SHRIMP U-Pb Geochronology of Transantarctic Mountains Basement

该奖项由极地计划办公室南极地质和地球物理计划提供，为与东南极大陆盾构造发展有关的地质年代学调查提供资金。东南极地盾是地球上最古老和最大的南极洲之一，有着悠久的太古代到元古代的历史。它是冈瓦纳大陆东部镶嵌体的中心部分，可能在新元古代罗迪尼亚超大陆的融合过程中发挥了重要作用。由于大部分的盾牌是由极地冰帽覆盖，我们的知识，早期太古代新元古代地质事件主要来自沿海露头地区，如恩德比地和毛德皇后地。然而，地壳厚度和地球物理模式表明，横贯南极山脉造山带形成东南极地盾的太平洋边缘。在中部横贯南极山脉的下面是地盾本身的结晶基底岩石（尼姆罗德群），与新元古代和下古生代边缘盆地沉积组合（Beardmore群和Byrd群）并列。这些岩石单元共同记录了太古代地壳生长、元古代地壳变化、新元古代裂谷边缘的沉积物沉积和早古生代板块边缘的汇聚。利用超高分辨率离子微探针（SHRIMP）对尼姆罗德群和Beardmore群进行U-Pb年龄测定，极大地扩展了我们对东南极大陆盾演化和从裂谷向活动过渡的认识。新元古代晚期和早古生代的边缘构造。从相对较少的样品分析到目前为止，SHRIMP分析表明，多阶段的太古代和元古代的尼姆罗德群的历史，并提出了新的限制Beardmore群的沉积时代和沉积物源。这一新项目将大大扩展越南盾山脉基底和表壳岩组合的年代学框架，其目标如下：1。详细研究了尼姆罗德群的变质岩和火成岩，以全面表征太古代和元古代前寒武纪火成岩、变质锆石和碎屑锆石组分的历史，以及罗斯时代构造前、构造同期和构造后的岩浆序列.对来自比尔德摩尔群和相关的下古生代层序的硅质岩石进行了扩展研究，主要通过碎屑锆石的年龄分析来限制沉积年龄和沉积物源。现有的样品材料和一些提供的其他研究人员从其他部分的跨南极山脉，它将有可能解决这些过渡新元古代-下古生代序列之间的区域物源变化。为了完成这项研究，将与堪培拉的澳大利亚国立大学的研究人员合作完成SHRIMP锆石U-Pb和磷钇矿分析。分析工作将在2000年7月至12月的6个月期间在SHRIMP设施内完成。ANU将免费提供样品处理，并以合作价格提供仪器访问。因此，这项工作的全部成本将由NSF（SHRIMP机器时间和附带支持成本）、南卫理公会大学（工资和基本办公室支持）和ANU（降低内部仪器费率、不收取样品处理费用以及办公空间、图书馆访问和计算机支持的休假支持）分担。

Goodge OPP 9912081This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a geochronological investigation relating to the tectonic development of the East Antarctic continental shield. The East Antarctic shield represents one of Earth's oldest and largest cratonic provinces, with a long-lived Archean to Proterozoic history. It is the central piece in the eastern Gondwanaland mosaic, and it likely played an important role in the Neoproterozoic amalgamation of the Rodinia supercontinent. Because much of the shield is covered by the polar ice cap, our knowledge of early Archean to Neoproterozoic geologic events comes mostly from coastal outcrops in areas such as Enderby Land and Queen Maud Land. However, crustal thicknesses and geophysical patterns show that the Transantarctic Mountains orogenic belt forms the Pacific edge of the East Antarctic shield. Underlying the central Transantarctic Mountains are crystalline basement rocks of the shield itself (Nimrod Group), juxtaposed against Neoproterozoic and lower Paleozoic marginal-basin sedimentary assemblages (Beardmore and Byrd groups). Together, these rock units record Archean crustal growth, Proterozoic crustal modifications, sediment deposition across a Neoproterozoic rift margin, and early Paleozoic plate-margin convergence. The central Transantarctic Mountains is therefore a critical area along the Pacific margin of East Antarctica to study both the Precambrian crystalline shield and its deformed supracrustal cover.Recent U-Pb age dating of the Nimrod and Beardmore groups by use of the Super High Resolution Ion MicroProbe (SHRIMP) has greatly expanded our understanding of East Antarctic shield evolution and the transition from rift- to active-margin tectonics during the late Neoproterozoic and early Paleozoic. From a relatively small number of samples analyzed to date, SHRIMP analysis has demonstrated a multi-stage Archean and Proterozoic history of the Nimrod Group, and placed new constraints on the depositional age and sedimentary provenance of the Beardmore Group. This new project will significantly expand the geochronological framework of basement and supracrustal assemblages in the Transantarctic Mountains, with goals as follows:1. Detailed study of metamorphic and igneous rocks from the Nimrod Group, in order to fully characterize the Archean and Proterozoic history of Precambrian igneous, metamorphic and detrital zircon components, as well as the Ross-age pre-, syn- and post-tectonic magmatic sequence.2. Expanded study of siliciclastic rocks from the Beardmore Group and related lower Paleozoic sequences, primarily by age analysis of detrital zircons in order to constrain depositional ages and sedimentary provenance. With existing sample material and some provided by other researchers from other parts of the Transantarctic Mountains, it will be possible to address regional provenance variations among these transitional Neoproterozoic-lower Paleozoic sequences. Diagenetic xenotime will also be analyzed in order to attempt direct dating of the depositional age of the different rock units.To complete this study, SHRIMP U-Pb zircon and xenotime analyses will be completed in collaboration with researchers at the Australian National University (ANU) in Canberra. Analyses will be completed in the SHRIMP facility during a 6-month period from July to December, 2000. ANU will provide sample processing at no charge and instrument access at collaborative rates. Therefore, the full costs of this work are to be shared between NSF (SHRIMP machine time and incidental support costs), Southern Methodist University (salary and basic office support), and ANU (reduced in-house instrument rates, no charge for sample processing, and sabbatical support with office space, library access, and computer support).