摘要:
甘肃北山地区的勒巴泉群是一套中,深变质岩系,主要由石英片岩、云母石英片岩组成,局部夹大理岩、片麻岩及磁铁矿,对其时代归属长期存在争论。作者通过野外工作,查明该群与志留系公婆泉群呈断层接触关系,对侵入该群的角闪岩脉采集样品测得Sm-Nd等时线年龄为644.5±49Ma数据;并据该群的岩石组合、变形与变质程度、含沉积变质铁矿等特征进行区域对比。作者认为该群层位与相邻白湖群基本相当,其时代应属于长城纪。
Abstract:
The Lebaquan Group in the Beishan Mountain area, Gansu Province, is a medium- to high-grade schist and mica-quartz schist, locally intercalated with marble, gneiss and magnetite. Its age assignment has long been disputed. Through field work, the authos have ascertained that this group has faulted contact with the Silurian Gongpoquan Group. The sample taken from amphibolite dikes intruded into this group were measured to have a Sm-Nd isochron age of 644.5±49Ma. According to regional correlation rock associations and degrees of deformation and metamorphism of this group and the occurrence of metamorphosed sedimentary iron deposits, the authors consider that the Lebaquan Group is stratigraphically equivalent to the Baihu Group adjacent it and that its age should be the Changchengian Period.
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