^(36)Cl断代法  

METHOD FOR CHLORINE-36 DATING

作　　者：黄麒[1] 

机构地区：[1]中国科学院盐湖研究所,西安710043

出　　处：《第四纪研究》1997年第3期240-247,共8页Quaternary Sciences

基　　金：国家自然科学基金;美国国家自然科学基金

摘　　要：本文讨论了^(36)Cl的成因、^(36)Cl断代法的原理及其在第四纪年代学中的应用范围和测试方法，重点论述了大陆蒸发盐的^(36)Cl断代法。作者等曾应用该法测得了柴达木盆地1．4MaB．P．以来的石盐年龄。该法也已在冰碛物、火山岩等第四纪地质体的测年中获得了成功。有理由可以相信^(36)Cl断代法将在第四纪年代学研究中得到更广泛的应用。Chlorine-36 production, principles and experimental method of ^(36)Cl dating are briefly described.1 Chlorine-36 productionChlorine-36 is produced in atmosphere, rocks or water near the land surface(epigene), and within rocks and water below the earth's surface (hypogene).2 Experimental MethodFor ^(36)Cl measurement by accelerator mass spectrometry (AMS), the samples are prepared by dissolving away about half of amount of the halite and rocks in distilled water for removing any exchanged or recently precipitated component. The samples are then dissolved in distilled water or deionized water, and the chlorine precipitated as AgCl. The supernatant is discarded. AgCl is purified by repeated dissolution in concentrated ammonia and Ba(NO_3)_2 solution. The solution reprecipitated by addition of HNO_3. Centrifugalized and dried at 80℃. AgCl is placed in small tightly sealed bottles and protected from light, and ^(36)Cl measurement by AMS.3 Chlorine-36 DatingChlorine-36 dating of continental evaporites.Water entering closed basin lakes, such as those in the Chaidamu Basin, carries ^(36)Cl and stable chlorine from meteoric, epigene and hypogene sources. Due to the high solubility of chloride, the chlorine isotopes will accumulate in the lake water until halite saturation is achieved. The ^(36)Cl will then be locked into the halite crystals,and will decay with time. The age of the halite may be computed by comparing the initial ^(36)Cl / Cl ratio (at the time of deposition) with measured one in the halite by using the basic equation:where λ_(36) is the decay constant (2.303 × 10^(-6)/ a)Successful dating halite by ^(36)Cl depends on two conditions: (1) constant of known input ^(36)Cl / Cl ratio, (2) negligible cosmic-ray production after deposition, and no significant halite translocation. These conditions have been tested on the evaporite deposits in the Searles Lake (U.S.A.) and Salt Lakes in Chaidamu Basin (China), and have been found valid there. They also support the hypothesis that ^(36)Cl production has been fa

关 键 词：断代法 大陆蒸发盐 冰碛物 氯36 第四纪 

分 类 号：P534.63[天文地球—第四纪地质学]