Sediment Provenance Analysis And Its Tectonic Significance Of Middle-uppertriassic Qiongda Formation In Mid-east Region Of Gangdise

Since Yang Jingsui found eclogite belt in songduo in the north side of Gangdise at 2006,many scholars do researches about songduo eclogite and tectonic evolution of the zhikong-songduo ocean,However,there has been no detailed studies on the sedimentary records of the zhikong-songduo ocean.In this paper,I did systematic studies about petrology characteristics,basin filling sequences,sedimentary environment and sedimentary facies,provenance background and evolution of sedimentary basin attribute of qiongda formation through the use of petrology,stratigraphy,geochemistry,zircon chronology.Qiongda formation shows a intermittent zonal distribution along the south of zhikong-songduo,its top conformable contacts with mailonggang formation and its bottom unconformable contacts with linbuzong formation?J₃K₁l?and chumulong formation?K₁c?.Slope deposition in the lower part of qiongda formation,partially developed underwater fan.The upper part is the accumulation of mixed shelf,volcanoes erupt at the top.We discover that the clastic rocks of qiongda formation from the mainland island arc and the active continental margin transition environment,by comparison of REE characteristics and feature elements of mixed sandstone in different tectonic background sedimentary basins.The composition of the original rock in the qiongda formation also shows that there may be island arc volcanic rocks mixed in.The zircon ages of qiongda group are large data span and high peak value,shows that the sedimentary deposits in the qiongda formation have multiple provenances or their original rocks have undergone multiple sedimentary cycles.It was found that the qiongda formation was from the central Lhasa and the northern Lhasa,and the main body was from the back of the Nyainqentanglha,by comparing the detrital zircon age spectrum of qiongda formation with the detrital zircon age spectrum of the surrounding terrane,and the analysis of the two peaks of²20Ma and³30Ma.The mailonggang formation was from the central Lhasa.Through the studies the distribution location,distribution range,tectonic property,development time,sedimentary response and provenance analysis of qiongda formation.we suggest that the qiongda formation should be deposited in foreland basin.From qiongda formation(T_2-3q)to mailonggang formation?T₃m?then to jialapu formation?J₁j?,the sedimentary basin underwent the transition from the slope to the shallow sea shelf and then to the continental transitional facies sedimentary basin.The overall performance is the transition from the active basin to the stability basin.