Geochemical characteristics of mudstone from the Late Permian Linxi Formation in Aluke'erqin Qi, Inner Mogolia and its structural significance

Abstract

The Taohaiyingzi section of the Linxi Formation in Aluke'erqin Qi, Inner Mongolia, is one of the typical sections in northeastern China. It consists mainly of black and gray-black sandstone and slate. The newly found conchostracans, pollen and spores, along with the detrital zircon age, suggest that the section is late Late Permian in age. The samples from the Linxi Formation are dominantly dark mudstones. The major chemical compositions are SiO2 62.90%, Al2O316.85%, MgO 1.78%, CaO 1.01%, Na2O 1.64%, K2O 4.0%, K2O/Na2O between 1.10 and 5.66, A12O3/(CaO+Na2O) between 3.57 and 12.69. The ΣREE ranges from 139.85×10-6 to 231.65×10-6, with an average of 190.74. δEu ranges from 0.49 to 0.87, with an average of 0.61. δCe ranges from 0.91 to 0.96. The clastic rocks are characterized by LREE enrichment and HREE depletion. Trace elements are characterized by depletion of Nb, Ta, Sr, enrichment of Rb, Ba, La, Ce, Pb, Nd and Sm. The analysis above shows that the Linxi Formation formed in the active continental marginal structural background near the continental island arc. Based on detrital zircon age, the sediment sources of the Linxi Formation are diverse and complex. Besides the blocks in the northeast, provenance information also points to the North China plate and the Siberia plate at the same time, suggesting that the North China plate and the Siberia plate may have started subducting process during the deposition period of the Linxi Formation.