The osmium-isotope mismatch commonly reported between mid-ocean-ridge basalts(MORBs) and residual mantle might reflect evolution of the MORB Re-Os system after extraction from the asthenosphere, or preferential contri...The osmium-isotope mismatch commonly reported between mid-ocean-ridge basalts(MORBs) and residual mantle might reflect evolution of the MORB Re-Os system after extraction from the asthenosphere, or preferential contribution of radiogenic Os components from mantle. However, in a MOR system, the role of dunite melt channels from the upper mantle and Moho transition zone in regulating isotopic systems between mantle and crust has rarely been evaluated. We report new Re-Os isotopic compositions of base-metal sulfides(BMS), chromites and dunites from dunite lenses with low spinel Cr# [Cr3+/(Cr3++Al3+) ≤ 0.66](products of interaction between MORB-like melts and upper-mantle harzburgites) from the Zedang ophiolite(South Tibet). Re-Os isotopic compositions of low-Cr# dunites from the Oman ophiolite are also shown for comparison. Mineralogical evidence suggests that the Zedang sulfides were originally precipitated as monosulfide solid solutions. The highly variable 187Os/188Os initial ratios(0.1191-0.1702) and low 187Re/188Os(<0.22) of the sulfides suggest that the chromite acted as a sink for Os-bearing sulfides, aggregating discrete Os components with heterogeneous isotopic signatures from asthenospheric or lithospheric mantle into dunite channels. The Zedang chromites and dunites show 187Os/188Os ratios similar to the primitive upper mantle(PUM), except for two dunites with sub-PUM ratios, reflecting the contribution of Os balanced by smaller volumes of Os-rich, unradiogenic sulfides(likely nucleating on Os nanoparticles) and larger volumes of Os-poor radiogenic BMS. Such isotopic heterogeneity, despite with less variation, has been observed in dunite channels from the Oman ophiolite and present-day mid-ocean ridges. Formation of dunite channels in the upper mantle thus can aggregate Os-bearing sulfides with chromite, leaving high Re/Os components into the residual melts. Once such channel systems were built up at the crust-mantle transition zone, the newly incoming MOR magmas would preferentially melt and dissolve the volumetrically abundant radiogenic BMS and retain Os-rich nanoparticles in the channels, further amplifying the Os-isotope mismatch between oceanic crust and mantle. This study sheds new light on the multistage evolution and small-scale behaviors of chalcophile and siderophile elements(e.g., Re-Os) and their isotopes(e.g., 187Re-187Os) with sulfides and chromites in a silicate-dominated melt plumbing system beneath mid-ocean ridges.展开更多
Kimberlite,which is the primary host rock for diamonds,originates from the deepest sources of all the mantle-derived magmas(Giuliani et al.,2023;Foley et al.,2019).This feature provides a vital perspective to explore ...Kimberlite,which is the primary host rock for diamonds,originates from the deepest sources of all the mantle-derived magmas(Giuliani et al.,2023;Foley et al.,2019).This feature provides a vital perspective to explore Earth's internal structure and evolution.The first primary diamond deposit discovered in China was the East No.1 kimberlite pluton(D1)in Maping(26°56′08″N,108°17′07″E),located on the southeastern margin of the Yangtze Craton(Figure 1).展开更多
Diamonds have been reported from Tibetan ＂ophiolites＂ for 〉30 years, but have been widely dismissed as contaminants, because their unusual morphology and light C （δ13C=-18 to -27） are unlike those of kimberlitic...Diamonds have been reported from Tibetan ＂ophiolites＂ for 〉30 years, but have been widely dismissed as contaminants, because their unusual morphology and light C （δ13C=-18 to -27） are unlike those of kimberlitic diamonds. However, the diamonds have now been found in situ in both the chromitites and the peridotites of ＂ophiolites＂ along the Yarlung-Zangbo suture （Tibet） and the Polar Urals （Yang et al., 2014）.展开更多
The Uralide orogenic belt suture zone extending more is a major early Paleozoic than 3000 km in a N-S direction, and geographically divides Europe from Asia （Chemenda et al., 1997）. Ophiolites, podiform chromitites ...The Uralide orogenic belt suture zone extending more is a major early Paleozoic than 3000 km in a N-S direction, and geographically divides Europe from Asia （Chemenda et al., 1997）. Ophiolites, podiform chromitites and high pressure metamorphic rocks are well developed in the orogenic belt （Leech and Ernst, 2000）.展开更多
基金supported by the National Natural Science Foundation of China(41520104003,41873032&41822301)the Fundamental Research Funds for the Central Universities,CUG Wuhan(CUG180604,CUGCJ1709)+1 种基金the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources(CUG,MSFGPMR15)the CCFS ARC Centre of Excellence
文摘The osmium-isotope mismatch commonly reported between mid-ocean-ridge basalts(MORBs) and residual mantle might reflect evolution of the MORB Re-Os system after extraction from the asthenosphere, or preferential contribution of radiogenic Os components from mantle. However, in a MOR system, the role of dunite melt channels from the upper mantle and Moho transition zone in regulating isotopic systems between mantle and crust has rarely been evaluated. We report new Re-Os isotopic compositions of base-metal sulfides(BMS), chromites and dunites from dunite lenses with low spinel Cr# [Cr3+/(Cr3++Al3+) ≤ 0.66](products of interaction between MORB-like melts and upper-mantle harzburgites) from the Zedang ophiolite(South Tibet). Re-Os isotopic compositions of low-Cr# dunites from the Oman ophiolite are also shown for comparison. Mineralogical evidence suggests that the Zedang sulfides were originally precipitated as monosulfide solid solutions. The highly variable 187Os/188Os initial ratios(0.1191-0.1702) and low 187Re/188Os(<0.22) of the sulfides suggest that the chromite acted as a sink for Os-bearing sulfides, aggregating discrete Os components with heterogeneous isotopic signatures from asthenospheric or lithospheric mantle into dunite channels. The Zedang chromites and dunites show 187Os/188Os ratios similar to the primitive upper mantle(PUM), except for two dunites with sub-PUM ratios, reflecting the contribution of Os balanced by smaller volumes of Os-rich, unradiogenic sulfides(likely nucleating on Os nanoparticles) and larger volumes of Os-poor radiogenic BMS. Such isotopic heterogeneity, despite with less variation, has been observed in dunite channels from the Oman ophiolite and present-day mid-ocean ridges. Formation of dunite channels in the upper mantle thus can aggregate Os-bearing sulfides with chromite, leaving high Re/Os components into the residual melts. Once such channel systems were built up at the crust-mantle transition zone, the newly incoming MOR magmas would preferentially melt and dissolve the volumetrically abundant radiogenic BMS and retain Os-rich nanoparticles in the channels, further amplifying the Os-isotope mismatch between oceanic crust and mantle. This study sheds new light on the multistage evolution and small-scale behaviors of chalcophile and siderophile elements(e.g., Re-Os) and their isotopes(e.g., 187Re-187Os) with sulfides and chromites in a silicate-dominated melt plumbing system beneath mid-ocean ridges.
基金supported by the National Natural Science Foundation of China(Nos.41963006,42363006)the Geological Research Project of the Bureau of Geology and Mineral Exploration and Development of Guizhou Province(Nos.QDKKH[2020]26,QDKKH[2024]6,QDKKH[2023]1)。
文摘Kimberlite,which is the primary host rock for diamonds,originates from the deepest sources of all the mantle-derived magmas(Giuliani et al.,2023;Foley et al.,2019).This feature provides a vital perspective to explore Earth's internal structure and evolution.The first primary diamond deposit discovered in China was the East No.1 kimberlite pluton(D1)in Maping(26°56′08″N,108°17′07″E),located on the southeastern margin of the Yangtze Craton(Figure 1).
文摘Diamonds have been reported from Tibetan ＂ophiolites＂ for 〉30 years, but have been widely dismissed as contaminants, because their unusual morphology and light C （δ13C=-18 to -27） are unlike those of kimberlitic diamonds. However, the diamonds have now been found in situ in both the chromitites and the peridotites of ＂ophiolites＂ along the Yarlung-Zangbo suture （Tibet） and the Polar Urals （Yang et al., 2014）.
文摘The Uralide orogenic belt suture zone extending more is a major early Paleozoic than 3000 km in a N-S direction, and geographically divides Europe from Asia （Chemenda et al., 1997）. Ophiolites, podiform chromitites and high pressure metamorphic rocks are well developed in the orogenic belt （Leech and Ernst, 2000）.
