Abstract:

Based on analysis on fission track dating of apatite and zircon in the granite and sand samples collected from the south, middle and north segment of Longmen Mountain, it is found that the uplift process of Longmen Mountain can be divided into different segments along strike direction and zones in East-West direction. From Songpan-Ganzi fold belt through Longmen thrust belt to western Sichuan foreland basin, the entire Songpan-Ganzi fold belt has experienced regional uplift, and the fission track age shows positive correlation with altitude; while in Longmen thrust belt, the fission track age has negative or no correlation with altitude, suggesting that thrust fault play a dominant role during the uplift process. However, in western Sichuan foreland basin, the samples partly or entirely annealed with burial depth. On both sides of Maoxian-Wenchuan fault, there is an obvious difference in zircon fission track age but no evident difference for apatite, suggesting that the west of Maoxian-Wenchuan fault has undergone more rapid uplift during 38-10 Ma. On both the sides of Beichuan fault, apatite shows obvious fission track age, suggesting a quick uplift process occurred in the west of Beichuan fault during 10-0 Ma. Along strike direction, zircon fission track age increases gradually from north to south part of Longmen Mountain, which may indicate a more rapid uplift process in the northern part during Late Indosinian or Early Yanshanian. Apatite fission track age generally decreases from north through middle and to south, reflecting a more rapid uplift in the middle and south than in the north during Cenezoic.

Key words: Longmen Mountain, fission track, differential uplift, granite