山东临朐地区新生代玄武岩同位素钾-氩年龄研究

A STUDY ON K-Ar ISOTOPIC AGES OF CENOZOIC BASALTS FROM LINQU AREA,SHANDONG PROVINCE

Isotopic determinations were made on basalts intercalated in the strata with abundant Upper Tertiary fossils. In order to satisfy the needs of K-Ar age determina.tions of younger basalts with lower potasium content, we have made some modifications on the China-made ZhT-1301 massspectrometer, Meanwhile, some improvements and refinements have been made as well on the mass-spectrometer and the argon-extraction system and argen-measureing technique. Our results are: 7.86---13.Sm.y. for the youngest basalts ; 20--24 m.y. for the Shanwang Group with abundant Miocene fossils;and: 44 m.y. for basalts from the lower part of the Shanwang Group. The chronological results are basically in agreement with the stratigraphic sequence.

Isotopic determinations were made on basalts intercalated in the strata with abundant Upper Tertiary fossils. In order to satisfy the needs of K-Ar age determina-tions of younger basalts with lower potasium content, we have made some modifications on the China-made ZhT-1301 massspectrometer. Meanwhile, some improvements and refinements have been made as well on the mass-spectrometer and the argon-extrac-tion system and argon-measureing technique. Our results are: 7.86-13.5 m.y. for the youngest basalts; 20-24 m.y. for the Shanwang Group with abundant Miocene fossils; and 44 m.y. for basalts from the lower part of the Shanwang Group. The chro-nological results are basically in agreement with the stratigraphic sequence.