Abstract: Basic volcanic and intrusive rocks are normally distributed in major source rocks in many rift basins. The analytical data such as volcanic composition, texture, structure and alteration features as well as K-Ar isotope data from member-3 of Shahejie formation in Dongying sag are used, combined with the structural geology characteristics in studied area, to determine the volcanic genesis type and its effect on neighboring rocks. Taking Binnan basalts and Chunxi gabbros as example, the underwater effusion model for the basalts in source rock sedimentary environment and the intrusion model for the gabbros in the shallow-buried source rocks are developed. The helpful effects of these two models on source rock 's formation, hydrocarbon generation and expulsion are discussed.

Key words: rift basin, source rock, igneous rock, volcanic activity mode, Dongying sag