The Bransfield Strait-South Shetland Islands/Trench: Structural and Stratigraphic Evolution of a Linked(?) Back-arc/Fore-arc System

该奖项支持一项利用最近收集的多通道地震数据对南极洲布兰斯菲尔德海峡地区进行的地球物理研究。德克萨斯大学地球物理研究所（UTIG）的多通道地震（MCS）数据（EW91-01数据）可以对Bransfield海峡的构造样式和裂陷过程进行详细分析。该分析为布兰斯菲尔德海峡正在进行的伸展过程带来了新的认识。本项目将在此工作的基础上，在弧前/弧后构造系统的完整背景下考虑布兰斯菲尔德海峡。该项目将主要使用UTIG (EW91-01) MCS数据，但也将纳入英国和意大利提供的该地区的其他地球物理数据。布兰斯菲尔德海峡是一个年轻的盆地，位于南极半岛和南设得兰群岛之间，南设得兰群岛是一个向西北方向与半岛大致平行的小岛屿链。虽然南设得兰群岛没有显示出最近的弧火山活动，但它们位于一个俯冲带之上，该俯冲带似乎仍然活跃，尽管俯冲发生的速度很慢。这种构造环境和对影响附近板块运动的其他事件的解释，导致了目前的观点，即布兰斯菲尔德海峡作为一个弧后盆地开放，是对南设得兰海沟回滚或后退的回应。然而，现代压力机制尚不清楚。到目前为止，研究的重点是在最近获得的Bransfield海峡的UTIG (EW91-01) MCS数据中观察到的构造样式和裂陷过程。初步的地震解释表明，上覆沉积物的断裂和相关的高振幅地震事件证明，地壳内底辟作用可能是观测到的伸展的重要因素。这一底辟作用除了对活动裂陷过程具有重要意义外，还对布兰斯菲尔德海峡拉张应力状态的演化具有启示意义。相对于海沟回缩，海峡东北部的张拉构造在推动海峡伸展方面的作用可能越来越重要。该项目将巩固对布兰斯菲尔德海峡的地球物理分析，并在此基础上考虑海峡与邻近的南设得兰海沟和“前弧”的关系。EW91-01 MCS数据非常适合分析在“弧后”看到的结构是否与海沟和“弧前”的结构和过程有关。该分析的一个关键部分将是检验海沟回滚导致布兰斯菲尔德海峡“弧后”延伸的假设。来自意大利和英国的高质量MCS数据将与EW91-01 MCS数据相结合，对“弧后”和“弧前”的结构样式进行更全面的区域覆盖和地震分析。EW91-01位场数据也将纳入研究。将南极半岛北部与其他具有类似（但不一定相同）活动构造环境的地区（如劳盆地、加利福尼亚湾）进行比较，可以估计出边缘盆地形成和演化过程在全球与局部尺度上的相对重要性。此外，南极半岛太平洋边缘与南美太平洋边缘共同的历史，作为Gondwanaland收敛板块边缘的一部分，意味着Bransfield海峡可以被认为是智利南部Rocas Verdes边缘盆地早白垩世至中白垩世演化的现代类比。罗卡斯佛得斯盆地的历史对于了解安第斯造山运动的早期阶段至关重要。

Abstract This award supports a geophysical study of the Bransfield Strait region of Antarctica using recently collected multichannel seismic data. University of Texas Institute of Geophysics (UTIG) multichannel seismic (MCS) data (EW91-01 data) has enabled detailed analysis of structural style and rifting processes in Bransfield Strait to be carried out. The analysis has brought new insight to the ongoing extensional processes in Bransfield Strait. This project will build on this work to consider Bransfield Strait in the full context of a fore-arc/back-arc tectonic system. This project will primarily use UTIG (EW91-01) MCS data, but will also incorporate other geophysical data from the region that are available from the United Kingdom and Italy. Bransfield Strait is a young basin apparently undergoing active (intracontinental?) extension located between the Antarctic Peninsula and the South Shetland Islands, a small chain of islands to the northwest trending roughly parallel with the Peninsula. Although the South Shetland Islands show no recent arc volcanism, they lie above a subduction zone which still appears to be active, albeit with subduction occurring at a slow rate. This tectonic setting and interpretation of other events affecting plate motions in the vicinity have lead to the currently-held view that Bransfield Strait has opened as a backarc basin in response to South Shetland Trench roll-back or retreat. However, the modern stress regime is unclear. The focus of study thus far has been on the structural style and rifting processes observed in recently-acquired UTIG (EW91-01) MCS data in Bransfield Strait. Initial seismic interpretation indicates that intracrustal diapirism, as evidenced by faulting of overlying sediment and associated high-amplitude seismic events, may be an important element of observed extension. Besides the significance of this diapirism with respect to active rifting processes, it also has implications regarding the evolutio n of the extensional stress regime in Bransfield Strait. It is possible that transtensional tectonics to the northeast of the Strait are increasingly important relative to trench rollback in driving extension in the Strait. This project will consolidate the geophysical analysis of Bransfield Strait and build upon it by considering the Strait's relationship with the adjacent South Shetland Trench and "forearc". EW91-01 MCS data are ideally suited to an analysis of whether structures seen in the "back-arc" relate to structures and processes at the trench and "fore- arc". A key part of this analysis will be to test the hypothesis that trench roll-back is causing "back-arc" extension in Bransfield Strait. High quality MCS data from Italy and the United Kingdom will be integrated with the EW91-01 MCS data for more comprehensive areal coverage and seismic analysis of structural style in the "back-arc" and `fore-arc". EW91-01 potential field data will also be incorporated in the study. Comparison of the northern Antarctic peninsula with other regions characterized by similar, though not necessarily identical, active tectonic settings (e.g., Lau Basin, Gulf of California) should allow an estimate of the relative importance of processes of marginal basin formation and evolution on global versus local scales. Furthermore, the common history that the Antarctic Peninsula Pacific margin shares with the South American Pacific margin as parts of the convergent plate margin of Gondwanaland means that Bransfield Strait can be considered a modern analog for Early to mid-Cretaceous evolution of the Rocas Verdes marginal basin of southern Chile. The Rocas Verdes Basin history is critical to understanding early stages of Andean orogenesis.