北祁连玉石沟蛇绿岩形成时代的上限——来自正长岩锆石U-Pb定年的证据

LA-ICP-MS zircon U-Pb dating of syenite from Yushigou in Northern Qilian Mountain

摘要: 北祁连地区玉石沟蛇绿岩以发育较完整和典型的蛇绿岩岩石组合而备受关注。对侵入于玉石沟蛇绿岩中的正长岩进行LA-ICP-MS锆石U-Pb定年，获得正长岩的结晶年龄为522.7±5.3Ma，属早寒武世。这是北祁连地区最早的碱性侵入岩浆活动记录。该年龄的获得限定了玉石沟蛇绿岩形成时代的上限，应不晚于522Ma，即玉石沟蛇绿岩所代表的洋盆的发育扩张过程至少在该时限前已结束。

Abstract: The Yushigou ophiolite in Northern Qilian Mountain, which has developed relatively complete and typical ophiolite rock association, has received widespread attention. The authors conducted the chronological study of zircons from the syenite by means of LA-ICP-MS U-Pb. The weighted mean age of the zircons is 522.7±5.3Ma, which belongs to the Early Cambrian and confirms the earliest record of alkaline intrusive magmatic activity in Northern Qilian Mountain. At the same time, this age gives a constraint that the upper limit of the age of Yushigou ophiolite should be no later than 522.7Ma.