Abstract:  Volcanic rocks of the Lower Cretaceous Huoshiling Formation are widely distributed in the southern Songliao basin. To reveal the petrogenesis of intermediateacidic volcanic rocks in the southern Songliao basin and fully understand the formation and evolution of the basin and its internal fault depressions, majorelement, traceelement, and Sr-Nd-Pb isotopic analyses were conducted on intermediateacidic volcanic rocks in the study area. Core observations and thin-section microscopic identification show that the volcanic rocks are dominated by intermediate and intermediateacidic rocks, including andesite, trachyte, rhyolite, andesitic tuff, dacitic tuff, and rhyolitic tuff, with relatively fewer intermediatebasic rocks. The volcanic rocks are silicarich and alkalirich, and belong to the calcalkaline series. Calcalkaline acidic and intermediate volcanic rocks exhibit consistent major and traceelement characteristics, similar to those of orogenic volcanic rocks. They are enriched in light rare earth elements, Rb, K, and large ion lithophile elements, with low initial (87Sr/86Sr)i ratios and εNd(t) values, as well as similar Pb isotopic compositions, suggesting a common magma source and significant fractional crystallization. The calcalkaline volcanic rocks of the Huoshiling Formation in the southern Songliao fault depression were derived from metasomatized lithospheric mantle, incorporating subductionrelated components. Calcalkaline basic magmas underwent fractional crystallization, experienced crustal contamination, and ascended to the surface, forming the calcalkaline intermediateacidic volcanic rocks in the southern Songliao area, corresponding to the initial stage of lithospheric extension.

Key words:  , calc-alkaline volcanic rocks, geochemistry, Huoshiling Formation, petrogenesis, southern Songliao fault depression ,