Deep seismic imaging of developing continental crust in oceanic island arcs

大洋岛弧发育大陆地壳的深部地震成像

• 批准号: 155519-2013
• 负责人: Calvert, Andrew
• 金额: $ 2.91万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=634083
• 关键词: Deep; seismic; imaging; developing; continental

Volcanic island arcs such as the present day Aleutian, Mariana and Solomon island chains in the Pacific Ocean form where an oceanic tectonic plate subducts into the mantle beneath another piece of oceanic lithosphere. Ancient island arcs are believed to have been the fundamental building blocks that were assembled by plate tectonics to create the continents over the last ~3 Ga. However, the process through which the relatively buoyant continental crust is derived from the denser rocks that form much island arc crust is unclear. When continental-like andesitic rocks are generated in the middle crust of an island arc, a larger volume of denser mafic-ultramafic rocks should also be produced in an underlying root. Seismic refraction surveys, which estimate a proxy for crustal composition, namely the seismic wave speed, indicate that arc crust is too thin (12-35 km) to contain this root. The root can be denser than the uppermost mantle, detach from the base of the evolving island arc, and sink into the underlying mantle, but the time-scale of this hypothesised foundering is unknown. Seismic reflection surveys have recently found evidence of two roots extending to 50 km depth beneath the Aleutian arc, and may be able to identify other "missing" dense arc roots if they are still present. The objective of this research proposal is to utilize previously recorded deep seismic reflection profiles over island arcs of different ages to determine the distribution of arc roots and to constrain the time-scale of their foundering. Crustal production rates are highest during initiation of an island arc, and these earliest arc rocks are now found in the outer forearc close to the deep bathymetric trench. Seismic reflection imaging across the forearc will help to unravel the early history of voluminous crustal production in island arcs and the subsequent transition to a more stable regime of crustal generation. Since reflections from the descending oceanic plate are also recorded, a valuable additional consequence of this work will be improved estimates of the width of the seismogenic zone of four subduction megathrust faults derived from changes in their characteristic reflection responses and/or intersections with the uppermost mantle where stable sliding occurs.

火山岛的弧形如今，阿留申岛，玛丽安娜和所罗门岛链中的太平洋形式形式，海洋构造板块俯冲进入另一块海洋岩石圈下方的地幔。据信，古代岛弧是由板块构造组装而成的基本构建块，以在最后一个〜3 GA中创建大陆。但是，相对浮动的大陆地壳源自形成许多岛屿外壳的浓密岩石的过程尚不清楚。当在岛弧的中部地壳中产生大陆般的安第斯山脉岩石时，还应在潜在的根部生产大量较大的镁铁质岩石岩石。地震折射调查估计了地壳组成的代理，即地震速度速度，表明弧形外壳太薄（12-35 km），无法包含该根。根可以比最上面的地幔较密集，从不断发展的岛屿弧的底部分离，然后沉入基础的地幔中，但是这种假设的基金会的时间尺度尚不清楚。地震反射调查最近发现了两种根部延伸至阿留申弧深度50公里的证据，如果仍然存在，则可能能够识别出其他“缺失”密集的弧根。这项研究建议的目的是利用以前记录的不同年龄岛弧上的深层地震反射曲线来确定弧根的分布并限制其建立的时间尺度。在岛弧开始期间，地壳生产率最高，现在这些最早的弧形岩石在靠近深层测深的沟槽的外前臂中发现。跨前臂的地震反射成像将有助于揭示岛弧中大量地壳生产的早期历史，并随后过渡到更稳定的地壳产生状态。由于还记录了从降海板的反射，因此这项工作的有价值的额外后果将得到改善的估计值，该估计值是从其特征反射响应的变化和/或与高层间的稳定滑动稳定滑动发生的四个俯冲巨型断层的地震区的宽度巨型断层。