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

该研究项目将记录大约1440到1.38亿年前地球磁场强度的变化，以测试地球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以及通信系统和电网的潜在干扰。要预测地球磁场的稳定性和强度，必须了解磁场是如何形成的，以及什么过程控制着它的强度。固体核的形核导致了地磁强度的显著和强劲的增加，但对核芯的形成时间存在争议。关于磁场强度的稀疏和可能有偏差的数据被用来证明内核形成于大约1.4亿年前，但最近对内核热导率的估计表明，内核的增长可能只在大约6亿年前的最晚前寒武纪才开始。该项目的研究将提供对地球磁场演化关键时期内古代磁场的高质量、准确的估计。来自1.43亿年前拉勒米斜长岩杂岩的综合磁学、岩石学和热年代学数据将被用来构建地磁强度(和方向)变化的时间序列。样品将从一系列8个钻芯中采集，每个钻芯的长度约为50米，并系统地从远离侵入体保留的冷却边缘的互补表面取心。古强度研究将重点放在旨在分离斜长石晶体中磁铁矿携带的高稳定性剩磁的小样本上。精确的冷却历史将根据矿物磷灰石的铀-铅放射性同位素年龄确定，该矿物磷灰石的热关闭温度约为450°C，接近获得剩磁的最低温度。原始岩芯将具有双重用途，因为它们还将用于研究原始火成岩岩石组构以及产生火成岩面理和任何线理的过程，从而加深我们对火成岩实体结晶过程的理解。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(地质和地球物理系)两个研究所的科学家之间的合作。

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).