华南沿海地貌及水系变迁：台湾新生代沉积记录的约束

The west-tilting topography of East Asia was reversed with uplift of the Tibetan Plateau and opening of the marginal seas, resulting in large scale drainage reorganization. Due to the discontinuous accumulation and ambiguous depositional ages of the terrestrial deposits, the timing and processes of topography reversal and drainage reorganization in southern China have been vigorously debated. Taiwan has been becoming a geological window to detect drainage reorganization in southern China because of its well-exposed and successive Cenozoic sedimentary sequences. In this proposal, sediment provenance of the Cenozoic deposits exposed in Western Foothills and Hsueshan Range in Taiwan will be investigated by sandstone petrographic analyses, Pb-isotopes-in-K-feldspar as well as whole rock Pb isotope compositions. By comparing provenance signals of the Cenozoic deposits in Taiwan with that of the major rivers and tectonic units in East Asia, this research allows to trace the sediment sources. In particular this study addresses sediment provenance of Taiwan and its implication to drainage reorganization of the southern China.

青藏高原隆升和边缘海打开是新生代亚洲最重要的地质事件，对东亚地貌、水系分布和季风发育等产生了重大影响。然而目前对华南沿海地区水系重组时限和过程存在较大争议，尤其是闽江与长江东流之间的关系仍不清楚。台湾完整出露了南海北坡及东海陆架盆地南缘的新生代地层，是研究华南地貌-水系变迁的重要陆上地质窗口。本申请拟选取台湾西部麓山带和雪山山脉的新生代地层为研究对象，在系统分析其沉积学特征的基础上，对关键层位开展以钾长石Pb同位素为主的多种物源指标分析，通过与中国东部主要构造单元和水系的物源信号进行详细对比分析，追溯沉积物的来源及时空演化，进而重建华南沿海地区地貌-水系变迁过程。

晚新生代北吕宋岛弧与亚洲大陆发生弧-陆碰撞，使得华南被动大陆边缘的新生代沉积地层变形和抬升，最后出露形成台湾岛，因此台湾就相当于“出露的边缘海”。结合海-陆地质对比，使得台湾成为研究东亚构造、地貌格局变迁及水系演化的重要窗口。通过详细解剖台湾的沉积记录可以梳理东亚边缘海新生代地质演化过程，了解水系演化在边缘海的沉积响应，进而更完整地理解东亚地貌变迁过程。本研究对台湾新生界开展了详细的钾长石Pb同位素组成研究，并与中国东部主要构造单元进行对比分析。结果显示，台湾始新统-下渐新统所含碎屑钾长石以高放射性成因Pb为主，表明其主要物源区为近源的华夏地体；晚渐新世，随着边缘海的打开，古闽江逐渐拓展至下扬子地区。早中新世以后，扬子克拉通及秦岭-大别造山带等成为华南大陆边缘的主要物源区，表明中国大陆东倾地貌格局已基本形成。结合珠江口盆地沉积记录，也显示珠江在晚渐新世向西拓展，流域范围已覆盖青藏高原东南缘。这些证据表明渐新世边缘海的打开是华南沿海水系向内陆拓展的主要驱动力，这一构造事件在东亚主要水系演化中的角色不亚于青藏隆升。