藏北改则地区鱼鳞山组火山岩同位素年代学

Isotope choronology of volcanic rocks in the Yulinshan Formation in the Gêrzê area,northern Tibet

鱼鳞山组火山岩是青藏高原隆升过程中一次重要的碱性钾质火山活动的产物,自发现之日起时代一直定为上新世末至早更新世,对比范围跨羌塘南部到冈底斯地区。通过对鱼鳞山组火山岩同位素测年研究,鱼鳞山组白榴石响岩40Ar-39Ar积分年龄为27.8Ma、K-Ar法年龄为30～18Ma,确定鱼鳞山组时代为渐新世至中新世,其分布仅限于班公湖-怒江缝合带以北地区。

The volcanic rocks in the Yulinshan Formation to the north of the Bangong Co-Nujiang River suture resulted from alkaline potassic volcanism during the uplift of Qinghai-Tibet Plateau.Since the dis-covery,they have been considered to be late Pliocene to early Pleistocene in age.They may be correlated within the areal extent from southern Qiangtang to Gangdise.According to the isotope chronological study of the volcanic rocks of the Yulinshan Formation,leucite phonolite of the Yulinshan Formation has an in-tergrated 40Ar / 39 Ar age of 27.8Ma and K-Ar ages of 30-18Ma ,which suggests that the age of the Yulinshan Formation should be Oligocene to Miocene.Its distribution is only limited to the area north of the Bangong Co-Nujiang River suture.