西藏林周地区帕那组火山岩时代及构造背景

Geochronology and Tectonic Setting of Pana Formation Volcanic Rock in Linzhou Area,Tibet

林子宗火山岩在冈底斯带上广泛发育,其中帕那组火山岩的形成时代、构造背景和成因都存在一定争议。对林周地区帕那组火山岩进行了年代学和岩石地球化学研究,结果表明,研究区火山岩以流纹岩和英安岩为主,w(SiO2)极高,表现由高钾钙碱性系列向钾玄岩系列过渡的特征。帕那组火山岩微量元素地球化学特征显示LREE、LILE富集,HFSE亏损,Eu负异常,与岛弧火山岩地球化学特征相似。此外,帕那组流纹岩LA-ICP-MS锆石U-Pb年龄为(51.3±0.7)Ma,是目前为止冈底斯带中东段中的最老年龄。帕那组火山岩形成于后碰撞背景之下,其岩浆为地壳源区的部分熔融作用所形成。

Linzizong Group volcanic rocks are widely located in Gangdise belt, but the formation age and tectonic setting and petrogenesis of Pana Formation volcanic rock is controversial. The study results of geochronology and geochemistry of the Pana Formation volcanic rock in Linzhou area indicate that this volcanic rock has a high content of SiO2 and is composed mostly of rhyolite and dacite, with the magma series transformed from high-K calc-alkaline series to shoshonite series. While the geochemical characteristics of the trace elements of Pana Formation volcanic rock show that the rocks are rich in LREE and LILE, poor in HFSE, revealing Eu negative anomaly. These geochemical characters are similar to arc-related volcanics. The LA-ICP-MS zircon U-Pb age of Pana Formation rhyolite in Linzhou area is （51.3±0.7） Ma,which is the oldest one in central-eastern Gandise belt. Pana Formation volcanic rocks are formed in post-collision setting and the magma derived from partial melting of the crust.