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Edward M. Ripley - One of the best experts on this subject based on the ideXlab platform.
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olivine o isotope and trace element constraints on source variation of Picrites in the emeishan flood basalt province sw china
Lithos, 2019Co-Authors: Junhua Yao, Edward M. Ripley, Weiguang Zhu, Hong Zhong, Zhongjie BaiAbstract:Abstract Like many continental flood basalt (CFB) provinces in the world, the source mantle compositions (peridotites or pyroxenites) of the Emeishan CFB province in SW China are still debated. We have used the combination of olivine O isotopes determined in situ using SIMS and trace element abundances measured in situ using LA-ICP-MS to address this fundamental problem. The newly discovered Picrites in the Emeishan CFB province at Yumen are used in this study. In addition, we have also analyzed primitive olivine phenocrysts with known O isotope ratios from four other Picrite occurrences (Maoniuping, Tanglanghe, Wuguijing and Wulongba) in the Emeishan CFB province for trace element abundances. Based on whole rock compositions the Picrite samples from Wulongba belong to the low-Ti group (Ti/Y 500). Mineral chemical data reveal that the two different groups of Picrites can be distinguished by using Ti/Al of olivine phenocrysts and Cr-spinel inclusions enclosed in olivine. Specifically, the high-Ti Picrite group is characterized by 10Ti/Al (molar) >0.9 and >0.5 for olivine phenocrysts and Cr-spinel inclusions, respectively. In the mantle source discrimination diagrams based on olivine 100Mn/Fe versus 100Ni/Mg or 100Ca/Fe, both groups of Picrites plot between the suggested fields of peridotite and pyroxenite mantle sources. In the same type of diagrams based on olivine Mn/Zn and 10000Zn/Fe, both groups of Picrites plot exclusively in the fields for a peridotite mantle source. The mean δ18O value of olivine phenocrysts from the Yumen high-Ti Picrites is 5.19 ± 0.25‰ (1σ, n = 35), which is significantly lower than that for the Wulongba low-Ti Picrites (5.6 ± 0.15‰) but is similar to values (5.1 ± 0.15 to 5.3 ± 0.15‰) for the high-Ti Picrites from elsewhere (Maoniuping, Talanghe and Wuguijing) in the Emeishan CFB province. The mean δ18O values of olivine phenocrysts from the Emeishan high-Ti Picrites at different locations are all within the range of typical mantle olivine values (5.1 ± 0.3‰). Based on these results, we conclude that the high-Ti Picrites in the Emeishan CFB province were primarily derived from a modally enriched peridotite mantle source. Our new olivine Zn-Mn-Fe data are consistent with the view that the Wulongba low-Ti Picrites were derived from a lithospheric peridotite mantle source.
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an integrated chemical and oxygen isotopic study of primitive olivine grains in Picrites from the emeishan large igneous province sw china evidence for oxygen isotope heterogeneity in mantle sources
Geochimica et Cosmochimica Acta, 2017Co-Authors: Songyue Yu, Chusi Li, Xieyan Song, Edward M. Ripley, Nengping Shen, Liemeng ChenAbstract:Abstract Recognition of the nature of potential mantle sources of continental flood basalts is complicated by possible overprinting related to crustal contamination as magmas migrate to the surface (Arndt and Christensen, 1992). However, in picritic lava flows primitive olivine phenocrysts that formed early in the crystallization sequence can potentially provide unperturbed information of their mantle source. We have carried out an integrated chemical and oxygen isotopic ( in situ SIMS) study of primitive olivine grains (Fo ranging from 88 to 92.6 mol%) in the Emeishan Picrites at different locations (Wulongba, Wuguijing, Tanglanghe and Maoniuping). We use these data to evaluate the geochemical nature of mantle sources for magmas from which the primitive olivine crystallized. The primitive olivine grains in the samples from Maoniuping, Wuguijing and Tanglanghe are characterized by mantle-like δ 18 O values (mean values are 5.1 ± 0.3‰ (2 σ , n = 53), 5.2 ± 0.3‰ (2 σ , n = 122) and 5.3 ± 0.3‰ ( n = 25), respectively) coupled with generally low Fo contents (mean values are 88.7 ± 1.4 mol% (2 σ , n = 53), 89.8 ± 1.8 mol% (2 σ , n = 122) and 89.4 ± 1.8 mol% (2 σ , n = 25), respectively). In contrast, the olivine grains in the samples from Wulongba are characterized by elevated δ 18 O values (mean = 5.6 ± 0.3‰ (2 σ , n = 58)) coupled with generally higher Fo contents (mean = 91 ± 2.8 mol% (2 σ , n = 58)) than primitive olivine in the samples from the other locations. Based on olivine compositions, primitive olivine in Picrites from Maoniuping, Tanglanghe and Wuguijing are consistent with derivation from hybrid mantle sources containing similar proportions of peridotite and pyroxenite/eclogite components. The δ 18 O values of these primitive olivine grains are consistent with melting of plume source materials. The chemical composition of the primitive olivine from Wulongba are also consistent with derivation from a hybrid peridotite/pyroxenite source, but the high δ 18 O values suggest that at least locally the pyroxenitic source was characterized by 18 O-enrichment related to a higher degree of seawater interaction with the oceanic crust protolith. An alternative explanation is that olivine in the Wulongba Picrite reflects derivation from lithospheric mantle that was modified by subduction-related processes in the Neoproterozoic. The high-Fo content of the Wulongba Picrites may be due to the higher fO 2 conditions of the partial melt generated in the subduction modified lithospheric mantle, or to a higher degree of partial melting.
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the significance of pge variations with sr nd isotopes and lithophile elements in the emeishan flood basalt province from sw china to northern vietnam
Lithos, 2016Co-Authors: Edward M. Ripley, Yan TaoAbstract:Abstract New analyses of siderophile–lithophile elements and Sr–Nd isotopes in the Permian basalts and Picrites from northern Vietnam, the southernmost occurrence of the Emeishan flood basalt province, together with previously published data, are used to address the question of whether any meaningful correlation between these elements and isotopes exists at a province scale. The available data show that negative correlations between e Nd, ( 87 Sr/ 86 Sr) i and mantle-normalized (Nb/Th) n are present in the basalts but not in the associated Picrites. This indicates that crustal contamination is negligible in the Picrites but significant in some of the basalts. The Picrites and basalts from the entire province show negative correlations between (Rh/Ru) n , (Pt/Ru) n , (Pd/Ru) n and Mg-number. This indicates that Ru behaves compatibly whereas Rh, Pt and Pd behave incompatibly during magma differentiation. The incompatible behavior of Rh in natural basaltic systems is also supported by the fact that (Pt/Rh) n remains constant with decreasing Mg-number in the lavas. Depletions of Pd and Pt, and to a lesser degree Cu, in some basaltic samples characterized by relatively low e Nd and (Nb/Th) n support the notion that sulfide saturation in the magmas was triggered by a combination of siliceous crustal contamination and addition of external sulfur. Within the entire flood basalt province only the Picrites from Song Da, northern Vietnam show clear depletion in Ir relative to Ru. These Picrites are also characterized higher Al 2 O 3 /TiO 2 and lower mantle-normalized La/Yb (0.2–2.4) than those from elsewhere in the province, possibly due to the involvement of an Ir-depleted, fertile mantle component in magma generation at this location.
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mineralogical petrological and geochemical studies of the limahe mafic ultramatic intrusion and associated ni cu sulfide ores sw china
Mineralium Deposita, 2008Co-Authors: Chusi Li, Xieyan Song, Edward M. RipleyAbstract:The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of Picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted Picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the Picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the Picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the Picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the Picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.
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mineralogical petrological and geochemical studies of the limahe mafic ultramatic intrusion and associated ni cu sulfide ores sw china
Mineralium Deposita, 2008Co-Authors: Chusi Li, Xieyan Song, Edward M. RipleyAbstract:The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of Picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted Picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the Picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the Picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the Picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the Picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.
Chusi Li - One of the best experts on this subject based on the ideXlab platform.
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an integrated chemical and oxygen isotopic study of primitive olivine grains in Picrites from the emeishan large igneous province sw china evidence for oxygen isotope heterogeneity in mantle sources
Geochimica et Cosmochimica Acta, 2017Co-Authors: Songyue Yu, Chusi Li, Xieyan Song, Edward M. Ripley, Nengping Shen, Liemeng ChenAbstract:Abstract Recognition of the nature of potential mantle sources of continental flood basalts is complicated by possible overprinting related to crustal contamination as magmas migrate to the surface (Arndt and Christensen, 1992). However, in picritic lava flows primitive olivine phenocrysts that formed early in the crystallization sequence can potentially provide unperturbed information of their mantle source. We have carried out an integrated chemical and oxygen isotopic ( in situ SIMS) study of primitive olivine grains (Fo ranging from 88 to 92.6 mol%) in the Emeishan Picrites at different locations (Wulongba, Wuguijing, Tanglanghe and Maoniuping). We use these data to evaluate the geochemical nature of mantle sources for magmas from which the primitive olivine crystallized. The primitive olivine grains in the samples from Maoniuping, Wuguijing and Tanglanghe are characterized by mantle-like δ 18 O values (mean values are 5.1 ± 0.3‰ (2 σ , n = 53), 5.2 ± 0.3‰ (2 σ , n = 122) and 5.3 ± 0.3‰ ( n = 25), respectively) coupled with generally low Fo contents (mean values are 88.7 ± 1.4 mol% (2 σ , n = 53), 89.8 ± 1.8 mol% (2 σ , n = 122) and 89.4 ± 1.8 mol% (2 σ , n = 25), respectively). In contrast, the olivine grains in the samples from Wulongba are characterized by elevated δ 18 O values (mean = 5.6 ± 0.3‰ (2 σ , n = 58)) coupled with generally higher Fo contents (mean = 91 ± 2.8 mol% (2 σ , n = 58)) than primitive olivine in the samples from the other locations. Based on olivine compositions, primitive olivine in Picrites from Maoniuping, Tanglanghe and Wuguijing are consistent with derivation from hybrid mantle sources containing similar proportions of peridotite and pyroxenite/eclogite components. The δ 18 O values of these primitive olivine grains are consistent with melting of plume source materials. The chemical composition of the primitive olivine from Wulongba are also consistent with derivation from a hybrid peridotite/pyroxenite source, but the high δ 18 O values suggest that at least locally the pyroxenitic source was characterized by 18 O-enrichment related to a higher degree of seawater interaction with the oceanic crust protolith. An alternative explanation is that olivine in the Wulongba Picrite reflects derivation from lithospheric mantle that was modified by subduction-related processes in the Neoproterozoic. The high-Fo content of the Wulongba Picrites may be due to the higher fO 2 conditions of the partial melt generated in the subduction modified lithospheric mantle, or to a higher degree of partial melting.
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the magma plumbing system of the emeishan large igneous province and its role in basaltic magma differentiation in a continental setting
American Mineralogist, 2015Co-Authors: Keith Putirka, Ruizhong Hu, Chusi LiAbstract:Magmatic activity of the Emeishan large igneous province (ELIP) of SW China is one of the most significant geological events of the late Paleozoic. The large volume flood basalts plus rare Picrites were erupted in Late Permian. Previous studies indicate that the basalts are the derivatives of primary mantle-derived magma by fractional crystallization, but the depths at which this process took place remain unknown. To answer this question, we use phenocryst compositions and mineral-liquid thermobarometers to determine the P-T conditions of the magma reservoirs where crystallization occurred, then use these data to reconstruct the magma plumbing system of the igneous province. Thermobarometric calculations show that most Picrite-hosted clinopyroxene phenocrysts crystallized at ~25 km and 1200–1280 °C, whereas most basalt-hosted clinopyroxene phenocrysts crystallized at depths <20 km and temperatures <1200 °C. Some Picrites containing primitive olivine with Fo up to Fo92 likely formed by eruption of the most primitive magma with composition similar to the primary magma from the deepest reservoir possibly at the Moho. Parental magmas yield mantle potential temperatures of 1740–1810 °C, which are the highest such temperatures yet recorded for terrestrial magmas of any age. Less primitive Picrites containing both olivine and clinopyroxene phenocrysts formed by eruption of moderately fractionated magma from a reservoir in the middle crust. Basalts and basaltic andesites formed by eruption of the most fractionated magmas from the reservoirs in the upper crust, coinciding with the depths of coeval sulfide ore-bearing and Fe-Ti-V oxide ore-bearing mafic-ultramafic intrusions. The reason that the Emeishan volcanic sequence is dominated by basalts is because most of the mantle-derived magma was trapped in the middle and upper crusts, undergoing variable degrees of crystal fractionation plus crustal contamination before eruption. Primitive Picrites are rare because their eruption requires a trans-lithosphere conduit, which is difficult to create and maintain due to increasing lithospheric pressure with depth. The results from this study reveal that magma reservoirs at the crustal levels play a critical role in magma differentiation in a continental setting.
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u pb age and hf isotopes of zircon from basaltic andesite and geochemical fingerprinting of the associated Picrites in the emeishan large igneous province sw china
Mineralogy and Petrology, 2015Co-Authors: Qingyan Tang, Chusi Li, Mingjie ZhangAbstract:The ages of many Picrites associated with Permian flood basalts in the Emeishan large igneous province, SW China have been debated for a long time. Some researchers believe that these Picrites are co-magmatic with the flood basalts whereas others believe that they are Triassic picritic porphyrites or Cenozoic olivine-rich dikes. We report a U–Pb age of 256.2 ± 1.4 Ma for the youngest zircon grains from the Binchuan volcanic sequence which contains the disputed Picrites. This age is within the range of values reported for the intrusive and extrusive rocks of the Emeishan large igneous province. The eHf values (−0.3 to 6.6) of the youngest zircon crystals from the Binchuan volcanic sequence are similar to those (−5 to 10) of co-magmatic zircon crystals from the intrusive rocks of the Emeishan large igneous province. Our new data confirm that the Binchuan volcanic sequence is an integral part of the Emeishan large igneous province. The disputed and undisputed Picrites in Sichuan and Yunnan have similar olivine Fo-Ni-Mn compositions and whole-rock incompatible trace element ratios such as Th/Nb and Ti/Dy. This, together with their spatially close association with the Emeishan flood basalts, indicates that the disputed Picrites also belong to the Emeishan large igneous province. The confusing Cenozoic olivine-rich dikes in the region can be distinguished from the Picrites of the Emeishan large igneous province by their different olivine Fo-Ni-Mn compositions and whole-rock incompatible trace element ratios such as Th/Nb and Ti/Dy. The results from this study vindicate the use of the previously-disputed Picrites as evidences for Permian mantle plume activity in SW China.
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mineralogical petrological and geochemical studies of the limahe mafic ultramatic intrusion and associated ni cu sulfide ores sw china
Mineralium Deposita, 2008Co-Authors: Chusi Li, Xieyan Song, Edward M. RipleyAbstract:The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of Picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted Picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the Picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the Picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the Picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the Picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.
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mineralogical petrological and geochemical studies of the limahe mafic ultramatic intrusion and associated ni cu sulfide ores sw china
Mineralium Deposita, 2008Co-Authors: Chusi Li, Xieyan Song, Edward M. RipleyAbstract:The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of Picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted Picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the Picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the Picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the Picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the Picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.
Xieyan Song - One of the best experts on this subject based on the ideXlab platform.
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controls of mantle source and condition of melt extraction on generation of the picritic lavas from the emeishan large igneous province sw china
Journal of Asian Earth Sciences, 2020Co-Authors: Liemeng Chen, Jiangbo Lan, Qi Chen, Xieyan SongAbstract:Abstract Like many continental flood basalt (CFB) provinces in the world, the source mantle compositions and melting conditions for generation of the Emeishan CFB are highly debated. We have carried out an integrated Sr-Nd-O-Mg isotopic study of the Emeishan picritic lavas to evaluate possible effects of mantle heterogeneity on the magma composition. Moreover, we have used PRIMELT3 ( Herzberg and Asimow, 2015 ) to calculate the primary magma compositions and melting conditions for these picritic lavas. Picrites from Maoniuping, Tanglanghe and Wuguijing exhibit depleted Sr-Nd isotopic compositions (87Sr/86Sri = 0.7038–0.7050; eNd = 0.27–3.89), normal mantle-like δ26Mg (−0.27 to −0.2‰) and δ18O (5.0–5.4‰), which can be explained by partial melting of plume materials with negligible contribution of sedimentary carbonates. The Wulongba Picrites are characterized by depleted Sr-Nd isotopic compositions (87Sr/86Sri = 0.7041–0.7045; eNd = 2.57–2.85), slightly lower δ26Mg (−0.36 to −0.23‰) and higher δ18O (5.6–5.7‰), which were attributed to involvement of minor sedimentary carbonates (magnesite) in their mantle source. The calculated mantle potential temperatures for the Emeishan Picrites range from 1516 to 1596 °C. The initial melting pressures range from 4 to 5 GPa. The final melting pressures for the Wulongba Picrites (2–3 GPa) are lower than those for the Tanglanghe, Maoniuping and Wuguijing Picrites (>3 GPa). This suggests that the Wulongba Picrites were generated in shallower garnet-spinel transition zone of the upper mantle. Picrites from other three localities are entirely generated in garnet stability field of the upper mantle.
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an integrated chemical and oxygen isotopic study of primitive olivine grains in Picrites from the emeishan large igneous province sw china evidence for oxygen isotope heterogeneity in mantle sources
Geochimica et Cosmochimica Acta, 2017Co-Authors: Songyue Yu, Chusi Li, Xieyan Song, Edward M. Ripley, Nengping Shen, Liemeng ChenAbstract:Abstract Recognition of the nature of potential mantle sources of continental flood basalts is complicated by possible overprinting related to crustal contamination as magmas migrate to the surface (Arndt and Christensen, 1992). However, in picritic lava flows primitive olivine phenocrysts that formed early in the crystallization sequence can potentially provide unperturbed information of their mantle source. We have carried out an integrated chemical and oxygen isotopic ( in situ SIMS) study of primitive olivine grains (Fo ranging from 88 to 92.6 mol%) in the Emeishan Picrites at different locations (Wulongba, Wuguijing, Tanglanghe and Maoniuping). We use these data to evaluate the geochemical nature of mantle sources for magmas from which the primitive olivine crystallized. The primitive olivine grains in the samples from Maoniuping, Wuguijing and Tanglanghe are characterized by mantle-like δ 18 O values (mean values are 5.1 ± 0.3‰ (2 σ , n = 53), 5.2 ± 0.3‰ (2 σ , n = 122) and 5.3 ± 0.3‰ ( n = 25), respectively) coupled with generally low Fo contents (mean values are 88.7 ± 1.4 mol% (2 σ , n = 53), 89.8 ± 1.8 mol% (2 σ , n = 122) and 89.4 ± 1.8 mol% (2 σ , n = 25), respectively). In contrast, the olivine grains in the samples from Wulongba are characterized by elevated δ 18 O values (mean = 5.6 ± 0.3‰ (2 σ , n = 58)) coupled with generally higher Fo contents (mean = 91 ± 2.8 mol% (2 σ , n = 58)) than primitive olivine in the samples from the other locations. Based on olivine compositions, primitive olivine in Picrites from Maoniuping, Tanglanghe and Wuguijing are consistent with derivation from hybrid mantle sources containing similar proportions of peridotite and pyroxenite/eclogite components. The δ 18 O values of these primitive olivine grains are consistent with melting of plume source materials. The chemical composition of the primitive olivine from Wulongba are also consistent with derivation from a hybrid peridotite/pyroxenite source, but the high δ 18 O values suggest that at least locally the pyroxenitic source was characterized by 18 O-enrichment related to a higher degree of seawater interaction with the oceanic crust protolith. An alternative explanation is that olivine in the Wulongba Picrite reflects derivation from lithospheric mantle that was modified by subduction-related processes in the Neoproterozoic. The high-Fo content of the Wulongba Picrites may be due to the higher fO 2 conditions of the partial melt generated in the subduction modified lithospheric mantle, or to a higher degree of partial melting.
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mineralogical petrological and geochemical studies of the limahe mafic ultramatic intrusion and associated ni cu sulfide ores sw china
Mineralium Deposita, 2008Co-Authors: Chusi Li, Xieyan Song, Edward M. RipleyAbstract:The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of Picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted Picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the Picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the Picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the Picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the Picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.
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mineralogical petrological and geochemical studies of the limahe mafic ultramatic intrusion and associated ni cu sulfide ores sw china
Mineralium Deposita, 2008Co-Authors: Chusi Li, Xieyan Song, Edward M. RipleyAbstract:The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of Picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted Picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the Picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the Picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the Picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the Picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.
Liemeng Chen - One of the best experts on this subject based on the ideXlab platform.
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controls of mantle source and condition of melt extraction on generation of the picritic lavas from the emeishan large igneous province sw china
Journal of Asian Earth Sciences, 2020Co-Authors: Liemeng Chen, Jiangbo Lan, Qi Chen, Xieyan SongAbstract:Abstract Like many continental flood basalt (CFB) provinces in the world, the source mantle compositions and melting conditions for generation of the Emeishan CFB are highly debated. We have carried out an integrated Sr-Nd-O-Mg isotopic study of the Emeishan picritic lavas to evaluate possible effects of mantle heterogeneity on the magma composition. Moreover, we have used PRIMELT3 ( Herzberg and Asimow, 2015 ) to calculate the primary magma compositions and melting conditions for these picritic lavas. Picrites from Maoniuping, Tanglanghe and Wuguijing exhibit depleted Sr-Nd isotopic compositions (87Sr/86Sri = 0.7038–0.7050; eNd = 0.27–3.89), normal mantle-like δ26Mg (−0.27 to −0.2‰) and δ18O (5.0–5.4‰), which can be explained by partial melting of plume materials with negligible contribution of sedimentary carbonates. The Wulongba Picrites are characterized by depleted Sr-Nd isotopic compositions (87Sr/86Sri = 0.7041–0.7045; eNd = 2.57–2.85), slightly lower δ26Mg (−0.36 to −0.23‰) and higher δ18O (5.6–5.7‰), which were attributed to involvement of minor sedimentary carbonates (magnesite) in their mantle source. The calculated mantle potential temperatures for the Emeishan Picrites range from 1516 to 1596 °C. The initial melting pressures range from 4 to 5 GPa. The final melting pressures for the Wulongba Picrites (2–3 GPa) are lower than those for the Tanglanghe, Maoniuping and Wuguijing Picrites (>3 GPa). This suggests that the Wulongba Picrites were generated in shallower garnet-spinel transition zone of the upper mantle. Picrites from other three localities are entirely generated in garnet stability field of the upper mantle.
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an integrated chemical and oxygen isotopic study of primitive olivine grains in Picrites from the emeishan large igneous province sw china evidence for oxygen isotope heterogeneity in mantle sources
Geochimica et Cosmochimica Acta, 2017Co-Authors: Songyue Yu, Chusi Li, Xieyan Song, Edward M. Ripley, Nengping Shen, Liemeng ChenAbstract:Abstract Recognition of the nature of potential mantle sources of continental flood basalts is complicated by possible overprinting related to crustal contamination as magmas migrate to the surface (Arndt and Christensen, 1992). However, in picritic lava flows primitive olivine phenocrysts that formed early in the crystallization sequence can potentially provide unperturbed information of their mantle source. We have carried out an integrated chemical and oxygen isotopic ( in situ SIMS) study of primitive olivine grains (Fo ranging from 88 to 92.6 mol%) in the Emeishan Picrites at different locations (Wulongba, Wuguijing, Tanglanghe and Maoniuping). We use these data to evaluate the geochemical nature of mantle sources for magmas from which the primitive olivine crystallized. The primitive olivine grains in the samples from Maoniuping, Wuguijing and Tanglanghe are characterized by mantle-like δ 18 O values (mean values are 5.1 ± 0.3‰ (2 σ , n = 53), 5.2 ± 0.3‰ (2 σ , n = 122) and 5.3 ± 0.3‰ ( n = 25), respectively) coupled with generally low Fo contents (mean values are 88.7 ± 1.4 mol% (2 σ , n = 53), 89.8 ± 1.8 mol% (2 σ , n = 122) and 89.4 ± 1.8 mol% (2 σ , n = 25), respectively). In contrast, the olivine grains in the samples from Wulongba are characterized by elevated δ 18 O values (mean = 5.6 ± 0.3‰ (2 σ , n = 58)) coupled with generally higher Fo contents (mean = 91 ± 2.8 mol% (2 σ , n = 58)) than primitive olivine in the samples from the other locations. Based on olivine compositions, primitive olivine in Picrites from Maoniuping, Tanglanghe and Wuguijing are consistent with derivation from hybrid mantle sources containing similar proportions of peridotite and pyroxenite/eclogite components. The δ 18 O values of these primitive olivine grains are consistent with melting of plume source materials. The chemical composition of the primitive olivine from Wulongba are also consistent with derivation from a hybrid peridotite/pyroxenite source, but the high δ 18 O values suggest that at least locally the pyroxenitic source was characterized by 18 O-enrichment related to a higher degree of seawater interaction with the oceanic crust protolith. An alternative explanation is that olivine in the Wulongba Picrite reflects derivation from lithospheric mantle that was modified by subduction-related processes in the Neoproterozoic. The high-Fo content of the Wulongba Picrites may be due to the higher fO 2 conditions of the partial melt generated in the subduction modified lithospheric mantle, or to a higher degree of partial melting.
Yigang Xu - One of the best experts on this subject based on the ideXlab platform.
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the origins of high ti and low ti magmas in large igneous provinces insights from melt inclusion trace elements and sr pb isotopes in the emeishan large igneous province
Lithos, 2019Co-Authors: Le Zhang, Monica R Handler, Yadong Wu, Lei Zhang, Shengping Qian, Qing Yang, Yigang XuAbstract:Abstract High-Ti and low-Ti lava series occur simultaneously in many large igneous provinces (LIP); however, their origins remain debated. To address this issue, we performed a detailed geochemical study of olivine and olivine-hosted melt inclusions from the Dali Picrites in the Emeishan LIP. Although the Dali Picrite lavas have a limited range of whole-rock Ti/Y ratios (~356–404; Wu et al., 2018), olivine-hosted melt inclusions have Ti/Y ratios that range from low-Ti to high-Ti (213–741). The Sr Pb isotopic compositions and trace element ratios (e.g., Nb/U and Nb/La) of the melt inclusions have a restricted range and display little correlation with Ti/Y ratios, indicating that the low-Ti and high-Ti lavas share compositionally similar source. Trace element mass balance modeling of the Emeishan lavas indicates a mantle source comprising ~84% peridotite from the lower mantle, ~15% recycled MORB, and ~1% pelagic sediment. Modeling results for the Emeishan and Karoo LIPs show that partial melts formed at greater depth in the mantle have higher Ti contents and Ti/Y ratios than those formed at shallower depths. Mixing between melts formed at different depths with different degrees of partial melting can produce the continuous range of Ti/Y ratios observed. The results demonstrate the strong influence of partial melting degree and pressure on the Ti content and Ti/Y ratio of partial melts.
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os nd and sr isotope and trace element geochemistry of the muli Picrites insights into the mantle source of the emeishan large igneous province
Lithos, 2010Co-Authors: Jie Li, Jifeng Xu, Katsuhiko Suzuki, Bin He, Yigang XuAbstract:Abstract A suite of Picrites and basalts from the Muli area, in the northwestern part of the Emeishan continental flood basalt province, provides new and valuable information on the geochemistry of the Emeishan Large Igneous Province (LIP) and its source. The Muli Picrites can be classified as type-1 or type-2. The former shows ocean–island basalt-like trace element characteristics, with γ Os (260 Ma) values and e Nd (260 Ma) values ranging from + 7.5 to + 11.5 and from + 6.0 to + 7.8, respectively. This is the first time that Picrites with highly radiogenic Os and high Os contents (up to 3.3 ppb) have been recognized in the Emeishan LIP. These characteristics probably reflect a relatively enriched component in the Emeishan LIP source. The type-2 Picrites are characterized by non-radiogenic γ Os (260 Ma) values ranging from − 4.2 to − 0.3, and they may be further subdivided into type-2A and type-2B Picrites. Type-2A Picrites contain moderate amounts of the light rare earth elements (LREEs), have low Ce N /Yb N values (1.1–2.0), and a relatively high initial e Nd (+ 5.0 to + 6.6). In terms of Os and Nd isotopes, the Muli type-2A Picrites are similar to the Song Da komatiites of Vietnam and the Gorgona Island Picrites, revealing the existence of a depleted mantle component in the Emeishan LIP source. In contrast with the type-2A Picrites, type-2B lavas exhibit a negative Nb anomaly and relatively lower initial e Nd and γ Os values (Nb/La > 1.8; e Nd (260 Ma) = − 5.5 to + 6.4; γ Os (260 Ma) = − 4.2 to − 1.9), suggesting that the type-2B lavas have a depleted mantle source, similar to type-2A, but that the type-2B lavas are also influenced by various degrees of mixing of depleted plume-derived melt, sub-continental lithospheric mantle, and/or continental crust. Given that the basalts in the Muli area show similar geochemical features to those of the type-2B Picrites, their origins are inferred to be similar.