ZIRCON U-PB GEOCHRONOLOGY OF THE VOLCANIC ROCKS ON BOZHONG 29-6 STRUCTURE IN THE HUANGHEKOU SAG, BOHAI SEA, AND ITS GEOLOGICAL SIGNIFICANCE

Petrology and zircon U-Pb geochronology studies were conducted in order to determine the stratigraphic position of the 90.5m thick volcanic rocks on the Bozhong 29-6 Structure in the Huanghekou Sag, Bohai Sea. Thin sections show that the suit of the volcanic rocks can be divided into three sections from top to bottom: the basalts at the top (2 880.5~2 910.5 m), the lamprophyres in the middle (2 910.5~2 959.5 m), and the tuff on the bottom (2 959.5~2 971 m). The zircon U-Pb ages suggest that the lamprophyres and the tuff were formed in Cretaceous after 124 Ma, while the basalts formed after 45.2 Ma by Cenozoic magmatism. Combined with the paleontological evidence from microfossils in the mudstone intercalations or on the top of the basalts, we defined that the basalts erupted during the stage while the 3rd Member of the Shahejie Formation was deposited. This study identified the Mesozoic and Cenozoic volcanic activities on the Bozhong 29-6 structure, and is of great significance for understanding the Mesozoic and Cenozoic magmatism and oil and gas exploration in the volcanic basin in the Huanghekou Sag.