Provenance And Tectonic Background Of Carboniferous To Early Permian Sedimentary Rocks In The East Kunlun Orogen

The East Kunlun Orogen underwent the tectonic evolution of the Proto-Tethys and Paleo-Tethys oceans.It is still controversial whether there was oceanic crust subduction in the Carboniferous to Early Permian.The Carboniferous system in the Alake Lake area on the southern slope of the eastern part of the Eastern Kunlun is an ideal research object to solve this problem.The stratigraphic sequence,age attribution,provenance characteristics,and tectonic setting of the Carboniferous and Lower Permian in the Alake Lake area of East Kunlun Orogen are thoroughly researched by systematic multidisciplinary methods such as stratigraphy,sedimentology,whole-rock geochemistry,and zircon U-Pb geochronology.On this basis,combined with the previous research results,the tectonic evolution process of the late Paleozoic-Early Mesozoic in the East Kunlun Orogen are discussed.The following progress and understanding have mainly been achieved:（1）The Carboniferous-Lower Permian in the southern slope of the East Kunlun Orogen includes the lower Carboniferous Halaguole and the upper Carboniferous-Lower Permian Haoteluowa formations.Lower Carboniferous Halaguole and Upper Carboniferous–Lower Permian Haoteluowa formations mainly consist of a package of shallow marine facies siliciclastic rocks and platform facies carbonate rocks.（2）Sandstone petrography and clastic skeleton composition statistics show that Halaguole and Haoteluowa formations have an average total quartz–feldspar–lithic fragment ratio of Q₆₇F₁₂L₂₁ and Q₅₀F₂₀L₃₀,respectively,indicating relatively high structural maturity and compositional maturity.（3）The Halaguole and Haoteluowa formations sandstones share similar geochemical characteristics.All the sandstone samples show flat rare earth element（REE）patterns with a slight enrichment in light REEs（LREEs）and relative depletion in heavy REEs（HREEs）.Additionally,most of the sandstones show distinctly negative Eu anomalies.Sandstone geochemical characteristics indicate that the Halaguole and Haoteluowa formations sandstones experienced a low degree of chemical weathering and the parental rocks in the provenance area are mainly acidic igneous rocks with minor intermediate igneous and old sedimentary components.（4）Detrital zircons from the Halaguole and Haoteluowa formations sandstones yield similar multimodal age distributions.Their age spectra are typically characterized by four distinct age populations at 405～503 Ma（peak at～437 Ma）,781～999 Ma（peak at～984 Ma）,1002～1529 Ma（peak at～1184 Ma）,and 1610～2997 Ma（peak at～2510 Ma）,which show similar tectono–thermal events with the North Qimatag Belt（NQB）,North Kunlun Terrane（NKT）,and South Kunlun Terrane（SKT）.In summary,detrital zircon U–Pb ages indicate that the NQB,NKT,and SKT should probably be the main sedimentary provenance of Halaguole and Haoteluowa formations.（5）Combining with the previous data,we argue that the Paleo-Tethys Ocean did not begin to subduct northward and that there was no oceanic subduction zone in the south EKO during Carboniferous to Early Permian times.Combining this information with that from previous studies suggests that the initial opening of the Paleo-Tethyan Ocean may have occurred before the Early Carboniferous time,and all the branches of the Paleo-Tethys Ocean constituted a complex ocean–continent configuration in the northern Tibetan Plateau during the Early Carboniferous to Early Permian.