Lithogenesis and eruption model of the eocene trachyte in eastern sag of Liaohe basin

A suit of potassium-rich trachyte has been found in Eastern Sag of Liaohe Basin,commonly with brecciated texture and glomerophyric texture.They have the characters of high alkalies (K₂O+Na₂O=9.68%~12.99%),high potassium,high aluminium,high LREE and low titanium.They are enriched in large ion lithophile elements ( e.g. U,Th,Pb,Rb).And they have variable Mg^#(16~49),SiO₂(57.3%~62.5%) and δEu(0.26~1).The results show that trachytic magma as a product of fractional crystallization of transitional alkali basaltic magma,formed in the tectonic settings for continental intraplate,and experienced slight assimilation and contamination during their ascending through the lithosphere.Trachytic magma generally comes into formation as dome-shaped with three-tier structure by extrusive pattern,and also generates trachytic dykes.