Research On Sedimentary Characteristics And Provenance Of Pliocene Epoch Formation In Husa Basin,Western Of Yunnan

Research onsedimentary characteristics and provenance of Pliocene epoch Formation by collecting datum of regional geology,remote sensing,geophysics,hydrology and hydrochemistry systematically,combination withgeochemical analysis,the mainachievements are summarized below:?1?Husa basin outcropping of granite.U-Pb zircon age was 49.28±0.66 Ma,belong to Eocene.Geochemical characteristics of rocks:higher SiO₂?67.86% 72.04%?,higher total alkali?Na₂O+K₂O??7.62% 8.64%?,high K₂O/Na₂O?1.53 3.01?,Rb?Th?U?K?P?Nd?Sm and other large ion lithophile elements are rich,Nb?Ta?Zr?Hf?Ti and other high field strength elements are loss,light and heavy rare earth element ratio?LREE/HREE??10.81⁸.57?,light,heavy rare earth element fractionation index?La/Yb?N?10.34¹4.35?,mean 12.36,showed light,heavy rare earth fractionation significantly,with Eu negative anomaly?deltaEu=0.31⁰.58?.FeO*/MgO-10-4×Ga/Al diagram ??K₂O+Na₂O?/CaO-?Zr+Nb+ Ce+Y?diagram and Sr?Ba?Eu?La?Yb analysis that the samples had week differentiation.Aluminum saturation index?A/CNK?,SiO₂-P₂O₅ diagram,Th?Y?-Rb graphical Show that the samples are I type granite.The samples melted from the earthcrust witch mixed from primary earthcrust and ancient earthcrust under the evidences of Ni-Mg# diagram?Mg#-SiO₂ diagram and areal geology.The primary earthcrust were formed by mantle source material.The samples have some relevant with the collision between India and Eurasian plate.The collision between India and Eurasian plate have finished before 49 Ma.?2?The study shows that the alluvial fan facies,braided delta facies,fan-delta facies,lake facies and 10 types of subfacies,18 types of microfacies were developed in lower Mangbang Formation.The braided delta facies was ascertained for the first time in this paper,its develop area,sedimentary scale,waterpower conditions in deposition,microfacies types and fossil plants feature were different from the the fan-delta facies'.Basing on above research,it was found that the sedimentary facies provide for the uranium mineralization not only the specific ore accumulation space but also the migration conditions.which manifested as the the uranium mineralization occurrence in the gravity flow sedimentary sand body from the braided channel in mid-fan subfacies and the underwater distributary channel in fan-delta front subfacies.And the specific favorable microfacies assemblage was built by the mudstone in the pro-fan delta,lake facies and the sandstone in the underwater distributary channel in fan-delta front subfacies.After all,the Mantong-Wanmingxiaozhai and Huangzesi-Xiaozhai area where develop fan facies and the steep slope belt where develop fan-delta facies could be the key investigation region.?3?The sandstone-type uranium deposits were recently discovered in Mangbang Formation,HuSa basin,western Yunnan.The Provenance and Source Weathering are closely related to the source of uranium.Geochemical characteristics of the Mangbang Formation mudstones were analyzed in order to study their provenance and source weathering.?Ce-?Eu??Ce-?REE??Ce-?Dy/Sm?N and A-CN-K diagram indicate that the diagenesishas no significant influence on their geochemical compositions,suggesting the information about provenance and source weatheringwas mostly retained in mudstones.The ratios of Th/Sc?Al₂O₃/TiO₂,the Content of ?Eu and K₂O-Rb?Co/Th-La/Sc?La/Yb-?REE?La-Th-Sc diagram indicate that the provenance of the Mangbang Formation mudstone is mainly Yanshangranites.The ratios of SiO₂/Al₂O₃ and the Content of ?Eu combined with regional geology indicate that the Mangbang Formation mudstone were rapidly cycle sedimentary under the active tectonic environment.The ratios of Rb/Sr?Fe/Mn and the CIA?CIW?PIA values describe that the sample have been experienced-moderate to strong intensity of chemical weathering,and the climate was warm and wet.?4?The sandstone-type uranium deposits were recently discovered in Mangbang Formation,Hu Sa basin,western Yunnan.The sedimentary environment and paleoclimate are closely related to the sandstone-type uranium deposit.Geochemical characteristics of the Mangbang Formation mudstones were analyzed in order to study their paleoclimate?water type and water oxidation-reduction quality.?Ce-?Eu??Ce-?REE and ?Ce-?Dy/Sm?N diagram indicate that thediagenesishas no significant influence on their geochemical compositions,suggesting the information about paleoenvironmentwas mostly retained in mudstones.The content of Cl?B?Sr,the ratios of B/Ga?Sr/Ba?Sr/Ca and B-Ga-Rb diagramindicate that the type of water is fresh water.The ratios of Rb/Sr?Mg/Ca?Fe/Mn?SiO₂/Al₂O₃??La/Yb?N indicate that the Mangbang Formation's environment iswarmer-wetter conditions.The ratios ofCe/Ce*?Eu/Eu*?V/Cr?V/Sc?Ce/La?V/?V+Ni??V/?V+Cr?indicate that the fossil water is reducing environment and oxidation-oxidation environment.?5?Geochemical analysis was conducted in this study for sandstones samples from the Mangbang formation in the Husa basin,western Yunnan.Sandstones from the Mangbang formation mainly comprise of feldspar sandstone and greywacke sandstone as well as minor shale.The mineral assemblage mainly contains quartz,K-feldspar,plagioclase and illite.These samples analyzed yielded consistent REE patterns with enriched LREE [LREE/HREE =9.75¹5.91);?La/Yb?N=13.06²6.41].The ratio of Si O₂/Al₂O₃?2.06⁶.01?and index of the chemistry variation?ICV=0.54¹.09?together with the features of sedimentation make it clear that these sandstones were resulted from recycling deposition in the passive tectonic setting,rather than the first cycle of sediments due to the relatively strong weathering.Furthermore,the value of Th/U?5.44¹2.10%?,CIA?59⁷6?,reflected a chemical weathering environment of medium intensity in warm and moist climate.Diagrams of A/CNK showed that the sandstone clastics has a higher content of K-feldspar relative to plagioclase,suggesting that the metasomatism played a key role in the weathering processes,which decreased the CIA values.The ratio of Th/Sc?4.43²5.35?and the diagrams of Co/Th versus La/Sc,K2 O versus Re,and La/Yb versus ?REE all suggestedthat sandstones in the study area were mainly derived from the previously formed granites.Besides,the tectonic discrimination diagrams of TiO₂ versus Fe2O3T+MgO,Al₂O₃/?Cao+Na₂O?versus Fe2O3T+MgO,K₂O/Na₂ O versus SiO₂,and La-Th-Scall reflectedthat these granites wereformed in the setting of passive continental margin and possibly corresponded to the long term steady stateof the Meso-Tethys Ocean which has been open during theLate Jurassic toEarly cretaceous.Husa basin was formed due to the extension along the previous Husatranspressional fault and started to receive depositions eroded from the peripheralgranites during this period.Those innovative outcomes and recognitions acquired by the author will not be only provide with important function inadd to understandingof sedimentary characteristics and provenance of Pliocene epoch Formation,Husa basin in western Yunnan,further more,it provide with important function in deploying prospecting sandstone-type uranium deposits of the minitype intermontane basins developed inner orogenics belt in western Yunnan.