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

布兰斯菲尔德海峡-南设得兰群岛/海沟：关联的（？）弧后/弧前系统的结构和地层演化

• 批准号: 9418135
• 负责人: Ian Dalziel
• 金额: $ 5.93万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-02-15 至 1997-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9418135&HistoricalAwards=false
• 关键词: Bransfield; Strait; South; Shetland; Islands

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.

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地球物理研究。 得克萨斯大学地球物理研究所（UTIG）的多道地震（MCS）数据（EW 91 -01数据），使详细分析的构造样式和断裂过程在布兰斯菲尔德海峡进行。 这一分析为布兰斯菲尔德海峡正在进行的伸展过程提供了新的认识。 该项目将在这项工作的基础上，在弧前/弧后构造系统的全面背景下考虑布兰斯菲尔德海峡。 该项目将主要使用UTIG（EW 91 -01）MCS数据，但也将纳入联合王国和意大利提供的该区域其他地球物理数据。 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？）位于南极半岛和南设得兰群岛之间的延伸部分，是一个向西北延伸的小岛链，大致与半岛平行。 虽然南设得兰群岛没有显示出最近的弧火山活动，但它们位于俯冲带之上，俯冲带似乎仍然活跃，尽管俯冲发生的速度很慢。这种构造背景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是作为南设得兰群岛海沟回滚或后退的弧后盆地而开放的。 然而，现代压力机制尚不清楚。 迄今为止，研究的重点一直是在最近获得的UTIG（EW 91 -01）MCS数据在布兰斯菲尔德海峡观察到的构造样式和裂谷过程。 初步地震解释表明，壳内底辟，证明了断层覆盖的沉积物和相关的高振幅地震事件，可能是一个重要的元素，观察到的扩展。这种底辟作用除了对主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体制的演化具有重要意义。海峡东北部的扭张构造可能对驱动海峡伸展的海沟回滚作用越来越重要。 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，考虑该海峡与邻近的南设得兰群岛海沟和“前弧”的关系。EW 91 -01 MCS数据非常适合于分析“弧后”中看到的结构是否与海沟和“弧前”的结构和过程有关。 这一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。 将把来自意大利和联合王国的高质量MCS数据与EW 91 -01 MCS数据结合起来，以便对“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。EW 91 -01位场数据也将纳入研究。 南极北方半岛与其他具有类似但不一定相同的活动构造环境的地区的比较（例如，Lau盆地，加州湾）应允许全球与局部尺度上的边缘盆地形成和演化过程的相对重要性的估计。 此外，南极半岛太平洋边缘与南美洲太平洋边缘作为冈瓦纳大陆会聚板块边缘的一部分的共同历史意味着布兰斯菲尔德海峡可以被认为是智利南部罗卡斯弗迪斯边缘盆地早白垩世至中白垩世演化的现代模拟。 Rocas Verdes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。