关键词: LA-ICP-MS, 锆石U-Pb年龄, 则弄群火山岩, 中冈底斯带, 构造演化

Abstract: The Late Mesozoic tectonic evolution models of the Gangdese belt in Tibet remain controversial. We present here the field
observations and zircon U-Pb ages of the volcanic rocks from the Zabuyechaka in the Mid-Gangdese belt. Zircon U-Pb dating results
suggest that the volcanic rocks of the Zenong Group were formed during 154.2-142.1 Ma. This study first obtain the Late Jurassic ages
of the Zenong Group (154 Ma), which is approximately 24 m.y. older than previously published data. The data from this study, and
combined with previously published data on Mesozoic volcanic rocks in the whole Gangdese belt show obviously northward younger
trends. It suggests that the Early Jurassic arc volcanic rocks in the south Gangdese belt were associated with the subduction of the
Neo-Tethys oceanic plate, and the Middle-Early Cretaceous arc volcanic rocks in the north Gangdese belt were related to the
subduction of the Bangonghu-Nujiang oceanic plate, and the Late Jurassic to Early Cretaceous arc volcanic rocks in the middle
Gangdese belt were jointly affected by the northward subduction of the Neo-Tethys and the southward subduction of the
Bangonghu-Nujiang oceanic plates. This study provides new evidence for the Late Mesozoic tectonic evolution of the Gangdese belt.

Key words: LA-ICP-MS, Zircon U-Pb age, volcanics of the Zenong Group, Mid-Gangdese belt, tectonic evolution