Geochronology and geochemistry of volcanic rocks from the Songliao basin and their implications

Volcanic rocks in basins are significant for us in understanding the tectonic settings and geodynamics of the basins. The Songliao basin is characterized vertically by double structural layers, which are the faulted and the depressed layers in the lower and the upper, respectively. The lower sequence developed bulk volcanic rocks. However, previous work ignored the systematic study on these volcanic rocks. The purpose of this paper is to explore the tectonic setting and the geodynamics of volcanic rocks from the Songliao basin, based on dating results of K/Ar and geochemical analyses for the volcanic rocks collected from the drilling cores. The results show that the volcanic samples from the Songliao basin define a melt evolution trend typical for calc alkaline suites. Compatible and incompatible major elements (e.g. MgO, Fe2O3, Al2O3, and K2O vs. SiO2) delineate continuous melt differentiation trends as observed along the subduction zones. Additionally, the volcanic rocks from the Songliao basin is characterized by high Al2O3, Cr, Ni and low MgO contents. The ratios of Nb/Th (2～20) and Ce/Pb (2～30) of basalts and basaltic andesites demonstrate that the igneous genesis of the Songliao basin was related to the subduction, and also is characterized by rocks of oceanic and continental crust affinity. As a consequence, it is suggested that the Songliao basin developed on a magmatic arc in an active continental margin during Late Mesozoic (ca. 150～70 Ma), and the arc was related to the oblique subduction of the Izanaqi plate. The magma genesis of volcanic rocks was complex, and characterized geochemically by multiple resources.