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

该奖项由极地项目办公室的南极地质和地球物理项目提供，支持一个调查南极横贯山脉和南极洲东部邻近地区的项目。东南极地盾是地球上最古老和最大的克拉通组合之一，具有很长的太古代到古生代早期的历史。在过去的十年中，构造模型将东南极洲与罗迪尼亚和冈瓦纳大陆的其他前寒武纪地壳元素联系起来，重新点燃了人们对这个地盾的地质演化的长期兴趣。假设东南极洲太平洋边缘在新元古代晚期罗迪尼亚分裂期间从劳伦西亚分裂出来，然后在最早古生代冈瓦纳大陆合并期间发展成为一个活跃的板块边界。在板块结构、陆表过程、海平面、海洋地球化学和生物群发生全球性变化的时期，东南极盾在超大陆转化中发挥了关键作用。因此，更好地了解东南极盾的地质演化对研究前寒武纪地壳演化、资源分布、生物圈演化以及地球历史后期的冰川和气候历史具有重要意义。然而，由于极地冰盖几乎完全覆盖，南极洲仍然是唯一一个地质上未被探索过的大陆。克拉通基底的暴露主要局限于乔治五世地和特雷阿德利（澳大利亚部分）、查尔斯王子山脉和恩德比地（印度部分）以及莫德女王地（非洲部分）的沿海露头，这些地区的地质情况相当有名。相比之下，人们对护盾内部的组成和结构知之甚少。考虑到广泛的冰盖，收集航空地球物理数据是表征大面积冰下基底的最具成本效益的方法，并扩大了我们对南极东部盾层内部的认识。该项目将在横贯南极山脉中部的宁罗德冰川地区，通过一个重要的窗口进行航空磁测量（与地面重力测量相结合）。具体目标是：1。2.南极东部罗斯边缘（Nimrod群）地壳基底的磁重特征。沿着极地冰帽的走廊向西扩展磁数据，以便在冰雪覆盖的地区成像地壳。获得罗斯造山带的磁数据，以便对基底和表壳岩石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构造的几何形状；利用磁异常的形状、趋势、波长和振幅来定义地盾中的磁域，这是大陆尺度前寒武纪地质结构和演化研究的共同组成部分。高分辨率航空磁数据将沿着从Nimrod群暴露的岩石延伸到邻近极地冰盖的样带收集。Nimrod群代表了南极洲太平洋边缘2500多公里的唯一真正的太古宙-元古代盾状基底。本次调查将首次使用地球物理方法对该地区地质上知名的盾构地形进行表征。暴露的盾层上的这条基线将有助于更好地解释其他冰覆盖地区的地球物理模式，并可用于未来的调查。在与BGR（德国）的同事们的合作下，将在2003- 2004年的南方夏季进行一次紧密间隔的“悬挂式”直升机磁测量，并辅以地面对暴露地下室的重力测量。数据精简、解释和地质对比将在第二年完成。该项目将加强学生的教育、弱势群体的进步、美国南极计划的研究仪器、联邦政府和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。通过创造关于南极大陆的新基础知识，它将造福社会，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.