青藏高原东北缘尖扎盆地沉积物矿物特征及其古环境意义  

Mineral Characteristics of Sediment in Jianzha Basin, the Northeastern Margin of Qinghai-Tibet Plateau, China and Their Paleo-environmental Significance

作　　者：王祎 符超峰[1,2] 宋友桂[2] 杨彦峰 WANG Yi;FU Chao-feng;SONG You-gui;YANG Yan-feng(School of Earth Science and Resources,Chang'an University,Xi'an 710054,Shaanxi,China;State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710061,Shaanxi,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,陕西西安710061

出　　处：《地球科学与环境学报》2020年第1期86-98,共13页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41772167,41140028);第二次青藏高原综合科学考察研究专题项目(2019QZKK0704)

摘　　要：应用X射线衍射对青藏髙原东北缘尖扎盆地加让剖面11.8~5.8 Ma的地层沉积物进行矿物分析,结果表明加让剖面沉积物矿物组分主要包括碎屑矿物、碳酸盐矿物和黏土矿物。其中,以碎屑矿物居多,主要是石英、斜长石、云母类矿物(白云母、黑云母),及少量尖晶石、辉石类矿物(普通辉石、锰钙辉石及顽火辉石等)、金红石、刚玉、磁铁矿、钛磁铁矿、榍石、霞石,偶见锆石、石榴子石、锐钛矿;碳酸盐矿物以方解石居为主,白云石占比较少;黏土矿物中,绿泥石占比最高,还有少量赤铁矿、蛭石和沸石。以全岩矿物指标研究为主,结合加让剖面沉积相演化特点,并以磁化率变化为参考,进行系统的矿物学研究,获得了尖扎盆地在11.8~5.8 Ma蕴含的古气候环境演化大致可分为4个阶段:11.8~10.0 Ma,气候干冷期;10.0~8.6 Ma,气候暖湿波动期;8.6~6.2 Ma,气候温暖湿润期;6.2~5.8 Ma,气候干冷期。在约10.0、8.6、7.2 Ma附近,主要矿物占比及组合特征有明显改变,当时的古环境状况发生急剧变化,可能揭示青藏高原东北缘在10~8 Ma期间广泛发生了一系列较强烈的构造运动,来源于周边山脉的剥蚀使得研究区沉积的近源物质增多,约7.2 Ma之后的古环境演化过程主要受青藏高原构造隆升以及全球气候变冷协同影响。By using X-ray diffraction(XRD) analysis technique, the mineral components of sediments from the sedimentary sequence spanning 11.8-5.8 Ma in Jiarang section of Jianzha Basin, the northeastern margin of Qinghai-Tibet Plateau, were analyzed. The results indicate that the mineral types of sediments in Jiarang section mainly include detrital minerals, carbonate minerals and clay minerals. Most are detrital minerals, including mainly quartz, plagioclase, muscovite and biotite, and a small amount of spinel, pyroxene(ordinary pyroxene, johannsenite and protoenstatite, etc.), rutile, corundum, magnetite, titanomagnetite, titanite and nepheline, and occasionally zircon, garnet and anatase, etc.;calcite is the main carbonate mineral, the proportion of dolomite is less;chlorite accounts for the highest proportion of clay minerals, and a small amount of hematite, vermiculite and zeolite are also found. Based on the whole rock mineral index, combined with the evolution of sedimentary facies in Jianzha Basin, and taking the variation of magnetic susceptibility as reference, the systematically mineralogical studies were carried out, and the paleo-climate environment informations of 11.8-5.8 Ma were obtained, which can be divided into 4 periods: 11.8-10.0 Ma, dry-cold climate;10.0-8.6 Ma, warm-humid climate fluctuates;8.6-6.2 Ma, warm-humid climate;6.2-5.8 Ma, dry-cold climate. At about 10.0, 8.6 and 7.2 Ma, the proportion and assemblage characteristics of the main minerals have significantly changes, and the paleo-environmental conditions change dramatically at that time. It may be revealed that a series of strong tectonic movements occur extensively in the northeastern margin of Qinghai-Tibet Plateau during the period of 10-8 Ma, and the denudation from the surrounding mountains increases the sedimentary material in the area. The paleo-environmental evolution after about 7.2 Ma is mainly affected by the tectonic uplift of Qinghai-Tibet Plateau and the global climate cooling synergistically.

关 键 词：沉积物 轻矿物 重矿物 矿物特征 X射线衍射 古环境 尖扎盆地 青藏高原 

分 类 号：P588.2[天文地球—岩石学] P532[天文地球—地质学]