Temporal And Spatial Distribution Of Bedrock In The Eastern Part Of The Altun Mountains In The Northwestern Qaidam Basin

Bedrock reservoirs in the eastern part of the Altun Mountains in the northwestern margin of the Qaidam Basin have shown abundant exploration value in recent years.In this thesis,through field outcrop observation,core observation,thin section identification,XRD method,CL,SEM,element geochemistry and isotope chronology analysis,combined with geophysical data and tectonic evolution,researching the petrological characteristics,chronological characteristics,diagenetic environment,and temporal and spatial distribution of bedrock in the study area.The lithology of bedrock is comprehensively identified through various methods.It can be seen that granite,granodiorite,granite gneiss,slate,schist,limestone,etc.are distributed in the study area.By dating the bedrock samples,the age of bedrock formation and the age of metamorphic rocks in various regions can be obtained.Through element analysis,it can be seen that the magmatic rocks in the study area belong to the volcanic island arc-collision series,the protolith of gneiss is volcanic,the protolith of slate is argillaceous limestone,the protolith of schist is quartz sandstone.Finally,combined with studies on age,diagenetic environment and tectonic evolution,it can be seen that the study area has experienced six stages of magmatic intrusion and two stages of metamorphic events.In the early Mesoproterozoic,the base of the study area was metamorphic rocks,with gneiss and slate distributed.About 800 Ma from now,the Altyn microcontinent is transformed into an island arc.Affected by the Jinning movement,collided granites formed in the Niudong area.From about 505 Ma to 600 Ma,the residual ocean basin in the southern margin of Altun stretched again.According to the marine environmental isotope indication,limestone in the Dongping 17 well area formed at this stage.About440 Ma ago,the Caledonian movement caused the closure of the South Altyn Ocean Basin and the formation of Jianbei granodiorite and Dongping granite.About 405 Ma ago,the Dongping granite was widely formed due to the closed compression of the two continental blocks and the intracontinental subduction.About 280 Ma ago,under the influence of the Hercynian movement,basalt and diabase were formed in Lengdong and other regions,and granite was formed in some wells in Niubei.Under the influence of Mesozoic and Cenozoic intraplate movements,granite intruded into Niudong.At the same time,the argillaceous limestone in Dongping 17 well was transformed into slate,and schist formed in Lengbei 1 well.The granite in some wells is metamorphic to gneiss,and the degree of metamorphism gradually weakened from the edge of the basin to the interior of the basin.Finally,the present bedrock distribution pattern is formed in the study area.