铧厂沟地区碧口群玄武岩呈带状和透镜状分布于凝灰岩和凝灰质千枚岩中。在详细野外观察基础上,利用显微镜观察、主微量元素及放射性同位素分析等综合分析技术对玄武岩的岩石学、地球化学以及年代学特征进行了研究。结果表明：碧口群玄...铧厂沟地区碧口群玄武岩呈带状和透镜状分布于凝灰岩和凝灰质千枚岩中。在详细野外观察基础上,利用显微镜观察、主微量元素及放射性同位素分析等综合分析技术对玄武岩的岩石学、地球化学以及年代学特征进行了研究。结果表明：碧口群玄武岩普遍经历了绿片岩相的变质作用,主要矿物为斜长石、绿泥石和绿帘石；SiO2（44.67%~49.76%）、TiO2（1.14%~1.34%）含量较低, TFe2O3（12.03%~15.47%）、MgO（7.57%~9.3%）、CaO（7.29%~10.54%）含量较高。稀土总量较低,轻稀土亏损,重稀土富集。岩石微量元素和锆石Hf同位素特征显示玄武岩形成环境可能类似N-MORB,起源于软流圈,并在上升过程中混入了古老的地壳物质。LA-ICP-MS锆石测年结果显示玄武岩的形成年龄为（316.3±6.0） Ma （MSWD=0.78；n=7）,表明碧口群火山岩系至少是两期（新元古代时期和晚古生代时期）火山作用的产物。其大规模形成时期为新元古代,后经晚古生代火山作用的叠加改造而成。展开更多
The geodynamic setting of the Bikou volcanic group is a critical question to trace the Precambrain tectonic framework and evolution for the Yangtze plate. This study has suggested that the Bikou volcanic group is comp...The geodynamic setting of the Bikou volcanic group is a critical question to trace the Precambrain tectonic framework and evolution for the Yangtze plate. This study has suggested that the Bikou volcanic group is composed of several residual oceanic crust units: MORB (mid-ocean ridge basalt), Alk-OIB (alkaline ocean island basalt) and Th-OIB (tholeiitic ocean island basalt) as well as subduction-related volcanic rocks. According to field observation, those distinct rocks occurred collectively in form of tectonic contact, implying that the Bikou volcanic group was an ophiolitic mélange. Coupled with geochronological data, a perished oceanic basin at the northern margin of the Yangtze block during Neoproterozoic was tested by this ophiolitic mélange. Meanwhile, the isogeochemical data suggest that the ocean occurred in the Southern Hemisphere identical to Indian, South Atlantic and South Pacific oceans in terms of their Dupal anomalies, and the original source of the rocks could be probably mixing by EMⅠand EMⅡ component caused by dehydration melting of subducting oceanic crust during subduction process. On the basis of geochemical characteristics of the studied rocks, the Bikou volcanic group could imply that a partial breakup event occurred in the northern margin of Yangtze plate during the Neoproterozoic era.展开更多
文摘铧厂沟地区碧口群玄武岩呈带状和透镜状分布于凝灰岩和凝灰质千枚岩中。在详细野外观察基础上,利用显微镜观察、主微量元素及放射性同位素分析等综合分析技术对玄武岩的岩石学、地球化学以及年代学特征进行了研究。结果表明：碧口群玄武岩普遍经历了绿片岩相的变质作用,主要矿物为斜长石、绿泥石和绿帘石；SiO2（44.67%~49.76%）、TiO2（1.14%~1.34%）含量较低, TFe2O3（12.03%~15.47%）、MgO（7.57%~9.3%）、CaO（7.29%~10.54%）含量较高。稀土总量较低,轻稀土亏损,重稀土富集。岩石微量元素和锆石Hf同位素特征显示玄武岩形成环境可能类似N-MORB,起源于软流圈,并在上升过程中混入了古老的地壳物质。LA-ICP-MS锆石测年结果显示玄武岩的形成年龄为（316.3±6.0） Ma （MSWD=0.78；n=7）,表明碧口群火山岩系至少是两期（新元古代时期和晚古生代时期）火山作用的产物。其大规模形成时期为新元古代,后经晚古生代火山作用的叠加改造而成。
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40234041 and 40272042)
文摘The geodynamic setting of the Bikou volcanic group is a critical question to trace the Precambrain tectonic framework and evolution for the Yangtze plate. This study has suggested that the Bikou volcanic group is composed of several residual oceanic crust units: MORB (mid-ocean ridge basalt), Alk-OIB (alkaline ocean island basalt) and Th-OIB (tholeiitic ocean island basalt) as well as subduction-related volcanic rocks. According to field observation, those distinct rocks occurred collectively in form of tectonic contact, implying that the Bikou volcanic group was an ophiolitic mélange. Coupled with geochronological data, a perished oceanic basin at the northern margin of the Yangtze block during Neoproterozoic was tested by this ophiolitic mélange. Meanwhile, the isogeochemical data suggest that the ocean occurred in the Southern Hemisphere identical to Indian, South Atlantic and South Pacific oceans in terms of their Dupal anomalies, and the original source of the rocks could be probably mixing by EMⅠand EMⅡ component caused by dehydration melting of subducting oceanic crust during subduction process. On the basis of geochemical characteristics of the studied rocks, the Bikou volcanic group could imply that a partial breakup event occurred in the northern margin of Yangtze plate during the Neoproterozoic era.
