Sm—Nd模式年龄和等时线年龄的适用性与局限性

A DISCUSSION ON THE MODEL AND ISOCHRON AGES OF Sm-Nd ISOTOPIC SYSTEMATICS:SUITABILITY AND LIMITATION

Ｓｍ—Ｎｄ模式年龄和等时线年龄的适用性与局限性李献华（中国科学院广州地球化学研究所广州５１０６４０）陈江峰（１９９）与杨晓松（１９９４）关于“二元混合体系的端元Ｓｍ—Ｎｄ同位素模式年龄计算方法”的讨论，提出了有关Ｓｍ—Ｎｄ同位素体系的基本原理和应用的...

Abstract Sm-Nd isotopes has been widely employed in the crust-mantle evvolution,geochronology,petrogenesis,and Precambrian research etc,in Chinese literatures dunng the last decade.The problem of abuse and muisinterpretation of the Sin Nd isotopic systematics,however,resulted in false conclusions in some of recently published papers.This paper mainly reviews methodologies,sultabilities and limitations of the model and isochron ages of Sm-Nd systematics.The emphasis is placed on that the Sm/Nd ratio of samples close to a continentlike one is of importance to calculate Nd model age correctly.Nd model age may provide only an estimate of the average time that the matelal in the sample has been resident in the continental crust.Sm Nd isotopic systematics of fine-grained elastic sediments can be not only a sensitivve indicator of sedimentary provenance which could be related to the contemporaneous tectonic activities,but also useful to constrain the maximum age of the deposition of the sediments.Sm Nd isotopes has bothadvantages and dlsavantages in the constitution of isochron in the light of REE geochemical behaviors.Cautions must be evoked in interpretation of Sm Nd regression line,which may be or may not be isochron,errochron,and binary mixing line.