Tectonic Contact Relationship of Continental Margins of the Southwest Sub-Basin, South China Sea in Late Mesozoic
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摘要: 为探究南海西南次海盆两侧陆缘地块在中生代晚期构造接触关系及其对南海形成演化的影响,利用过南海西南次海盆两侧陆缘采集的地球物理资料以及公开发表的数据资料,对两侧陆缘的地壳结构及前新生界构造变形特征进行了研究.研究结果显示,西南次海盆两侧陆缘的地壳结构及物质组成存在差异,属于性质不同的两个微地块;两侧陆缘前新生代地层在晚中生代经历了来自不同方向的挤压作用,且遭受抬升剥蚀.结合南海及邻区中生代花岗岩分布特征及区域构造背景,进一步推测两侧陆缘地块在晚中生代以俯冲碰撞的方式完成拼贴缝合,该俯冲碰撞带是南海北部俯冲带在南海西南方向的延伸,并且新生代南海的扩张可能与该俯冲碰撞带这个先存的软弱带有关,是南海海盆初始破裂的部位.Abstract: In order to study the tectonic contact relationship of continental margins of the southwest sub-basin, South China Sea in the Late Mesozoic, and its influence on the formation and evolution of the South China Sea, this paper analyzes the crustal structure and Pre-Cenozoic structural deformation of the continental margins of the southwest sub-basin of the South China Sea by the geophysical data and the published data collected from continental margins of the southwest sub-basin. The crust structure and material composition of the continental margins of the southwest sub-basin are different, belonging to two micro blocks with different properties. The Pre-Cenozoic strata of continental margins of the southwest sub-basin experienced compression from different directions in the Late Mesozoic, and suffered uplift and denudation. The continental margins of the southwestern sub-basin were stitched together in the form of subduction collisions in the Late Mesozoic. The subduction zone is the extension of the northern South China Sea subduction zone to the southwest of the South China Sea. The expansion of the South China Sea in Cenozoic is related to the subduction zone, which is the initial fracture site of the South China Sea basin.
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图 1 研究区区域位置及测线分布
红色虚线框表示研究区范围,底图据杨胜雄等(2015)修改. TXNB.台西南盆地;PRMB.珠江口盆地;QDNB.琼东南盆地;YGHB.莺歌海盆地;ZJNB.中建南盆地;MGB.眉公盆地;WAB.万安盆地;NWXB.南薇西盆地;ZMB.曾母盆地;BKB.北康盆地;LYB.礼乐盆地
Fig. 1. The location of the study area and the locations of the multichannel seismic profiles
图 2 西南次海盆两侧陆缘地块地壳速度结构模型
a、b剖面位置见图 1;a.OBS973-3测线,修改自Lü et al.(2017);b.OBS973-1测线,修改自丘学林等(2011)
Fig. 2. Crustal velocity structure models and 1D velocity structure comparison of the margins of the southwest sub-basin
图 3 南海西南次海盆两侧陆缘盆地地层柱状图与构造演化简图
全球海平面变化曲线据Haq et al.(1987)
Fig. 3. Comprehensive strata diagram and tectonic evolution stage of the continental marginal basins of the southwestern sub-basin, South China Sea
图 4 94N10测线地震剖面及其地质解释
剖面位置见图 1;a.原始地震剖面;b.地震地质解释剖面
Fig. 4. Geological interpretation of the seismic line 94N10
图 5 94N10测线反映多重逆冲构造的典型地震剖面段(a)及其地质解释(b)
a.图 4中局部放大未解释剖面;b.地质解释剖面
Fig. 5. Typical seismic section (a) and geological interpretation (b) of the line 94N10 reflecting multiple thrust structures
图 6 N973-1测线南段地震剖面及其地质解释
剖面位置见图 1;a.原始地震剖面;b.地震地质解释剖面
Fig. 6. Local seismic section and geological interpretation of the south of the seismic line N973-1
图 7 TP3测线地震剖面及其地质解释
剖面位置见图 1;a.原始地震剖面;b.地震地质解释剖面
Fig. 7. Local seismic section and geological interpretation of the seismic line TP3
图 8 TP3测线反映残留褶皱构造放大图
a.图 7中局部放大未解释剖面;b.地震地质解释剖面
Fig. 8. Enlarged view of residual fold structure of the line TP3
图 9 南海及邻区中生代花岗岩分布特征
图中南海北部中生代俯冲带位置据闵慧等(2010);南海北部断裂据周蒂等(2006);花岗岩数据综合自Areshev et al.(1992)、李平鲁等(1999)、Yan et al.(2010)、Nguyen et al.(2004a, 2004b)、修淳等(2016)
Fig. 9. Distribution characteristics of Mesozoic granites in the South China Sea and its adjacent regions
图 10 南海及邻区中生代花岗岩构造环境判别图解
判别模板据Pearce et al. (1984);VAG.火山弧花岗岩;WPG.板内花岗岩;Syn-COLG.同碰撞花岗岩;ORG.洋中脊花岗岩;A-ORG.异常洋中脊花岗岩;PRMB.珠江口盆地;NSB.南沙地块;DZ.大叻地区
Fig. 10. Discrimination diagrams of structural environment for Mesozoic granitoids in the South China Sea and its adjacent areas
图 11 南海北部俯冲带形成示意
古礼乐北海盆参考Liu et al.(2011)
Fig. 11. Schematic diagram of the formation of the Late Mesozoic subduction zone in the northern South China Sea
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