Structure and Sedimentology of the Beardmore Group, Antarctica: Latest Neoproterozoic to Early Paleozoic Tectonic Evolution of the East Antarctic Margin

新元古代到早古生代的过渡期（7亿~ 5亿年前）是地球历史上的一个关键时期。 在此期间，一个被称为Rodinia的超大陆合并，然后分裂，在第二个被称为Gondwanaland的超大陆合并之前。 这些事件表现为主要的造山运动、大陆侵蚀、物种多样化、海平面波动和海水成分的变化。 这一时期的大陆边缘沉积序列（特别是在北美西部和东部、东北亚、南部非洲、澳大利亚东部和南极洲的罗斯边缘）提供了海平面波动、动物群分布和沉积后构造作用的详细记录。 其中一个层序，南极洲的Beardmore群，代表了东南极克拉通演化的重要因素，但对其沉积或构造历史知之甚少。 Beardmore群是一个厚的杂砂岩和碳酸盐岩序列，传统上与跨南极山脉其他地方的类似岩石相关。 Beardmore岩大部分不含碳酸盐，岩性单一，与结晶基底岩和含碳酸盐的下寒武统碳酸盐的沉积关系不确定。 先前的研究者认为，整个比尔德摩尔群的年龄是新元古代，它记录了两个不同的变形，著名的罗斯造山带（约500 Ma）和更早的神秘的“比尔德摩尔”造山带。 勘测现场和地质年代学研究表明，比尔德摩尔群的部分比以前认为的要年轻得多（600 Ma），而且它只显示了罗斯变形的证据。 这些初步数据反映了这些岩石的地质关系的不确定性，它们表明，该地区的新元古代构造历史必须修订。 该项目将调查中部横贯南极山脉的Beardmore群，以便更好地了解其沉积历史及其在塑造冈瓦纳大陆外缘的造山事件中的作用。 研究将包括：（1）详细的地层学、沉积学和构造的野外研究;（2）杂砂岩的物源（源）研究以限制浊积岩的沉积环境;（3）测定碳酸盐同位素组成以与全球碳同位素记录进行比较;（4）通过碎屑和火成锆石的U-Pb定年来修正沉积年龄;（5）Ar同位素热年代学对变形时代的制约。 实地工作将于1998-99年度和1999-2000年度夏季完成。 这项工作将测试最近提出的模型Beardmore群沉积和变形，涉及最新新元古代早古生代（？）裂谷边缘沉积和构造反转是罗斯活动的早期表现。 这些结果将有助于直接解决南极地质历史中长期存在的不确定性，并将有助于我们加深对元古代末超大陆转换期间全球古地理和板块构造关系的理解。

The Neoproterozoic to early Paleozoic transition (700-500 million years ago (Ma)) is a critical period in Earth history. During this period one supercontinent known as Rodinia was coalesced, then fragmented, prior to amalgamation of a second supercontinent referred to as Gondwanaland. These events were manifested by major mountain building, continental erosion, species diversification, sea-level fluctuations, and changes in sea- water composition. Continental-margin sedimentary sequences from this era (notably in western and eastern North America, northeastern Asia, southern Africa, eastern Australia, and the Ross margin of Antarctica) provide detailed records of sea-level fluctuations, faunal distributions, and post- depositional tectonism. One of these sequences, the Beardmore Group in Antarctica, represents a significant element in the evolution of the East Antarctic craton, yet very little is known about its depositional or tectonic history. The Beardmore Group is a thick sequence of graywacke and carbonate that is traditionally correlated with similar rocks elsewhere in the Transantarctic Mountains. Beardmore rocks are largely unfossiliferous, lithologically monotonous, and lie in uncertain depositional relation with both crystalline basement rocks and fossiliferous Lower Cambrian carbonates. Previous workers have suggested that the entire Beardmore Group is Neoproterozoic in age and that it records two distinct deformations, the well-known Ross orogeny (~500 Ma) and an earlier cryptic "Beardmore" orogeny. Reconnaissance field and geochronologic studies indicate that portions of the Beardmore Group are significantly younger (600 Ma) than previously thought, and that it only shows evidence for Ross deformation. These preliminary data reflect uncertainty in the geologic relations of these rocks, and they indicate that the Neoproterozoic tectonic history for the region must be revised. This project will investigate the Beardmore Group in the ce ntral Transantarctic Mountains in order to better understand its depositional history and its role in orogenic events shaping the outer margin of Gondwanaland. The study will include: (1) detailed field study of the stratigraphy, sedimentology, and structure; (2) provenance (source) study of graywackes to constrain the depositional setting of the turbidites; (3) determination of carbonate isotopic compositions for comparison with the global C-isotopic record; (4) refinement of depositional age(s) through U-Pb dating of detrital and igneous zircons; and (5) constraint on the age(s) of deformation(s) with Ar-isotope thermochronology. Field work will be completed during the 1998-99 and 1999-2000 austral summers. This work will test a recently proposed model for Beardmore Group deposition and deformation that involves latest Neoproterozoic-early Paleozoic(?) rift-margin sedimentation and structural inversion as an early expression of Ross activity. The results will help to directly resolve long- standing uncertainties in the geologic history of the Antarctica and they will improve our understanding of global paleogeographic and plate-tectonic relations during supercontinent transformation at the close of the Proterozoic.