滇西高黎贡山南段公养河群变质基性火山岩LA-ICP-MS锆石U-Pb年龄及其地质意义

LA-ICP-MS zircon U-Pb age of metamorphic basic volcanic rock in Gongyanghe Group of southern Gaoligong Mountain,western Yunnan Province,and its geological significance

滇西公养河群1965年创名,为一套浅变质砂岩与泥板岩,夹少量硅质岩(或硅质页岩)及灰岩,生物稀少,常具类复理石韵律,为一套浊流至半深海相沉积;其时代一般认为属震旦纪—中寒武世,但一直缺乏准确的化石或测年依据。本次1∶5万区调在龙陵县邦迈村地层剖面中,确定了该套地层夹数层变质基性火山岩序列,根据地球化学研究恢复其原岩为玄武岩,形成于陆内拉张环境,可能与泛非造山期后的伸展有关。获得了变质基性火山岩的锆石U-Pb激光探针(LA-ICP-MS)499.2Ma±2.1Ma的年龄。这是测区首次获得的有关公养河群的高精度测年数据,为该群的划分及其时代约束提供了可靠的年代学依据。这一新的发现和成果对于进一步深入研究高黎贡山变质变形带泛非期的构造属性与演化历史具有重要意义。

Gongyanghe Group,which was named in 1965,is composed of epimetamorphic sandstone and shale interlayered with small amounts of siliceous rock（or siliceous shale） and limestone and represents a set of turbid flow and bathyal facies sediments with flyschoid rhythm and rare organisms.Its age has been generally considered to be between Sinian and Middle Cambrian,which,however,is not based on the evidence of fossils or accurate dating.In this study,the authors identified the stratigraphic sequence composed of several layers of metamorphic basic volcanic rock in Bangmai Village of Longling County.It is held that its original rock was basalt formed in an intra-continental tension environment and probably related to extension after the Pan-African orogenic period.The authors got for the first time the U-Pb age（499.2Ma±2.1Ma） of zircon from metamorphic basic volcanic rock and thus provided a reliable chronological basis for the division of the Gongyanghe Group and the restriction of the age.This achievement is very important for the further study of the tectonic characteristics and history of the deformed metamorphic belt of the Gaoligong Mountain.