In this study, 30 sediment samples were collected from the lower reaches of the Shichuanhe River in Xi’an, Shaanxi Province, China, to test the distribution of heavy metal elements in this area and for an analysis of...In this study, 30 sediment samples were collected from the lower reaches of the Shichuanhe River in Xi’an, Shaanxi Province, China, to test the distribution of heavy metal elements in this area and for an analysis of the pollution levels of this area, hope to provide guidance on agricultural production activities in this region. The results show that the heavy metal elements in this area are mainly concentrated at the Qinghe River and Shichuanhe River confluences. Furthermore, the element contents are higher than that of the background levels of the continental crust(UCC) and close to the background levels of the soil from Shaanxi Province;the two most enriched elements are Cd and As, with contents of 0.79 and 22.7 mg·kg-1, respectively, and their contents are 3.8 and 1.72 times higher than that of the background values. Herein, the heavy metal pollution assessment methods applied indicated that Cd and As are the two most abundant pollutant elements in the area’s soils. As has a peak geo-accumulation index value of 3, and the pollution level is high, while Cd exhibits high potential ecological risks due to its high toxicity(potential risk index of 143) and an active fraction of more than 64%.In addition, a principal component analysis and hierarchical cluster analysis study showed that there are two sources of the heavy metals in this area. The Zn, As, Ni, Cu, Pb,and Cr are mainly from natural sources, and the Cd likely comes from a discharge of untreated agricultural wastewater in the region. The Cd which poses a high potential risk and mainly results from human activities, needs to be further monitored.展开更多
Post-orogenic alkaline intrusions from the Sulu Orogenic Belt of eastern North China Craton consist of A-type granites.In this study,we report U-Pb zircon ages,geochemical data,Sr-Nd-Pb,and zircon Hf isotopic data for...Post-orogenic alkaline intrusions from the Sulu Orogenic Belt of eastern North China Craton consist of A-type granites.In this study,we report U-Pb zircon ages,geochemical data,Sr-Nd-Pb,and zircon Hf isotopic data for these rocks.The LA-ICP-MS U-Pb zircon analyses yield consistent ages ranging from 127.1±2.4 to 119.5±4.8 Ma for four samples.The alkaline rocks are characterized by high total alkalis(K2 O+Na2 O=8.32-10.11 wt%),light rare-earth element enrichment,and heavy rare-earth element depletion,with a wide range(La/Yb)N values(20-48),moderate negative Eu anomalies(Eu/Eu*=0.50-0.74),enrichment in large-ion lithophile elements(LILEs,i.e.,Rb,Th,U and Pb),and depletion in Ba,Sr and high field strength elements(HFSEs,i.e.,Nb,Ta,and Ti),high(87Sr/86Sr)i ranging from 0.708 to 0.7089,low sNd(t)values from-19.4 to-16.8,(206Pb/204Pb)i=16.751-16.935,(207Pb/204Pb)i=15.381-15.535,(208-Pb/204Pb)i=37.472-37.838,negativeεHf(t)values between-21.3 and-25.7 for the magmatic zircons,and larger TDM2 model ages from 2.5 to 2.8 Ga.These results suggest that the rocks were derived from a common enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials before magma generation.Furthermore,the geochemical and isotopic feature implies that the primary magma of these rocks originated through partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from lower crust eclogite.These rocks in this study may have been generated by subsequent fractionation of potassium feldspar,plagioclase,ilmenite,and/or rutile.However,negligible crustal contamination occurred during the diagenesis process.展开更多
The Baiyangping Cu-Ag polymetallic ore district is located in the northern part of the Lanping-Simao foreland fold belt,between the Jinshajiang-Ailaoshan and Lancangjiang faults,and the deposit can be divided into eas...The Baiyangping Cu-Ag polymetallic ore district is located in the northern part of the Lanping-Simao foreland fold belt,between the Jinshajiang-Ailaoshan and Lancangjiang faults,and the deposit can be divided into eastern and western ore zones.Based upon microscope observation of ore minerals and analysis of zinc,copper,and strontium isotope composition,we conclude that:(1)the zinc isotopic compositions of sphalerite from the eastern and western ore belt of the Baiyangping polymetallic ore deposits are enriched in both the heavy(-0.09‰ to+0.15‰) and light(-0.19‰ to-0.01‰)zinc isotopes.Rayleigh fractionation is likely the additional factor controlling the observed temporal and spatial variations in zinc isotopes in the two studied ore zones.The zinc isotopic composition in the Baiyangping polymetallic Pb-Zn deposits may have the same fractionation as that of magmatic-hydrothermal,VHMS,SEDEX,and MVT deposits,as demonstrated by geological and other geochemical evidence;(2) the range of δ^(65)Cu in massive tetrahedrite is from-0.06‰ to+0.12 ‰ that relates to the early stages of ore-formation,which are higher than that of venial chalcopyrite(from-0.72‰ to-0.07‰)formed at a late ore-forming stage in the western ore belt.Different ore-forming stages and alteration or leaching processes are likely the main factors controlling the observed variations in copper isotopes in the western ore zone;(3) the ^(87)Sr/^(86)Sr value of hydrothermal calcite in eastern(0.7080-0.7093) and western(0.7085-0.7113) ore belt suggested that mineralization of early calcite,with^(87)Sr/^(86)Sr values much higher than in ancient Late Triassic seawater,may be related to recrystallization from a radiogenic Sr-rich or silicifying fluid,either from the strata that the ore-forming fluid flows through or from other fluids.展开更多
Se-rich black rock series of the Middle and Late Permian system is widely distributed in Enshi Prefecture with an exposed area of 850 km~2,among which the unique Yutangba black rock series independent selenium deposit...Se-rich black rock series of the Middle and Late Permian system is widely distributed in Enshi Prefecture with an exposed area of 850 km~2,among which the unique Yutangba black rock series independent selenium deposit with industrial mining significance in the world is produced.However,the source and metallogenic mechanisms of Se are still controversial.In general,terrestrial weathering and submarine hydrothermal processes are the main source end members of Si and Se,and the related siliceous rocks record the deposition process of Si and Se from different sources.The study of lithofacies and paleogeography shows that western Hubei belongs to the near eastwest turn of the Yangzi platform in the Middle and Late Permian and becomes an inter-platform basin with nearly north-south direction.Therefore,the comparative study of the Yutangba deposit and the selenium-rich black rock series in the northern Shadi with high selenium content is expected to reveal the provenance evolution of the two sections in space,and further restrict the Se mineralization mechanism in the Enshi basin.From the element geochemistry study,the black rock series in two study areas may have formed in a transitional position of either the continental margin or continental slope,in the process of sedimentary,more terrigenous clastic materials entered.They are rich in lithophile elements V and Cr.δU>1.0,U/Th and V/(V+Ni)ratio indicate that the Se-rich strata of black rock series in the Enshi areas occurred in an anoxic reducing environment and formed in an environment between the ocean basin and the continental margin.From Si-O isotope geochemistry,the original Si source of the study area is thought to relate to a volcanic eruption,which leads to the enrichment of Si in the seawater.The determined values of S isotope in the black rock series of the two study areas both show the characteristics related to organic reduction/biogenic.展开更多
This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic d...This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic dykes cropping out in eastern NCC,within the Hebei Province,China.New zircon LA-ICP-MS U-Pb ages,geochemical,and Sr-Nd-Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9±1.3 and 263.9±2.6 Ma.The mafic rocks fall into the alkaline and calc-alkaline series.They are enriched in light rare earth elements,some large ion lithophile elements(e.g.,Rb.Ba,and Sr),K,and Pb,and depleted in Nb,Ta,and Ti.The dykes have high initial 87Sr/86Sr ratios(0.7034-0.7178),negative eNd(t)values(—2.2 to—5.9),and relatively constant initial Pb isotopic ratios,that are EMI-like:(206Pb/204Pb)i=16.39-16.74,(207pb/204pb)j=15.22-15.24,and(208Pb/204Pb)i_=36.66-36.86,respectively.Our results indicate that the Hebei Province dolerites were likely derived from magma gen erated through low-medium degree partial melting(3.0-20%)of an EMI-like garnet-lherzolite mantle source.The parental magmas fractionated olivine,clinopyroxene,and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke emplacement.Since the possible influence of subduction of the Yangtze Plate has been excluded,we propose a model for the origin of the investigated mafic rocks,involving the Pennian collision between the Siberian Block and the NCC.The mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision.展开更多
The mafic dykes(dolerites)during the Early Paleozoic are widely spread in Langao-Ziyang,southern Qiling Block,and the investigation on these dykes are very important.Previous studies have mainly focused on the Siluria...The mafic dykes(dolerites)during the Early Paleozoic are widely spread in Langao-Ziyang,southern Qiling Block,and the investigation on these dykes are very important.Previous studies have mainly focused on the Silurian mafic dykes;however,research on the Earlier Paleozoic mafic dykes is relatively weak at present.Therefore,the overall understanding of the mantle source and genetic dynamic setting during the Early Paleozoic in this area is lacking.To study the accurate age and origin of the Early Paleozoic mafic dykes in Ziyang,southern Shaanxi Province,the mafic dykes from dabacunand Qinmingzhai were selected and the petrology,zircon U-Pb chronology,geochemistry,and Sr-Nd-Hf isotopes were studied.Analysis indicates that the mafic dykes studied are mainly composed of dolerite,and they are the products of the Early Ordovician(475.8-480.7 Ma).Furthermore,the dolerites belong to alkaline rock series,and they are characterized by enrichment in LREE,Rb,Ba,Sr,Nb,(87Sr/86Sr)i=0.7020-0.7050,εNd(t)=3.0-4.0),εHf(t)=4.5-12.1,176Hf/177Hf=0.282681-0.282844.This suggests that the mafic dyke were derived from the partial melting of a depleted lithospheric mantle,and the genetic process is mainly controlled by the mantle plume based on the discussion of the genetic model.Furthermore,the genetic process experienced the separation and crystallization of olivine and clinopyroxene at the same time,with little crustal contamination.展开更多
As a part of a giant trending fault system in the Asian continent and one where a strong zone of left strikeslip fault is present,the Altyn Orogenic belt(AOB)has become an important focus for research.Magmatic rocks a...As a part of a giant trending fault system in the Asian continent and one where a strong zone of left strikeslip fault is present,the Altyn Orogenic belt(AOB)has become an important focus for research.Magmatic rocks are widely distributed across the AOB.However,many investigations have focused primarily on Paleozoic igneous rocks;discussion of Mesozoic related igneous activity is often ignored.Here we present the result of studies of representative diorite and granite rocks outcropping in the AOB,within the Xinjiang Uygur Autonomous Region,South Altyn,China.We present new zircon LA-ICP-MS U-Pb age,geochemical,and Sr-Nd-Pb-Hf isotopic data for these sample suites,identifying them as typical igneous rocks formed between 238±1.5 and 238.8±1.1 Ma.The rocks that we studied fall into the alkaline series,also enriched in light rare earth elements(LREE),some large ion lithophile elements(LILE;e.g.,Rb,Ba,Sr,and K),Pb,Th and U,and depleted in heavy rare earth elements(HREE),Nb,Ta,Hf,and Ti.The granite and diorite have high initial 87Sr/86Sr ratios(0.7062-0.7114),negativeεNd(t)values(-8.8 to-11.3),εHf(t)values(-8.7 to-18.7),and relatively constant Pb isotopic ratios((206-Pb/204Pb)i=6.74-17.884,(207Pb/204Pb)i=15.51-15.58,and(208Pb/204Pb)i=35.36-38.04),respectively.This suggests that the magmas parental to these rocks were generated from the partial melting of the ancient crust.The parental magmas to these rocks experienced a degree of fractionation of plagioclase,K-feldspar,and hornblende,possibly during rapid magma ascent.Based on these studies,we propose a reasonable model for the origin of the investigated rocks from the Xinjiang Uygur Autonomous Region of South Altyn,which involves crustal thickening,lithospheric extension,and asthenosphere upwelling,that induced crustal melting.展开更多
Post-collision felsic rocks in Southeastern Yunnan province contain granodiorites. U-Pb zircon ages, geochemical data and Sr-Nd isotopic data for these rocks are reported in the present paper. Laser ablation inductive...Post-collision felsic rocks in Southeastern Yunnan province contain granodiorites. U-Pb zircon ages, geochemical data and Sr-Nd isotopic data for these rocks are reported in the present paper. Laser ablation inductively coupled plasma mass spectrometry U-Pb zircon analyses yielded consistent age 252.5 ± 1.0 Ma for one sample of the felsic rocks. The granodiorites were characterized by variational and high (87Sr/86Sr)i, ranging from 0.7223 to 0.7236 and very low εNd (t) values from –29.1 to –30.4. In addition, these rocks are characterized by slight Eu negative anomalies, Nb, Ta, Ti and Sr negative anomalies on primitive mantle normalization spider. Geochemical and isotopic characteristics suggest that these rocks were derived from an enriched crust source. The granodiorites resulted from the fractionation of potassium feldspar, plagioclase and ilmenite or rutile. However, the granodiorites were unaffected by visible crustal contamination during ascent. As a result, the granodiorites may have been formed due to partial melting of crust-derived sedimentary rocks beneath southeastern Yunnan province, southern China.展开更多
基金financially supported by the Key Project of Shaanxi Provincial Natural Science Basic Research Program(2023-JC-ZD-16).
文摘In this study, 30 sediment samples were collected from the lower reaches of the Shichuanhe River in Xi’an, Shaanxi Province, China, to test the distribution of heavy metal elements in this area and for an analysis of the pollution levels of this area, hope to provide guidance on agricultural production activities in this region. The results show that the heavy metal elements in this area are mainly concentrated at the Qinghe River and Shichuanhe River confluences. Furthermore, the element contents are higher than that of the background levels of the continental crust(UCC) and close to the background levels of the soil from Shaanxi Province;the two most enriched elements are Cd and As, with contents of 0.79 and 22.7 mg·kg-1, respectively, and their contents are 3.8 and 1.72 times higher than that of the background values. Herein, the heavy metal pollution assessment methods applied indicated that Cd and As are the two most abundant pollutant elements in the area’s soils. As has a peak geo-accumulation index value of 3, and the pollution level is high, while Cd exhibits high potential ecological risks due to its high toxicity(potential risk index of 143) and an active fraction of more than 64%.In addition, a principal component analysis and hierarchical cluster analysis study showed that there are two sources of the heavy metals in this area. The Zn, As, Ni, Cu, Pb,and Cr are mainly from natural sources, and the Cd likely comes from a discharge of untreated agricultural wastewater in the region. The Cd which poses a high potential risk and mainly results from human activities, needs to be further monitored.
基金supported by the National Natural Science Foundation of China(41373028 and 41573022)。
文摘Post-orogenic alkaline intrusions from the Sulu Orogenic Belt of eastern North China Craton consist of A-type granites.In this study,we report U-Pb zircon ages,geochemical data,Sr-Nd-Pb,and zircon Hf isotopic data for these rocks.The LA-ICP-MS U-Pb zircon analyses yield consistent ages ranging from 127.1±2.4 to 119.5±4.8 Ma for four samples.The alkaline rocks are characterized by high total alkalis(K2 O+Na2 O=8.32-10.11 wt%),light rare-earth element enrichment,and heavy rare-earth element depletion,with a wide range(La/Yb)N values(20-48),moderate negative Eu anomalies(Eu/Eu*=0.50-0.74),enrichment in large-ion lithophile elements(LILEs,i.e.,Rb,Th,U and Pb),and depletion in Ba,Sr and high field strength elements(HFSEs,i.e.,Nb,Ta,and Ti),high(87Sr/86Sr)i ranging from 0.708 to 0.7089,low sNd(t)values from-19.4 to-16.8,(206Pb/204Pb)i=16.751-16.935,(207Pb/204Pb)i=15.381-15.535,(208-Pb/204Pb)i=37.472-37.838,negativeεHf(t)values between-21.3 and-25.7 for the magmatic zircons,and larger TDM2 model ages from 2.5 to 2.8 Ga.These results suggest that the rocks were derived from a common enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials before magma generation.Furthermore,the geochemical and isotopic feature implies that the primary magma of these rocks originated through partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from lower crust eclogite.These rocks in this study may have been generated by subsequent fractionation of potassium feldspar,plagioclase,ilmenite,and/or rutile.However,negligible crustal contamination occurred during the diagenesis process.
基金financially supported by General Project of Natural Science Foundation of Shaanxi Province (2020JM-423)。
文摘The Baiyangping Cu-Ag polymetallic ore district is located in the northern part of the Lanping-Simao foreland fold belt,between the Jinshajiang-Ailaoshan and Lancangjiang faults,and the deposit can be divided into eastern and western ore zones.Based upon microscope observation of ore minerals and analysis of zinc,copper,and strontium isotope composition,we conclude that:(1)the zinc isotopic compositions of sphalerite from the eastern and western ore belt of the Baiyangping polymetallic ore deposits are enriched in both the heavy(-0.09‰ to+0.15‰) and light(-0.19‰ to-0.01‰)zinc isotopes.Rayleigh fractionation is likely the additional factor controlling the observed temporal and spatial variations in zinc isotopes in the two studied ore zones.The zinc isotopic composition in the Baiyangping polymetallic Pb-Zn deposits may have the same fractionation as that of magmatic-hydrothermal,VHMS,SEDEX,and MVT deposits,as demonstrated by geological and other geochemical evidence;(2) the range of δ^(65)Cu in massive tetrahedrite is from-0.06‰ to+0.12 ‰ that relates to the early stages of ore-formation,which are higher than that of venial chalcopyrite(from-0.72‰ to-0.07‰)formed at a late ore-forming stage in the western ore belt.Different ore-forming stages and alteration or leaching processes are likely the main factors controlling the observed variations in copper isotopes in the western ore zone;(3) the ^(87)Sr/^(86)Sr value of hydrothermal calcite in eastern(0.7080-0.7093) and western(0.7085-0.7113) ore belt suggested that mineralization of early calcite,with^(87)Sr/^(86)Sr values much higher than in ancient Late Triassic seawater,may be related to recrystallization from a radiogenic Sr-rich or silicifying fluid,either from the strata that the ore-forming fluid flows through or from other fluids.
基金supported by the General Project of Natural Science Foundation of Shaanxi Province(2020JM423)。
文摘Se-rich black rock series of the Middle and Late Permian system is widely distributed in Enshi Prefecture with an exposed area of 850 km~2,among which the unique Yutangba black rock series independent selenium deposit with industrial mining significance in the world is produced.However,the source and metallogenic mechanisms of Se are still controversial.In general,terrestrial weathering and submarine hydrothermal processes are the main source end members of Si and Se,and the related siliceous rocks record the deposition process of Si and Se from different sources.The study of lithofacies and paleogeography shows that western Hubei belongs to the near eastwest turn of the Yangzi platform in the Middle and Late Permian and becomes an inter-platform basin with nearly north-south direction.Therefore,the comparative study of the Yutangba deposit and the selenium-rich black rock series in the northern Shadi with high selenium content is expected to reveal the provenance evolution of the two sections in space,and further restrict the Se mineralization mechanism in the Enshi basin.From the element geochemistry study,the black rock series in two study areas may have formed in a transitional position of either the continental margin or continental slope,in the process of sedimentary,more terrigenous clastic materials entered.They are rich in lithophile elements V and Cr.δU>1.0,U/Th and V/(V+Ni)ratio indicate that the Se-rich strata of black rock series in the Enshi areas occurred in an anoxic reducing environment and formed in an environment between the ocean basin and the continental margin.From Si-O isotope geochemistry,the original Si source of the study area is thought to relate to a volcanic eruption,which leads to the enrichment of Si in the seawater.The determined values of S isotope in the black rock series of the two study areas both show the characteristics related to organic reduction/biogenic.
文摘This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic dykes cropping out in eastern NCC,within the Hebei Province,China.New zircon LA-ICP-MS U-Pb ages,geochemical,and Sr-Nd-Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9±1.3 and 263.9±2.6 Ma.The mafic rocks fall into the alkaline and calc-alkaline series.They are enriched in light rare earth elements,some large ion lithophile elements(e.g.,Rb.Ba,and Sr),K,and Pb,and depleted in Nb,Ta,and Ti.The dykes have high initial 87Sr/86Sr ratios(0.7034-0.7178),negative eNd(t)values(—2.2 to—5.9),and relatively constant initial Pb isotopic ratios,that are EMI-like:(206Pb/204Pb)i=16.39-16.74,(207pb/204pb)j=15.22-15.24,and(208Pb/204Pb)i_=36.66-36.86,respectively.Our results indicate that the Hebei Province dolerites were likely derived from magma gen erated through low-medium degree partial melting(3.0-20%)of an EMI-like garnet-lherzolite mantle source.The parental magmas fractionated olivine,clinopyroxene,and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke emplacement.Since the possible influence of subduction of the Yangtze Plate has been excluded,we propose a model for the origin of the investigated mafic rocks,involving the Pennian collision between the Siberian Block and the NCC.The mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision.
基金This study was supported by the National Natural Science Foundation of China(Grant:41573022).
文摘The mafic dykes(dolerites)during the Early Paleozoic are widely spread in Langao-Ziyang,southern Qiling Block,and the investigation on these dykes are very important.Previous studies have mainly focused on the Silurian mafic dykes;however,research on the Earlier Paleozoic mafic dykes is relatively weak at present.Therefore,the overall understanding of the mantle source and genetic dynamic setting during the Early Paleozoic in this area is lacking.To study the accurate age and origin of the Early Paleozoic mafic dykes in Ziyang,southern Shaanxi Province,the mafic dykes from dabacunand Qinmingzhai were selected and the petrology,zircon U-Pb chronology,geochemistry,and Sr-Nd-Hf isotopes were studied.Analysis indicates that the mafic dykes studied are mainly composed of dolerite,and they are the products of the Early Ordovician(475.8-480.7 Ma).Furthermore,the dolerites belong to alkaline rock series,and they are characterized by enrichment in LREE,Rb,Ba,Sr,Nb,(87Sr/86Sr)i=0.7020-0.7050,εNd(t)=3.0-4.0),εHf(t)=4.5-12.1,176Hf/177Hf=0.282681-0.282844.This suggests that the mafic dyke were derived from the partial melting of a depleted lithospheric mantle,and the genetic process is mainly controlled by the mantle plume based on the discussion of the genetic model.Furthermore,the genetic process experienced the separation and crystallization of olivine and clinopyroxene at the same time,with little crustal contamination.
基金supported by the National Natural Science Foundation of China(Grant No.:41573022)。
文摘As a part of a giant trending fault system in the Asian continent and one where a strong zone of left strikeslip fault is present,the Altyn Orogenic belt(AOB)has become an important focus for research.Magmatic rocks are widely distributed across the AOB.However,many investigations have focused primarily on Paleozoic igneous rocks;discussion of Mesozoic related igneous activity is often ignored.Here we present the result of studies of representative diorite and granite rocks outcropping in the AOB,within the Xinjiang Uygur Autonomous Region,South Altyn,China.We present new zircon LA-ICP-MS U-Pb age,geochemical,and Sr-Nd-Pb-Hf isotopic data for these sample suites,identifying them as typical igneous rocks formed between 238±1.5 and 238.8±1.1 Ma.The rocks that we studied fall into the alkaline series,also enriched in light rare earth elements(LREE),some large ion lithophile elements(LILE;e.g.,Rb,Ba,Sr,and K),Pb,Th and U,and depleted in heavy rare earth elements(HREE),Nb,Ta,Hf,and Ti.The granite and diorite have high initial 87Sr/86Sr ratios(0.7062-0.7114),negativeεNd(t)values(-8.8 to-11.3),εHf(t)values(-8.7 to-18.7),and relatively constant Pb isotopic ratios((206-Pb/204Pb)i=6.74-17.884,(207Pb/204Pb)i=15.51-15.58,and(208Pb/204Pb)i=35.36-38.04),respectively.This suggests that the magmas parental to these rocks were generated from the partial melting of the ancient crust.The parental magmas to these rocks experienced a degree of fractionation of plagioclase,K-feldspar,and hornblende,possibly during rapid magma ascent.Based on these studies,we propose a reasonable model for the origin of the investigated rocks from the Xinjiang Uygur Autonomous Region of South Altyn,which involves crustal thickening,lithospheric extension,and asthenosphere upwelling,that induced crustal melting.
文摘Post-collision felsic rocks in Southeastern Yunnan province contain granodiorites. U-Pb zircon ages, geochemical data and Sr-Nd isotopic data for these rocks are reported in the present paper. Laser ablation inductively coupled plasma mass spectrometry U-Pb zircon analyses yielded consistent age 252.5 ± 1.0 Ma for one sample of the felsic rocks. The granodiorites were characterized by variational and high (87Sr/86Sr)i, ranging from 0.7223 to 0.7236 and very low εNd (t) values from –29.1 to –30.4. In addition, these rocks are characterized by slight Eu negative anomalies, Nb, Ta, Ti and Sr negative anomalies on primitive mantle normalization spider. Geochemical and isotopic characteristics suggest that these rocks were derived from an enriched crust source. The granodiorites resulted from the fractionation of potassium feldspar, plagioclase and ilmenite or rutile. However, the granodiorites were unaffected by visible crustal contamination during ascent. As a result, the granodiorites may have been formed due to partial melting of crust-derived sedimentary rocks beneath southeastern Yunnan province, southern China.
