鞍山地区陈台沟表壳岩时代归属的初步研究

THE MINIMUM AGE OF THE CHENTAIGOU SUPRACRUSTAL ROCKS IN ANSHAN AREA

鞍山市东部约８ｋｍ处的陈台沟村附近，出露一套以斜长角闪岩类、石英岩类和长英质片麻岩类组成的表壳岩。长期以来，大多数地质学者一直将该表壳岩划归为鞍山群，但在岩石组合、变质变形特征和含矿性等诸多方面，都与鞍山地区公认的鞍山群明显不同，因表壳岩本身缺少准确定年的对象，难以直接测年，笔者将侵入于长英质片麻岩中的花岗质岩脉中的锆石颗粒，用Ｋｏｂｅｒ，方法和离子探针质谱计（ＳＨＲＩＭＰ）测定年龄，取得了表壳岩的沉积年龄为３３７６±５Ｍａ－３３５７±４Ｍａ。说明该表壳岩形成时代远老于鞍山群。

There are some supracrustal rocks near the Chentaigou village,8km east to Anshan City.The rocks are composed mainly of amphibolites,quartzites and felsic gneisses. They had been considered as Anshan Group but the the characters of the combinations of rocks,metamorphisms & deformations, and mineralizations are different from that of the typical Anshan Group in the area. The zircons,in the a granitic sheet that intrudes into the supracrustal rocks ard a felsic volcanic-sediment rock in the supracrustal rocks,were dated by using the technique of single zircon evaporation method on a thermal inoization mass spectrometer proposed by Kober(1986,1987).The zircon(￣(207)Pb/￣(206)Pb)age in the granitic sheet is 3337±12 Ma ,and in the felsic volcanic-sedi-ment rock the ages range from 3357±4 Ma to 3315±4Ma. The ages mean that the Chentaigou supracrustal rock is older than 3337±12 Ma and probably is 3 357 Ma, and it is one of the oldest supracrustal rocks in China.