西藏伦坡拉盆地渐新世——中新世之交黏土矿物特征及其古气候意义

为揭示伦坡拉盆地渐新世—中新世之交黏土矿物蕴含的古气候信息，探讨其与青藏高原隆升及全球气候响应过程的关系，利用X射线衍射和荧光光谱分析对蒋日阿错剖面的黏土矿物特征进行了深入研究。结果表明:区内泥质岩中黏土矿物以伊/蒙混层矿物为主，伊利石次之，仅含有少量绿泥石和蒙脱石。黏土矿物的垂向组合特征显示伊利石和绿泥石含量在剖面下部低、上部高，伊/蒙混层含量与之相反，伊/蒙混层和伊利石在剖面中部呈明显波动变化，蒙脱石只出现在剖面中下部，可能为区域火山喷发产物在碱性环境中蚀变而成。伊利石结晶度变化于0.24°~0.48°，平均值为0.41°，表明样品未发生明显成岩蚀变，主微量元素比值指示研究区物源位置未发生较大改变，因此研究剖面黏土矿物特征可以有效反映伦坡拉盆地古气候演化过程。根据自生黏土矿物的习性指出伦坡拉盆地在渐新世—中新世之交出现了一次明显的降温事件，并且这次降温在青藏高原内部及周缘地区普遍存在，但造成这次降温事件的根本原因仍值得进一步探讨。

Characteristics of Clay Mineralogy and Its Paleoclimatic Significance Across the Oligocene-Miocene Transition in the Lunpola Basin,Central Tibet

Paleoclimatic investigations based on clay minerals analysis of samples from the Oligocene-Miocene boundary in the Lunpola Basin were conducted to explore the relationship between the Tibetan Plateau uplift and global climate response. Modern techniques of X-ray diffraction（XRD）and X-ray fluorescence（XRF）spectrometry were implemented to examine major clay minerals characteristics from the Jiangriacuo section. Results show that the majority of samples in the study area are dominated by illite/montmorillonite mixed-layer minerals， followed by illite with minor contents of chlorite and montmorillonite. The stratigraphic vertical composition of clay minerals shows that the illite and chlorite content is low in the lower part of the studied section compared to higher composition at the upper part， whereas the mixed-layer illite/montmorillonites show an overall converse trend to the illite and chlorite. At the middle part of the section， the illite/montmorillonite interlayer and illite content exhibit significant fluctuations. The montmorillonite that originates from the alteration of the volcanic eruption products under alkaline conditions only appears in the middle and lower intervals of the profile. The crystallinity of illite ranges from 0.24° to 0.48° with an average of 0.41°， indicating no significant diagenetic overprint of the studied samples， and the major/trace-elemental data also show that the provenance source for the Jiangriacuo section is not significantly changed. This indicates that the characteristics of clay minerals in the Jiangriacuo profile are related to the paleoclimatic evolution of the Lunpola Basin. Based on geochemical and clay mineral characteristics， an obvious cooling event in the Lunpola Basin at ca. 23 Ma is documented， which is a widespread event that impacted the inner and peripheral areas of the Tibetan Plateau. However， the fundamental factor that triggered this cooling event at times of the Oligocene-Miocene transition is still worthy of further discussion.