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东喜马拉雅构造结多雄拉混合岩和花岗片麻岩锆石U-Pb年龄及其地质意义 被引量:6

U-Pb zircon ages of migmatite and granitic gneiss from Duoxiongla in eastern Himalayan syntaxis and their geological implications.
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摘要 位于东喜马拉雅构造结的南迦巴瓦岩群是研究喜马拉雅构造带基底演化的重要对象之一。在构造样式上,南迦巴瓦岩群为一个背形构造,该背形构造的核部由多雄拉混合岩和花岗片麻岩组成。本文开展了南迦巴瓦岩群多雄拉混合岩的锆石 LA-ICP-MS U-Pb 定年研究。结果表明,多雄拉混合岩深色体的原岩形成年龄为1759±10Ma,浅色体的形成年龄为1594±13Ma,代表发生混合岩化的年龄。另外,一个多雄拉花岗片麻岩的原岩形成年龄为1583±6Ma,该年龄在误差范围内与区域发生混合岩化作用的时代相近,表明在混合岩化过程中存在着一定程度的地壳深熔作用。区域对比表明,低喜马拉雅和高喜马拉雅构造单元内存在着明显不同的构造-岩浆事件,其中低喜马拉雅构造单元广泛存在1.6~1.8Ga 的构造-岩浆事件。与之相对比,多雄拉混合岩和花岗片麻岩的锆石 U-Pb 年代学说明南迦巴瓦岩群核部应属于低喜马拉雅结晶岩系,而明显不同于高喜马拉雅结晶岩系,这与西喜马拉雅构造结相似,表明东喜马拉雅构造结与西喜马拉雅构造结有着相似的地质演化。 The basement of the eastern Himalayan syntaxis consists mainly of the Namche Barwa Group. Tectonically, the Namche Barwa Group is a larger north-plunging antiform. The Duoxiongla Formation ( migmatite and granitic gneiss) from the Namche Barwa Group form the core of the antiform. This paper carries out U-Pb zircon dating from the Duoxiongla migmatite and granitic gneiss using LA-ICP-MS method. Obtained U-Pb zircon age of 1759 ± 10Ma from the melanosome of the Duoxiongla migmatite represents its protolith age, and the U-Pb zircon age of 1594 ± 13Ma from the leucosome of the Duoxiongla migmatite is interpreted as migmatism time. A granitic gneiss from the Duoxiongla Formation yielded U-Pb zircon age of 1583±6Ma, which is interpreted as protolith age of the granitic gneiss. The age similarity between the protolith of granitic gneiss and the leucosome of the migmatite within errors indicates crustal anatexis and melt generation during the migmatization. Regional data show that the High-Himalayan unit and the Lesser- Himalayan unit have distinct tectono-magmatic events. In the Lesser-Himalayan unit, 1.6 - 1. 8Ga tectono-magmatic events are unique. The tectono-magmatic events of the Duoxiongla Formation are good consistent with those of the Lesser-Himalayan unit, implying that the Duoxiongia Formation has an affinity with the Lesser-Himalayan unit but is distinct from the High-Himalayan unit. The crustal structure of the eastern Himalayan syntaxis resembles that of the western Himalayan syntaxis in Pakistan, indicating that both syntaxises have similar geological evolution.
出处 《岩石学报》 SCIE EI CAS CSCD 北大核心 2008年第3期421-429,共9页 Acta Petrologica Sinica
基金 国家自然科学基金(40521001 40773019) 教育部长江学者和创新团队发展计划(IRT0441)资助项目
关键词 东喜马拉雅构造结 南迦巴瓦岩群 多雄拉混合岩 U-Pb锆石年龄 Eastern Himalayan syntaxis Namche Barwa Group Duoxiongla migmatite U-Pb zircon dating
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