Geochronology and geochemistry of the five magmatic rocks in the Ningzhen region, China

【摘要】 The Ningzhen region of China is located in the easternmost part of the middle-lower Yangtze River Cu–Fe polymetallic metallogenic belt. From west to east, it comprises five main intermediate–acidic intrusive complexes: the Qilinmen, Anjishan, Xiashu–Gaozi, Shima, and Jianbi complexes. Geochemical investigations show that these five intrusive complexes exhibit high contents of SiO₂, at 64.74–73.40 wt%, Al₂O₃, at 14.15–17.37 wt%, and K₂O + Na₂O, at 6.49–8.68 wt%. The majority of the samples belong to the high-K calc-alkaline series, with a few samples plotting in the calc-alkaline and tholeiitic series. Trace element analysis shows that the samples are enriched in large ion lithophile elements（LILE） and are depleted in high field strength elements（HFSE）.The chondrite-normalized rare earth element（REE） patterns are characterized by right-inclined curves, showing light rare earth element（LREE） enrichment. In addition,the（La/Yb）Nratios are high at 15.02–37.28, with an average of 29.13, and slightly negative or none Eu anomalies are present. In the（La/Yb）N–d Eu diagram, the samples plot within the crust-mantle type field. Laser ablation–inductively coupled plasma–mass spectrometry（LA–ICP–MS） zircon U–Pb dating yielded ages of122.0 ± 1.0 Ma, 106.1 ± 0.8 Ma, 108.7 ± 1.4 Ma,103.5 ± 1.9 Ma, and 96.8 ± 1.7 Ma for the Qilinmen,Anjishan, Xiashu–Gaozi, Shima, and Jianbi complexes,respectively. On the basis of this research and knowledge of several known metal deposits related to these complexes, we suggest that the Mesozoic large-scale diagenesis and metallogenesis in the Ningzhen region may have ceased at 100 Ma or about 95 Ma.更多还原

【Abstract】 The Ningzhen region of China is located in the easternmost part of the middle-lower Yangtze River Cu–Fe polymetallic metallogenic belt. From west to east, it comprises five main intermediate–acidic intrusive complexes: the Qilinmen, Anjishan, Xiashu–Gaozi, Shima, and Jianbi complexes. Geochemical investigations show that these five intrusive complexes exhibit high contents of SiO₂, at 64.74–73.40 wt%, Al₂O₃, at 14.15–17.37 wt%, and K₂O + Na₂O, at 6.49–8.68 wt%. The majority of the samples belong to the high-K calc-alkaline series, with a few samples plotting in the calc-alkaline and tholeiitic series. Trace element analysis shows that the samples are enriched in large ion lithophile elements（LILE） and are depleted in high field strength elements（HFSE）.The chondrite-normalized rare earth element（REE） patterns are characterized by right-inclined curves, showing light rare earth element（LREE） enrichment. In addition,the（La/Yb）Nratios are high at 15.02–37.28, with an average of 29.13, and slightly negative or none Eu anomalies are present. In the（La/Yb）N–d Eu diagram, the samples plot within the crust-mantle type field. Laser ablation–inductively coupled plasma–mass spectrometry（LA–ICP–MS） zircon U–Pb dating yielded ages of122.0 ± 1.0 Ma, 106.1 ± 0.8 Ma, 108.7 ± 1.4 Ma,103.5 ± 1.9 Ma, and 96.8 ± 1.7 Ma for the Qilinmen,Anjishan, Xiashu–Gaozi, Shima, and Jianbi complexes,respectively. On the basis of this research and knowledge of several known metal deposits related to these complexes, we suggest that the Mesozoic large-scale diagenesis and metallogenesis in the Ningzhen region may have ceased at 100 Ma or about 95 Ma.更多还原