Long Term Variations in Geomagnetic Intensity From Layered Intrusions

GEE 0087551地球磁场强度记录跨越了适合行星演化的时间尺度--数亿至数十亿年--是关于地球及其地球发电机早期发展的重要信息来源。层状侵入岩的古地磁提供了这种类型的记录。初步数据表明，许多来自层状侵入体的岩石保留了由单域磁铁矿携带的原始热磁--这是研究古强度的理想情况。大型侵入杂岩的缓慢冷却可能会平均地磁场方向和强度的短期变化。如果仔细考虑缓慢冷却和剩磁各向异性的影响，层状侵入岩可能会产生高质量的古强度测定。研究人员提议对层状侵入体的样品进行三套相关的实验：(1)利用从太古宙Stillwater复合体(美国蒙大拿州)收集的定向样品和Stillwater矿业公司的钻芯更完整地研究古强度变化；(2)对大约15个其他层状侵入体的样品进行古强度实验；以及(3)测试以确定大型缓慢冷却的深成岩块平均地磁场变化的空间和时间尺度。

Gee 0087551 Records of geomagnetic intensity that span time scales appropriate to planetary evolution -- hundreds of millions to billions of years - are important sources of information about the early development of the Earth and of its geodynamo. The paleomagnetism of layered intrusive rocks provides this type of record. Preliminary data suggest that many rocks from layered intrusions retain primary thermoremanence carried by single-domain magnetite -- an ideal situation for paleointensity studies. The slow cooling of large intrusive complexes is likely to average short-term variations in the direction and intensity of the geomagnetic field. Providing that care is taken to account for the effects of slow cooling and remanence anisotropy, layered intrusive rocks will likely yield high-quality determinations of paleointensity. The investigators propose three related sets of experiments on samples from layered intrusions: (1) a more complete study of paleointensity variations using their collection of oriented specimens from the Archean Stillwater Complex (Montana, USA) and drill cores from the Stillwater Mining Company; (2) paleointensity experiments on samples from approximately 15 other layered intrusions; and (3) tests to determine the spatial and temporal scales over which large, slowly-cooled plutons average geomagnetic field variations.