Zircon U-Pb geochronology and geochemistry of the granodiorites in Xiarihamu Cu-Ni mining area are studied to determine the formation age,genesis and tectonic setting. The results show that the granodiorites formed in...Zircon U-Pb geochronology and geochemistry of the granodiorites in Xiarihamu Cu-Ni mining area are studied to determine the formation age,genesis and tectonic setting. The results show that the granodiorites formed in the Middle Triassic with weighted average age of 242 ± 1 Ma. The granodiorites comprise of SiO_2 of 61. 34%--62. 54%,Al_2 O_3 of 16. 46%--16. 87%,MgO of 2. 37%--2. 66%,( Na_2 O + K_2 O) of 5. 39%--5. 74%with the Na2 O/K_2 O of 1. 46--1. 88,Mg~# of 47. 03--48. 04,and show metaluminous characteristics with A/CNK of 0. 94--0. 96,belonging to calc-alkaline I-type granites geochemically. The light and heavy rare earth elements in the rocks are distinctly fractionated and have " right-inclined" distribution patterns with weak negative Eu anomalies( δEu = 0. 84--0. 91). Moreover,these samples show enrichments in LILEs( e. g.,Rb,Ba,K and Sr),especially in Sr [( 343--452) × 10^(-6)],and obvious depletions in HFSEs( e. g.,Nb,Ta,Ti and P),indicating geochemical characteristics similar to subduction-related magmatic rocks. According to the regional tectonic evolution,the Xiarihamu granodiorites were emplaced under an Andean-type active continental margin environment in the early Indosinian,possessing a crust-mantle mixing origin.展开更多
基金Supported by Project of Qinghai Bureau of Geological Survey,2017
文摘Zircon U-Pb geochronology and geochemistry of the granodiorites in Xiarihamu Cu-Ni mining area are studied to determine the formation age,genesis and tectonic setting. The results show that the granodiorites formed in the Middle Triassic with weighted average age of 242 ± 1 Ma. The granodiorites comprise of SiO_2 of 61. 34%--62. 54%,Al_2 O_3 of 16. 46%--16. 87%,MgO of 2. 37%--2. 66%,( Na_2 O + K_2 O) of 5. 39%--5. 74%with the Na2 O/K_2 O of 1. 46--1. 88,Mg~# of 47. 03--48. 04,and show metaluminous characteristics with A/CNK of 0. 94--0. 96,belonging to calc-alkaline I-type granites geochemically. The light and heavy rare earth elements in the rocks are distinctly fractionated and have " right-inclined" distribution patterns with weak negative Eu anomalies( δEu = 0. 84--0. 91). Moreover,these samples show enrichments in LILEs( e. g.,Rb,Ba,K and Sr),especially in Sr [( 343--452) × 10^(-6)],and obvious depletions in HFSEs( e. g.,Nb,Ta,Ti and P),indicating geochemical characteristics similar to subduction-related magmatic rocks. According to the regional tectonic evolution,the Xiarihamu granodiorites were emplaced under an Andean-type active continental margin environment in the early Indosinian,possessing a crust-mantle mixing origin.
