摘要
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.
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.
基金
Supported by Project of Geological Exploration Foundation of Jilin Province(No.22201300111)
