青海可可西里地区新生代火山岩的岩石特征与时代

Petrological Characteristics and Ages of Cenozoic Volcanic Rocks from the Hoh Xil Mts., Qinghai Province

可可西里地区的新生代火山岩属于藏北火山岩带的东段。火山岩主要以熔岩台地、桌状山的形式产出，熔岩厚约４０—１００ｍ。除少量的高钾流纹岩、粗面岩和粗面英安岩外，在数量和分布上以普遍含二辉石斑晶的安粗岩占优势。岩石以富碱（尤其富钾）和富ＬＲＥＥ为特征。火山活动发生在中新世，根据Ｋ／Ａｒ定年结果划分为早、中、晚三期。本区火山岩的特征与西藏境内的同时代岩石完全可以对比。

Cenozoic volcanic rocks distributed at the Hoh Xil Mts. belong to eastern segment of the Cenozoic volcanic rock belt outcropped along the north Tibetan plateau. In this area volcanic rocks occur mainly in the forms of lava plateau and table mountains, about 40 100m in thickness. Excepting a few high-K 2O rhyolite, trachydacite and trachyte, latites commonly having clino and orthopyroxenes phenocrysts are superior in quantity and distribution. These volcanic rocks are characterized by enrichment of alkalis (specially K 2O) and REE. The volcanic activity took place only in Miocene and might be divided into early (17.3 15.4Ma), middle (14.5-11.7Ma) and late (7.5-6.95Ma) stages based on K/Ar dating. Petrological and geochemical characteristics and ages of volcanic rocks in the Hoh Xil Mts. are consistent with those of Cenozoic volcanic rocks in Tibet. The volcanic activities have been closely related to the lithospheric evolution of the Tibetan plateau since Cenozoic.