我国北方风成沉积物质来源的微观矿物地球化学示踪研究

The dust provenance, that is where eolian deposits on Chinese Loess Plateau (CLP) came from, is one of frontier area that paleoclimatic studies focused on. This study especially concentrates upon whether dust source is different between glacial and interglacial periods. To evaluate the potential difference, new explicit index is urgently needed. This project aims at systematical microscale in situ mineralogy and geochemistry studies on deserts from North China and eolian dust deposits on CLP since the Miocene. Based on the the general rock mineral geochemical and Quaternary geologic investigations,this project is mainly focused on applying in situ techniques as electron microprobe analysis (EMPA), secondary ion mass spectrometer (SIMS) and mineral liberation analyzer (MLA), to study the variation, distribution and geochemical characteristics of the muti-minerals particles (rock fragments). Accurate quantification of mineral compositions and in situ microscopic elemental mapping on mineral particles will be organized to provide novel comprehensive methodology for the geochemical and mineralogical tracing of dust provenance. These new microscopic rock and mineral evidences will reveal the difference and similarity on both single mineral and rock fragments components in deserts, loess, paleosol and Red Clays. A schematic map of how eolian dust particles evolved in composition and texture will be depicted including mineral particles erosion, transportation and deposition. Armed with the new techniques mentioned above, tracing the eolian dust and rebuilding the ancient wind patterns will be realized in a new explicit way. This project will enlighten fruitful implications in exploring mechanism of dust material forming and transportation, rebuilding the ancient atmospheric circulation, decoding the long term paleoclimatic record and remediating airborne dust pollution.

黄土高原风尘物质来源，特别是在冰期和间冰期来源是否不同，是风尘物源和古气候研究的关键和热点问题。为了寻找直观明确的风尘物源指标，本项目拟对我国北方重要沙漠和黄土高原中新世以来风尘堆积剖面进行系统微观尺度的矿物学和地球化学研究。在岩矿地球化学和第四纪地质学研究基础上，项目将主要采用电子探针、矿物解析仪和离子探针等技术，查明多矿物颗粒（岩屑）的种类、分布和地球化学特征，开展矿物成分精确定量和矿物原位微区地球化学分析，建立风尘物源矿物地球化学示踪方法体系，揭示沙漠、黄土、古土壤和红粘土中岩屑和单矿物颗粒的微观岩矿地球化学异同性及其物源指示意义，阐明风尘矿物颗粒在不同时间尺度以及从源区到沉积区的组成和结构演化,为探讨黄土高原物质来源和古风场重建提供新证据和新方法。风尘物源研究对理解风尘物质的产生与搬运机制、重建古大气环流方向、解译风尘沉积的古气候记录以及沙尘环境治理等具有重要意义。

我国北方及其邻近的蒙古处于亚洲内陆，气候干旱，是全球第二大风尘释放中心。风尘物源研究对揭示风尘物质的产生与搬运机制、解读风尘沉积的古气候信息等具有重要意义。本项目以我国北方塔里木-中朝克拉通沙漠（塔克拉玛干、柴达木沙漠、腾格里、巴丹吉林沙漠、毛乌素沙地和库布齐沙漠）、中亚造山带沙漠（蒙古戈壁、科尔沁沙地、呼伦贝尔沙地和浑善达克沙地）和黄土高原多个风尘堆积剖面为主要研究对象，进行了系统的常量元素、微量元素、矿物组成、Hf、Nd和Sr以及碳氧同位素组成分析，在沙漠风尘地球化学特征与全球传输示踪、黄土物源单颗粒矿物示踪与冰川作用、黄土物质搬运过程与起源以及风成沉积中碎屑碳酸盐矿物的来源与气候变化等多个方面取得了新认识和进展。包括（1）查明了我国北方沙漠的元素、矿物及同位素组成特征及其差异，发现沙漠存在明显的矿物和地球化学分区特征，为黄土和东亚风尘物源示踪提供新的基础资料。（2）创建了风尘粘粒Sr-Nd-Hf同位素“源-汇”示踪体系，并应用于北太平洋、格陵兰冰芯、北非沙漠矿物尘和北美黄土的物源识别。（3）建立了区别指示物源和化学风化变化的单颗粒矿物指标（长石系列等），揭示冰期-间冰期和百万年尺度上的黄土物源变化与冰川作用增强之间的耦合关系；结合对黄土物源重要地区-青藏高原东部山区沉积地貌、第四纪地质及光释光测年等分析，进一步论证了黄土物质产生、快速堆积与极端寒冷事件有关。（4）获得了我国北方主要沙漠和黄土剖面碎屑白云石等矿物的精确定量数据，论证了碎屑白云石在轨道尺度上输入的稳定性，其含量变化可指示东亚夏季风降雨强度变化；发现塔克拉玛干沙漠全岩和<63微米中的白云石和方解石含量高于黄土高原黄土，柴达木沙漠接近，而其他沙漠全样中几乎不含或者含有低含量的白云石和方解石，提出了塔克拉玛干沙漠细颗粒组分是黄土高原黄土的重要物源。相关成果在《Earth and Planetary Science Letters》等SCI刊物上发表学术论文20篇以上。