Collaborative Research: A geomagnetic intensity time series from the Proterozoic Laramie anorthosite

合作研究：元古代拉勒米斜长岩的地磁强度时间序列

• 批准号: 1722604
• 负责人: Jeffrey Gee
• 金额: $ 22.28万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1722604&HistoricalAwards=false
• 关键词: Collaborative; Research; geomagnetic; intensity; time

The research project will document variations of the Earth's magnetic field strength for the period from approximately 1440 to 1380 million years ago to test models of geomagnetic field formation and the thermal evolution of the Earth. The Earth's magnetic field protects the Earth's surface from harmful cosmic radiation and potential interruptions of communication systems and electrical grids. To predict the stability and strength of the Earth's magnetic field, it is essential to understand how the field formed and what processes control its strength. It has been argued that the nucleation of the solid inner core led to a prominent and robust increase in geomagnetic strength, but the timing of inner core formation is in some dispute. Sparse and possibly biased data on the intensity of the magnetic field have been used to argue for inner core formation at about 1400 million years ago, but recent estimates of core thermal conductivity suggest that inner core growth may have begun only in the latest Precambrian, approximately 600 million years ago. The research in this project will provide high-quality, well-dated estimates of the ancient magnetic field over a critical time period in the evolution of Earth's magnetic field.Integrated magnetic, petrologic and thermochronologic data from the well-dated 1430 million year old Laramie anorthosite complex will be used to construct a time series of geomagnetic intensity (and directional) variations. Samples will be collected from a series of eight drill cores, each about 50m in length, and complementary surface coring systematically away from the preserved cooling margin of the intrusion. The paleointensity study will focus on small subsamples designed to isolate the high-stability remanence carried by magnetite within plagioclase crystals. The precise cooling history will be determined from U-Pb radioisotopic dates of the mineral apatite, which has a thermal closure temperature of approximately 450°C, close to the minimum temperatures of remanence acquisition. The pristine cores will be dual purposed as they will also be used to investigate primary igneous petro-fabrics and the processes by which igneous foliations and any lineations have been produced, thereby deepening our understanding of the crystallization processes of igneous bodies. The project will train several undergraduate students, form the basis for one PhD dissertation, and strengthen collaboration among scientists at two institutes, the University of California San Diego (Scripps Institution of Oceanography) and the University of Wyoming (Department of Geology and Geophysics).

该研究项目将记录大约1440至1380万年前地球磁场强度的变化，以测试地磁场形成和地球热演化的模型。地球磁场保护地球表面免受有害的宇宙辐射和通信系统和电网的潜在中断。为了预测地球磁场的稳定性和强度，有必要了解磁场是如何形成的，以及是什么过程控制了它的强度。有人认为，固体内核的成核导致了地磁强度的显著而强劲的增加，但内核形成的时间存在一些争议。关于磁场强度的稀疏和可能有偏差的数据被用来争论内核在大约14亿年前形成，但最近对核心热导率的估计表明，内核的增长可能只在最近的前寒武纪开始，大约6亿年前。该项目的研究将为地球磁场演化的关键时期提供高质量、准确的古代磁场估计。来自1430万年前的拉勒米斜长杂岩的综合磁、岩石学和热年代学数据将用于构建地磁强度（和方向）变化的时间序列。样品将从一系列8个钻孔岩心中收集，每个岩心长度约为50米，并系统地从保留的入侵冷却边缘处进行互补的表面取心。古强度研究将集中在小的亚样品上，以分离斜长石晶体中由磁铁矿携带的高稳定性残留物。精确的冷却历史将由矿物磷灰石的U-Pb放射性同位素日期确定，磷灰石的热闭合温度约为450°C，接近剩余物获取的最低温度。原始岩心将具有双重用途，因为它们还将用于研究原始火成岩石油结构以及火成岩叶理和任何线理产生的过程，从而加深我们对火成岩体结晶过程的理解。该项目将培养几名本科生，形成一篇博士论文的基础，并加强加州大学圣地亚哥分校（斯克里普斯海洋研究所）和怀俄明大学（地质与地球物理系）两个研究所科学家之间的合作。