Large-scale Cenozoic alkali-rich magmatic rocks are exposed at the eastern margin of Tibet due to the interaction between the Indian and Eurasian plates.However,their petrogenesis and associated geodynamic processes r...Large-scale Cenozoic alkali-rich magmatic rocks are exposed at the eastern margin of Tibet due to the interaction between the Indian and Eurasian plates.However,their petrogenesis and associated geodynamic processes remain poorly understood.We analyzed the Xifanping porphyries in the Sanjiang orogenic belt to provide new insights.Our study shows a successive assembly of porphyry intrusions during three magmatic episodes.The magnitude and duration of the magmatic activities diminished sequentially,and mineralization occurred during the intermediate phase.Geochemically,the Xifangping porphyries display an adakitic affinity.According to zircon Hf isotope data,we propose that these porphyries originated from the partial melting of the thickened mafic lower crust beneath the western Yangtze Craton in response to lithospheric extension and asthenospheric upwelling.Analogous to the coeval alkali-rich porphyries in western Yunnan,the petrogenetic model of the Xifanping porphyries indicates regional north-south and east-west fractures caused by the clockwise rotation of the continental lithosphere and the Jinshajiang-Red River strike-slip during the post-collision phase of the India-Eurasia collision.In this context,we argue that the collision in eastern Tibet may have extended eastward to southwestern Sichuan during the post-collision period,persisting until approximately 30 Ma.展开更多
Although previous researchers have attempted to decipher ore genesis and mineralization in the Erdaokan Ag-Pb-Zn deposit,some uncertainties regarding the mineralization process and evolution of both ore-forming fluids...Although previous researchers have attempted to decipher ore genesis and mineralization in the Erdaokan Ag-Pb-Zn deposit,some uncertainties regarding the mineralization process and evolution of both ore-forming fluids and magnetite types still need to be addressed.In this study,we obtained new EPMA,LA-ICP-MS,and in situ Fe isotope data from magnetite from the Erdaokan deposit,in order to better understand the mineralization mechanism and evolution of both magnetite and the ore-forming fluids.Our results identified seven types of magnetite at Erdaokan:disseminated magnetite(Mag1),coarse-grained magnetite(Mag2a),radial magnetite(Mag2b),fragmented fine-grained magnetite(Mag2c),vermicular gel magnetite(Mag3a1 and Mag3a2),colloidal magnetite(Mag3b)and dark gray magnetite(Mag4).All of the magnetite types were hydrothermal in origin and generally low in Ti(<400 ppm)and Ni(<800 ppm),while being enriched in light Fe isotopes(δ^(56)Fe ranging from−1.54‰to−0.06‰).However,they exhibit different geochemical signatures and are thus classified into high-manganese magnetite(Mag1,MnO>5 wt%),low-silicon magnetite(Mag2a-c,SiO_(2)<1 wt%),high-silicon magnetite(Mag3a-b,SiO_(2)from 1 to 7 wt%)and high-silicon-manganese magnetite(Mag4,SiO_(2)>1 wt%,MnO>0.2 wt%),each being formed within distinct hydrothermal environments.Based on mineralogy,elemental geochemistry,Fe isotopes,temperature trends,TMg-mag and(Ti+V)vs.(Al+Mn)diagrams,we propose that the Erdaokan Ag-Pb-Zn deposit underwent multi-stage mineralization,which can be broken down into four stages and nine sub-stages.Mag1,Mag2a-c,Mag3a-b and Mag4 were formed during the first sub-stage of each of the four stages,respectively.Additionally,fluid mixing,cooling and depressurization boiling were identified as the main mechanisms for mineral precipitation.The enrichment of Ag was significantly enhanced by the superposition of multi-stage ore-forming hydrothermal fluids in the Erdaokan Ag-Pb-Zn deposit.展开更多
基金sponsored by the National Key R&D Project of China(2016YFC0600304)the National Natural Science Foundation of China(42121002)+3 种基金the International Science&Technology Cooperation Program of China(2011DFA22460)China Geological Survey(DD20190370)Geological Exploration Fund of Inner Mongolia Autonomous Region Program(2020YS-01)Major Science and Technology Projects in Yunnan Province(202303AA080006).
文摘Large-scale Cenozoic alkali-rich magmatic rocks are exposed at the eastern margin of Tibet due to the interaction between the Indian and Eurasian plates.However,their petrogenesis and associated geodynamic processes remain poorly understood.We analyzed the Xifanping porphyries in the Sanjiang orogenic belt to provide new insights.Our study shows a successive assembly of porphyry intrusions during three magmatic episodes.The magnitude and duration of the magmatic activities diminished sequentially,and mineralization occurred during the intermediate phase.Geochemically,the Xifangping porphyries display an adakitic affinity.According to zircon Hf isotope data,we propose that these porphyries originated from the partial melting of the thickened mafic lower crust beneath the western Yangtze Craton in response to lithospheric extension and asthenospheric upwelling.Analogous to the coeval alkali-rich porphyries in western Yunnan,the petrogenetic model of the Xifanping porphyries indicates regional north-south and east-west fractures caused by the clockwise rotation of the continental lithosphere and the Jinshajiang-Red River strike-slip during the post-collision phase of the India-Eurasia collision.In this context,we argue that the collision in eastern Tibet may have extended eastward to southwestern Sichuan during the post-collision period,persisting until approximately 30 Ma.
基金financially supported by the Heilongjiang Provincial Key R&D Program Project(No.GA21A204)Heilongjiang Provincial Natural Science Foundation of China(No.LH2022D031)the Research Project of Heilongjiang Province Bureau of Geology and Mineral Resources(No.HKY202302).
文摘Although previous researchers have attempted to decipher ore genesis and mineralization in the Erdaokan Ag-Pb-Zn deposit,some uncertainties regarding the mineralization process and evolution of both ore-forming fluids and magnetite types still need to be addressed.In this study,we obtained new EPMA,LA-ICP-MS,and in situ Fe isotope data from magnetite from the Erdaokan deposit,in order to better understand the mineralization mechanism and evolution of both magnetite and the ore-forming fluids.Our results identified seven types of magnetite at Erdaokan:disseminated magnetite(Mag1),coarse-grained magnetite(Mag2a),radial magnetite(Mag2b),fragmented fine-grained magnetite(Mag2c),vermicular gel magnetite(Mag3a1 and Mag3a2),colloidal magnetite(Mag3b)and dark gray magnetite(Mag4).All of the magnetite types were hydrothermal in origin and generally low in Ti(<400 ppm)and Ni(<800 ppm),while being enriched in light Fe isotopes(δ^(56)Fe ranging from−1.54‰to−0.06‰).However,they exhibit different geochemical signatures and are thus classified into high-manganese magnetite(Mag1,MnO>5 wt%),low-silicon magnetite(Mag2a-c,SiO_(2)<1 wt%),high-silicon magnetite(Mag3a-b,SiO_(2)from 1 to 7 wt%)and high-silicon-manganese magnetite(Mag4,SiO_(2)>1 wt%,MnO>0.2 wt%),each being formed within distinct hydrothermal environments.Based on mineralogy,elemental geochemistry,Fe isotopes,temperature trends,TMg-mag and(Ti+V)vs.(Al+Mn)diagrams,we propose that the Erdaokan Ag-Pb-Zn deposit underwent multi-stage mineralization,which can be broken down into four stages and nine sub-stages.Mag1,Mag2a-c,Mag3a-b and Mag4 were formed during the first sub-stage of each of the four stages,respectively.Additionally,fluid mixing,cooling and depressurization boiling were identified as the main mechanisms for mineral precipitation.The enrichment of Ag was significantly enhanced by the superposition of multi-stage ore-forming hydrothermal fluids in the Erdaokan Ag-Pb-Zn deposit.
