青藏高原新生代火山作用与构造演化
Cenozoic Yolcanism and Tectonic Evolution on the Tibetan Plateau
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摘要: 青藏高原的新生代火山作用是印度-亚洲大陆碰撞的火山响应,它显示了系统的时、空变化。随着印度-亚洲大陆碰撞从~65 Ma的接触-碰撞(即"软碰撞")转变到~45 Ma的全面碰撞(即"硬碰撞"),火山作用也逐渐从钠质+钾质变为钾质-超钾质+埃达克质。65~40 Ma的钾质和钠质熔岩主要分布于藏南的拉萨地块,少量分布于藏中的羌塘地块。从45~26 Ma,在藏中的羌塘地块中广泛发育钾质-超钾质熔岩和少量埃达克岩。随后的碰撞后火山作用向南迁移,在拉萨地块中产生~26~10 Ma间的同时代超钾质和埃达克质熔岩。尔后,从~18 Ma始,钾质和少量埃达克质火山作用重新向北,在西羌塘和松潘-甘孜地块中呈广泛和半连续状分布。此种时-空变异对形成青藏高原的深部地球动力学过程提供了重要约束。该过程包括:已消减的新特提斯大洋板片的回转、断离及随后增厚拉萨岩石圈根的去根作用,及因此而造成的印度岩石圈向北下插。青藏高原的隆升是自南向北穿时发生的。高原南部被创建于渐新世晚期,并保持至今;直到中新世中期,由于下插印度岩石圈的持续向北推挤,西羌塘和松潘-甘孜岩石圈的下部开始塌陷和拆离,高原北部才达到其现今的高度和规模。Abstract: Cenowic volcanign on the Tibetan plateau, which shows systematic variations in space and tine, is the volcanic response to the India-A sia continental collision. The volcanign gradually changed from Na-rich+K-rich to potassic-ultrapotassic+adakitic compo sitions along with the India-A sia collision shifting from contact-collisionof 65Ma (i. e,"soft collision") to all-sided collision of 45Ma (i. e,"hard collision". The sodium-rich and potassium-rich lavas with ages of 65~40 Ma distribute mainly in the Lhasa terrane of southern Tibet and subordinately in the Qiangtang terrane of central Tibet. The widespread potassic-ultrapotassic lavas and subordinate adakites were generated from~45 to 26 Ma in the Qiangtang terrane of central Tibet.
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Key words:
- Tibetan plateau /
- India-A sia collision /
- Cenowic volcanign /
- geochemistry /
- tectonic evolution
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