翁通爪哇海台俯冲在新几内亚-所罗门弧体系中所罗门海盆的构造记录

Analysis of the oceanic plateau subduction, thousands of meters above the ocean floor, is very important for revealing the dynamics of plate tectonics, crust-mantle interaction and other scientific problems at the plate convergence boundary. This project will focus on the largest oceanic plateau-Ontong Java Plateau and the Solomon Sea basin of the New Guinea-Solomon arc tectonic system, which exhibits the most prominent response to the subduction of the oceanic plateau. We will use the two-dimensional seismic dataset across the Ontong Java Plateau and Solomon Sea basin. The division and interpretation of the tectonic sequence and identification of fracture structure along the two-dimensional seismic profile will be worked on. The episodes and timing of the major tectonic events recorded in the Solomon Sea basin will be investigated. The regional geological structural characteristics and attributes of the Solomon Sea basin will be explored. The properties of the stress field around the Solomon Sea basin will be analyzed based on focal mechanisms. According to the tectonic history of the Ontong Java Plateau and Solomon Sea basin, we try to reveal the relationship between the tectonic deformation of the Solomon Sea back-arc basin and the subduction of the Ontong Java Plateau. Ultimately, we would like to clarify the role played by the subduction of the buoyant oceanic plateau in the subduction polarity reversal and multidirectional subduction of the back-arc basin. The results from this project will enrich the studies on the convergent deformation of oceanic plates and the theoretical system of subduction of the oceanic plateau.

解析横亘在大洋板块之上高达数千米的海台俯冲碰撞活动，对于揭示汇聚边界板块构造动力学、壳幔相互作用等科学问题有着非常重要的理论意义。本项目将以世界上最大的海台——翁通爪哇海台及新几内亚-所罗门弧体系中对于海台俯冲有着最为强烈构造响应的所罗门海盆为研究对象，利用横跨翁通爪哇海台、所罗门海盆等丰富构造单元的二维地震观测资料，划分构造层序，识别断裂结构，厘定所罗门海盆经历的重大构造幕次，搞清所罗门海盆的构造属性，应用震源机制信息解析区域应力场特征，综合翁通爪哇海台、所罗门海盆构造活动研究，阐明弧后所罗门海盆构造形变与翁通爪哇海台俯冲之间的响应关系，最终明确海台俯冲在弧后海盆“反向”、“多向”俯冲汇聚形变中扮演的角色。项目的成功实施为大洋板块聚合形变研究添砖加瓦的同时，进一步丰富海台俯冲碰撞理论体系。

本项目围绕全球最大的海台俯冲与弧后海盆构造形变间的关系，尝试搞清翁通爪哇海台俯冲在弧后所罗门海盆传递的构造形变，揭示二者之间的耦合关系。基于反射地震的构造、沉积分析可知，在翁通爪哇海台汇聚背景下，毗邻新爱尔兰岛弧的弧前地带整体表现出强烈的伸展应力场特征，与所罗门岛弧地区弧前地带强烈收缩、逆冲叠瓦拼贴特征形成鲜明对比，意味着翁通爪哇海台于新爱尔兰岛弧地带并没有俯冲下去。综合垂直重力梯度、反射地震及震源机制数据分析，厘定出所罗门海盆内部广布原始扩张形成的E-W向正断层，控制海盆形成典型的堑、垒构造。在翁通爪哇海台俯冲阻滞诱发反向俯冲背景下，沿新不列颠海沟差异性的俯冲作用致使所罗门海盆~8 Ma以来呈现出典型的逆时针旋转运动特征，海盆早期扩张时期形成的伸展构造及转换断层结构最终与所罗门岛弧方向呈斜交状态，而毗邻新不列颠海沟的外缘隆起带，在年轻俯冲板块的挠曲形变作用下形成大量的平行海沟的正断层。据层析成像、天然地震数据分析，可知所罗门海板块沿新不列颠海沟呈现高角度-回卷俯冲样式，且发现翁通爪哇海台俯冲阻滞作用在所罗门海盆的俯冲起始动力过程中扮演关键角色。当阻滞效应诱发的挤压应力偏小时，所罗门海板块以高角度（>80º）前延形式俯冲，自~8 Ma至<1.8 Ma时期弧前、弧间盆地及翁通爪哇海台范围内多期岩浆记录的厘定，则充分反映所罗门海板块在高角度、多幕次的快速俯冲的同时发生强烈的脱水作用。当翁通爪哇海台阻滞效应诱发的挤压应力偏大时，所罗门海板块则以板块回卷形式俯冲，致使岩浆活动仅分布于弧前-弧间盆地有限地带内。