Collaborative Research: The Tectonic and Magmatic Structure and Dynamics of Back-arc Rifting in Bransfield Strait: An International Seismic Experiment

板块构造的一个基本过程是大陆地壳的裂谷或分离，产生新的海底，这些海底可以扩大并最终形成新的海洋盆地，后者是一个被称为海底扩张的过程。分隔南极西部半岛和南设得兰群岛的布兰斯菲尔德海峡是大陆地壳分离的结果，目前正在扩大。独特的是，该系统似乎正在接近向海底扩展的过渡，使其成为研究过渡过程的理想场所。以前的海底测绘和实地调查提供了盆地的区域结构；然而，关于裂谷作用导致的盆地构造和火山活动的区域性地震研究却很少。这将是首次对地壳分离最活跃的盆地中心火山的地震活动性和结构进行局地尺度的研究。新的地震数据将使科学家们能够将布兰斯菲尔德海峡目前的地壳分离和火山活动模式与其他经过充分研究的海底扩张中心进行比较。这个国际合作项目由西班牙牵头，美国、德国和其他欧洲国家的科学家也参与其中，将对陆地和海底的地震活动进行为期一年的监测。西班牙进行的一项活跃的地震研究将对可能与地震分布有关的断层和火山结构进行成像。本研究支持来自纽约市立大学皇后学院（Queens College， CUNY）的8名本科生作为科学小组成员在R/V Hesperides上进行实地工作，并将为数据分析做出贡献。弧后盆地是在俯冲背景下发现的，形成于两个阶段，即大陆裂谷的初始阶段过渡到海底扩张的后期阶段。研究这一过渡过程对于理解俯冲带的动力学和演化具有重要意义，而在弧后裂陷破坏大陆地壳的位置，对理解被动大陆边缘的形成具有重要意义。布兰斯菲尔德中部盆地的不同寻常之处在于，南设得兰群岛缺乏近期的弧火山活动，似乎俯冲作用正在停止，但该系统具有广泛的意义，因为它似乎正在接近从裂谷向海底扩张的过渡。该奖项将支持由西班牙极地委员会领导的一项国际倡议的美国部分，该倡议旨在对布兰斯菲尔德中部盆地的地震活动性和火山结构进行研究。目的是表征盆地活动伸展的分布特征，确定裂谷的火山构造和变形是否与由裂谷向海底扩张过渡的弧后盆地相一致。美国将提供一个由6个水声系泊所组成的网络来监测区域地震活动，并提供15个短周期地震仪来研究盆地中最活跃的火山之一奥卡火山的构造和火山地震活动分布。一项横跨裂谷紧密间隔的多通道地震线的活跃地震研究将提供将地震与断层结构联系起来所需的数据，从而使Orca火山的断层扫描研究成为可能，并为火山结构与裂谷的关系提供深入了解。本研究将限定布兰斯菲尔德盆地中部活动裂谷的分布，确定裂谷的断裂模式和火山部分的构造是否与裂谷的扩散带相一致，还是与向洋壳生产过渡的单一扩张中心相一致。Bransfield盆地是进行地震和水声地震位置比较研究的理想地点，这将提高对t波信号产生和传播的理解，并有助于将t波研究结果与传统固体地震研究数据进行比较。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the fundamental processes in plate tectonics is the rifting or separating of continental crust creating new seafloors which can widen and ultimately form new ocean basins, the latter is a process known as seafloor spreading. The Bransfield Strait, separating the West Antarctic Peninsula from the South Shetland Islands, formed and is presently widening as a result of the separation of continental crust. What is unique is that the system appears to be approaching the transition to seafloor spreading making this an ideal site to study the transitional process. Previous seafloor mapping and field surveys provide the regional structure of the basin; however, there exists a paucity of regional seismic studies documenting the tectonic and volcanic activity in the basin as a result of the rifting. This would be the first local-scale study of the seismicity and structure of the volcanoes in the center of the basin where crustal separation is most active. The new seismic data will enable scientists to compare current patterns of crustal separation and volcanism at the Bransfield Strait to other well-studied seafloor spreading centers. This collaborative international project, led by the Spanish and involving scientists from the U.S., Germany and other European countries, will monitor seismicity for one year on land and on the seafloor. An active seismic study conducted by the Spanish will image fault and volcanic structures that can be related to the distribution of earthquakes. This study supports eight undergraduates from Queens College, CUNY, an ethnically-diverse institution, to conduct field work as members of the scientific party on board the R/V Hesperides and will contribute to the analysis of the data.Back-arc basins are found in subduction settings and form in two stages, an initial interval of continental rifting that transitions to a later stage of seafloor spreading. Studying the transitional process is important for understanding the dynamics and evolution of subduction zones, and in locations where back-arc rifting breaks continental crust, it is relevant to understanding the formation of passive continental margins. The Central Bransfield Basin is unusual in that the South Shetland Islands have lacked recent arc volcanism and it appears subduction is ceasing, but this system has broad significant because it appears to be nearing the transition from rifting to seafloor spreading. This award will support the U.S. component of an international initiative led by the Spanish Polar Committee to conduct a study of the seismicity and volcanic structure of the Central Bransfield Basin. The objective is to characterize the distribution of active extension across the basin and determine whether the volcanic structure and deformation of the rift are consistent with a back-arc basin that is transitioning from rifting to seafloor spreading. The U.S. component of the experiment will contribute a network of six hydroacoustic moorings to monitor regional seismicity and 15 short-period seismometers to study the distribution of tectonic and volcanic seismicity on Orca volcano, one of the most active volcanoes in the basin. An active seismic study across closely spaced multichannel seismic lines across the rift will provide the data necessary to link earthquakes with fault structures enabling a tomography study of Orca volcano and provide insight into how the volcano's structure relates to rifting. This research will constrain the distribution of active rifting across the Central Bransfield Basin and determine whether the patterns of faulting and the structure of volcanic portion of the rift are consistent with a diffuse zone of rifting or a single spreading center that is transitioning to the production of oceanic crust. The Bransfield Basin is an ideal site for a comparative study of seismic and hydroacoustic earthquake locations that will improve the understanding of the generation and propagation of T-wave signals and contribute to efforts to compare the result of T-wave studies with data from traditional solid-earth seismic studies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.