摘要
南海东北部地处欧亚板块与太平洋板块的交接处,经历了复杂的地质作用,它包括了已有丰富油气资源的珠江口盆地和具有重要研究价值的台湾西南盆地。因此对该地区新生代沉积盆地基底特征的研究对于南海北部陆缘油气资源的进一步勘探和南海的形成演化研究都是很有意义的。本论文研究课题来源于国家重点基础研究发展规划项目(973)“中国边缘海形成演化及重大资源的关键问题”中的二级课题(课题编号:G2000046702-02):南海东北部新生代沉积盆地基底特征及其构造格局研究。重点研究南海东北部新生代沉积盆地的基底特征,包括基底深度、基底岩性、岩浆活动、断裂展布和构造单元的划分,并讨论基底构造对新生代沉积的控制作用:研究南海东北部中生代沉积尤其是中生代海相沉积的展布、厚度、岩性及其大地构造控制因素,并讨论中生代海相沉积与特提斯洋东延的关系。论文充分收集了现有的地质、地球物理资料,以刘光鼎院士所倡导的用活动论构造历史观为指导,以岩石物理性质和物理—地质模型为基础,实行物探与地质、定性与定量、正演与反演相结合并进行多次反馈的综合地球物理地质解释原则作为总的研究思路。具体的研究方案是针对南海东北部尤其是珠江口盆地的地质、地球物理条件和勘探现状,提出了一套关于新生代沉积盆地基底深度、岩性、断裂和深部结构的研究思路和方法。其要点是以地震和钻井资料为控制,对剥离后的重磁场进行反演,求取新生界基底和中生界的厚度;以重磁资料为主、地震资料为辅,通过求取基底视密度和视磁化强度,研究基底岩性;以常规处理与小波分析、图像处理等方法相结合以重磁资料,结合地震剖面,确定基底断裂:以区域重磁资料为主,结合声纳浮标资料,探索深部地质结构。结合上述研究思路,开展了有关分离重磁位场、重磁与地震资料结合的正反演方法研究。对南海东北部重磁力资料的处理体现了常规处理与小波分析、图像处理相结合的原则,重点研究了小波多尺度分析在重力异常分离中的作用,开展了各种小波基函数进行重力异常分解的研究,总结了小波分析在重力场分离的一些规律及小波母函数的特征对场分离的影响,选择了合适的小波母函数进行小波变换,取得了良好应用效果。论文在正反演方法中使用了学科组研制的变物性重磁迭代反演法、变深度基底视密度、视磁化率反演方法、以剥离法为主的重力—地震的联合反演方法等。这些方法的有效使用,为提高分离场和正反演精度有效地进行综合地球物理解释发挥了重要作用。利用综合地球物理方法首次获得了南海东北部全区前新生代基底深度图,通过基底岩性研究推断了本区基底主要由前寒武褶皱基底、古生代变质岩、中生代中酸性侵入岩、中生代沉积岩、中基性岩浆岩等组成,区内广泛发育火成岩,尤其重要的是推测了珠一凹陷东部和潮汕坳陷为中生代沉积岩的分布区,并被后来钻探所证实。综合物探解释圈定了盆地基底断裂35条,这些断裂不仅造成了盆地“南北分带,东西分块”的构造格局,而且与基底性质和油气聚集关系密切。以基底特征和中生代分布为主要依据对南海东北部划分了七个构造单元:北部华南沿海中生代沉积区、珠江口—琼东南中生代缺失区、南海东北部中生代弧盆区、台西南盆地、新生代海盆区、西沙—中沙地块区和台湾—吕宋构造带。在上述工作基础上研究了南海东北部中生代沉积尤其是中生代海相沉积的展布、岩性及其大地构造控制因素,重点讨论了中生代的构造演化,认为潮汕坳陷由于地质历史上曾位于中特提斯及中特提斯洋与太平洋转换大陆边缘的交接部位,从而受控于中特提斯及中生代弧盆系这一地质构造上的演化史,提出了潮汕坳陷为中生代的弧前盆地的观点,初步确定了南海北部中生代俯冲带及沟弧盆系统的展布。最后还探讨了该系统对南海北部新生代沉积盆地形成的控制作用,认为新生代构造演化,主要受控于欧亚板块与菲律宾板块汇聚,并受印度板块与欧亚板块的碰撞、青藏高原的隆升和南海扩张引起沉降的影响。
Passing through complicated geological process, the northeast area of SouthChina Sea locates at the common border of Eurasia Plate and PacificPlate. It includesthe Pearl River Mouth Basin having abundant oil & gas resources and the SouthwestBasin of Taiwan who have important research prospects. Therefore, aimed for furtheroil & gas exploration in the north continental margins and the studies of theformation & evolution of the South China Sea, it is quite important and meaningfulto study the features of Cenozoic sedimentary basement of this area. Stemming fromthe projects of national major research program of 973 'The key problems of formation& evolutionand resources of Chinese marginal seas' and its 2nd level project withthe series No. G2000046702-02 'Studies of basement features and tectonic patternsof the Cenozoic sedimentary basin in the northeast area of South China Sea', thedissertation firstly emphasizes on the studies of the basement features of theCenozoic sedimentary basin in the northeast area of South China Sea which includesthe basement depth and lithology, the igneous activity, the fault layout and thedivision of tectonic units, then makes discussion on the control roles on theCenozoic sediments played by basement tectonics, the distribution, the thickness,the lithology and the tectonic control factors of the Mesozoic sediments especiallythe sea-facies Mesozoic sediments in the northeast area of South China Sea, alsothe relationship between the Mesozoic sea-facies sediments and the extensiontowards east of Tethys.Related finished achievements of geology and geophysics about the studied areawere extensively collected and analyzed in the dissertation. Guided by the tectonicconception of history proposed by Academician Liu Guangding, the overall researchroute for integrated geophysical & geological interpretation which fulfills thecombinations of geophysics & geology, qualitative & quantitative analyses, forwardmodeling & inversion calculation by multiple feedbacks on the basis of rocks physicalproperties and physical & geological models, is determined. A set of researchtechniques and methods concerning the basement depth and lithology, faults and deepstructure of the Cenozoic sedimentary basin is put forward in accordance with thegeological & geophysical conditions and exploration situations of the northeast areaof South China Sea especially the Pearl River Mouth Basin. The specific researchessentials are as follows, the Cenozoic basement and the Mesozoic thickness arecalculated by inversion using gravity & magnetic stripped data from the known strataconstrained by seismic and drills; the basement lithologies are studied by thecalculations of apparent density & apparent magnetic intensity of the basement usinggravity & magnetic and seismic data; the basement faults are determined by thecombinations of conventional processing methods, the wavelet analyses and graphicprocessing methods using gravity & magnetic data and seismic profiles; the deepgeological structure is revealed mainly by regional gravity & magnetic dataintegrated with the sonar floating buoy materials.In the dissertation, the methods for forward modeling & inversion calculationrelated to the separation of potential fields and the integration with seismic dataare studied in accordance with the research route mentioned above. The gravity &magnetic data processing in the northeast of South China Sea represents theprinciples of the combinations of conventional processing, the wavelet analyses andgraphic processing. Furthermore, the roles that the wavelet multi-scale analyses playing in the separation of gravity anomalies, different wavelet basic functionsin the decomposition of gravity anomalies, are particularly studied. Theregularities of the wavelet analyses and the features of the wavelet generatingfunction in gravity field separation are summarized consequently. Then appropriatewavelet generating function is chosen to fulfill the wavelet transformation andquite good application results are yielded. In addition, the characteristic forwardmodeling& inversion methods developed by the discipline group, including gravity& magnetic iterative inversion method with changing physical properties, basementapparent density & magnetic susceptibility inversion method with changing depth,the joint inversion method of gravity and seismic data usingstripping process, areall put into use in the dissertation. The effective applications of these methodsgive full play to the accuracy of separated field calculation and forward modeling& inversion in the course of integrated geophysical interpretation.Overall speaking, using integrated geophysical methods, the Pre-Cenozoicbasement depth map of the whole studied area in the northeast of South china Sea.is obtained for the first time, the basement in this area. is inferred by lithologystudies as the composition of Precambrian folded basement, Paleozoic metamorphicrock, Mesozoic middle acidic intrusion rock, Mesozoic sedimentary rock and middlebasic igneous rock. Igneous rocks widely distribute in the studied area.Particularly an important Mesozoic sediments distribution zone in Chaoshan Sag andin the eastern of Zhuyi Sag is deduced and verified by later borehole drilling.Moreover, 35 basement faults in the basin are determined through integratedgeophysical interpretation, which results in the tectonic pattern with stripe stylein north-south direction and block style in west-east direction in the basin andkeeps close relationship with the basement property and oil & gas accumulation.Totally 7 tectonic units in the northeast area of South China Sea are divided mainlyin accordance with the basement features and Mesozoic distribution, which are theMesozoic sedimentary unit along the south China coast in the north of the studiedarea, the Mesozoic missing deposit area from the Pearl River Mouth Basin toQiondongnan Basin, the Mesozoic arc basin unit in the northeast area of South ChinaSea, the Southwest Basin of Taiwan, the Cenozoic sea basin area, the land block unitin Xisha-Zhongsha area and the tectonic zone in Taiwan-Lusong area. Based on theachievements finished above, the distribution of the Mesozoic especially thesea-facies Mesozoic sediments, the lithologiesand the tectonic control factors inthe northeast area of South China Sea, are studied. The tectonic evolut-ion ofMesozoic is focally discussed. With a view to the point that Chaoshan Sag ever locatedat the joint position of middle Tethys and the transformed continental margin ofmiddle Tethys and Pacific ocean in geology history and was controlled by middleTethys and Mesozoic arc basins in the geological tectonic evolution history, anewviewpoint that Chaoshan Sag is a Mesozoic forearc basin is brought forward in thedissertation, then the distribution of the system of Mesozoic subduction zone andthe trough arc basin in the northeast of South China Sea is preliminarily determined.Finally, the control impacts for the formation of Cenozoic sedimentary basin in thestudied area resulting from this system are also discussed. The Cenozoic tectonicevolution is regarded mainly controlled by the convergence of Eurasia Plate andPhilippine Plate and influenced by the collision of India Plate and Eurasia Plate,the uplift of Qingzang Plateau and the subsidence resulting from the expansion ofSouth China Sea.