陨石云带形成作为古磁场强度和微行星冷却速率的定量指示
Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals
摘要：
缓慢冷却的富铁陨石中的金属微观结构反映了其母星子的热历史和磁历史。特别令人感兴趣的是多云区，富Ni岛在Ni贫乏基质内的纳米级共生体，其通过亚稳分解在低于350°C下形成。这些岛屿的大小一直被认为反映了陨石母体的低温冷却速率。然而，一直缺乏一个能够提供定量的冷却速率估计岛屿的大小。此外，这些岛屿也能够保留记录的环境磁场，因为他们的成长，但一些关键的物理参数所需的恢复可靠的paleointensity估计从这些岛屿的磁性测量一直制约不佳。为了解决这两个问题，我们提出了一个数值模型的结构和组成的演变的多云区作为一个功能的冷却速率和当地的组成。我们的模型产生的岛屿大小与目前测量的大小一致。该模型能够大大改善古强度估计和相关的不确定性的校准。特别是，我们现在可以准确地量化与岛屿数量有限相关的统计不确定性以及记录时岛屿大小的不确定性。我们使用这种新的理解，重新审视古强度从以前的开创性古地磁研究的多云区。我们表明，这些可能被高估，但仍然需要大量的磁场已经存在于其母体。我们的模型还允许我们估计冷却速度低于10000°C My-1的陨石的绝对冷却速率。我们演示了如何这些冷却速率估计可以唯一地限制陨石母体的低温热历史。
英文摘要：
Metallic microstructures in slowly-cooled iron-rich meteorites reflect the thermal and magnetic histories of their parent planetesimals. Of particular interest is the cloudy zone, a nanoscale intergrowth of Ni-rich islands within a Ni-poor matrix that forms below 350°C by spinodal decomposition. The sizes of the islands have long been recognized as reflecting the low-temperature cooling rates of meteorite parent bodies. However, a model capable of providing quantitative cooling rate estimates from island sizes has been lacking. Moreover, these islands are also capable of preserving a record of the ambient magnetic field as they grew, but some of the key physical parameters required for recovering reliable paleointensity estimates from magnetic measurements of these islands have been poorly constrained. To address both of these issues, we present a numerical model of the structural and compositional evolution of the cloudy zone as a function of cooling rate and local composition. Our model produces island sizes that are consistent with present-day measured sizes. This model enables a substantial improvement in the calibration of paleointensity estimates and associated uncertainties. In particular, we can now accurately quantify the statistical uncertainty associated with the finite number of islands and the uncertainty on their size at the time of the record. We use this new understanding to revisit paleointensities from previous pioneering paleomagnetic studies of cloudy zones. We show that these could have been overestimated but nevertheless still require substantial magnetic fields to have been present on their parent bodies. Our model also allows us to estimate absolute cooling rates for meteorites that cooled slower than 10000°C My-1. We demonstrate how these cooling rate estimates can uniquely constrain the low-temperature thermal history of meteorite parent bodies.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
