This study investigates the leaching and purification processes for dunite slurry,a common mining waste material,and the carbonation processes for the mineralization of CO_(2) with Mg^(2+).Results indicate that HCl is...This study investigates the leaching and purification processes for dunite slurry,a common mining waste material,and the carbonation processes for the mineralization of CO_(2) with Mg^(2+).Results indicate that HCl is a promising leaching agent,and pH and temperature are major factors in controlling the efficiency of the leaching process,with leaching efficiencies of 82%achieved after 4 h using 2 M HCl solution at 75℃.The removal of other ions like Fe^(3+),Fe^(2+),and Al^(3+)through the purification of the leachate using ammonium hydroxide was also proven to be effective,completely removing iron and aluminum from the leachate from starting concentrations of 3.10 and 0.40 g/L,respectively.The carbonation of magnesium at room temperature was investigated with both purified leachate and pure MgCl_(2) aqueous solution.Nesquehonite crystals began to form after 1.5 h with a conversion of Mg^(2+)to nesquehonite of approximately 5%.The produced crystals possess a needle-like shape,which could be modified using the biopolymers pectin and xanthan.Pectin had a limited influence on the length of the crystals,reducing the needle length with increasing pectin concentration.Xanthan,on the other hand,shortened and widened the needle-like structure into a column shape as more xanthan was added.This study demonstrates the potential for this process to utilize mining wastes and sequester CO_(2),producing useful mineral products in the process.展开更多
This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi＇anli （西安里） hornblende （Hb）-gahbros from the southern Taihang （太行） ...This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi＇anli （西安里） hornblende （Hb）-gahbros from the southern Taihang （太行） Mountains, with the aim of constraining the nature of the Mesozoic lithospheric mantle in Central China. Rounded dunite xenoliths are 1-3 cm3 in size and display porphyroelastic, tabular, and protogranular textures. Chromite with Cr#=60-89 is common in the xenoliths. Oilvine xenocrysts of 4-6 mm in size are also found in the Hb-gabbros. Orthopyroxene reaction rims are commonly observed around olivine xenocrysts or between dunite xenoliths and host rocks. The porphyroclastic olivines within dunite xenoliths and olivine xenoerysts have kink bands and Mg#=83-94. The Mg# of olivine cores and rims are 89-94 （average, 90） and 83-86 （average, 84.4）, respectively. The CaO contents of all olivines from the xenoliths and xenocrysts are less than 0.1 wt.%, suggesting a Hthospheric mantle origin. The Ca content （214 ppm-818 ppm） and Ti content （15 ppm-137 ppm） in the xenoliths and xenocrysts are similar to those of olivines from the dunite xenoliths, but are much higher than those of olivines from harzburgite and lherzolite xenoliths in the Fushan （符山） intrusion. This finding implies that the xenoliths and xenocrysts may have originated from harzburgites or lherzolites that were intensively modified by silica-rich melts. This result, combined with high Mg# （92-94） of olivine cores from the dunite xenoliths and xenocrysts, indicates that these ofivine xenocrysts and dunite xenoliths could represent the residue of ancient （Archean or Paleopro. terozoic） lithospheric mantle and might have experienced the same intensive modification by silica-rich melts as the host magma, resulting in enrichment in MgO and SiO2.展开更多
The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%） ＋ chr...The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%） ＋ chromite （1%-4%） ＋ diopside （〈1%）. Two types of olivine are found in thin sections： one （Fo = 94） is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other （Fo = 96） is fine-grained and poly-angied. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system （EDS） with unitary analytical method, the average compositions of the inclusions are： Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3, 9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%- 5.27%, which is quite similar to those of amphibole. Diopside is anhedral f＇dling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines, sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and A! and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAI2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na^＋, Al^3＋, Ca^2＋, Fe^3＋, Cr^3＋. With temperature decreasing, the olivine solid solution decomposed; and Fe^3＋, Cr^3＋ diffused into magnetite and Ca^2＋ and Na^＋ into clinopyroxene, both of which formed intergrowth textures. A few Fe^3＋ and Cr^3＋ entered interstitial chromite. Through later tectonism, the peridotite recrystallized and formed deformational coarse grained olivine, fine grained and poly-angled olivine, and euhedral grained chromite. Due to the fast cooling rate of the rock or rapid tectonic emplacement, the exsolution textures in olivine and compositional zones of chromite are preserved.展开更多
Exsolution microstructures in olivine grains from dunite units in a few selected tectonic environments are reported here. They include lamellae of clinopyroxene and clinopyroxene-magnetite intergrowth in the Gaositai ...Exsolution microstructures in olivine grains from dunite units in a few selected tectonic environments are reported here. They include lamellae of clinopyroxene and clinopyroxene-magnetite intergrowth in the Gaositai and Yellow Hill Alaskan-type complexes, clinopyroxene-magnetite intergrowth in the Klzildag ophiolite, and chromite lamellae in the Hongshishan mafic-ultramafic intrusive complex. These lamellae commonly occur as needle- or rod-like features and are oriented in olivine grains. The host olivine grains have Fo contents of 92.5-92.6 in the Gaositai complex, 86.5-90.1 in the Yellow Hill complex, 93.2-93.4 in the Klzlldag ophiolite and 86.9-88.3 in the Hongshishan complex. Clinopyroxene in the rod-like intergrowth exsolved in olivine grains in the Gaositai and Yellow Hill is diopside with similar major element compositions of CaO （23.6-24.3wt%）, SiO2 （52.2-54.0wt%）, A1203 （0.67-2.15wt%）, Cr203 （0.10-0.42wt%） and Na20 （0.14-0.26wt%）. It falls into the compositional field of hydrothermal clinopyroxene and its origin is thus probably related to reaction between dunite and fluids. The enrichment of the fluids in Ca2＋, Fe3＋, Cr3＋ and Na＋, resulted in elevated concentrations of these cations in olivine solid solutions via the reaction. With decreasing temperature, the olivine solid solutions altered to an intergrowth of magnetite and clinopyroxene. The Fe3＋ and Cr3＋ preferentially partitioned into magnetite, while Ca2＋ and Na＋ entered clinopyroxene. Since the studied Alaskan-type complexes and ophiolite formed in a subduction environment, the fluids were probably released from the subducted slab. In contrast, the exsolved chromite in olivine grains from the Hongshishan complex that formed in post-orogenic extension setting can be related to olivine equilibrated with Cr-bearing liquid. Similarly, these lamellae have all been observed in serpentine surrounding olivine grains, indicating genetic relations with serpentinization.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
Phlogopiie-and diopside-bearing dunite occurs as rounded inclusions in hornblende-diorite. Thepetrofabrics, mineral composition and abundances of the trace elements in the dunite indicate that the inclu-sions were der...Phlogopiie-and diopside-bearing dunite occurs as rounded inclusions in hornblende-diorite. Thepetrofabrics, mineral composition and abundances of the trace elements in the dunite indicate that the inclu-sions were derived from the upper mantle and are the residues of high-degree partial melting of mantlepeirdotite. The study of trace elements in the inclusions and their host rocks shows that the magma was origi-nated from the mantle which was enriched in incompatible elements by mantle metasomatism prior to the par-tial melting.展开更多
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
The thermal conductivity, thermal diffusivity and heat capacity per unit volume of dunite rocks taken from Chillas near Gilgit, Pakistan have been measured simultaneously using transient plane source technique. The te...The thermal conductivity, thermal diffusivity and heat capacity per unit volume of dunite rocks taken from Chillas near Gilgit, Pakistan have been measured simultaneously using transient plane source technique. The temperature dependence of thermal transport properties is studied in the temperature range 83-303 K. Different relations for the estimation of thermal conductivity are also tested. Thermal conductivity data obey the modified Eucken’s law in the temperature range of measurements.展开更多
The Songshugou dunite body, which occupies an area of about 20 km2, is the largest ultramafic massif in the eastern Qinling orogenic belt, Central China. The major compo-nent of this body is dunitic rocks including my...The Songshugou dunite body, which occupies an area of about 20 km2, is the largest ultramafic massif in the eastern Qinling orogenic belt, Central China. The major compo-nent of this body is dunitic rocks including mylonitic dunite and coarse-grained dunite; they oc-cupy about 95 vol% of the total body. Petrography, mineral composition, major and trace ele-ments and primitive melt inclusions have been investigated in this paper; all revealed that this dunite body is the product of melt-rock interaction by porous percolation flow. In comparison with dunite sills or veins in harzburgite from the basal part of Oman ophiolite, this dunite body is characterized by lower contents of Al2O3, CaO and HREE but higher content of highly incom-patible elements and Zr and Hf. The LREE enriched patterns and primitive mantle normalized spidergrams of trace elements are also different from the Oman dunite. Combining with melt in-clusions observed in olivines, we conclude that this dunite body is the product of large- scale porous percolation flow of high-MgO melts within depleted mantle peridotites. The high-MgO magma, in essence, was most probably produced at the hot head of an upwelling mantle plume. The occurrence of the Songshugou dunite body is closely associated with the activity of mantle super-plume in Neo-Proterozoic era in the Yangtze Craton.展开更多
The electrical conductivities of the dunite from the Qinghai-Xizang (Tibetan) Plateau were measured with the impedance spectra method at 1.0-4.0 GPa and 643-1093 K. The experimental results indicated that activation e...The electrical conductivities of the dunite from the Qinghai-Xizang (Tibetan) Plateau were measured with the impedance spectra method at 1.0-4.0 GPa and 643-1093 K. The experimental results indicated that activation enthalpies of the dunite are smaller than 0.9 eV, the conduction mechanism in dunite may be attributed to the mixed electrical conduction involving grain interiors and boundaries. On the basis of the results of this experiment, we can deduce that there exists cold mantle in the area of Gaize-Lugu in the Qinghai-Xizang (Tibetan) Plateau by reverse methods from the magnetotelluric sounding data (conductivity-depths profile) available for western Tibet. The result provides the present cold mantle viewpoint with strong proof on the basis of high temperature and pressure experiments.展开更多
Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The fir...Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The first type shows tabular texture and high Mg# values (93—94) in olivines. The second type is characterized by the metamorphic-deformation texture superimposed by later metasomatism and relatively low olivine Mg# values (86—87). The mineral chemical data indicate that the former could be derived from ancient lithospheric mantle and the latter could have resulted from silica-rich melt metasomatism. The exsolution texture and the high Mg# value in clinopyroxenes, together with the rather high equilibrium temperature, imply that the pyroxenite xenoliths could be the cumulates of mantle-derived magma in the uppermost mantle or near the crust-mantle boundary in the Mesozoic.展开更多
A megacrystal zircon occurs in serpentinized dunite veins from North Qaidam, northwestern China. It is red-brown and 3―4 mm long and 2 mm wide in size. BSE imaging shows the presence of micro-grains (30―50 μm) of z...A megacrystal zircon occurs in serpentinized dunite veins from North Qaidam, northwestern China. It is red-brown and 3―4 mm long and 2 mm wide in size. BSE imaging shows the presence of micro-grains (30―50 μm) of zircon between olivine and serpentine, part of them gathering into clusters (100―300 μm). Thus we infer that these zircon crystals were precipitated from hydrothermal fluid. Inclusions of baddeleyite (white) in the shape of isolated island locally occur in the large zircon (grey), implying that the former formed earlier than the latter. The mirco-baddeleyite (50―100 μm) aggregate consists of baddeleyite (3―5 μm) and olivine (<5 μm), indicating the zircon formation through interaction between baddeleyite and silica-bearing fluid. Therefore, we consider a genetic link between the formation of the large zircon and the serpentinization of dunite. SHIRIMP U-Pb dating of the large zircon gave two groups of concordant ages at 414 ± 13 Ma and 371 ± 9 Ma, respectively. This might reflect two episodes of zircon growth in response to two episodes of fluid action.展开更多
Four dunite xenoliths from the Tietonggou intrusion of western Shandong,China,were subjected to SHRIMP zircon U-Pb dating to constrain timing of the North China Craton(NCC) destruction,a topic of much controversy.Cath...Four dunite xenoliths from the Tietonggou intrusion of western Shandong,China,were subjected to SHRIMP zircon U-Pb dating to constrain timing of the North China Craton(NCC) destruction,a topic of much controversy.Cathodoluminescence images revealed that 15 of the 18 zircon grains from the xenoliths display striped absorption.The rest showed oscillatory growth zoniation.All the zircons had variable contents of Th(49-3569 ppm;average,885 ppm) and U(184-5398 ppm;average,1277 ppm),and variable Th/U ratios(0.15-2.04).These zircon characteristics indicate a magmatic origin.The zircon age data can be divided into five groups:131-145,151-164,261-280,434-452,and 500-516 Ma.Group I(131-145 Ma) is consistent with timing of formation of the Tietonggou high-Mg diorites.Group II(151-164 Ma) is similar in age to Middle-Late Jurassic magmatism in the eastern NCC,which included both mantle-derived and intensive crust-derived magmatism.Group III(261-280 Ma) is similar in age to the Emeishan large igneous province,and Group IV(434-452 Ma) is similar in age to Paleozoic high-silica magmatism in the eastern NCC.Group V(500-516 Ma) may correspond to the global Pan-African event.Results indicate repeated modification of lithospheric mantle in the eastern NCC,and suggest that the most intensive modification occurred in the late Mesozoic(131-164 Ma).展开更多
基金supported by Fonds Wetenschappelijk Onderzoek-Vlaanderen(FWO).D.M.acknowledges support from FWO in the form of strategic basic research fellowships(File number:1S13924N).
文摘This study investigates the leaching and purification processes for dunite slurry,a common mining waste material,and the carbonation processes for the mineralization of CO_(2) with Mg^(2+).Results indicate that HCl is a promising leaching agent,and pH and temperature are major factors in controlling the efficiency of the leaching process,with leaching efficiencies of 82%achieved after 4 h using 2 M HCl solution at 75℃.The removal of other ions like Fe^(3+),Fe^(2+),and Al^(3+)through the purification of the leachate using ammonium hydroxide was also proven to be effective,completely removing iron and aluminum from the leachate from starting concentrations of 3.10 and 0.40 g/L,respectively.The carbonation of magnesium at room temperature was investigated with both purified leachate and pure MgCl_(2) aqueous solution.Nesquehonite crystals began to form after 1.5 h with a conversion of Mg^(2+)to nesquehonite of approximately 5%.The produced crystals possess a needle-like shape,which could be modified using the biopolymers pectin and xanthan.Pectin had a limited influence on the length of the crystals,reducing the needle length with increasing pectin concentration.Xanthan,on the other hand,shortened and widened the needle-like structure into a column shape as more xanthan was added.This study demonstrates the potential for this process to utilize mining wastes and sequester CO_(2),producing useful mineral products in the process.
基金supported by the National Natural Science Foundation of China (No. 90814003)the Ministry of Science and Technology of China (No. 2009CB825005)+1 种基金the Ministry of Education of China (No. 200801830039)the MOST Special Fund from the State Key Laboratory of Geo-logical Processes and Mineral Resources, China University of Geosciences
文摘This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi＇anli （西安里） hornblende （Hb）-gahbros from the southern Taihang （太行） Mountains, with the aim of constraining the nature of the Mesozoic lithospheric mantle in Central China. Rounded dunite xenoliths are 1-3 cm3 in size and display porphyroelastic, tabular, and protogranular textures. Chromite with Cr#=60-89 is common in the xenoliths. Oilvine xenocrysts of 4-6 mm in size are also found in the Hb-gabbros. Orthopyroxene reaction rims are commonly observed around olivine xenocrysts or between dunite xenoliths and host rocks. The porphyroclastic olivines within dunite xenoliths and olivine xenoerysts have kink bands and Mg#=83-94. The Mg# of olivine cores and rims are 89-94 （average, 90） and 83-86 （average, 84.4）, respectively. The CaO contents of all olivines from the xenoliths and xenocrysts are less than 0.1 wt.%, suggesting a Hthospheric mantle origin. The Ca content （214 ppm-818 ppm） and Ti content （15 ppm-137 ppm） in the xenoliths and xenocrysts are similar to those of olivines from the dunite xenoliths, but are much higher than those of olivines from harzburgite and lherzolite xenoliths in the Fushan （符山） intrusion. This finding implies that the xenoliths and xenocrysts may have originated from harzburgites or lherzolites that were intensively modified by silica-rich melts. This result, combined with high Mg# （92-94） of olivine cores from the dunite xenoliths and xenocrysts, indicates that these ofivine xenocrysts and dunite xenoliths could represent the residue of ancient （Archean or Paleopro. terozoic） lithospheric mantle and might have experienced the same intensive modification by silica-rich melts as the host magma, resulting in enrichment in MgO and SiO2.
文摘The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%） ＋ chromite （1%-4%） ＋ diopside （〈1%）. Two types of olivine are found in thin sections： one （Fo = 94） is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other （Fo = 96） is fine-grained and poly-angied. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system （EDS） with unitary analytical method, the average compositions of the inclusions are： Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3, 9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%- 5.27%, which is quite similar to those of amphibole. Diopside is anhedral f＇dling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines, sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and A! and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAI2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na^＋, Al^3＋, Ca^2＋, Fe^3＋, Cr^3＋. With temperature decreasing, the olivine solid solution decomposed; and Fe^3＋, Cr^3＋ diffused into magnetite and Ca^2＋ and Na^＋ into clinopyroxene, both of which formed intergrowth textures. A few Fe^3＋ and Cr^3＋ entered interstitial chromite. Through later tectonism, the peridotite recrystallized and formed deformational coarse grained olivine, fine grained and poly-angled olivine, and euhedral grained chromite. Due to the fast cooling rate of the rock or rapid tectonic emplacement, the exsolution textures in olivine and compositional zones of chromite are preserved.
基金financially supported by the National Natural Science Foundation of China (Grants 41522203, 41673037 and 41772055)Youth Innovation Promotion Association, Chinese Academy of Sciences (Grant 2017095)
文摘Exsolution microstructures in olivine grains from dunite units in a few selected tectonic environments are reported here. They include lamellae of clinopyroxene and clinopyroxene-magnetite intergrowth in the Gaositai and Yellow Hill Alaskan-type complexes, clinopyroxene-magnetite intergrowth in the Klzildag ophiolite, and chromite lamellae in the Hongshishan mafic-ultramafic intrusive complex. These lamellae commonly occur as needle- or rod-like features and are oriented in olivine grains. The host olivine grains have Fo contents of 92.5-92.6 in the Gaositai complex, 86.5-90.1 in the Yellow Hill complex, 93.2-93.4 in the Klzlldag ophiolite and 86.9-88.3 in the Hongshishan complex. Clinopyroxene in the rod-like intergrowth exsolved in olivine grains in the Gaositai and Yellow Hill is diopside with similar major element compositions of CaO （23.6-24.3wt%）, SiO2 （52.2-54.0wt%）, A1203 （0.67-2.15wt%）, Cr203 （0.10-0.42wt%） and Na20 （0.14-0.26wt%）. It falls into the compositional field of hydrothermal clinopyroxene and its origin is thus probably related to reaction between dunite and fluids. The enrichment of the fluids in Ca2＋, Fe3＋, Cr3＋ and Na＋, resulted in elevated concentrations of these cations in olivine solid solutions via the reaction. With decreasing temperature, the olivine solid solutions altered to an intergrowth of magnetite and clinopyroxene. The Fe3＋ and Cr3＋ preferentially partitioned into magnetite, while Ca2＋ and Na＋ entered clinopyroxene. Since the studied Alaskan-type complexes and ophiolite formed in a subduction environment, the fluids were probably released from the subducted slab. In contrast, the exsolved chromite in olivine grains from the Hongshishan complex that formed in post-orogenic extension setting can be related to olivine equilibrated with Cr-bearing liquid. Similarly, these lamellae have all been observed in serpentine surrounding olivine grains, indicating genetic relations with serpentinization.
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Phlogopiie-and diopside-bearing dunite occurs as rounded inclusions in hornblende-diorite. Thepetrofabrics, mineral composition and abundances of the trace elements in the dunite indicate that the inclu-sions were derived from the upper mantle and are the residues of high-degree partial melting of mantlepeirdotite. The study of trace elements in the inclusions and their host rocks shows that the magma was origi-nated from the mantle which was enriched in incompatible elements by mantle metasomatism prior to the par-tial melting.
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.
文摘The thermal conductivity, thermal diffusivity and heat capacity per unit volume of dunite rocks taken from Chillas near Gilgit, Pakistan have been measured simultaneously using transient plane source technique. The temperature dependence of thermal transport properties is studied in the temperature range 83-303 K. Different relations for the estimation of thermal conductivity are also tested. Thermal conductivity data obey the modified Eucken’s law in the temperature range of measurements.
基金the Major State Basic Resesrch Development Projects(Gant No.2001CB409801)the National Natural Science Foundation of China(Grant No.49972075) the Foundation of Continental Dynamic Laboratory of Northwestern Univeristy.
文摘The Songshugou dunite body, which occupies an area of about 20 km2, is the largest ultramafic massif in the eastern Qinling orogenic belt, Central China. The major compo-nent of this body is dunitic rocks including mylonitic dunite and coarse-grained dunite; they oc-cupy about 95 vol% of the total body. Petrography, mineral composition, major and trace ele-ments and primitive melt inclusions have been investigated in this paper; all revealed that this dunite body is the product of melt-rock interaction by porous percolation flow. In comparison with dunite sills or veins in harzburgite from the basal part of Oman ophiolite, this dunite body is characterized by lower contents of Al2O3, CaO and HREE but higher content of highly incom-patible elements and Zr and Hf. The LREE enriched patterns and primitive mantle normalized spidergrams of trace elements are also different from the Oman dunite. Combining with melt in-clusions observed in olivines, we conclude that this dunite body is the product of large- scale porous percolation flow of high-MgO melts within depleted mantle peridotites. The high-MgO magma, in essence, was most probably produced at the hot head of an upwelling mantle plume. The occurrence of the Songshugou dunite body is closely associated with the activity of mantle super-plume in Neo-Proterozoic era in the Yangtze Craton.
基金This work was supported by the National Climbing Program (Grant No. 95-P-39) under the auspices of the National Key Project on the Tibetan Plateau (Grant No. G1998040800) the National Natu- ral Science Foundation of China (Grant No. 49674221).
文摘The electrical conductivities of the dunite from the Qinghai-Xizang (Tibetan) Plateau were measured with the impedance spectra method at 1.0-4.0 GPa and 643-1093 K. The experimental results indicated that activation enthalpies of the dunite are smaller than 0.9 eV, the conduction mechanism in dunite may be attributed to the mixed electrical conduction involving grain interiors and boundaries. On the basis of the results of this experiment, we can deduce that there exists cold mantle in the area of Gaize-Lugu in the Qinghai-Xizang (Tibetan) Plateau by reverse methods from the magnetotelluric sounding data (conductivity-depths profile) available for western Tibet. The result provides the present cold mantle viewpoint with strong proof on the basis of high temperature and pressure experiments.
基金supported by the Foundation for Doctorate Subjects of the Ministry of Education of China(Grant No.20010183007)the National Natural Science Foundation of China(Grant No.40133020).
文摘Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The first type shows tabular texture and high Mg# values (93—94) in olivines. The second type is characterized by the metamorphic-deformation texture superimposed by later metasomatism and relatively low olivine Mg# values (86—87). The mineral chemical data indicate that the former could be derived from ancient lithospheric mantle and the latter could have resulted from silica-rich melt metasomatism. The exsolution texture and the high Mg# value in clinopyroxenes, together with the rather high equilibrium temperature, imply that the pyroxenite xenoliths could be the cumulates of mantle-derived magma in the uppermost mantle or near the crust-mantle boundary in the Mesozoic.
基金Supported by the Basic Outlay of Scientific Research Work from Ministry of Science and Technology of the People's Republic of China (Grant No. J0710)China Geological Survey Project (Grant No. 1212010611811)
文摘A megacrystal zircon occurs in serpentinized dunite veins from North Qaidam, northwestern China. It is red-brown and 3―4 mm long and 2 mm wide in size. BSE imaging shows the presence of micro-grains (30―50 μm) of zircon between olivine and serpentine, part of them gathering into clusters (100―300 μm). Thus we infer that these zircon crystals were precipitated from hydrothermal fluid. Inclusions of baddeleyite (white) in the shape of isolated island locally occur in the large zircon (grey), implying that the former formed earlier than the latter. The mirco-baddeleyite (50―100 μm) aggregate consists of baddeleyite (3―5 μm) and olivine (<5 μm), indicating the zircon formation through interaction between baddeleyite and silica-bearing fluid. Therefore, we consider a genetic link between the formation of the large zircon and the serpentinization of dunite. SHIRIMP U-Pb dating of the large zircon gave two groups of concordant ages at 414 ± 13 Ma and 371 ± 9 Ma, respectively. This might reflect two episodes of zircon growth in response to two episodes of fluid action.
基金supported by the National Basic Research Program of China (2009CB825005)the National Natural Science Foundation of China (90814003,90714010,91014004 and 41002018)
文摘Four dunite xenoliths from the Tietonggou intrusion of western Shandong,China,were subjected to SHRIMP zircon U-Pb dating to constrain timing of the North China Craton(NCC) destruction,a topic of much controversy.Cathodoluminescence images revealed that 15 of the 18 zircon grains from the xenoliths display striped absorption.The rest showed oscillatory growth zoniation.All the zircons had variable contents of Th(49-3569 ppm;average,885 ppm) and U(184-5398 ppm;average,1277 ppm),and variable Th/U ratios(0.15-2.04).These zircon characteristics indicate a magmatic origin.The zircon age data can be divided into five groups:131-145,151-164,261-280,434-452,and 500-516 Ma.Group I(131-145 Ma) is consistent with timing of formation of the Tietonggou high-Mg diorites.Group II(151-164 Ma) is similar in age to Middle-Late Jurassic magmatism in the eastern NCC,which included both mantle-derived and intensive crust-derived magmatism.Group III(261-280 Ma) is similar in age to the Emeishan large igneous province,and Group IV(434-452 Ma) is similar in age to Paleozoic high-silica magmatism in the eastern NCC.Group V(500-516 Ma) may correspond to the global Pan-African event.Results indicate repeated modification of lithospheric mantle in the eastern NCC,and suggest that the most intensive modification occurred in the late Mesozoic(131-164 Ma).
