同位素稀释质谱法对年青玄武岩K－Ar年龄的测定  

Determination of K-Ar Ages on Some Young Basalts by IDMS

作　　者：桑海清[1] 裘冀[1] 王松山[1] 胡世玲[1] 

机构地区：[1]中国科学院地质研究所

出　　处：《质谱学报》1996年第4期19-24,共6页Journal of Chinese Mass Spectrometry Society

基　　金：国家自然科学基金

摘　　要：用同位素稀释质谱法在ＲＧＡ－１０质谱计和析Ａｒ仪联合系统中，分析测定了一批年青（第四纪）玄武岩样品的常规Ｋ－Ａｒ年龄。绝大多数样品的年龄值在０．１～０．７Ｍａ之间，只有少数几个样品的年龄值在１～２Ｍａ之间，所测年龄都在第四纪范围内。部分样品经过重复检测获得了良好的重现性，这表明测量精度和准确度都比较高。经检测样品的大气４０Ａｒ／３６Ａｒ比值在２９５．５±５以内。这与当今大气Ａｒ比值２９５．５无明显差别，证明样品不含过剩４０Ａｒ和３６Ａｒ，测得的年龄值是真实可信的。大多数样品的测定误差在±５％以内，仅有少数几个样品的测定误差在±５～±１０％之间，这样的测试水平对年青的第四纪地质样品而言是完全可以接受的。The present paper reports some results of K-Ar ages in young basalts from northwest and northeast region of China.These results are determined by 38Ar isotope dilutien mass spectrometry(IDMS).The particle size of samples analysed sanes in a range from 0.20 to 0.63 mm in diameter is selected.We use an ultra-high vacuum system for argon extraction and a RGA-10 mass spectrometer operated in static mode for isotopic measurement.The isotopic ratios of argon for spike are40Ar/38Ar=7.4364×10-3,36Ar/38Ar=5.0868×10-5.All argon isotopes has been corrected for memory effect.Using flame photometry the potassium is determined.Finally,we use following contants λe=0.581×10-10/year,λβ=4.962×10-10/year,λ=5.543×10-10/year and 40Ar/K=1.167×10-104(mole/mole)for age calculation.The age range of all basalts is from 0.116 to 2.101 Ma.Also,the standard diviation is given for every measured age.The measurement precision of most samples is within ±5%.The results indicate well for young samples.

关 键 词：玄武岩 同位素稀释质谱 钾-氩年龄 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]