摘要
在内蒙地宙东段广泛分布的红旗营子群是一套低角闪岩相的火山沉积岩。由于地层富含水,在地质热事件中容易造成子体同位素的活化转移,往往出现地质年龄的年轻化,但仍保留有下伏各群均见及的2450Ma 的晚太古宙主幕变质年龄,而其中部相对含水少的变基性熔岩的 Sm-Nd 模式年龄则为2600±100Ma,故红旗营子群应归属晚太古宙晚期,经历过2350Ma,2200Ma,2050Ma,1850Ma,1700Ma 的早元古市热事件,并结合上覆地层有长城系,因此,不应归属早古生代。故内蒙地轴仍然存在。
Hongqiyingzi Group (i. e. The upper part of Dantazi Group in broad sense) is distributed widely in the eastern part of Nei Mongol Axis and Yanshan Platformal Fold Belt. It is a set of metamorphosed volcanic-sedimentary rocks of amphibolite facis. Because of the strata rich in water, the daughter isotopes could beactivated and transferred during geological thermal events, which result in younger age usually. Although clastic zircons remain, the age obtained from their U -Pb uniformity lines has been known to be those sealed during the early metamorphism of geological thermal events later. The age 2450±Ma of the main spisode of late Archean metamorphism was obtained for the strata and for underlying groups. Considering of poor water content in the instrusions and the sealing effects of their formation temperatures on the isotopes, their formation ages could be easily traced; So diorites, granites and other rocks intruded inside Hongqiyingzi Group have been age-determined older than 24-50Ma. Furthermore, the meta-basic lava of the same characteristics occuring in the middle part of this group has been age-determined 2600±100 Ma by Sm-Nd model age. For reasons above, Hongqiyingzi Group should belong, to the late stage of late Archean, undergone the early Proterozoic geological thermal events of 2350, 2200, 2050, 1850 and 1700Ma. This conclusion is drawn ofter analysis and study on various kinds of age-determination values, and considering the overlying strata Changcheng System which has not been metamorphosed and can be compared to the same layers distributed over the up lift and marginal parts of Yanshan Platformal Fold Belt in respect of layer sequences, marker beds and iron deposite types. Therefore, it is not rational to ignore the geological ages and geological relations and to put Hongqiyingzi Group into early Palaeozoicera just only by the so-called 'microfossils with special characteristics' found in it.
出处
《地质科学》
CAS
CSCD
北大核心
1992年第A12期17-24,共8页
Chinese Journal of Geology(Scientia Geologica Sinica)
关键词
红旗营子群
年龄
地质热事件
Hongqiyingzi Group, age-determination late Archean, geological thermal events
