辽宁弓长岭含铁建造年代学研究

用热离子质谱计双带源蒸发—沉积测定单个锆石晶体年龄的方法对弓长岭含铁建造中黑云变粒岩、混合岩化浅粒岩和石英岩中的锆石作了测定,获得了2.60—2.54 Ga,3.36—2.62 Ga和3.53—3.08 Ga等年龄数据。结合已有的研究资料可以认为,黑云变粒岩的原岩来自2.7 Ga左右的中酸性火山物质,浅粒岩和石英岩的原岩来自3.0 Ga以上的花岗质地壳物质;含铁建造形成于陆壳基底之上,形成时间约2.7 Ga,并于2.5—2.7 Ga之间发生首次变质作用。

Geochronology Research of the Iron Formation of Gongchangling,Liaoning Province

The zircon was dated by using the technique of single-zircon stepwiseevaporation-deposition with a thermal ion mass spectrometry (Bernd Kober, 1986and 1987). The zircon ages are 2.60--2.54 Ga for biotite-leptynite (BL), 3.36-2.62 for mimatized leptite (ML), and 3.53--3.08 Ga for quartzite(Q) from theiron formation. Combined with available data, it is comidered that the sourcerock of biotite--leptynite might be intermediate--acid volcanic material of ca.2.7 Ga, and that of migmatized leptite and quartzite might come from graniticcrust older than 3.0 Ga. The iron formation was formed on the continental crustbase at about 2.7 Ga, and was immediately metamorphosed for the first time.