Abstract:

Zircon U-Pb dating results show that the intermediatebasic volcanic rocks from Changling depression in the Songliao basin formed at Early Cretaceous, rangingd from 101 Ma to 116 Ma, which belong to Yingcheng Formation rather than Huoshiling Formation. Petrologically, the volcanic rocks are composed dominantly of olivine basalt and andesite, but geochemical data show that the volcanic rocks belong to alkaline series and are composed mainly of basalt, trachybasalt and basaltic trachyandesite. The intermediate-basic volcanic rocks have low contents of MgO and small Mg^# (0.27-0.53); The chondrite-normalized rare earth element (REE) patterns indicate that the volcanic rocks show significant fractionation of HREE and LREE \[(La/Yb)_N=6.60-10.96\] and weak Eu anoalies(δEu=0.85-1.02); The trace element geochemistry are characterized by enrichment in large ionic lithophile elements and LREEs, weak positive anomalies in Nb，Ta, depletion in compatible elements (Cr, Co, Ni) and Rb，K. All of the samples display highly consistent REE patterns and trace elements spider diagrams with OIB. The magma source is situated in the asthenospheric mantle, and experienced deep mantle fluid metasomatism enrichment. These rocks were not accompanied by contamination of continent crustal materials during their magmatic evolution.

Key words: Changling depression, intermediate-basic volcanic rocks, zircon U-Pb dating, petrogenesis, geochemistry