ON THERMAL HISTORY OF TIANSHAN GEOSYNCLINE ACCORDING TO THE DATA ON K-Ar DATING OF EASTERN TIANSHAN

On the basis of the data of 45 K-Ar ages in the Eastern Tianshan, Uygur AutonomousRegion of Xinjiang, China, and the geological environment, the following conclusions aregiven. The Tianshan Hercynian geosyncline had passed through about 200 m.y. before itsformation, and it was in the late Kercynian at about 234.9±20 m.y. ago. The Yenshanmagmatism in this region has been first verified by the authors, and its K-Ar age is esti-mated at 196.6-157.6±20 m.y. The Hercynian magmatic activities may be divided intotwo substages: the early substage is of 300-350±20 m.y., and the later is of 230±20 m.y. By using the results of the determination of the ages, the thermal history ofTianshan geosyncline is preliminarily discussed.     

据天山东段K-Ar年龄测定结果对天山地槽热历史的探讨

本文根据我国新疆天山东段的45个K-Ar年龄数据,结合地质实际,得出结论认为,天山海西期地槽的形成大约经历了200百万年,海西晚期约234.9±20百万年为天山海西地槽形成的时间上限。初步证实了本区有燕山期岩浆活动的存在,其年龄值在196.6—157.6±20百万年之间。应用各项年龄测定结果,初步讨论了天山地槽的热历史。     

华北麻粒岩相带铅同位素组成特征及其与全球对比

本文通过对华北麻粒岩相岩石的Pb同位素组成特征的研究表明,华北太古宙地幔μ值在7.81±0.03。其下地壳μ值在2—4左右,Th/U在1.6—13.6,与全球范围内下地壳深变质作用引起的U和Th的亏损程度相似。通过对全球麻粒岩相岩石Pb同位素组成的对比研究表明,全球太古宙地幔的μ值存在明显的区域性的差异,南半球的μ值高于北半球,表明地球存在初始不均一性。