藏北羌塘菊花山那底岗日组火山岩锆石SHRIMP定年及其意义

Zircon SHRIMP Dating of Volcanic Rock from the Nadigangri Formation in Juhuashan, Qiangtang, Northern Tibet and Its Geological Significance

那底岗日组主要为一套中酸性火山岩、火山碎屑岩,夹砂砾岩的岩石组合,主要分布在藏北羌塘中部地区,龙木错-双湖缝合带的北侧。对那底岗日组底部安山岩进行锆石SHRIMP测年,时代为219±4Ma,确定那底岗日组火山岩早期喷发时间为晚三叠世而不是早侏罗世,与龙木错-双湖一线的低温高压变质带的时代基本一致。结合区域地质资料,那底岗日组火山岩可能形成于板块消减的火山弧构造环境,为龙木错-双湖缝合带晚三叠世向北俯冲消减的产物。

The Nadigangri Formation consist of intermediate-acidic volcanics, volcaniclastic rocks intercalated with glutenite, in the central Qiangtang area, north of the Longmu Co-Shuanghu suture, northern Tibet. The SHRIMP U-Pb age of zircons from andesite at the bottom of volcanics is 2194 Ma, which indicates the volcanisms started in the late Triassic and accords with the age of low-temperature high-pressure metamorphism in this area. According to regional geological data, the volcanics of the Nadigangri Formation probably formed in a volcanic arc tectonic setting and was the result of a northward subduction of the Longmu Co-Shuanghu suture in the late Triassic.