SHRIMP U-Pb Geochronology of Transantarctic Mountains Basement

横贯南极山脉地下室的 SHRIMP U-Pb 年代学

• 批准号: 9912081
• 负责人: John Goodge
• 金额: $ 8万
• 依托单位: Southern Methodist University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-06-01 至 2002-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9912081&HistoricalAwards=false
• 关键词: SHRIMP; Pb; Geochronology; Transantarctic; Mountains

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).

Goodge OPP 9912081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。东南极盾牌代表着地球上最古老和最大的克拉通省份之一，具有从太古代到元古界的悠久历史。它是东冈瓦兰镶嵌体的中心部分，可能在罗迪尼亚超大陆新元古代的融合过程中发挥了重要作用。由于地盾的大部分被极地冰盖覆盖，我们对早太古宙至新元古代地质事件的了解主要来自恩德比地和莫德皇后地等地区的沿海露头。然而，地壳厚度和地球物理模式表明，横贯北极的山脉造山带形成了东南极地盾的太平洋边缘。在横贯北极的中部山脉之下，是地盾本身的结晶基底岩(Nimrod群)，与新元古代和下古生界边缘盆地沉积组合(Beardmore群和Byrd群)并列。这些岩石单元共同记录了太古宙地壳生长、元古界地壳改造、新元古代裂谷边缘沉积和早古生代板块边缘汇聚。因此，横贯南极中部山脉是研究南极东部太平洋边缘前寒武纪晶盾及其变形的表壳盖层的关键地区。最近利用超高分辨率离子探针(SHRMP)对Nimrod和Beardmore群进行U-Pb年龄测定，极大地扩展了我们对新元古代晚期和早古生代由裂谷边缘构造向活动边缘构造转变的认识。从迄今分析的相对较少的样品中，SHRIMP分析证明了Nimrod群的多阶段太古代和元古界历史，并对Beardmore群的沉积年龄和沉积物源施加了新的限制。这一新项目将大大扩展横贯北极山脉的基底和表壳组合的年代学框架，目标如下：1.详细研究宁姆罗德群的变质岩和火成岩，以全面描述前寒武纪火成岩、变质岩和碎屑锆石组分的太古代和元古界历史，以及罗斯时代的前、同构造和后构造岩浆序列。扩大对Beardmore群和相关下古生界层序的硅质碎屑岩的研究，主要是通过碎屑锆石的年龄分析，以限制沉积年龄和沉积物源。利用现有的样品材料和来自横贯北极山脉其他地区的其他研究人员提供的一些材料，将有可能解决这些新元古代-下古生界过渡序列之间的区域物源差异。为了完成这项研究，将与堪培拉的澳大利亚国立大学(ANU)的研究人员合作，完成SHRIMP锆石U-Pb和Xen-Time分析，以尝试直接测定不同岩石单元的沉积年龄。分析将在2000年7月至12月的6个月期间在虾设施内完成。ANU将免费提供样品处理，并以协作费率提供仪器访问。因此，这项工作的全部费用将由NSF(虾机时间和附带支持费用)、南方卫理公会大学(工资和基本办公室支持)和ANU(降低内部仪器费率，样品处理免费，以及提供办公室空间、图书馆访问和计算机支持的休假支持)分摊。