Authigenic smectite in Cape Roberts Project cores, Antarctica: implications for environmental, basin and tectonic history

南极洲罗伯茨角项目岩心中的自生蒙脱石：对环境、盆地和构造历史的影响

• 批准号: 0126218
• 负责人: Sherwood Wise
• 金额: $ 16.7万
• 依托单位: Florida State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0126218&HistoricalAwards=false
• 关键词: Authigenic; smectite; Cape; Roberts; Project

0126218WiseThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a study of clays (specifically smectite) in cores from the Ross Sea, Antarctica, toward an understanding of the age and origin. One of the most surprising discoveries of the recently concluded geological drilling of the Cape Roberts Project (CRP) in the eastern Ross Sea, Antarctica, was the presence of authigenic smectite clays in lower Oligocene (or older) sandstones in the lower portion of Hole CRP-3, which was diamond-cored continuously to 941 meters below sea floor with 98% recovery. This is the first confirmed report of authigenic smectite in sandstones from the Antarctic continental margin. Situated along the eastern margin of the Victoria Land Basin, adjacent to the rising Transantarctic Mountains, CRP-3 was drilled to elucidate the paleoclimatic and tectonic history of the region; however, the base of the Cenozoic section is poorly dated, with limited constraints from biostratigraphy and paleomagnetics. This project is designed to shed additional light on the spatial extent, source, timing, and mode of emplacement of the authigenic smectite, which were probably emplaced shortly after deposition of the host sediments. This will help constrain the age of the basal Cenozoic sediments and the environment in which the smectite formed. This in turn will lead to a better understanding of the tectonic processes at work during the early history of the basin.Because this serendipitous discovery was not anticipated prior to drilling, only a pilot study could be undertaken within the time and funding constraints dictated by the science plan for the project. Work to date allows the definition of three multiple working hypotheses to account for the source and mode of emplacement of the authigenic smectite: 1) Burial diagenesis with necessary components sourced from volcanogenic materials and heavy minerals within the Cenozoic sequence or from a dolerite intrusion in the Paleozoic sandstones below; 2) Precipitation from hydrothermal waters associated with possible igneous intrusion(s) and nearby faults; 3) Mobilization and injection of fluids along a nearby fault that bounds a major graben parallel to the Transantarctic Front. The data gathered form the preliminary study was insufficient, however, to arbitrate among these three possibilities.This award supports work to test, to the extent possible, these three hypotheses and to allow completion of the study through: 1) a thorough examination of the core by scanning electron microscope/energy-dispersive microprobe analysis to determine the extent of the smectite in CRP-3 and the nearby CRP-2 core (also predominantly of Oligocene age), and 2) radiometric dating of the authigenic clays and potential source rock(s) by the 40Ar/39Ar method. Completion of the study will help answer fundamental tectonic an paleoenvironmental questions posed by the CRP project, will help guide future exploration of the Antarctic margin (such as by the ANDRIL, SHALDRIL, and IODP projects), and will impact major Antarctic initiatives such as ANTEC, MARGINS, and STRATAFORM.

0126218 Wise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，为研究南极罗斯海岩芯中的粘土（特别是蒙皂石）提供资金，以了解年龄和起源。最近在南极洲罗斯海东部结束的罗伯茨角项目（CRP）地质钻探中最令人惊讶的发现之一是CRP-3孔下部渐新统（或更早）砂岩中存在自生蒙皂石粘土，该孔连续钻取金刚石岩心至海底以下941米，回收率为98%。这是首次证实南极大陆边缘砂岩中存在自生蒙皂石的报道。CRP-3位于沿着维多利亚陆盆地的东部边缘，毗邻上升的横贯南极山脉，钻探目的是阐明该地区的古气候和构造历史;然而，新生代剖面的基底年代测定不佳，生物地层学和古地磁学的限制有限。该项目旨在进一步阐明自生蒙皂石的空间范围、来源、时间和就位模式，这些蒙皂石可能在宿主沉积物沉积后不久就位。这将有助于限制底部新生代沉积物的年龄和蒙皂石形成的环境。这反过来又将导致更好地了解盆地早期历史中起作用的构造过程。由于在钻探之前没有预料到这一偶然发现，因此只能在该项目科学计划规定的时间和资金限制范围内进行试点研究。迄今为止的工作允许定义三个多工作假说来解释自生蒙皂石的来源和侵位方式：1）埋藏成岩作用，其必要成分来自新生代层序内的火山物质和重矿物或来自下面古生代砂岩中的粗玄岩侵入体：2）与可能的火成岩侵入体和附近断层有关的热液沃茨的沉淀;（3）流体沿着附近的断层流动和注入，该断层界定了一个平行于横贯南极洲前缘的主要地堑。然而，从初步研究中收集的数据不足以在这三种可能性之间进行仲裁。本裁决支持尽可能测试这三种假设的工作，并通过以下方式完成研究：1）通过扫描电子显微镜/能量分散微探针分析对岩心进行彻底检查，以确定CRP-3和附近CRP-2岩心中蒙皂石的范围（也主要是渐新世）;（2）用40 Ar/39 Ar法测定自生粘土和潜在烃源岩的放射性年龄。研究的完成将有助于回答CRP项目提出的基本构造和古环境问题，将有助于指导未来对南极边缘的勘探（如ANDRIL，SHALDRIL和IODP项目），并将影响主要的南极倡议，如ANTEC，MARGINS和STRATAFORM。