本文报道了柴北缘大陆型超高压变质带沙柳河地区发现的蛇绿岩型地幔橄榄岩,其原始矿物组合为橄榄石+斜方辉石+铬铁矿。方辉橄榄岩中识别出两个世代的橄榄石,第一世代橄榄石(OI^1)残晶发育扭折带,化学成分与现代大洋地幔橄榄岩的橄榄石一致,第二世代橄榄石(OI^2)Fo 值高达94～97,其内部含有细小的流体包裹体,是第一世代橄榄石蛇纹石化后再次变质的产物。斜方辉石残晶的成分具有高 Al 和 Ca 的特征,与大洋地幔橄榄岩中斜方辉石的成分一致。温压条件的估算反映该橄榄岩体属于典型的尖晶石相方辉橄榄岩。其围岩是由堆晶辉长岩变质的条带状蓝晶石榴辉岩,二者构成了大洋蛇绿岩套的下部层位,并且与区内具有 N-MORB 和 OIB 性质的榴辉岩共生。这些特征表明该方辉橄榄岩应代表洋壳下伏地幔橄榄岩,从而揭示大陆造山带从早期的大洋俯冲消亡到大陆俯冲碰撞的完整过程。展开更多
Tectonically emplaced peridotites from North Hebei Province, North China Craton, have retained an original harzburgite mineral assemblage of olivine （54%-58%） ＋ orthopyroxene （40%-46%） ＋minor clinopyroxene （〈1...Tectonically emplaced peridotites from North Hebei Province, North China Craton, have retained an original harzburgite mineral assemblage of olivine （54%-58%） ＋ orthopyroxene （40%-46%） ＋minor clinopyroxene （〈1%）＋spinel. Samples with honinite-like chemical compositions also coexist with these peridotites. The spinels within the peridotites have high-A1 end-members with A1203 content of 30 wt%-50 wt%, typical of mantle spinels. When compared with experimentally determined melt extraction trajectories, the harzburgites display a high degree of melting and enrichment of SiO2, which is typical of cratonic mantle peridotites. The peridotites display variably enriched light rare earth elements （REEs）, relatively depleted middle REEs and weakly fractionated heavy REEs, which suggest a melt extraction of over 25% in the spinel stability field. The occurrence of are- and SSZ-type chromian spinels in the peridotites suggests that melt extraction and metasomatism occurred mostly in a subduction-related setting. This is also supported by the geochemical data of the coexisting boninite-like samples. The peridotites have lS7Os/lSSOs ratios ranging from 0.113-0.122, which is typical of cratonic iithospheric mantle. These lSTOs/ISSOs ratios yield model melt extraction ages （TRD） ranging from 981 Ma to 2054 Ma, which may represent the minimum estimation of the melt extraction age. The Ai203- lSTOs/lSSOs-proxy isochron ages of 2.4 Ga-2.7 Ga suggest a mantle melt depletion age between the Late Achaean and Early Paleoproterozoic. Both the peridotites and boninite-like rocks are therefore interpreted as tectonically exhumed continental lithospheric mantle of the North China Craton, which has experienced mantle melt depletion and subduction-related mantle metasomatism during the Neoarchean- Paleoproterozoic.展开更多
This paper presents new major and trace element data from 150 garnet xenocrysts from the V.Grib kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province（ADP）.Based on the concentrations...This paper presents new major and trace element data from 150 garnet xenocrysts from the V.Grib kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province（ADP）.Based on the concentrations of Cr_2O_3,CaO,TiO_2 and rare earth elements（REE） the garnets were divided into seven groups：（1） lherzolitic ＂depleted＂ garnets（ ＂Lz 1＂）,（2） lherzolitic garnets with normal REE patterns（ ＂Lz2＂）,（3） lherzolitic garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂）,（4） lherzolitic garnets with strongly sinusoidal REE patterns（ ＂Lz 4＂）,（5） harzburgitic garnets with sinusoidal REE patterns（ ＂Hz＂）,（6）wehrlitic garnets with weakly sinusoidal REE patterns（ ＂W＂）,（7） garnets of megacryst paragenesis with normal REE patterns（ ＂Meg＂）.Detailed mineralogical and geochemical garnet studies and modeling results suggest several stages of mantle metasomatism influenced by carbonatite and silicate melts.Carbonatitic metasomatism at the first stage resulted in refertilization of the lithospheric mantle,which is evidenced by a nearly vertical CaO-Cr_2O_3 trend from harzburgitic（ ＂Hz＂） to lherzolitic（ ＂Lz 4＂） garnet composition.Harzburgitic garnets（ ＂Hz＂） have probably been formed by interactions between carbonatite melts and exsolved garnets in high-degree melt extraction residues.At the second stage of metasomatism,garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂, ＂W＂） were affected by a silicate melt possessing a REE composition similar to that of ADP alkaline mica-poor picrites.At the last stage,the garnets interacted with basaltic melts,which resulted in the decrease CaO-Cr_2O_3 trend of ＂Lz 2＂ garnet composition.Cr-poor garnets of megacryst paragenesis（ ＂Meg＂） could crystallize directly from the silicate melt which has a REE composition close to that of ADP alkaline mica-poor picrites.P-T estimates of the garnet xenocrysts indicate that the interval of-60-110 km of the lithospheric mantle beneath the V.Grib pipe was predominantly affected by the silicate melts,whereas the lithospheric mantle deeper than150 km was influenced by the carbonatite melts.展开更多
Thcre are two grades of network-type texture in metamorphic peridotite from the Kuda ophiolite, Xinjiang, China. The first graduation consisls of coarse-grained olivine with plastic deformation fabrics , orthopyroxene...Thcre are two grades of network-type texture in metamorphic peridotite from the Kuda ophiolite, Xinjiang, China. The first graduation consisls of coarse-grained olivine with plastic deformation fabrics , orthopyroxene and minor clinopyroxene and Cr-spinel. The second graduation consists of snlall minerals filling among the mineral grains of the first graduation. Four kinds of assemblagcs containing tremolite have been discovered in the second graduation,which were formed during mantle partial melting and mantle metasomatism of a highly depleted peridotite.展开更多
基金supported by a Vinci grant (Italian-French University) and by Italian-PRIN prot.2015C5LN35
文摘The New Caledonia ophiolite(Peridotite Nappe)consists primarily of harzburgites,locally overlain by mafic-ultramafic cumulates,and minor spinel and plagioclase lherzolites.In this study,a comprehensive geochemical data set(major and trace element,Sr-Nd-Pb isotopes)has been obtained on a new set of fresh harzburgites in order to track the processes recorded by this mantle section and its evolution.The studied harzburgites are low-strain tectonites showing porphyroclastic textures,locally grading into protomylonitic textures.They exhibit a refractory nature,as attested by the notable absence of primary clinopyroxene,very high Fo content of olivine(91-93 mol.%),high Mg#of orthopyroxene(0.91-0.93)and high Cr#of spinel(0.44-0.71).The harzburgites are characterised by remarkably low REE concentrations(<0.1 chondritic values)and display"U-shaped"profiles,with steeply sloping HREE(DyN/YbN=0.07-0.16)and fractionated LREE-MREE segments(LaN/SmN=2.1-8.3),in the range of modern fore-arc peridotites.Geochemical modelling shows that the HREE composition of the harzburgites can be reproduced by multi-stage melting including a first phase of melt depletion in dry conditions(15%fractional melting),followed by hydrous melting in a subduction zone setting(up to 15%-18%).However,melting models fail to explain the enrichments observed for some FME(i.e.Ba,Sr,Pb),LREE-MREE and Zr-Hf.These enrichments,coupled with the frequent occurrence of thin,undeformed films of Al2 O3,and CaO-poor orthopyroxene(Al2O3=0.88-1.53 wt.%,CaO=0.31-0.56 wt.%)and clinopyroxene with low Na2 O(0.03-0.16 wt.%),Al2 O3(0.66-1.35 wt.%)and TiO2(0.04-0.10 wt.%)contents,point to FME addition during fluid-assisted melting followed by late stage metasomatism most likely operated by subductionrelated melts with a depleted trace element signature.Nd isotopic ratios range from unradiogenic to radiogenic(-0.80<εNdi≤+13.32)and negatively correlate with Sr isotopes(0.70257≤87Sr/86Sr≤0.70770).Pb isotopes cover a wide range,trending from DMM toward enriched,sediment-like,compositions.We interpret the geochemical signature displayed by the New Caledonia harzburgites as reflecting the evolution of a highly depleted fore-arc mantle wedge variably modified by different fluid and melt inputs during Eocene subduction.
基金financially supported by the National Natural Science Foundation of China(92062215,41720104009,42172069)the China Geological Survey(DD20221886,DD20221817,DD20221657,DD20230340,DD20221630)+1 种基金the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0201)the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0801)。
文摘The ultramafic massif of Feragen,which belongs to the eastern ophiolitic belt of Norway,has abundant amounts of chromite ores.Recent studies have revealed a complex melt evolution in a supra-subduction zone(SSZ)environment.This study presents new whole-rock major element,trace element,and platinum-group element chemistry to evaluate their petrogenesis and tectonic evolution.Harzburgites have high CaO,Al_(2)O_(3),TiO_(2),MgO,and REE contents corresponding to abyssal peridotites,whereas dunites have low CaO,Al_(2)O_(3),TiO_(2),MgO,and REE contents corresponding to SSZ peridotites.The Cr^(#)and TiO_(2) of chromian spinels in the harzburgites suggest as much as about 15%–20%melting and the dunites are more depleted with>40%melting.The harzburgites and the dunites and high-Cr chromitites represent,respectively,the products of low-degree partial melting in a back-arc setting,and the products of melt-rock interaction in a SSZ environment.The calculated fO_(2) values for dunites and high-Cr chromitites(-0.17–+0.23 and+2.78–+5.65,respectively and generally above the FMQ buffer)are also consistent with the interaction between back-arc ophiolites with oxidized boninitic melts in a SSZ setting.
基金Key Research Program of Frontier Sciences of CAS(ZDBS-LY-DQC015)National Natural Science Foundation of China(Nos.41973056,41773056,41303048)Science Foundation of Guizhou Province(2017-1196,2018-1176).
文摘Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil apparatus.The results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing pressure.By combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic ages.The present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.
文摘本文报道了柴北缘大陆型超高压变质带沙柳河地区发现的蛇绿岩型地幔橄榄岩,其原始矿物组合为橄榄石+斜方辉石+铬铁矿。方辉橄榄岩中识别出两个世代的橄榄石,第一世代橄榄石(OI^1)残晶发育扭折带,化学成分与现代大洋地幔橄榄岩的橄榄石一致,第二世代橄榄石(OI^2)Fo 值高达94～97,其内部含有细小的流体包裹体,是第一世代橄榄石蛇纹石化后再次变质的产物。斜方辉石残晶的成分具有高 Al 和 Ca 的特征,与大洋地幔橄榄岩中斜方辉石的成分一致。温压条件的估算反映该橄榄岩体属于典型的尖晶石相方辉橄榄岩。其围岩是由堆晶辉长岩变质的条带状蓝晶石榴辉岩,二者构成了大洋蛇绿岩套的下部层位,并且与区内具有 N-MORB 和 OIB 性质的榴辉岩共生。这些特征表明该方辉橄榄岩应代表洋壳下伏地幔橄榄岩,从而揭示大陆造山带从早期的大洋俯冲消亡到大陆俯冲碰撞的完整过程。
基金financially supported by the NSFC(grant no.41430207, 41602340)China Postdoctoral Science Foundation ( 2016M591246)
文摘Tectonically emplaced peridotites from North Hebei Province, North China Craton, have retained an original harzburgite mineral assemblage of olivine （54%-58%） ＋ orthopyroxene （40%-46%） ＋minor clinopyroxene （〈1%）＋spinel. Samples with honinite-like chemical compositions also coexist with these peridotites. The spinels within the peridotites have high-A1 end-members with A1203 content of 30 wt%-50 wt%, typical of mantle spinels. When compared with experimentally determined melt extraction trajectories, the harzburgites display a high degree of melting and enrichment of SiO2, which is typical of cratonic mantle peridotites. The peridotites display variably enriched light rare earth elements （REEs）, relatively depleted middle REEs and weakly fractionated heavy REEs, which suggest a melt extraction of over 25% in the spinel stability field. The occurrence of are- and SSZ-type chromian spinels in the peridotites suggests that melt extraction and metasomatism occurred mostly in a subduction-related setting. This is also supported by the geochemical data of the coexisting boninite-like samples. The peridotites have lS7Os/lSSOs ratios ranging from 0.113-0.122, which is typical of cratonic iithospheric mantle. These lSTOs/ISSOs ratios yield model melt extraction ages （TRD） ranging from 981 Ma to 2054 Ma, which may represent the minimum estimation of the melt extraction age. The Ai203- lSTOs/lSSOs-proxy isochron ages of 2.4 Ga-2.7 Ga suggest a mantle melt depletion age between the Late Achaean and Early Paleoproterozoic. Both the peridotites and boninite-like rocks are therefore interpreted as tectonically exhumed continental lithospheric mantle of the North China Craton, which has experienced mantle melt depletion and subduction-related mantle metasomatism during the Neoarchean- Paleoproterozoic.
基金supported by the FBRF(Grants No.15-05-07758)by state assignment project No.Ⅷ.72.1.1
文摘This paper presents new major and trace element data from 150 garnet xenocrysts from the V.Grib kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province（ADP）.Based on the concentrations of Cr_2O_3,CaO,TiO_2 and rare earth elements（REE） the garnets were divided into seven groups：（1） lherzolitic ＂depleted＂ garnets（ ＂Lz 1＂）,（2） lherzolitic garnets with normal REE patterns（ ＂Lz2＂）,（3） lherzolitic garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂）,（4） lherzolitic garnets with strongly sinusoidal REE patterns（ ＂Lz 4＂）,（5） harzburgitic garnets with sinusoidal REE patterns（ ＂Hz＂）,（6）wehrlitic garnets with weakly sinusoidal REE patterns（ ＂W＂）,（7） garnets of megacryst paragenesis with normal REE patterns（ ＂Meg＂）.Detailed mineralogical and geochemical garnet studies and modeling results suggest several stages of mantle metasomatism influenced by carbonatite and silicate melts.Carbonatitic metasomatism at the first stage resulted in refertilization of the lithospheric mantle,which is evidenced by a nearly vertical CaO-Cr_2O_3 trend from harzburgitic（ ＂Hz＂） to lherzolitic（ ＂Lz 4＂） garnet composition.Harzburgitic garnets（ ＂Hz＂） have probably been formed by interactions between carbonatite melts and exsolved garnets in high-degree melt extraction residues.At the second stage of metasomatism,garnets with weakly sinusoidal REE patterns（ ＂Lz 3＂, ＂W＂） were affected by a silicate melt possessing a REE composition similar to that of ADP alkaline mica-poor picrites.At the last stage,the garnets interacted with basaltic melts,which resulted in the decrease CaO-Cr_2O_3 trend of ＂Lz 2＂ garnet composition.Cr-poor garnets of megacryst paragenesis（ ＂Meg＂） could crystallize directly from the silicate melt which has a REE composition close to that of ADP alkaline mica-poor picrites.P-T estimates of the garnet xenocrysts indicate that the interval of-60-110 km of the lithospheric mantle beneath the V.Grib pipe was predominantly affected by the silicate melts,whereas the lithospheric mantle deeper than150 km was influenced by the carbonatite melts.
文摘Thcre are two grades of network-type texture in metamorphic peridotite from the Kuda ophiolite, Xinjiang, China. The first graduation consisls of coarse-grained olivine with plastic deformation fabrics , orthopyroxene and minor clinopyroxene and Cr-spinel. The second graduation consists of snlall minerals filling among the mineral grains of the first graduation. Four kinds of assemblagcs containing tremolite have been discovered in the second graduation,which were formed during mantle partial melting and mantle metasomatism of a highly depleted peridotite.
