The development of fluvial systems in East Asia is closely linked to the evolving topography following India-Eurasia collision.Despite this,the age of the Yangtze River system has been strongly debated,ranging from pre-Tertiary,Early Tertiary,Late Tertiary to Pleistocene.Here,we present new 40Ar/39Ar ages from basalts interbedded with fluvial sediments from the lower reaches of the Yangtze together with detrital zircon U/Pb ages from sand grains within these sediments.We show that a river containing sediments indistinguishable from the modern river was established before ca.23Ma.We argue that the connection through the Three Gorges must postdate 36.5Ma because of evaporite and lacustrine sedimentation in the Jianghan basin before that time.We propose that the present Yangtze River system formed in response to regional extension throughout Eastern China,synchronous with the start of strike-slip tectonism and surface uplift in eastern Tibet and fed by strengthened rains caused by the newly intensified summer monsoon.%新生代亚洲水系发育和演化与印度-亚洲碰撞导致的宏观地形地貌演化紧密相关,是研究青藏高原隆升和亚洲季风演化的重要切入点.一个世纪以来,中外科学家围绕长江演化历史开展了专门的研究,取得了丰硕的成果,但对于“长江东流水系形成于何时”这一关键科学问题却一直存在重大争议,计有前第三纪、第三纪早期(古近纪)、第三纪晚期(新近纪)、更新世早期和更新世晚期等多种观点,成为地球科学领域著名的“世纪谜题”.本文对长江中下游新生代盆地开展了沉积学与年代学研究,基于碎屑锆石U-Pb年龄谱示踪结果,结合上游构造地貌与盆地记录,提出长江东流水系建立于渐新世/中新世之交的观点.长江水系的重大调整尤其是东流水系的最终建立,是对青藏高原整体隆升、高原东南缘大型走滑运动、中国东部区域拉张凹陷以及东亚季风形成的综合响应.
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