南极罗斯海陆架盆地幕式张裂构造和过程的时空变化研究

Due to single goal, constant parameters and geothermal disregard in the modeling of basin extensional rifting and subsidence, present conclusions on the multi-episodes of rifting pattern and influence are usually extreme or absolute for the Ross Sea continental shelf. This project will focus on spatial-temporal changes of episodically-rifting structures and processes of the Ross Sea continental shelf basins, Antarctica. With constraint of heat flow, magnetic anomalies are used to inverse the Curie isotherm and to model the geothermal field, and free-air gravity anomalies are corrected for waters, ices, terrains and heats to inverse and refine both the basement and the Moho, which would directly provide the total stretching factors of crust. Using the spatial domain convolution method of the flexure isostatic model, different bottom compensation surfaces are given for different effective elastic thicknesses (EET) of lithosphere to compare with the Moho or various isotherms, then a set of EET will be selected to be favorable in the Ross Sea. In combination with reflect seismic and OBS profiles, three cross-sections of integrated geophysical interpretation would made to cut the northern, middle and southern Ross Sea from west to east. Applying the extensional rifting model of lithosphere incorporated with the concept of necking level along these three cross-sections, with constraints of seafloor bathymetries and gravity anomalies, the spatial distributions of stretching factor and EET will be modeled to recover the changes of necking levels and paleo-topography undulations during multi-episodes of rifting. Based on the inversion and modeling results, high gravity anomalies within the Ross Sea sedimentary basins will be highlighted among the relations of crust extensional subsidence with mantle magmatism, glacial deposition and erosion. The inversion and modeling results will also be used to display tectonics of the Victoria Land Basin with relation to Transantarctic Mountains, the boundary between oceanic and continental crust and the paleo-topography evolution of the shelf break in the Northern Basins. The study results will be helpful to assess potentials of oil and gas resources in the Ross Sea and deepen in understandings of the West Antarctic rift system and the Gondwana breakup.

针对罗斯海陆架盆地伸展张裂、沉降模拟中目标单一、参数固定和热效应兼顾不够，导致有关多幕张裂方式和影响过于极端或绝对的情形，开展其幕式张裂构造和过程的时空变化研究。结合热流异常，由地磁异常反演居里面和模拟地温场，进行重力异常的各种剥离改正和地温场效应分离，精化沉积基底、莫霍面起伏模型，给出地壳伸张因子空间分布。采用沉积负荷挠曲的空间域褶积方法，通过拟合莫霍面及不同等温面，优化岩石圈有效弹性厚度（EET）空间分布。进行综合地球物理剖面解释和模拟，通过拟合地形和重力，模拟多幕张裂期伸展因子和EET的时空变化，恢复各幕张裂期的颈缩水平深度、地形升降变化。将地壳伸展沉降与冰川沉积剥蚀、地幔岩浆作用结合起来，重点解剖罗斯海盆地高重力异常的成因，维多利亚盆地张裂特点及与横贯南极山脉之间的关系，洋陆分界及陆架破折带的古地形演变。研究成果有助于评估罗斯海油气资源潜力，深化认识西南极裂谷系统和冈瓦纳大陆裂解。

南极罗斯海具有宽阔的陆架和海湾，盆地级别的地层和构造格架显示油气资源前景，欧美及俄罗斯、日本早期重视对其调查研究，美国、新西兰、意大利、德国和韩国目前更重视海陆联合考察，美国和新西兰联合推出的“罗斯海海洋保护区”更是成为全球最大的第一个海洋保护区。调查研究罗斯海可以推动我国积极参与国际极地治理。本课题重点研究其陆架盆地张裂过程、构造动力特点，火山岩浆活动与裂谷活动之间的关系。.课题执行期间，在国内外期刊上发表论文11篇，在国际学术会议报告交流3次和展板交流6次，博士后出站1人，培养博士2人和硕士2人。.构建的罗斯海地球物理数据库，融合了课题组和国际上最新采集的6类专业数据（多波束水深、重力、磁力、地震、热流和地质构造），由此推演了超过25套精度可靠、分辨率高的位场和岩石圈结构数字网格模型。.课题取得的进展如下：来自南太平洋的早期ENE-SWS向走滑断裂，分割了罗斯海陆架盆地构造和陆坡及洋盆区的盆地构造；作为西南极裂谷系统的罗斯海陆架盆地，第一、二幕张裂时期地幔岩浆超高压力与地壳拉张减薄的耦合，加大了莫霍面的抬升量，但目前地壳底部温度低于周边高地，维持了盆地轴部重力高；来自南极—澳大利亚之间的转换断裂作用诱发原有的近N-S向正断裂向张扭性断裂转变，地幔物质熔融上涌，沿特拉裂谷及其两端火山活动区热流异常和地壳底部温度升高，原有的地幔岩浆超高压力得到部分释放，重力异常降低；罗斯海地区存在巨量的天然气水合物赋存，盆地内部甲烷资源量可达2.77×1011 m3；西罗斯海遗留的一些海底冰川地貌早于前人认为的末次盛冰期，显示冰川地质作用能够构造海底地形地貌、扩展外陆架和掩盖构造地貌。.这些认识有助于深化认识西南极裂谷系统及其与横贯南极山脉抬升之间的关系，冈瓦纳大陆裂解延续机理，弥补现今板块构造研究环节中的极地短板，了解极区陆海域资源的分布格局和成矿潜力，揭示重大地质事件影响古海洋和古气候效应以及冰盖演化的机制。