海南岛晚古生代沉积演化、物源示踪及对其构造属性限定

It has been a hot research area on eastern extension of Paleotethyan. Some researchers believe there has been a collision between Indochina Block and South China Block during the Late Paleozoic to Early Mesozoic, through the geophysical and magmatic data, however, the location of the suture zone is still debated. Methods such as stratigraphy, sedimentology, source tracing and basin analysis are applied in this project to investigate outcrops and process the data of Late Paleozoic strata to find out if the Changjiang-Qionghai Fault or Jiusuo-Lingshui Fault can be treated as the tectonic boundary between Indochina Block and South China Block. The aim for this project is to (1) research the basic geological characteristics of Late Paleozoic in Hainan Island, such as tecto-stratigraphic system,sedimentary features and provenance of materials, and then to contrasted with those of Indochina Block and South China Block. (2) rebuild tecto-palaeogeographic framework, and find out tectonic attribute of source-sink. (3) discuss tecto-sedimentary coupling between Hainan Island and Indochina-South China Block, to confirm if the Changjiang-Qionghai Fault or Jiusuo-Lingshui Fault can be treated as the suture zone between Indochina Block and South China Block. (4) restrain the tectonic attribute of Hainan Island, and provide evidence of Paleotethyan evolution of South China.

古特提斯的东延问题一直是地学界研究的热点，部分学者通过地球物理和岩浆岩等资料，认为晚古生代-早中生代印支陆块与华南陆块沿海南岛内发生过碰撞拼合，但缝合带的位置仍存在昌江-琼海构造带和九所-陵水构造带的争议。本项目运用地层学、沉积学、物源示踪、盆地分析等理论手段，对海南岛出露完整的晚古生代地层进行系统的野外地质调查和室内分析，来论证昌江-琼海构造带、九所-陵水构造带是否具有分隔印支、华南地块的构造属性。查明海南岛晚古生代构造-地层系统、沉积特征、物质来源等基本地质特征，并与印支、华南地块进行对比。重建海南岛晚古生代构造-古地理格局，阐明源区构造属性。进一步讨论海南岛与印支、华南陆块不同阶段的构造-沉积耦合关系，明确海南岛晚古生代构造归属及缝合带的位置。本研究的开展为阐明晚古生代海南岛构造属性及理解古特提斯洋在华南东南缘的演化提供突破性资料。

古特提斯的东延问题一直是地学界研究的热点，部分学者通过地球物理和岩浆岩等资料，认为晚古生代-早中生代印支陆块与华南陆块沿海南岛内发生过碰撞拼合，但“邦溪-晨星”构造带作为缝合带的位置仍需更多的证据支撑。此外，晚古生代盆地的性质，是古特提斯支洋盆地还是弧后盆地，依然存在争议。本次研究对海南岛出露完整的晚古生代地层进行系统的野外地质调查和室内分析，来论证“邦溪-晨星”缝合带的存在。查明海南岛晚古生代构造-地层系统、沉积特征、物质来源等基本地质特征，重建海南岛晚古生代构造-古地理格局，进一步阐明晚古生代海南岛构造属性及古特提斯洋在华南东南缘的演化。. 石炭纪整体发育滨海相碎屑岩沉积，局部出现稳定的开阔台地相灰岩，青天峡组中期，盆地的南缘沉积了厚度稳定、次圆状磨圆的细至中粒石英砂岩。二叠纪整体上为一个大的海侵序列，垂向上发育滨浅海-台地相-半深海相的连续的沉积序列；横向上由南向北峨查组为稳定的滨浅海环境，鹅顶组则是发育连续的由滨浅海至半深海的沉积序列；盆地的南侧延续了石炭纪稳定的构造背景，为被动大陆边缘环境。二叠纪鹅顶组时期，屯昌地区沉积一套巨厚的复理石建造，该套砂岩中碎屑锆石含有273Ma-252Ma左右的同沉积锆石，这与岩浆事件给出的古特提斯碰撞造山的时间相吻合，该套复理石建造可以作为邦溪-晨星缝合带的沉积学证据。. 晚古生代碎屑锆石年龄与地层沉积年龄差值频率图都是落在碰撞造山带与岛弧俯冲带之间，海南岛晚古生代地层同华南板块在垂向上沉积演化趋势接近、横向上沉积组合可对比，结合岩浆岩地球化学的数据，认为晚古生代海南岛为弧后盆地环境，盆地的构造环境由石炭纪的汇聚环境向二叠纪碰撞环境转变。海南岛自早石炭世开始俯冲，通过石炭纪、二叠纪地层、沉积及古地理的恢复，盆地南缘为稳定的被动大陆边缘环境，垂向和横向上都为稳定过度的沉积体系，可以推断邦溪-晨星缝合带是向北俯冲的。