U-Pb zircon ages of migmatite and granitic gneiss from Duoxiongla in eastern Himalayan syntaxis and their geological implications.

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±10 Ma from the melanosome of the Duoxiongla migmatite represents its protolith age, and the U-Pb zircon age of 1594± 13 Ma 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±16 Ma, 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 Duoxiongla 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.