铀系等时线法测定腾冲地区火山岩的年龄  

URANIUM-SERIES DATING OF YOUNG VOLCANIC ROCKS FROM TENGCHONG REGION,SOUTHWESTERN CHINA

作　　者：梁卓成[1] 周秀云[1] 

机构地区：[1]中国科学院地球化学研究所

出　　处：《地球化学》1985年第3期227-235,共9页Geochimica

摘　　要：天然^238U放射性系列中，^230Th是^238U的子体，其半衰期为75，200年。铀钍是两种不同的元素，它们的地球化学行为不同，在岩浆作用过程中会发生分馏现象。根据放射性衰变关系，^230Th-^238U体系适用于测定发生在30万年内的地质事件年龄。1965年，E．The application of U-series technique to late Quaternary volcanic rocks is feasible because chemical fractionations between uranium and thorium isotopes commonly occur during magmatic processes. The isochron method is used to calculate ages of geological samples. The technique covers ages ranging from 5,000 to 300,000 yr. B. P. Generally, the 230Th/232Th and 238U/232Th radioactive ratios measured on different mineralphases are valuable for plotting an isochron.In this paper, an acid-leaching procedure was designed to isolate different frac-tions, acid-soluble (L) and acid-insoluble (E) phases, from volcanic rock samples. Then the isochron diagrams were constructed based on radioactive ratios in the L, R, and whole-rock (W) phases. The ages determined on three volcanic rocks from different volcanos of the Tengchong region, Yunnan Province, China are in good agreement with geological evidence. The analytical data of the L, R, W, and mineral phases from Maan-shan volcanic samples show that its eruption took place in Holocene. This is of great significance in evaluating geothermal water sources in this region.

关 键 词：火山岩 等时线法 地质年龄 铀 腾冲地区 

分 类 号：P597.3[天文地球—地球化学]