摘要
西域砾岩是分布于青藏高原北缘天山、昆仑山一带的一套晚新生代砾石堆积地层,获知其可靠的年代信息对于理解高原隆升及地貌演化过程尤为关键.宇宙成因核素26Al/10Be埋藏测年是近年来发展起来的同位素测年新技术.本文对帕米尔高原西昆仑山山前的两个西域砾岩剖面采集的砾石样品进行了26Al/10Be埋藏测年分析.简单快速埋藏模式计算获得亚马勒剖面西域砾岩下部混合砾石样品的埋藏年龄＞3.5Ma,对该剖面西域砾岩上部5个样品加权平均得到的年龄为2.11＋0.60/-0.46Ma;另一处奥依塔克西域砾岩生长地层底部砾石样品的埋藏年龄在0.46 ～ 7.12Ma.研究表明,研究区的西域砾岩堆积具有穿时性.本文是26Al/10Be埋藏测年方法应用于西域砾岩年代学研究的一次有益探索和尝试,并对在西域砾岩26Al/10Be埋藏测年中存在的问题进行了探讨.
Distributed along the periphery of Tianshan and Kunlun Mountains in the northern margin of Tibetan Plateau, Xiyu conglomerate formation is a unit of Late Cenozoic gravel deposit which provides significant information of tectonic activities of the Northern Tibetan Plateau and global climate changes. It is crucial for attaining its depositional age in order to better understand the growth of Tibetan Plateau and related landscape evolution process. Cosmogenic nuclides 26A1/10Be burial dating is an emerging radioisotopic dating technique which could be used in dating gravel samples containing quartz mineral up to 5Ma. This study intends to explore the possibility of using Z6A1/10Be burial dating method to determine the age range of the Xiyu conglomerates of two sections-Yamale （39°03＇N, 75°35＇E） and Oytake （38°58＇N, 75°26＇E） in the foreland of western Kunlun Mountain on Pamir Plateau, which has intact and well-preserved stratigraphy in great depth. Calculating with simple burial model, the burial age of lower layer sample of Yamale section is older than 3.5Ma. Weighted mean age of five samples from upper layer is 2.11 ±0.60/0.46Ma. The simple burial age of another amalgamated sample from the bottom of growth strata of Xiyu conglomerate section in Oytake at 0.46 - 7.12Ma. In this study, we find several difficulties and problems of 26A1/10Be burial dating of Xiyu conglomerate ： （ 1 ） High erosion rates in the source area results in a low initial concentration of nuclides and large analytical uncertainty because of approaching lower limit of AMS measurement; （2）The ages of certain samples reach the limit of maximum age of 26A1/10Be burial dating; （3）High concentration of stable 27A1 and other nuclides in the samples interfere the chemical separation and the precision of AMS measurement ; （4） Multiple periods of erosion and deposition will change the apparent age of the sample, and isochron analysis may not always work in some cases. Weighted mean of isolevel multiple samples could give meaningful geological ages. This study is an exploration work of applying 26A1/10Be burial dating method on Xiyu conglomerate. Although this work does not give a precise chronological framework of this deposition, it shows the potential for the future study of burial dating of Late Cenozoic gravel deposits in the Northwestern China.
出处
《第四纪研究》
CAS
CSCD
北大核心
2015年第1期109-117,共9页
Quaternary Sciences
基金
国家自然科学基金项目（批准号：41302139）资助
关键词
西域砾岩
埋藏测年
cosmogenic nuclides, 26A1/10Be burial dating, Xiyu conglomerate
