This Division of Earth Sciences Instrumentation and Facilities Program grant supports acquisition of a 2G Enterprises 4K-755 high-resolution superconducting rock magnetometer (SRM) with a small access bore (6 mm) at Michigan Technological University. The small bore SRM allows for paleomagnetic directional and paleointensity analysis of single crystals of ancient (Precambrian) silicates hosting magnetic and paramagnetic fine grained mineral inclusions. These igneous phase single crystals are likely to hold the most pristine record of Earth?s early magnetic field and yet to date very few reliable paleointensity measurements from Precambrian rocks have been made. The analytical sensitivity now available with a small bore SRM makes proposed measurements possible. The PI is in possession of numerous plagioclase separates from Precambrian dikes sampled around the word (e.g., the ~2.45 Ga Burakovka dikes (Russia), the ~2.9 Ga Munni-Munni intrusion and the ~2.42 Ga Widgiemooltha dikes (Western Australia), the ~2.37 Ga Bangalore dikes and the ~2.2 Ga Mahhubnagar dikes (India), and the ~1.1 Ga Portage Lake basalts (USA)) from previous NSF/EAR research support. The PI is well poised to immediately make use of the requested small bore SRM for NSF/EAR funded research on the nature of Earth?s early magnetic field with implications for Precambrian tectonics and the generation and early behavior of the geodynamo; the magnetic field which shields the Earth surface from the highly energized solar wind and allowed for the evolution of Earth?s biota. This instrument will be only the second of its kind in a U.S. academic laboratory. The infrastructural impacts of this acquisition are very significant for the U.S. paleomagnetic research community. The instrument will complement existing paleomagnetic analysis equipment in the PI?s lab and serve an active student research group including an active PI-undergraduate mentoring program at MTU.
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The Earth’s magnetic field is generated by convection of molten iron in the planet’s outer core. This process, or the geodynamo, is powered by density settling and heat of fusion of the crystallizing inner core. The Earth’s magnetic field can be well approximated by that of a dipole (i.e. bar magnet) positioned at Earth’s center and aligned with the rotational axis. This allows us to apply the dipole equations to reconstruct past positions of continents using the direction of ancient magnetic field recorded in rocks (fossil magnetism). It is well established that the field has had this dipolar geometry for at least 500 milion years, and that the field has been strong enough to provide magnetic shielding of the biosphere and atmosphere from solar radiation. However, the characteristics of geomagnetic field for the earlier time period (the Precambrian) remain poorly understood, especially the field strength(paleointensity). Determination of paleointensity becomes increasingly difficult with the age of rocks. Although the Precambrian represents more than 85% of the geological history, it is represented by less than 5% of the existing paleointensity data. The conventional approach of measuring paleointensity from the bulk rock samples often fails for the Precambrian rocks because of their geological and experimental alteration. In order to circumvent this problem, an alternative approach has been recently proposed to measure paleointensity from mm-size single silicate crystals containing minute magnetic inclusions. Such crystals are much less prone to alteration and may provide more reliable paleointensity data. However, their magnetic moments are very weak and require the use of very sensitive high-resolution magnetometers. In the frame of this project, the Earth Magnetism Laboratory of Michigan Technological University recently acquired an ultra-sensitive superconducting rock magnetometer which allows to perform paleointensity experiments on silicate crystals with high precision and accuracy. The acquisition of this instrument will support the PI in achieving one of his lifelong career research goals: to advance the understanding of early evolution of the Earth system through comprehensive investigation of the evolution of Earth’s magnetic field during the Precambrian. Paleointensity experiments on several Precambrian rock suites ranging in age between 1.1 and 2.9 Gyr are planned to be conducted in the nearest future. The new magnetometer will significantly increase the number of high-quality paleointensity determinations for the Precambrian, including the time periods for which no determinations of paleofield strength currently exist. On a broader scale, the extended capabilities of the instrument will enhance the research of PI’s graduate and undergraduate students.
