【摘要】 <正> 过去人们曾把变质程度最深的迁西群上川组作为冀东也是华北最老的地层。但近年来,多数同位素年龄的数据都表明,主要出露在太平寨和郭家沟等地的上川组麻粒岩其年龄为25亿年左右。这样,冀东地区是否有老于30亿年的早太古岩石,就成为一个令人瞩目又尚待解决的问题了。更多还原

【Abstract】 Available data for plagio-amphibolites in Chaozhuang Group from east-ern Hebei Province are examined. All these rocks occur in layer intercala-ted either with metasediments or with gneisses. In AFM diagram the plagioamphibolites mainly belong to calc-alkaline series and showed a higher con-tent of potassium. All rare-raeth elements patterns are fractionated withslight enrichment in light rare-earth elements, (Ce/Yb)_n ratios range from1.1 to 4.4. The rare-earth elements patterns observed here are quite similarto those of calc-alkaline basalts and continental basalts. These imply thatthe occurrence of plagio amphibolite from Chaozhuang Group may be rala-ted to underplating beneath the Archaean continental crust.更多还原