Abstract:

:Kongtongshanconglomeratedeposits,generallycomposedofKongtongshanFormationandSanqiaoFormation,distributein thePingliangareaofthesouthwesternOrdosBasin.ThestratigraphicageandprovenanceoftheKongtongshanconglomeratehavebeen controversialforalongtime.By usingtheLA-ICP-MSzirconU-Pbisotopegeochronologicmethod,twosamplesofclasticrockswere collectedfromKongtongshanFormationandSanqiaoFormationinthesouthandnorthsidesofKongtongshanpeakstodiscussthesourceandtectonicsignificanceofKongtongshanconglomerate.TheresultsshowthatthedetritalzirconagesoftheUpperTriassic KongtongshanFormationmainlyinclude438~778Ma(n=16),827~1269Ma(n=40),1354~1706Ma(n=16),1826~2080Ma(n=15) and2410~2809Ma(n=17),andthecorrespondingpeakagesare540Ma,995Ma,1660Ma,1930Maand2480Ma.Thedetritalzircon agesoftheLowerCretaceousSanqiaoFormationmainlyinclude281~413Ma(n=6),445~643Ma(n=12),712~1386Ma(n=45),1563~ 1808Ma(n=14),1888~2039Maand(n=10)and2150~2633Ma(n=23),andthecorrespondingpeakagesare335Ma,488Ma,980Ma, 1676Ma,1805Ma,1970Maand2488Ma.ThecomparativeanalysesofzirconU-PbagesshowthatthemainsourcesofKongtongshan Formation and Sanqiao Formation come from the sedimentary rocks, igneous rocks and metamorphic rocks of Pre-Silurian and Pre-PermianfromtheeasternpartofQilianMountainandthewesternpartofNorthQinlingMountainrespectively.Andthereisafew sourcesofthesedimentaryrocksandmetamorphicbasementrocksintheNorthChina(Ordos)oldland.Furthermore,theKongtongshan Formation Conglomerate is composed by the main sources of Qinling Group, Kuanping Group, Dacaotan Group and Caledonian magmaticrocksinthewesternpartoftheNorthQinlingMountain,anditiscontrolledbytheIndosiniantectonismoftheQinlingand QiliancollisionalOrogenicBelts.TheSanqiaoFormationConglomerateiscomposedbythemainsourcesofMaxianshanGroup,Huluhe Group and Caledonian magmatic rocks in the eastern part of Qilian Mountain, and it is controlled by the Qinling and Qilian intracontinentalorogenyduringtheMiddleYanshanintheSouthwesternmarginoftheNorthChina(Ordos).

Key words: OrdosBasin;KongtongshanConglomerate;LA-ICP-MSzirconU-Pb