Age And Provenance Of The Ergunahe Group And Wubingaobao Formation In The Northeastern Inner Mongolia, NE China: Evidence From U-Pb Geochronology Of Detrital Zircons

In this paper we present U-Pb dating results of detrital zircons from the ErgunaheGroup and Wubinaobao Formation in the northeastern Inner Mongolia, NE China, withthe aim of constraining their formation age and provenance and further revealing thetectonic attribution of the Erguna Massif. Most of detrital zircons from five samplescollected from the Ergunahe Group and Wubinaobao Formation are euhedral-subhedral inshape and display striped absorption and oscillatory zoning in CL images. Combined withtheir Th/U ratios, it is suggested that they are of magmatic origin. Additionally, somezircons show a metamorphic growth rim. The dating results indicate that the zircons frombiotite schist, white mica quartz schist, and feldspar quartz sandstone from the ErgunaheGroup yield age populations of738Ma,760Ma,792Ma,837Ma,890Ma,964Ma, and1050Ma, and that the zircons from two quartz sandstones in the Wubinaobao Formationgive age populations of466Ma,484Ma,515Ma,738Ma,795Ma,837Ma, and894Ma.Combined with the age populations of detrital zircons from the Xinghuadukou Group inadjacent area, the field relationships of the Ergunahe Group intruded by Caledoniangabbros and overlied by the upper Silurian, we conclude that the Ergunahe Group formedbetween714Ma and738Ma, i.e., Neoproterozoic. The previously believed WubingaobaoFormation can be subdivided into two parts, one (calcareous siltstone) in western part ofthe study area formed between714Ma and795Ma, similar to the Ergunahe Group, andthe other (quartz sandstone) in the eastern part of the study area formed between466Ma and late Silurian based on the fact that the Wubingaobao Formation overlied by upperSilurian, i.e., the late stage of Early Paleozoic. The age spectrum of detrital zircons fromthe Ergunahe Group and Wubinaobao Formation reveal that their sediment sourcesmainly come from the terranes outcroped around the basin. The widespread occurrence ofthe Neoproterozoic detrital zircons in the Ergunahe Group and Wubinaobao Formationsuggest that Precambrian terranes occur in the Erguna Massif, similar to the magmaticevents within the massifs around the southern margin of the Siberia Craton.