The Relationship between the NS-Trending Grabens and the Ultrapotassic Volcanic Rocks in Lhasa Block, Qinghai-Tibetan Plateau

• 责任者：Chen Jianlin (Key Laboratory of Isotope Geochronology and Geochemistry ; Guangzhou Institute of Geochemistry ; Chinese Academy of Sciences ; Guangzhou 510640 ; China) ; Xu Jifeng
• 刊名：Acta Petrologica et Mineralogica
• 出版年：2010
• 卷期：29(4)
• 关键词：碱性岩 ; alkali rocks ; 地堑 ; grabens ; 青藏高原 ; Qinghai-Tibetan Plateau
• 页码：p.341-354
• 图表：10 illus., 81 refs.
• 分类号：0801
• issnNo：ISSN1000-6524
• isbnNo：CN11-1966/P

Cenozoic ultrapotassic volcanic rocks have typical lamproite characteristics such as high SiO₂, MgO, K₂O and TiO₂, low Al₂O₃ and Na₂O, and high K₂O/Na₂O ratios. Geochemical and Sr-Nd-Pb isotopic characteristics of these ultrapotassic volcanic rocks in Lhasa block suggest that they were probably derived from a phlogopite-bearing enriched mantle source related closely to metasomatism during earlier subduction events. The ultrapotassic rocks in southern Tibet may imply the uplift and extension of Tibetan Plateau after the collision of Indian plate and Eurasian plate. Meanwhile, there are a number of N-S grabens (rifts) mostly formed in 23～8 Ma in Lhasa block, which might have cut the lower crust or lithosphere into the depth, suggesting the extension of southern Tibet in Miocene.