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

该研究项目将记录大约14.4亿至13.8亿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以及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，必须了解磁场是如何形成的，以及是什么过程控制着它的强度。有人认为，固体内核的成核导致了地磁强度的显着和强劲的增加，但内核形成的时间是在一些争议。关于磁场强度的稀疏和可能有偏见的数据已经被用来论证内核在大约14亿年前形成，但最近对内核热导率的估计表明内核的生长可能只在最近的前寒武纪开始，大约6亿年前。该项目的研究将提供地球磁场演化关键时期的古磁场的高质量、准确的估计，将使用来自14.3亿年前的拉勒米斜长岩杂岩体的综合磁性、岩石学和热年代学数据来构建地磁强度（和方向）变化的时间序列。将从一系列的8个钻芯中采集样本，每个钻芯长约50米，并在远离侵入体保存的冷却边缘的系统性补充表面取芯。古强度研究将侧重于小的子样本，旨在隔离斜长石晶体内磁铁矿携带的高稳定性剩磁。精确的冷却历史将由矿物磷灰石的U-Pb放射性同位素测年确定，磷灰石的热封闭温度约为450°C，接近剩磁采集的最低温度。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岩石组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。该项目将培训几名本科生，为一篇博士论文奠定基础，并加强加州圣地亚哥大学（斯克里普斯海洋学研究所）和怀俄明州大学（地质和地球物理系）这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).