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
The authors studied zircon U-Pb age and geochemical data of Baicaogou tuff in Yanji,Jilin Province.The results indicate that the rocks formed in Early Cretaceous( 125. 6 ± 2. 3 Ma). Geochemically,these tuffs have...The authors studied zircon U-Pb age and geochemical data of Baicaogou tuff in Yanji,Jilin Province.The results indicate that the rocks formed in Early Cretaceous( 125. 6 ± 2. 3 Ma). Geochemically,these tuffs have high Si O2 and total Na2 O + K2 O,low Mg O and Fe O,and they belong to metaluminous series,the rock are enriched in LREEs and LILEs,depleted in HREEs and HFSEs such as Nb,Ta,Ti,and P,exhibiting an affinity to I-type granite. All these characteristics implied that the volcanic rocks were derived from partial melting of lower crust. Combined with the geochronology and geochemical features of the coeval igneous rocks within NE China,it is concluded that Yanji area was in a back-arc extensional setting in response to the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.展开更多
The Liudaogou area underwent multiple large-scale tectonic movements since Archean. Little studies have been carried out on the age of Mesozoic magmatism and petrogenesis in the area. Zircon U-Pb geochronology and geo...The Liudaogou area underwent multiple large-scale tectonic movements since Archean. Little studies have been carried out on the age of Mesozoic magmatism and petrogenesis in the area. Zircon U-Pb geochronology and geochemistry of the Liudaogougranodiorite were undertaken in this study to determine the forming-age of the granodiorite and to understand its petrogenesis and tectonic background of diagenesis. Zircon in the rock samples show good idiomorphic and obvious rhythmic growth girdle zone,belonging to typical magmatic zircon.Zircon LA-ICP-MS U-Pb dating results show that the emplacement of rock mass occurred in late Early Cretaceous( 125 ± 1 Ma,MSWD = 0. 53). The geochemical data show that the rock belongs to quasi-aluminous granite of type I which has the properties of high potassium calc-alkaline adakite,with A/CNK ratio of 0. 82--0. 98( < 1. 1). The rock shows obvious enrichment of LILE and LREE but depletion of HFSE,and is characterized by high Sr( 374. 9 × 10^(-6)--777. 6 × 10^(-6)) and low Y( 8. 84 × 10^(-6)--12. 4 × 10^(-6)). The samples are rich in Si,and the K_2 O/Na_2 O ratio( 0. 99--1. 30) is very high,indicating that magma might have originated from melting upper crust. The high content of Mg~#( 49. 68--56. 92) in the samples implies that mantle-derived materials might have involved in magma. It can be concluded that in the process of delamination,the lower crust sank,and was heated by asthenosphere mantle,and partially melted. The primitive magma should be the mixture of the mantle-derived magma and the partially melting lower crust. Integrating research results on the regional contemporary igneous rock,it can be concluded that the rocks were formed in an active continental margin environment related to the subduction of the Paleo-Pacific Plate to the Eurasian Plate.展开更多
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.
文摘The authors studied zircon U-Pb age and geochemical data of Baicaogou tuff in Yanji,Jilin Province.The results indicate that the rocks formed in Early Cretaceous( 125. 6 ± 2. 3 Ma). Geochemically,these tuffs have high Si O2 and total Na2 O + K2 O,low Mg O and Fe O,and they belong to metaluminous series,the rock are enriched in LREEs and LILEs,depleted in HREEs and HFSEs such as Nb,Ta,Ti,and P,exhibiting an affinity to I-type granite. All these characteristics implied that the volcanic rocks were derived from partial melting of lower crust. Combined with the geochronology and geochemical features of the coeval igneous rocks within NE China,it is concluded that Yanji area was in a back-arc extensional setting in response to the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.
基金Supported by Project of Geological Exploration Foundation of Jilin Province(No.22201300111)
文摘The Liudaogou area underwent multiple large-scale tectonic movements since Archean. Little studies have been carried out on the age of Mesozoic magmatism and petrogenesis in the area. Zircon U-Pb geochronology and geochemistry of the Liudaogougranodiorite were undertaken in this study to determine the forming-age of the granodiorite and to understand its petrogenesis and tectonic background of diagenesis. Zircon in the rock samples show good idiomorphic and obvious rhythmic growth girdle zone,belonging to typical magmatic zircon.Zircon LA-ICP-MS U-Pb dating results show that the emplacement of rock mass occurred in late Early Cretaceous( 125 ± 1 Ma,MSWD = 0. 53). The geochemical data show that the rock belongs to quasi-aluminous granite of type I which has the properties of high potassium calc-alkaline adakite,with A/CNK ratio of 0. 82--0. 98( < 1. 1). The rock shows obvious enrichment of LILE and LREE but depletion of HFSE,and is characterized by high Sr( 374. 9 × 10^(-6)--777. 6 × 10^(-6)) and low Y( 8. 84 × 10^(-6)--12. 4 × 10^(-6)). The samples are rich in Si,and the K_2 O/Na_2 O ratio( 0. 99--1. 30) is very high,indicating that magma might have originated from melting upper crust. The high content of Mg~#( 49. 68--56. 92) in the samples implies that mantle-derived materials might have involved in magma. It can be concluded that in the process of delamination,the lower crust sank,and was heated by asthenosphere mantle,and partially melted. The primitive magma should be the mixture of the mantle-derived magma and the partially melting lower crust. Integrating research results on the regional contemporary igneous rock,it can be concluded that the rocks were formed in an active continental margin environment related to the subduction of the Paleo-Pacific Plate to the Eurasian Plate.
