| The study area is located in the Daxinganling orogen southeast of the northern section,with complicated tectonic background.One purpose of this paper is to explain the rock types and sedimentary environment of Gegenaobao Fm in Upper carbonic-lower Permian,based on the outcrop sections,zircon U-Pb dating,geochemical analytical data,granularity characteristic and clastic composition;the other is to discuss the basin characteristics in the Later Paleozoic.Based on the rock assemblages,cross-section surveys and stratigraphic correlation,the Paleozoic clastic and volcanic rocks in the study area can be classified into Gegenaobao Fm.According to the isotopic dating(about 310Ma),the Gegenaobao Fm(C2-P1)g)are classified into Upper carbonic-lower Permian,especially Late Carboniferous.Through the petrography characteristic of the Gegenaobao Fm,the strata are divided into conglomerate facies,sandstone facies,mudstone facies and tuff facies.And the comprehensive stratigraphic column shows fan delta facies caused by sediment gravity flow deposition.According to the grain size parameters,Particle size distribution histograms and probability cumulative grain size curves,The clasolite is a set of turbidity current deposition.And the sandstone detrital composition and provenance analysis indicated that the clastic rocks are from the volcanic island arc.Through the petrogeochemical analysis of the volcanic rocks in Gegenaobao Fm,it can be found in the major elements that the volcanic rocks is a set of alkaline rock combination.And the rare earths and trace element shows the characteristic of the Island-arc volcanic rocks.According to the study above,combined with tectonic background,previous research achievements of intrusive rocks,the strata distribution and rock types of Later Paleozoic in adjacent areas,it can be deduced that the study area is a retroarc foreland basin,which formed in compressional background caused by Eerguna-xingan and Songnen crustal blocks. |
PDF Full Text Request