Ground-truthing magnetic recording in meteorites

太阳系中的原始天体是否拥有内部发电机是理解早期行星形成的动力学和时间的基本约束。对几颗陨石的古强度研究表明，它们的宿主行星拥有的磁场与现在的地球磁场相差一个数量级。古强度数据的解释在很大程度上依赖于磁性载体的磁性的基础知识，如单域到多域尺寸阈值或饱和磁化强度如何随粒度的变化而变化，但对陨石中一些主要磁性记录器的关键参数知之甚少：铁镍合金。此外，大多数陨石在其历史上经历了一定程度的冲击，但即使是非常小的应力对古强度数据的后果知之甚少。我们希望通过磁性表征Fe-Ni合金作为粒度的函数，并通过确定绝对和相对古强度数据是如何被低于岩石学上可观察到的应变水平（< 4-5 GPa）的偏差来填补这些空白。例如，我们的初步工作表明，0.6 GPa的外加应力将使单域磁铁矿岩石的绝对古强度估计值降低46%。一般来说，古地震强度测定在测量精度和人类投入过多时间方面具有固有的缺点。我们打算通过扩展和改进我们的全自动磁工作站SushiBar来克服这些限制。

Whether primordial bodies in the solar system possessed internally-generated dynamos is a fundamental constraint to understand the dynamics and timing of early planetary formation. Paleointensity studies on several meteorites reveal that their host planets possessed magnetic fields within an order-of magnitude of the present Earth’s field. Interpretation of paleointensity data relies heavily on fundamental knowledge of the magnetic properties of the magnetic carriers, such as the single to multidomain size threshold or how the saturation magnetization varies as a function of grain size, yet very little knowledge exists about these key parameters for some of the main magnetic recorders in meteorites: the iron-nickel alloys. Moreover, most meteorites have experienced some amount of shock during their histories, yet the consequence of even very small stresses on paleointensity data is poorly known.We wish to fill these gaps by magnetically characterizing Fe-Ni alloys as a function of grain size and by determining how absolute and relative paleointensity data are biased by strain levels lower than those petrologically observable (< 4-5 GPa). For example, our preliminary work shows that an imposed stress of 0.6 GPa will reduce absolute paleointensity estimates by 46% for single domain magnetite-bearing rocks. In general, paleointensity determinations possess inherent disadvantages regarding measurement precision and the inordinate amount of human time investment. We intend to overcome these limitations by extending and improving our fully automated magnetic workstation known as the SushiBar.