Initial Rifting Age of the Nearly N–S Rifts in Southern Tibetan Plateau:New Evidence from the Age limit of the Early Sediments

Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the dikes probably related to the activity of the nearly N-S faulting and micas from hydrothermal activity and the low- temperature thermochronology of plateau uplift. Previous research shows that there are at least three different ideas about the age of the rifts： （1） older than 16-12 Ma, （2） 14- 10 Ma, and （3） 8-4 Ma （Fig. la）. For the old sedimentary strata represented the beginning of the rifting, the dating of the sediments helps to better define the initial rifting age.

日喀则—吉隆铁路活动断裂特征及其工程影响

日喀则—吉隆铁路位于藏南地区板块碰撞的构造边界带上,跨越定结、岗嘎和佩枯错三条大的第四纪活动裂谷,各裂谷内分布的活动断层对铁路的选线及工程设计具有重要影响。通过对日喀则—吉隆铁路沿线各裂谷内共25条断裂的现场调查测试,查明工程共穿越晚更新世活动断裂10条,其中有全新世活动断裂4条,分别为定结裂谷中的定结、郭家、登么错断裂和佩枯错裂谷中的岗彭庆断裂。对于定结、郭家断裂,可选择其活动性相对较弱的南段以简易工程通过,而对全线全新世活动性最强的登么错断裂,建议以路基形式通过。岗彭庆断裂带因未来地震危险性高,应避免隧道工程穿越该断裂带。