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，支持一个调查横贯南极山脉和东南极邻近地区的项目。东南极盾牌是地球上最古老和最大的克拉通组合之一，具有太古代到早古生代的漫长历史。在过去的十年里，将南极洲东部与罗迪尼亚和冈瓦兰超大陆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个盾体地质演化的长期兴趣。推测东南极太平洋边缘是在新元古代晚期Rodinia裂解时从劳伦蒂亚裂解出来的，随后在早古生代冈瓦瓦兰德拼合过程中形成了活动的板块边界。如果是真的，在全球板块形态、陆地表面过程、海平面、海洋地球化学和生物群发生变化的时候，东南极地盾在超大陆转换中发挥了关键作用。因此，更好地了解东南极地盾的地质演化对于总体上研究前寒武纪地壳演化以及地球历史后期的资源分布、生物圈演化以及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了南极，南极洲仍然是地质上最未开发的大陆。克拉通地下室的暴露在很大程度上仅限于乔治五世陆地和Terre Adele(澳大利亚部分)、查尔斯王子山脉和Enderby土地(印度部分)和Maud皇后土地(非洲部分)的沿海露头，这些地区的地质情况相当知名。相比之下，人们对盾牌内部的组成和结构知之甚少。考虑到广阔的冰盖，收集航空地球物理数据是确定冰下大片区域特征和扩大我们对东南极盾体内部知识的最具成本效益的方法。该项目将在横贯北极山脉中部的尼姆罗德冰川地区的一个重要窗口上进行一次航空磁力测量(结合地面重力测量)，以了解暴露在那里的盾牌。具体目标是：1.描述暴露在罗斯边缘(Nimrod群)的东南极地壳基底的磁性和重力特征；2.沿着一条横跨极地冰盖的走廊向西延伸磁性数据，以便对冰盖地区的地壳进行成像；3.获得罗斯造山带上的磁性数据，以便对基底和表壳岩石之间的冰盖边界进行成像，使我们能够更好地约束罗斯基本构造的几何形状，以及4.利用磁异常的形状、趋势、波长和幅度来定义屏蔽中的磁域，这是大陆范围内研究前寒武纪地质结构和演化的常见构件。高分辨率的航空磁数据将沿着横跨相邻极地冰盖的Nimrod群裸露岩石的横断面收集。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暴露在太古界-元古界的地盾基底。这项调查将首次使用地球物理方法描述该地区地质上著名的盾构地形。露出的屏蔽层上的基线将允许更好地解释其他冰盖区域的地球物理模式，并可用于未来的调查。与BGR(德国)的同事合作，将在2003-04年南半球夏季期间进行一次紧密间隔、“覆盖”的直升机磁力测量，并在裸露的地下室上空进行地面重力测量。数据整理、解释和地质对比将在第二年完成。该项目将加强对学生的教育，促进代表不足的群体的进步，加强美国南极计划的研究工具，加强联邦政府和高等教育机构之间的合作，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来造福社会，这反过来可能有助于在其他领域的应用研究，如南极洲的冰川史。

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.