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

该奖项支持使用最近收集的多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)的多道地震(MCS)数据(EW91-01数据)使人们能够对布兰斯菲尔德海峡的构造样式和裂谷过程进行详细分析。这一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见解。该项目将在这项工作的基础上，在弧前/弧后构造系统的整个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，但也将纳入来自该地区的联合王国和意大利提供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，显然正在经历活动(陆内？)南设得兰群岛的延伸部分位于南极半岛和南设得兰群岛之间，南设得兰群岛是一个小岛链，向西北方向与半岛大致平行。尽管南设得兰群岛没有表现出近期的弧形火山活动，但它们位于俯冲带上方，俯冲带看起来仍然活跃，尽管俯冲发生的速度很慢。这种构造背景和对附近影响板块运动的其他事件的解释导致了目前所持的观点，即布兰斯菲尔德海峡是作为南设得兰海沟的退缩或后退而开放的弧后盆地。然而，现代的压力机制尚不清楚。到目前为止，研究的重点一直是在布兰斯菲尔德海峡最近获得的UTIG(EW91-01)MCS数据中观察到的构造样式和裂谷过程。初步的地震解释表明，壳内底辟作用，如上覆沉积物的断层作用和伴随的高振幅地震事件所证明的，可能是观察到的伸展的重要因素。这种底辟作用除了对活动裂谷作用具有重要意义外，还对布兰斯菲尔德海峡伸展应力机制的演化具有重要意义。相对于海沟后退，海峡东北部的伸展构造可能在推动海峡伸展方面变得越来越重要。该项目将巩固布兰斯菲尔德海峡的地球物理分析，并通过考虑该海峡与邻近的南设得兰海沟和“前弧形”的关系而进一步发展。EW91-01MCS数据非常适合于分析在“弧后”看到的结构是否与海沟和“弧前”的结构和过程有关。这项分析的一个关键部分将是检验这一假设，即海沟回滚导致布兰斯菲尔德海峡的“弧后”延伸。意大利和联合王国的高质量MCS数据将与EW91-01MCS数据相结合，以便更全面地覆盖区域，并对“弧后”和“弧前”的结构风格进行地震分析。EW91-01位场数据也将纳入研究。将南极半岛北部与具有相似但不一定相同的活动构造环境的其他区域(例如加州湾的刘盆地)进行比较，应该能够估计边缘盆地形成和演化过程在全球和地方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作为冈瓦兰岛会聚板块边缘的一部分具有共同的历史，这意味着布兰斯菲尔德海峡可以被认为是智利南部Rocas Verdes边缘盆地白垩纪早期至中期演化的现代模拟。罗卡斯韦尔德斯盆地的历史对于理解安第斯造山作用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.