青藏高原东部新生代钾质碱性系列岩石地球化学特征:岩石成因及其地质意义

Qinghai-Tibet Plateau and Its Genesis and Geological Implications

青藏高原东部新生代钾质碱性系列的岩石,包括深成岩、火山岩和煌斑岩,在时空上具有一致性,岩石化学成分均富碱、高钾、K2O/Na2O比值远大于1,高度富集Sr、Ba等大离子亲石元素(LILE)和轻稀土元素(LREE),亏损Nb、Ta等高场强元素(HFSE),及物质来源于富集地幔源区的Sr、Nd、Pb同位素组成等,均显示钾质碱性系列的岩石特有的特征,其形成与印度和欧亚两大陆碰撞,导致青藏高原北、东部在40Ma左右出现的大型走滑拉分带,致使地壳变薄以及地幔上拱的构造背景有关。

Cenozoic potassic alkaline rocks in the eastern Qinghai-Tibet plateau include plutons, volcanics, lamprophyre and acidic porphyry. They are consistent in the spatial and temporal aspect. They are rich in alkali, especially potassium （K2O/Na2O ratio 〉〉1）. The trace elements are characterized by enrichment of large ion lithophile elements including strontium and barium, and depletion of light REE and high field strength including niobium and tantalum. The source rocks are enriched mantle rich in Sr, Nd and Pb. The collision of India and Eurasia led to large strike-slipping in the eastern and northern Qinghai-Tibet Plateau in -40 Ma, and these events correlate to the tectonic events of lithosphere thinning and mantle uplifting in which the rocks formed.