宇宙成因核素埋藏年龄测定及其在地球科学中的应用  

TERRESTRIAL IN SITU COSMOGENIC NUCLIDES BURIAL DATING AND ITS APPLICATION IN GEOSCIENCES

作　　者：袁兆德[1] 陈杰[1] 张会平[1] 

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029

出　　处：《地震地质》2011年第2期480-489,共10页Seismology and Geology

基　　金：地震动力学国家重点实验室自主研究课题(LED2010A04);国家自然科学基金(40672109);科技部国际科技合作计划项目(2008DFA20860)共同资助

摘　　要：原地生成宇宙成因核素埋藏测年方法,在晚新生代沉积物尤其是陆相碎屑沉积物测年上具有广泛的应用前景。在同一岩石或矿物中的宇宙成因核素对,例如26Al和10Be在地表的生成速率比值是固定的,不受纬度和海拔的影响,但是这一核素对分别具有不同的半衰期。在地表经历了暴露的沉积物被埋藏后,该比值会随着时间而降低,因此具有不同的半衰期的核素对(例如26Al/10Be)可以作为一种地质时钟,测年范围在几十万a至5Ma。文中简要介绍了目前常用的4种方法及其应用:暴露-埋藏图解法、深度剖面法、等时线法以及26Al-21Ne和10Be-21Ne法。Terrestrial in situ cosmogenic nuclides burial dating has a promising application in dating of late Cenozoic detrital sediments,for example,cave sediments,fluvial sediments and moraine.This method relies on a pair of cosmic-ray-produced nuclides that are produced in the same rock ormineral target at a fixed ratio,but have different half-lives.For example,26Al and 10Be are produced in quartz at 26Al：10Be=6.75：1.The ratio is not affected by latitude and altitude.After sediments are buried,the ratio would become less as time goes.Therefore,26Al/10Be ratio can be used as a geological clock.The dating range can be from several hundreds of thousand years to five million years.In this article,we introduce four methods and their applications：exposure-burial diagram method,depth profile method,isochron method,26Al-21Ne and 10Be-21Ne method.Exposure-burial diagram method is often applied to cave sediments dating,for exposure-burial history of cave deposits is easy.Depth profile method is applied to fluvial sediments dating.There is a good application for isochron approach in till-paleosol sequences in North America.26Al-21Ne and 10Be-21Ne method has a great potential applicaton in future for its larger dating time and less uncertainty than other methods.The dating method still has many problems.Firstly,there are no exact half-lives.For example,there is still controversy for 10Be half-life.Its estimate is 1.51±0.06Ma or 1.36±0.07Ma.Secondly,it is also a debate how to determine nuclides＇ production rates.In addition,post-burial or preburial erosion rate,inheritance nuclides concentration,post-burial nuclide production,effect of post-burial or preburial muonic production,sediment rework,complicated exposure-burial history of sediments all bring great challenges to cosmogenic nuclides dating.

关 键 词：宇宙成因核素 埋藏年龄测定 晚新生代 沉积物 

分 类 号：P597[天文地球—地球化学]