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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.
On the basis of the data of 45 K-Ar ages in the Eastern Tianshan, Uygur Autonomous Region of Xinjiang, China, and the geological environment, the following conclusions are given. The Tianshan Hercynian geosyncline had passed through about 200 my before itsformation, and it was in the late Kercynian at about 234.9 ± 20 my 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 my The Hercynian magmatic activities may be divided intotwo substages: the early substage is of 300-350 ± 20 my, and the later is of 230 ± 20 my By using the results of the determination of the ages, the thermal history of Twians geosyncline is preliminarily discussed.