ANALYSIS ON THE PETROCHEMICAL CHARACTERISTICS AND GENESES OF THE TERTIARY IGNEOUS ROCK IN THE JIYANG DEPRESSION, THE BOHAIWAN BASIN

Based on the chemical composition, REE and isotopic analyses of rocks, the petrochemical characteristics and geneses of the Tertiary igneous rock in the Jiyang Depression, the Bohaiwan Basin were discussed. The Tertiary basalt in the Jiyang Depression can be divided into tholeiite and alkali two series. The alkali series basalt was mainly agpaitic series, and the Tertiary basaltic magmatite of this area whose eruptive depth was 150-230km was mainly continental tholeiite of continental rift genesis. The differentiation degree of magma decreased when the horizon of volcanic rock in the Jiyang Depression got newer. The magma formed later basically represented primary magma. The Tertiary basalt of different horizons and its basic intrusive rock had the source areas of upper mantle, and intrusive rock was of same sources with volcanic rock. During the forming process of magma, mixing reaction happened among different source area, and melting degree decreased gradually from the Paleocene to the Oligocene, which suggested that the mantle source depth of magma increased gradually. These cognitions will of important reference significance to hydrocabon exploration in magmatic rock.