青藏高原拉萨地块碰撞后超钾质岩石的时空分布及其意义
Post-collisional ultrapotassic rocks in Lhasa Block,Tibetan Plateau:Spatial and temporal distribution and its'''' implications.
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摘要: 对西藏拉萨地块超钾质岩石的研究是近10年来青藏高原研究的重要进展之一。本文对西藏拉萨地块中部当若雍错和许如错地区的超钾质火山岩进行了透长石和黑云母的~(40)Ar/~(39)Ar定年。当若雍错粗面岩的黑云母~(40)Ar/~(39)Ar等时线年龄为13.2±0.3Ma,3个透长石的等时线年龄分别为13.0±0.3Ma、13.7±0.3Ma和13.0±0.3Ma;许如错辉石粗面岩黑云母的~(40)Ar/~(39)Ar等时线年龄为11.2±0.3Ma。结合已有研究结果,探讨了拉萨地块碰撞后钾质和超钾质岩石的分布特征。超钾质岩石产出于大约东经87度以西的地区,岩石年龄介于8~25Ma之间,而钾质岩石则在东部和西部都有产出,时代为9~24Ma。超钾质和钾质岩石在野外产出的构造背景上,显示了与南北向裂谷、新生代盆地、南北延长的湖泊等分布的密切关系。拉萨地块碰撞后岩浆作用的时间与裂谷发育、岩脉侵入、埃达克岩形成等岩浆-构造事件的时间相互重叠不是偶然的,预示着可能存在一个深部岩石圈演化的统一事件,而最为可能的是高原南部岩石圈地幔的减薄作用。超钾质岩浆作用在拉萨地块与羌塘地区同时发育表明拉萨地块与藏北在构造和岩石圈演化方面具有一致性。
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Key words:
- Ar-Ar dating /
- Dangreyongcuo /
- Xurucuo /
- Ultrapotassic rock /
- Lhasa block /
- Tibet
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