柴达木盆地西部千米深钻记录的晚上新世以来化学风化过程

There has been much debate on the relationships among tectonic uplift, climate change and continental chemical weathering. One effective way to solve this is to reconstruct a regional high-resolution chemical weathering sequence in typical area of climate and tectonic interactions. The Qaidam basin in the northeastern part of Tibetan Plateau, the unique location and continuous deposits provide a good opportunity for investigating the relationships between tectonic uplift, climate change and continental chemical weathering. This proposal intends to focus on high quality continuous fine-grained lacustrine of the new acquired SG-1 drill hole (2.8-0.1Ma) in the western Qaidam Basin, excluding the impact of evaporites and carbonates, carrying out major and trace element analysis for the silicate fractions in the sediments, selecting the well used proxies with clear mechanism (e.g., CIA and Rb/Sr) to reconstruct a drainage area high-resolution chemical weathering sequence since the late Pliocene. The stable major and trace elements in the supergene processes and Nd isotopes are used to play strong constraints on possible provenance change. Then we compare the drainage area silicate weathering records with regional and global climate records as well as regional tectonic activity history to reveal the major impact factors. This study will provide an important basis for further understanding of the relationship between watershed-scale tectonic, climatic and silicate chemical weathering.

长期以来关于构造隆升、气候变化和大陆化学风化的相互关系存在诸多争议。在气候和构造相.互作用典型区域建立高精度大陆化学风化序列是解决上述科学问题的有效途径之一。位于青藏高原东北缘长期封闭的柴达木盆地，独特的位置和连续的沉积使其成为研究构造隆升、气候变化和大陆化学风化的理想场所。本项目拟以柴达木盆地西部新获取的千米深钻SG-1钻(2.8-0.1Ma)高质量连续细粒湖相岩芯为研究对象，在去除岩芯样品的蒸发岩和碳酸盐后，对硅酸盐组分进行常量和微量元素分析，选用常用和机理清楚的指标(如CIA和Rb/Sr)，重建该区晚上新世以来高分辨率湖泊流域硅酸盐化学风化序列；通过物源示踪元素和Nd同位素分析，约束可能的物源变化影响；通过流域风化记录与不同时间尺度上区域和全球气候记录以及构造活动的对比，揭示流域风化的主控因素，从而为深入理解流域尺度构造、气候和硅酸盐化学风化之间的关系提供重要依据。

长期以来关于构造隆升、气候变化和大陆化学风化的相互关系存在诸多争议。位于青藏高原东北缘长期封闭的柴达木盆地，其独特的位置和连续的沉积使其成为研究构造隆升、气候变化和大陆化学风化的理想场所。本研究以柴达木盆地西部千米深钻SG-1钻孔高质量的连续细粒湖相岩芯为研究对象，开展岩心样品硅酸盐组分化学蚀变指数（CIA）和Nd同位素分析，结合机理清楚的蒸发岩和碳酸盐指标，重建该区第四纪以来湖泊流域气候变化过程和硅酸盐化学风化及可能的物源变化。结果表明柴达木盆地西部第四纪以来流域物源相对稳定，流域整体呈现出气候干旱化、流域硅酸盐风化强度减弱、湖水盐度增加和湖面降低的长期一致性演化过程；上述演化进程在2.2Ma到2.0Ma期间短暂加强，在约1.2Ma和约0.6~0.5Ma出现逐步加强趋势。过去60万年，柴达木盆地西部在冰期存在的相对高湖面时期与黄土高原粒度指标反映的冬季风减弱阶段可以很好对比。北大西洋海表温度反映的高纬过程是长时间尺度（＞十万年）驱动柴达木盆地西部气候变化和流域硅酸盐风化强度变化的主要因素；西伯利亚高压系统和西风系统的“跷跷板关系”可能是冰期－间冰期或者更短尺度影响柴达木盆地西部气候变化的主要因素。