西藏措勤地区发现第三纪富钾岩浆岩

Discovery of Tertiary potassium-rich magmatic rocks in the Coqên area,Tibet

西藏措勤地区发现了第三纪富钾火山岩及正长岩,其同位素年龄分别为15.8～15.9Ma和27.15Ma。火山岩主要岩石类型为粗安岩,少量粗面岩、玄武粗安岩、白榴石玄武粗安岩;正长岩主要岩性为中—中粗粒或似斑状霓辉正长岩。岩石学、岩石化学初步研究表明其属于钾玄质-超钾质火山岩和碱性正长岩。这一发现填补了冈底斯北部新生代富钾质岩浆活动的空白,为进一步研究青藏高原形成和演化提供了重要资料。

Tertiary potassium-rich volcanic rocks and syenite were first discovered during the1∶250000re-gional geological survey in the Coqên area of Tibet.Their isotopic ages are15.8-15.9Ma and27.15Ma respectively.The main rock type of the volcanic rock is trachyandesite with small amounts of trachyte,basaltic-trachyandesite and leucite basaltic-trachyandesite.The syenite is mainly medium-grained and medi-um-coarse-grained or porphyra ceous aegirine-augite syenite.Preliminary petrological and geochemical studies indicate that these rocks belong to potassic basaltic-ultrapotassic volcanic rocks.This discovery proves the occurrence of Cenozoic potassium-rich magmatic activity in the northern part of the Gangdise belt and provides important data for the further study of the formation and evolution of the Qinghai-Tibet Plateau.