Collaborative Research: Geophysical Mapping of the East Antarctic Shield Adjacent to the Transantarctic Mountains

该奖项由极地方案办公室南极地质和地球物理方案提供，支持一个调查南极洲横贯山脉和东南极洲邻近地区的项目。东南极地盾是地球上最古老和最大的南极组合之一，具有悠久的太古代至早古生代历史。在过去的十年中，将东南极洲与Rodinia和Gondwanaland超大陆中的其他前寒武纪地壳元素联系起来的构造模型重新点燃了人们对这一盾牌地质演化的长期兴趣。据推测，东南极洲的太平洋边缘是在新元古代晚期Rodinia解体时从Laurentia断裂出来的，然后在随后的冈瓦纳大陆合并过程中，在最早的古生代，它发展成为一个活动的板块边界。如果这是真的，那么在板块结构、陆地表面过程、海平面、海洋地球化学和生物群发生全球变化的时候，东南极盾在超大陆转型中发挥了关键作用。因此，更好地了解东南极地盾的地质演化对于研究前寒武纪地壳演化以及地球历史后期的资源分布、生物圈演化、冰川和气候历史至关重要。然而，由于极地冰盖几乎完全覆盖，南极洲仍然是地质上最未开发的大陆。超声波基底的出露主要限于乔治五世地和Terre Adelie（澳大利亚地段）、查尔斯王子山和恩德比地（印度地段）以及毛德皇后地（非洲地段）的沿海露头，这些地方的地质相当有名。相比之下，人们对屏蔽层内部的组成和结构知之甚少。鉴于冰盖覆盖面很广，收集航空地球物理数据是确定冰下基底广大地区的特征和扩大我们对东南极盾内部的了解的最具成本效益的方法。该项目将在横贯南极山脉中部尼姆罗德冰川地区的一个重要窗口进行一次航空磁力测量（结合地面重力测量）。具体目标是：1.描述出露于罗斯边缘（尼姆罗德群）的东南极地壳基底的磁、重力特征。沿沿着穿过极地冰帽的走廊向西扩展磁测数据，以便对冰雪覆盖地区的地壳成像。获得罗斯造山带的磁性数据，以便对基底和表壳岩之间的冰覆盖边界进行成像，使我们能够更好地约束基本罗斯结构的几何形状，以及4。利用磁异常的形状、趋势、波长和振幅来确定屏蔽层中的磁畴，这是前寒武纪地质结构和演化的大陆尺度研究的共同组成部分。将沿着一条从尼姆罗德群暴露的岩石延伸到邻近的极地冰盖的横断面收集高分辨率航空磁数据。尼姆罗德群是南极洲太平洋边缘2500多公里范围内唯一真正的太古代-元古代地盾基底。这项调查将首次使用地球物理方法来描述这一地区地质上众所周知的盾构地形。暴露的屏蔽层上的这一基线将允许更好地解释其他冰覆盖区域的地球物理模式，并可用于未来的调查。与来自BGR（德国）的同事合作，将在2003- 2004年南半球夏季进行一次紧密间隔的“悬挂式”直升机磁力测量，并辅之以对裸露地下室的地面重力测量。第二年将完成数据整理、解释和地质对比。该项目将加强学生的教育、代表性不足群体的进步、美国南极计划的研究仪器、联邦政府与高等教育机构之间的伙伴关系以及国家研究计划之间的合作。它将通过创造关于南极大陆的新的基本知识而造福社会，这反过来又可能有助于其他领域的应用研究，如南极洲的冰川历史。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate the Transantarctic Mountains and an adjacent region of East Antarctica. The East Antarctic shield is one of Earth's oldest and largest cratonic assemblies, with a long-lived Archean to early Paleozoic history. Long-standing interest in the geologic evolution of this shield has been rekindled over the past decade by tectonic models linking East Antarctica with other Precambrian crustal elements in the Rodinia and Gondwanaland supercontinents. It is postulated that the Pacific margin of East Antarctica was rifted from Laurentia during late Neoproterozoic breakup of Rodinia, and it then developed as an active plate boundary during subsequent amalgamation of Gondwanaland in the earliest Paleozoic. If true, the East Antarctic shield played a key role in supercontinent transformation at a time of global changes in plate configuration, terrestrial surficial process, sea level, and marine geochemistry and biota. A better understanding of the geological evolution of the East Antarctic shield is therefore critical for studying Precambrian crustal evolution in general, as well as resource distribution, biosphere evolution, and glacial and climate history during later periods of Earth history. Because of nearly complete coverage by the polar ice cap, however, Antarctica remains the single most geologically unexplored continent. Exposures of cratonic basement are largely limited to coastal outcrops in George V Land and Terre Adelie (Australian sector), the Prince Charles Mountains and Enderby Land (Indian sector), and Queen Maud Land (African sector), where the geology is reasonably well-known. By contrast, little is known about the composition and structure of the shield interior. Given the extensive ice cover, collection of airborne geophysical data is the most cost-effective method to characterize broad areas of sub-ice basement and expand our knowledge of the East Antarctic shield interior. This project will conduct an airborne magnetic survey (coupled with ground-based gravity measurements) across an important window into the shield where it is exposed in the Nimrod Glacier area of the central Transantarctic Mountains. Specific goals are to:1. Characterize the magnetic and gravity signature of East Antarctic crustal basement exposed at the Ross margin (Nimrod Group),2. Extend the magnetic data westward along a corridor across the polar ice cap in order to image the crust in ice-covered areas,3. Obtain magnetic data over the Ross Orogen in order to image the ice-covered boundary between basement and supracrustal rocks, allowing us to better constrain the geometry of fundamental Ross structures, and4. Use the shape, trends, wavelengths, and amplitudes of magnetic anomalies to define magnetic domains in the shield, common building blocks for continent-scale studies of Precambrian geologic structure and evolution.High-resolution airborne magnetic data will be collected along a transect extending from exposed rocks of the Nimrod Group across the adjacent polar ice cap. The Nimrod Group represents the only bona fide Archean-Proterozoic shield basement exposed for over 2500 km of the Pacific margin of Antarctica. This survey will characterize the geologically well-known shield terrain in this sector using geophysical methods for the first time. This baseline over the exposed shield will allow for better interpretation of geophysical patterns in other ice-covered regions and can be used to target future investigations. In collaboration with colleagues from the BGR (Germany), a tightly-spaced, "draped" helicopter magnetic survey will be flown during the 2003-04 austral summer, to be complemented by ground measurements of gravity over the exposed basement. Data reduction, interpretation and geological correlation will be completed in the second year. This project will enhance the education of students, the advancement of under-represented groups, the research instrumentation of the U.S. Antarctic Program, partnerships between the federal government and institutions of higher education, and cooperation between national research programs. It will benefit society through the creation of new basic knowledge about the Antarctic continent, which in turn may help with applied research in other fields such as the glacial history of Antarctica.