东海盆地西湖凹陷南部火成岩发育区G构造油气成藏特征

G构造是一个大型挤压反转背斜，位于西湖凹陷西南角的天台斜坡带火成岩发育区。由于目前对该区火山活动规律及后期油气保存等成藏演化条件认识不清，严重限制了天台斜坡带的油气勘探进程。通过对研究区地震资料进行解释，研究了G构造区火成岩的岩石学、年代学和时空分布特征，重建了火山活动、圈闭形成与油气成藏过程的关系。结果表明，G构造范围内发育的火成岩为中新世中期的浅层侵入岩、溢流相喷出岩和通道相火成岩，该火成岩的发育使得平湖组和花港组的地层碎裂化，由于该背斜核部存在早期火山通道，后期挤压形成的圈闭有效性差。龙井运动（中新世末期，5.3 Ma）至上新世三潭组沉积期，该背斜转折端发育了一系列近EW向次级断层，进一步破坏了圈闭的完整性。由于背斜翼部未受火成岩影响，该处的构造-岩性圈闭应该是下一步勘探的重要方向。

Oil and gas accumulation characteristics of Structure G in the igneous rock area south of Xihu Sag,East China Sea Basin

Structure G is a large compressional inversion anticline located in the igneous rock development area of the Tiantai Slope Zone in the southwest corner of the Xihu Sag. Due to the lack of understanding of the volcanic activity and later oil-gas preservation and accumulation evolution conditions in this area, the oil-gas exploration process in the Tiantai Slope Zone is severely restricted. Therefore, we interpreted the seismic sounding data in this area, studied the petrology, chronology, and temporal and spatial distribution characteristics of igneous rocks in Structure G, and reconstructed the interrelationship among volcanic activity, trap formation, and hydrocarbon accumulation. Results show that the igneous rocks developed in Structure G are shallow intrusive rocks, effusive extrusive rocks, and channel igneous rocks in the middle Miocene. The development of the igneous rocks fragmented the strata of the Pinghu Formation and Huagang Formation. Due to the existence of early volcanic channels in the core of the Structure G anticline, the traps formed by later extrusion are less effective. From the Longjing Movement (late Miocene, 5.3 Ma) to the depositional period of the Santan Formation (Pliocene), a series of nearly EW-trending secondary faults developed at the turning end of the anticline, further destroying the integrity of the trap. We believe that since the anticline wing is not affected by igneous rocks, the structural-lithological traps there should be an important direction for further exploration.