Provenance Evolution And Its Tectonic Significance Of Chang 10-Chang 8 Formation At Southeast Ordos Basin

Detrital zircon U-Pb dating of sandstone from Chang 10,Chang 9 and Chang 8 formation is conducted.Detrital zircon age structure of Chang 8 formation sandstone(DN-40)gives rise to 4 groups:220Ma?257Ma(23,26%),259Ma?371Ma(12,13%),1796Ma?2126Ma(14,12%),2126Ma?2639Ma(43,48%).The all age values span from 221 ±2Ma to 2639±18Ma.Age structure of Chang 9 formation sandstone(DN-02)in Jinsuoguan area also shows 4 groups:228Ma?256Ma(16,25%),259Ma?357Ma(13,21%),1760Ma?2182Ma(9,14%),2341Ma?2585Ma(25,40%).The all age values range from 228±2Ma to 2586±18Ma.Chang 10 formation sandstone DN-42 and DN-23 give rise to 4 age groups,respectively.DN-23 consists of:221Ma?257Ma(16,14%),265Ma?349Ma(12,11%),1695Ma?1864Ma(24,22%),2316Ma?2680Ma(59,53%),3069Ma(1,1%)and all the age values vary from 221±2Ma to 3069±19Ma.DN-42 comprises of:226Ma?257Ma(11,11%),258Ma?366Ma(18,18%),1752Ma?1999Ma(21,21%),2205Ma?2647Ma(48,48%),2857Ma(1,1%)and all the age values span from 226±2Ma to 2857±22Ma.The age structure of DN-40,DN-02,DN-42 and DN-23 have similar characteristics,which are featured by paleoproterozoic and neo-archean age peaks.The four age groups stand for Indosinian movement,Hercynian movement,paleoproteroic tectonic-thermal event and neo-arechan tectonic-thermal event,respectively.Based on the age structure comparison between Chang 10-Chang 8 formation and its priphery old land,the results indicate that Chang 10 formation to Chang 8 formation have consistent source,which are mainly northern and southern margin of Huabei block.However,the north-east Alashan old land and south Qinlin-Qilian tectonic belts may just supply few detrital sediments.According to the age structure comparison between Chang 10-Chang 8 formation(this study)and Chang 7 formation of southeast Ordos basin,combined with analysis of paleo-water direction,light and heavy mineral analysis,sedimentary facies analysis,the result shows that:the change of age structure from Chang 10-Chang 8 to Chang 7-Chang 6(obvious increase of Jinning epoch and Caledonian detrital zircon age)is attributed to the strong uplift of Qinling Orogenic belt at the middle/late period of Late Triassic(deposition time of Chang 7 Formation).The result is also consistent with the event deposition usually found in Chang 7 Formation of southern Ordos margin Yanchang Formation and these series of deposition events just occur at the deposition time of Chang 7 formation.Based on the detrital zircon age structure,our study precisely reflects the main uplifting time of Qinling orogenic belt and the well coupling relationship between Ordos basin and Qinling Orogenic belt.