中文摘要：

琼东南盆地发育于前新生代基底之上,作为南海被动大陆边缘一部分,记录了南海北部裂陷盆地结构及其演化.利用最新钻井、反射地震、重力等资料,分析新生代盖层和前新生代基底地壳结构,建立盆地地层结构模型,然后计算全盆地地壳伸展变化特征.结果表明：新生代地层序列的盆地充填由西向东逐渐减薄,古近纪、新近纪以及第四纪期间（45 Ma~现今）最后沉积中心呈现逐渐向西或西南迁移趋势.下地壳局部表现为地震速度偏高（厚度2-4km,vP〉7.0km·s^-1,水平延伸范围约为40~70km）.重震联合模拟显示这里存在密度偏高特征,推测存在可能与张裂晚期和扩张早期岩浆物质底侵或混合到伸展程度较低的大陆地壳有关.计算获得的前新生代基底地壳厚度由在弱展区域陆架区约25km,在减薄最大区域中央坳陷为3km.伸展系数（β）最高值大于6.0出现在中央坳陷,低值小于2.0在坳陷南北两侧,说明地壳在盆地中央拉伸比较剧烈.

英文摘要：

Rifting of the Qiongdongnan basin initiated in the Cenozoic above the Pre-Cenozoic basement which was overprinted by rifting basin tectonics soon after becoming part of a rifted passive continental margin of the South China Sea. Using integrated data of sedimentary horizons,wells,seismic reflection,and the observed gravity field,we constructed a crust-scale structural model of the Qiongdongnan basin.Many characteristics of this model reflect the tectonostratigraphic history of the basin.The structural and isopach maps of the basin allow us to retrace the well-established history of the basin comprising a dominant structural trend ofgradually shifting depocentre from the Paleogene sequence（45Ma-23.3Ma）to the Neogene to Quaternary sequence（23.3 Ma-present）towards the west or southwest.The present-day configuration of the basin implies that the basin fill of Cenozoic sediments becomes thinner towards the east.By integrating several reflection seismic profiles,interval velocity and performing gravity modeling, we have modeled the sub-sedimentary basement of the Qiongdongnan basin.The results show some high-velocity bodies in the lower part of crust（vP7.0 km ·s^-1）,and most probably is igneous magma underplated to the lower stretched continental crust during the final rifting and early spreading phase.The crystalline continental crust spans from the weakly stretched domains（as thick as about 25km）near the continental shelf to the extremely thinned domains（of less than 2.8km thickness）in the central depression,representing the continental margin rifting process in the Qiongdongnan basin.The estimated distribution of the crustal extension factor（β）of the basin shows that the factor in central depression is maximum value（6.0）,while that in northern and southern side wings is minimum value（2.0）.This model can shed light on future numerical simulation researches,including the reconstruction of the evolutionary processes from the rifted basin to the passive margin one and the evolution of t