藏南错那洞淡色花岗岩年代学研究及其对藏南拆离系活动时间的限定

Geochronology of leucogranites in the Cuonadong dome, southern Tibet and limitation of the timing of the Southern Tibet Detachment System(STDS)

北喜马拉雅片麻岩穹窿带(NHGD)内保存了大陆碰撞后青藏高原中下地壳的构造变形、高级变质、陆壳深熔作用等重要信息,是研究喜马拉雅造山带的深部岩浆作用和构造变形之间的耦合关系、深部岩浆活动乃至青藏高原隆升历史等大陆动力学过程的关键部位。本文对藏南错那洞穹窿内淡色花岗岩进行锆石LA MC-ICP-MS U-Pb、白云母^(40)Ar/^(39)Ar年代学和岩石地球化学分析。锆石U-Pb定年和白云母^(40)Ar/^(39)Ar测年结果表明错那洞淡色花岗岩形成于19.5±0.3Ma^19.7±0.7Ma,冷却年龄为15Ma。岩石地球化学特征显示该花岗岩具有明显的Eu负异常,稀土配分模式和微量元素蛛网图与以Manaslu为代表的高喜马拉雅淡色花岗岩一致,而不同于具有加厚地壳的埃达克岩的特征的北喜马拉雅淡色花岗岩,其形成于与南北向拆离相关的伸展环境。

The information of the middle-lower crustal deformation,high-grade metamorphism and anatexis since the IndianEurasian collision was preserved in the North Himalayan Gneiss Dome （NHGD）.Therefore,the NHGD is a critical area for study the geodynamic processe,including the coupling relationship between deep magmatism and deformation,the deep magmatic activity and the uplift history of the Tibetan Plateau.Geochronology and geochemistry of leucogranites in the Cuonadong dome were studied.The zircon LA MC-ICP-MS U-Pb dating for the leucogranite in Cuonadong dome,southern Tibet,yielded the crystalline ages of 19.5 ± 0.3Ma ～19.7 ± O.7Ma.The muscovite 40Ar/39Ar plateau age is 15Ma,which represent the cooled age of the leucogranite in Cuonadong dome.Compared with the Tethyan Himalaya leucogranites （Dala leucogranite） and the Greate Himalaya leucogranites （Manaslu leucogranite）,the Cuonadong leucogranite has the same geochemical compositions with the Greate Himalaya leucogranites.They are characterized by obvious negative Eu abnormity.However,they are notably different from the Tethyan Himalaya leucogranites,which show characteristics of adakite-like rocks resulted from the thickened crust.Therefore,the formation of the Cuonadong leucogranite is consistent with the Great Himalaya leucogranites,may associated with S-N extensional event.