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

南极洲比尔德莫尔群的结构和沉积学：南极东部边缘新元古代至早古生代的构造演化

• 批准号: 0306704
• 负责人: John Goodge
• 金额: $ 3.11万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2004-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0306704&HistoricalAwards=false
• 关键词: Structure; Sedimentology; Beardmore; Group; Antarctica; Structure; Sedimentology; Beardmore; Group; Antarctica

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.

新元古代到早期的古生代过渡（700亿年前（MA））是地球历史上的关键时期。 在此期间，在合并第二个被称为Gondwanaland的超大陆之前，将一个称为Rodinia的超大陆被合并，然后分散。 这些事件由主要的山区建筑，大陆侵蚀，物种多样化，海平面波动以及海水组成的变化表现出来。 来自这个时代的大陆局限度沉积序列（尤其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缘）提供了详细的海平面波动，动物动物分布和后沉积构造的记录。 这些序列之一是南极洲的Beardmore群体，代表了东南极craton进化中的一个重要元素，但对其沉积或构造历史知之甚少。 Beardmore组是厚实的灰色和碳酸盐序列，传统上与​​跨北极山脉其他地方的类似岩石相关。 Beardmore Rocks在很大程度上是无毒的，在岩性上是单调的，并且与晶体基底岩石和化石下寒冷的碳酸盐岩相处不确定。 以前的工人表明，整个Beardmore组的年龄都是新元古代，并且记录了两个不同的变形，即众所周知的Ross造口症（〜500 mA）和早期隐秘的“ Beardmore”造型。 侦察领域和地质学研究表明，比尔德莫尔组的一部分比以前想象的明显年轻（600 mA），并且仅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，它们表明必须修改该地区的新元古代构造历史。 该项目将调查CENTRAL跨界山脉中的Beardmore群体，以更好地了解其沉积历史及其在造型事件中的作用，从而塑造了Gondwanaland的外缘。 该研究将包括：（1）地层，沉积学和结构的详细现场研究； （2）灰色瓦克的出处（来源）研究，以限制浊积岩的沉积设置； （3）测定碳酸盐同位素组合物，以与全局C-同位素记录进行比较； （4）通过碎屑和火成岩锆石的U-PB年代的改进； （5）对AR-异位热量学的变形年龄的约束。 现场工作将在1998-99和1999-2000澳大利亚夏季完成。 这项工作将测试一个最近提出的Beardmore组沉积和变形模型，涉及最新的新元古代 - 古生代（？）Rift-Margin沉积和结构反演，作为Ross活性的早期表达。 结果将有助于直接解决南极地质历史上的长期不确定性，它们将在protererozoic结束时在超大陆转化期间对我们对全球古地理和板块建筑关系的理解提高我们的理解。