Geochronology,geochemistry and tectonic setting of volcanic rocks from Bai-yingaolao Formation in Changtuxili area,southern Da Hinggan Mountains
This paper is the result of the research on the geochronology,geochemistry and tectonic setting of volcanic rocks.[Objective]The volcanic rocks of Baiyingaolao Formation in the southern section of Da Hinggan Mountains are the host rocks of the Changtuxili Ag-Pb-Zn-Mn polymetallic deposit.Conducting research on volcanic rock chronology,geochemistry,and tectonic environment is of great significance for identifying the geological background of the deposit and guiding the next exploration of the deposit.[Methods]This study conducted petrological,zircon U-Pb geochronological,and geochemical studies on the volcanic rocks of the Baiyingaolao Formation to clarify their formation age,petrogenesis,and tectonic evolution environment.[Results]The main body of the Baiyingaolao Formation in this area is a set of rhyolite and rhyolite volcanic clastic rocks.The zircon U-Pb dating result is(133.85±0.81 Ma),which was formed in the Early Cretaceous.The main elements have the characteristics of high silicon(SiO2=71.00%～74.43%),rich alkali(ALK=7.10～8.78),rich potassium,high FeOT/MgO ratio(7.51～22.54),poor magnesium(MgO=0.11%～0.45%),and poor calcium(Ca=0.88%～1.83%),belonging to the high potassium calcium alkaline series rocks.All samples have a similar REE pattern with medium total REE contents(ΣREE=156.66～211.81),significant fractionation of LREE and HREE((La/Yb)N=9.39～16.91),attributed to the enrichment type with strong negative Eu anomalies(δEu=0.38～0.59).Similar REE distribution patterns imply that the volcanic rocks came from the same magma source.The trace element geochemistry shows evident enrichment of LILE Rb,K,Th and U,deficit of HFSE Nb,Ta,Ti,P.[Conclusions]Based on regional geological data and the research results of this article,it is believed that the volcanic magma of the Baiyingaolao Formation in the study area originated from partial melting of crustal rocks and was generated in the post orogenic extensional tectonic background.Its formation is mainly related to the lithospheric extension after the closure of the Mongol-Okhotsk Ocean,and the subduction of the ancient Pacific Plate also has a certain influence on it.
万方数据
维普
