The Niutougou gold deposit, located in the center of the Xiong'ershan gold district, western Henan Province, is a large gold deposit with many quartz porphyries found in the area. Based on the field geological invest...The Niutougou gold deposit, located in the center of the Xiong'ershan gold district, western Henan Province, is a large gold deposit with many quartz porphyries found in the area. Based on the field geological investigation of quartz porphyry of Niutougou gold deposit and by using the cathodoluminescence (CL) images analysis and in situ LA-ICP-MS U-Pb isotope dating method of zircons, the inner structure, trace element compositions and U-Pb age of the zircons separated from quartz porphyry were analyzed and determined. Cathodoluminescence (CL) images of zircons show clear magmatic zonations. Trace element analyses of zircons reveal that all zircons show high concentrations of Th, U, and HREE, and the REE patterns of depletion in LREE, with a positive Ce anomaly. Zircon LA-ICP-MS U-Pb dating results show that the quartz porphyry in the Niutougou gold deposit was formed at 159.714-0.99 Ma (about 160 Ma), belonging to the product of magmatic activity in late Middle Jurassic. Combined with the geological characteristics of the Niutougou gold deposit, the formation age of the quartz porphyry and the analysis of the formation age of the granite body exposed in the Niutougou gold deposit, the study suggests that the metallogenic epoch of the Niutougou gold deposit may be Yanshanian in age.展开更多
1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margi...1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different展开更多
The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region,with the aim to constraining its formation age,magma source and tectonic setting.LA-ICP-MS U-Pb dating re...The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region,with the aim to constraining its formation age,magma source and tectonic setting.LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic( 171± 2 Ma,MSWD = 1.19).Geochemically,these rocks have Si O_2 concentrations of 52.52%--54.90%,K_2 O of2.14%--3.84%,Na_2 O of 3.17%--3.35%,Mg O of 7.43%--9.34% and high Mg~# of 68.57-72.57.These rocks are characterized by enrichment in large ion lithophile elements( LILE,such as K,Ba,Rb and Sr) and light rare earth elements( LREE),relatively depletion in high field strength elements( HFSE,such as Ta,Nb,Ti and Zr),and heavy rare earth elements( HREE).These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination,which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust.Based on former and present studies,the authors consider that the Nancha ore deposit high-Mg diorites were formed in compressional structural setting which is similar to volcanic arc.It could be related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.展开更多
Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh reg...Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh region contains ophiolite,high-to ultrahigh-pressure metamorphic rocks,and igneous rocks.Previous research has virified the occurrence of continental rifting,subduction,slab roll-back,and collision between the Tarim block and Proto-Tethys oceanic plate.Moreover,Kaladaban volcanic rocks are mainly distributed in the north Altyn region.Studies of the magmatic evolution of this region have proposed that Altyn oceanic plate was subducted during the Ordovician(Han et al.,2012;Wang et al.,2017).However,the specific timing and other aspects of the subduction are debated,and an investigation of granite porphyry in the Kaladaban area would improve our understanding of this subduction event.In this study,we present new U-Pb zircon dating result and Sr-Nd isotope composition data for granite porphyry from the North Altyn region.The objective is to constrain the timing of subduction of the North Altyn oceanic plate and establish the petrogenesis and magma source of the granite porphyry.展开更多
Objective As the uplift belt on the southem margin of the Tarim block, the Tiekelike block consists mainly of a set of Precambrian metamorphic rocks with granulite and gneisses. The Heluositan group-complex is the mo...Objective As the uplift belt on the southem margin of the Tarim block, the Tiekelike block consists mainly of a set of Precambrian metamorphic rocks with granulite and gneisses. The Heluositan group-complex is the most ancient rock series in the area, and is a key area for studying the formation and evolution of the Precambrian basement of the Tarim craton. LA-ICP-MS zircon U-Pb dating and Hf isotopic analysis of granulite in this area provide new evidence for revealing the formation and evolution of the Precambrian basement in the Tarim Basin.展开更多
The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to...The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of εHf(t)(+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U-Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with εHf(t) values between-20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter-arc basin, while the Hongchicun Formation was formed in an accretionary wedge-top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter-arc basin to accretionary wedge-top basin,which represents the collision between the Shuangxiwu arc and the Yangtze Plate.展开更多
The calculation of a maximum depositional age(MDA)from a detrital zircon sample can provide insight into a variety of geological problems.However,the impact of sample size and calculation method on the accuracy of a r...The calculation of a maximum depositional age(MDA)from a detrital zircon sample can provide insight into a variety of geological problems.However,the impact of sample size and calculation method on the accuracy of a resulting MDA has not been evaluated.We use large populations of synthetic zircon dates(N≈25,000)to analyze the impact of varying sample size(n),measurement uncertainty,and the abundance of neardepositional-age zircons on the accuracy and uncertainty of 9 commonly used MDA calculation methods.Furthermore,a new method,the youngest statistical population is tested.For each method,500 samples of n synthetic dates were drawn from the parent population and MDAs were calculated.The mean and standard deviation of each method ove r the 500 trials at each n-value(50-1000,in increments of 50)were compa red to the known depositional age of the synthetic population and used to compare the methods quantitatively in two simulation scenarios.The first simulation scenario varied the proportion of near-depositional-age grains in the synthetic population.The second scenario varied the uncertainty of the dates used to calculate the MDAs.Increasing sample size initially decreased the mean residual error and standard deviation calculated by each method.At higher n-values(>~300 grains),calculated MDAs changed more slowly and the mean resid ual error increased or decreased depending on the method used.Increasing the p roportion of near-depositional-age grains and lowering measurement uncertainty decreased the number of measurements required for the calculated MDAs to stabilize and decreased the standard deviation in calculated MDAs of the 500 samples.Results of the two simulation scenarios show that the most successful way to increase the accuracy of a calculated M DA is by acquiring a large number of low-uncertainty measurements(300300)approach is used if the calculation of accurate MDAs are key to research goals.Other acquisition method s,such as high-to moderate-precision measurement methods(e.g.,1%-5%,2σ)acquiring low-to moderate-n datasets(50300).Additionally,they are most susceptible to producing erroneous MDAs due to contamination in the field or laboratory,or through disturbances of the youngest zircon’s U-Pb systematics(e.g.,lead loss).More conservative methods that still produce accurate MDAs and are less susceptible to contamination or lead loss include:youngest grain cluster at 1σunce rtainty(YGC 1σ),youngest grain clusterat 2σuncertainty(YGC 2σ),and youngest statistical population(YSP).The ages calculated by these methods may be more useful and appealing when fitting calculated MDAs in to pre-existing chronostratigraphic frameworks,as they are less likely to be younger than the true depositional age.From the results of our numerical models we illustrate what geologic processes(i.e.,tectonic or sedimentary)can be resolved using MDAs derived from strata of different ages.展开更多
The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt.It is a diorite-quartz diorite-granodiorite-granite series,spreading in a NW-SE direction,and intrudes into the Erlangping Grou...The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt.It is a diorite-quartz diorite-granodiorite-granite series,spreading in a NW-SE direction,and intrudes into the Erlangping Group.The SiO2 content ranges from 57.04% to 76.56%,Na2O from 2.05% to 4.65%,K2O from 0.84% to 3.40%.Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids.SREE ranges from 36.51 ppm to 473.25 ppm,and LREE/ HREE ratios lie between 3.95 and 22.18.Negative Eu anomalies are not obvious in most samples,though there are obvious Nb,P and Ti positive anomalies.The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma-486.9±9.3 Ma.Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876,εHf(t) values from 8.5 to 14,all positive,and corresponding modal ages (TDM2) range from 559 Ma to 908 Ma.Based on Hf isotope characteristics and existing SmNd and Rb-Sr isotope data,we consider that the Banshanping granitoid rocks originate from mantlederived material,i.e.the igneous rocks that formed in Neoproterozoic,and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks.展开更多
A large number of Eocene-Oligocene alkaline/alkali-rich igneous rocks were developed in the Tuotuohe region of the Qinghai-Tibetan Plateau.In this study,we present zircon U-Pb ages,Hf isotope data,and major and trace ...A large number of Eocene-Oligocene alkaline/alkali-rich igneous rocks were developed in the Tuotuohe region of the Qinghai-Tibetan Plateau.In this study,we present zircon U-Pb ages,Hf isotope data,and major and trace element compositions of the Cenozoic alkaline rocks from the Tuotuohe region in order to constraint the petrogenesis and tectonic evolution history of Qiangtang Block.Zircon U-Pb ages were measured via LA-ICP-MS to be39.6,37.6 and 32.0 Ma.The 39.6 Ma trachyte was characterized by low SiO2 and high K2O and MgO contents.The 37.6 and 32.0 Ma orthophyres show enrichment in SiO2 and K2O,but deficient in MgO.All of the samples belong to the alkaline rocks.These rocks display enrichment in REE,LREE,and LILE,depletion in HFSE,and no obvious Eu anomalies.Geological and geochemical features suggest that there were two possible mechanisms for the origin of the alkaline rocks in the Tuotuohe region:(1)the removed mafic lower crust dropped into the asthenosphere,forming the mix magma(Nariniya trachyte);(2)the upwelling asthenosphere triggered the crustal melting(Nariniya and Zamaqu orthophyre).The Eocene-Oligocene alkaline rocks in the study and adjacent areas are likely to be the result of the same tectonic-magmatic event of deep lithospheric evolution that is the crustal material melting triggered by lithospheric delamination.This conclusion extends the influence scope of lithospheric delamination eastward to the Tuotuohe region(*92°E)from Banda Co(*82°E).展开更多
基金funded by the Program forthe New Century Excellent Tallents in Ministry of Education (No.NCET-09-0710)the National Natural Science Foundation of China (No.40872068 and40672064)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in Ministry of Education(No.IRT0755)the "111" Project (No.B07011)
文摘The Niutougou gold deposit, located in the center of the Xiong'ershan gold district, western Henan Province, is a large gold deposit with many quartz porphyries found in the area. Based on the field geological investigation of quartz porphyry of Niutougou gold deposit and by using the cathodoluminescence (CL) images analysis and in situ LA-ICP-MS U-Pb isotope dating method of zircons, the inner structure, trace element compositions and U-Pb age of the zircons separated from quartz porphyry were analyzed and determined. Cathodoluminescence (CL) images of zircons show clear magmatic zonations. Trace element analyses of zircons reveal that all zircons show high concentrations of Th, U, and HREE, and the REE patterns of depletion in LREE, with a positive Ce anomaly. Zircon LA-ICP-MS U-Pb dating results show that the quartz porphyry in the Niutougou gold deposit was formed at 159.714-0.99 Ma (about 160 Ma), belonging to the product of magmatic activity in late Middle Jurassic. Combined with the geological characteristics of the Niutougou gold deposit, the formation age of the quartz porphyry and the analysis of the formation age of the granite body exposed in the Niutougou gold deposit, the study suggests that the metallogenic epoch of the Niutougou gold deposit may be Yanshanian in age.
基金co-funded by the China Geological Survey (No.12120114052801)the DREAM project of MOST, China (NO. 2016YFC0600401)
文摘1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different
文摘The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region,with the aim to constraining its formation age,magma source and tectonic setting.LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic( 171± 2 Ma,MSWD = 1.19).Geochemically,these rocks have Si O_2 concentrations of 52.52%--54.90%,K_2 O of2.14%--3.84%,Na_2 O of 3.17%--3.35%,Mg O of 7.43%--9.34% and high Mg~# of 68.57-72.57.These rocks are characterized by enrichment in large ion lithophile elements( LILE,such as K,Ba,Rb and Sr) and light rare earth elements( LREE),relatively depletion in high field strength elements( HFSE,such as Ta,Nb,Ti and Zr),and heavy rare earth elements( HREE).These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination,which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust.Based on former and present studies,the authors consider that the Nancha ore deposit high-Mg diorites were formed in compressional structural setting which is similar to volcanic arc.It could be related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.
基金jointly supported by the National Key R&D Program of China(Grant No.2018YFC0603704)a Geological Survey Project of the China Geological Survey(DD20160050).
文摘Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh region contains ophiolite,high-to ultrahigh-pressure metamorphic rocks,and igneous rocks.Previous research has virified the occurrence of continental rifting,subduction,slab roll-back,and collision between the Tarim block and Proto-Tethys oceanic plate.Moreover,Kaladaban volcanic rocks are mainly distributed in the north Altyn region.Studies of the magmatic evolution of this region have proposed that Altyn oceanic plate was subducted during the Ordovician(Han et al.,2012;Wang et al.,2017).However,the specific timing and other aspects of the subduction are debated,and an investigation of granite porphyry in the Kaladaban area would improve our understanding of this subduction event.In this study,we present new U-Pb zircon dating result and Sr-Nd isotope composition data for granite porphyry from the North Altyn region.The objective is to constrain the timing of subduction of the North Altyn oceanic plate and establish the petrogenesis and magma source of the granite porphyry.
基金supported by Xinjiang Uygur Autonomous Region 1:50000 special funds to support the transfer(grant No.1212011140056)
文摘Objective As the uplift belt on the southem margin of the Tarim block, the Tiekelike block consists mainly of a set of Precambrian metamorphic rocks with granulite and gneisses. The Heluositan group-complex is the most ancient rock series in the area, and is a key area for studying the formation and evolution of the Precambrian basement of the Tarim craton. LA-ICP-MS zircon U-Pb dating and Hf isotopic analysis of granulite in this area provide new evidence for revealing the formation and evolution of the Precambrian basement in the Tarim Basin.
基金supported by the Geological Survey Project of the Chinese Geological Survey(DD20190043,DD20160038)。
文摘The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of εHf(t)(+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U-Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with εHf(t) values between-20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter-arc basin, while the Hongchicun Formation was formed in an accretionary wedge-top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter-arc basin to accretionary wedge-top basin,which represents the collision between the Shuangxiwu arc and the Yangtze Plate.
基金Funding for this research was provided by a NSERC Discovery Grant(No.RGPIN/341715-2013)to S.Hubbard and a Queen Eliz-abethⅡscholarship from the University of Calgary to D.Coutts
文摘The calculation of a maximum depositional age(MDA)from a detrital zircon sample can provide insight into a variety of geological problems.However,the impact of sample size and calculation method on the accuracy of a resulting MDA has not been evaluated.We use large populations of synthetic zircon dates(N≈25,000)to analyze the impact of varying sample size(n),measurement uncertainty,and the abundance of neardepositional-age zircons on the accuracy and uncertainty of 9 commonly used MDA calculation methods.Furthermore,a new method,the youngest statistical population is tested.For each method,500 samples of n synthetic dates were drawn from the parent population and MDAs were calculated.The mean and standard deviation of each method ove r the 500 trials at each n-value(50-1000,in increments of 50)were compa red to the known depositional age of the synthetic population and used to compare the methods quantitatively in two simulation scenarios.The first simulation scenario varied the proportion of near-depositional-age grains in the synthetic population.The second scenario varied the uncertainty of the dates used to calculate the MDAs.Increasing sample size initially decreased the mean residual error and standard deviation calculated by each method.At higher n-values(>~300 grains),calculated MDAs changed more slowly and the mean resid ual error increased or decreased depending on the method used.Increasing the p roportion of near-depositional-age grains and lowering measurement uncertainty decreased the number of measurements required for the calculated MDAs to stabilize and decreased the standard deviation in calculated MDAs of the 500 samples.Results of the two simulation scenarios show that the most successful way to increase the accuracy of a calculated M DA is by acquiring a large number of low-uncertainty measurements(300300)approach is used if the calculation of accurate MDAs are key to research goals.Other acquisition method s,such as high-to moderate-precision measurement methods(e.g.,1%-5%,2σ)acquiring low-to moderate-n datasets(50300).Additionally,they are most susceptible to producing erroneous MDAs due to contamination in the field or laboratory,or through disturbances of the youngest zircon’s U-Pb systematics(e.g.,lead loss).More conservative methods that still produce accurate MDAs and are less susceptible to contamination or lead loss include:youngest grain cluster at 1σunce rtainty(YGC 1σ),youngest grain clusterat 2σuncertainty(YGC 2σ),and youngest statistical population(YSP).The ages calculated by these methods may be more useful and appealing when fitting calculated MDAs in to pre-existing chronostratigraphic frameworks,as they are less likely to be younger than the true depositional age.From the results of our numerical models we illustrate what geologic processes(i.e.,tectonic or sedimentary)can be resolved using MDAs derived from strata of different ages.
基金granted by China Geological Survey Projects (1212011120160, 1212010918007, 1212010818090, 1212010611803, 1212010711816)Special Project of Deep Exploration and Experimental Study–Pre-study of Scientific Drilling in Mineralized Cluster Area in Eastern China (SinoProbe-05-05)National Science Foundation Project (40921001, 49772106,40472034,40672049)
文摘The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt.It is a diorite-quartz diorite-granodiorite-granite series,spreading in a NW-SE direction,and intrudes into the Erlangping Group.The SiO2 content ranges from 57.04% to 76.56%,Na2O from 2.05% to 4.65%,K2O from 0.84% to 3.40%.Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids.SREE ranges from 36.51 ppm to 473.25 ppm,and LREE/ HREE ratios lie between 3.95 and 22.18.Negative Eu anomalies are not obvious in most samples,though there are obvious Nb,P and Ti positive anomalies.The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma-486.9±9.3 Ma.Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876,εHf(t) values from 8.5 to 14,all positive,and corresponding modal ages (TDM2) range from 559 Ma to 908 Ma.Based on Hf isotope characteristics and existing SmNd and Rb-Sr isotope data,we consider that the Banshanping granitoid rocks originate from mantlederived material,i.e.the igneous rocks that formed in Neoproterozoic,and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks.
基金supported by Dr. Huo Liang, College of Earth Science, Jilin Universitysupported by colleagues in Qinghai Geological Survey+1 种基金the Qinghai Fifth Geological and Mineral Exploration Institutefunded by the National Natural Science Foundation of China (Grant No. 41402060)
文摘A large number of Eocene-Oligocene alkaline/alkali-rich igneous rocks were developed in the Tuotuohe region of the Qinghai-Tibetan Plateau.In this study,we present zircon U-Pb ages,Hf isotope data,and major and trace element compositions of the Cenozoic alkaline rocks from the Tuotuohe region in order to constraint the petrogenesis and tectonic evolution history of Qiangtang Block.Zircon U-Pb ages were measured via LA-ICP-MS to be39.6,37.6 and 32.0 Ma.The 39.6 Ma trachyte was characterized by low SiO2 and high K2O and MgO contents.The 37.6 and 32.0 Ma orthophyres show enrichment in SiO2 and K2O,but deficient in MgO.All of the samples belong to the alkaline rocks.These rocks display enrichment in REE,LREE,and LILE,depletion in HFSE,and no obvious Eu anomalies.Geological and geochemical features suggest that there were two possible mechanisms for the origin of the alkaline rocks in the Tuotuohe region:(1)the removed mafic lower crust dropped into the asthenosphere,forming the mix magma(Nariniya trachyte);(2)the upwelling asthenosphere triggered the crustal melting(Nariniya and Zamaqu orthophyre).The Eocene-Oligocene alkaline rocks in the study and adjacent areas are likely to be the result of the same tectonic-magmatic event of deep lithospheric evolution that is the crustal material melting triggered by lithospheric delamination.This conclusion extends the influence scope of lithospheric delamination eastward to the Tuotuohe region(*92°E)from Banda Co(*82°E).