Magnetic Intensities of Ocean-Floor Basalts: Electron Microscopy, Rock and Paleomagnetic Studies

海底岩石产生的磁异常导致了海底扩张模式和板块构造。磁性存在于新鲜玄武岩中的钛磁铁矿中，但随着地质时间的推移，钛磁铁矿氧化为钛磁铁矿。这种钛磁铁矿是否具有忠实地反映古代磁场的磁化强度，仍然是一个没有答案的问题。研究人员计划研究磁信号的衰减与年龄的关系。特别是，玄武岩的磁化强度（以及伴随而来的异常峰值）似乎在大约2000万年前逐渐减弱，在早第三纪和白垩纪时期，磁化强度逐渐增加。研究人员将研究氧化的速率和影响，未改变和氧化岩石的磁场强度，以及可能更古老的玄武岩可能具有由两个反平行分量组成的自然剩余磁化的想法，这两个分量是在连续的正常和反向极性间隔中获得的。将采用的方法包括古地磁和岩石磁技术以及氧化物的电子显微镜。这个项目将表明，磁场退化的原因是否需要重新评估全球极性时间尺度的细节，或者磁场强度变化是否是全球地磁场的一个函数。后一种可能性将使我们对地磁场的起源有新的认识，而这一点目前仍是争论不休的话题。

VanderVooEAR-0207257magnetic anomalies generated by ocean-floor rocks have led to sea-floor spreading models and plate tectonics. The magnetism resides in titanomagnetite in fresh basalts, but the titanomagnetite oxidizes to titanomaghemite over geological time. Whether this titanomaghemite carries a magnetization that faithfully reflects the ancient magnetic field, is still an unanswered question. The investigators plan to study the degradation of the magnetic signal as a function of age. In particular, the intensity of the magnetization of the basalts (and, concomitantly, the peak values of the anomalies) appears to show a gradual degradation up to some 20 million years ago, beyond which the intensity gradually increases for Early Tertiary and Cretaceous times. The researchers will be studying the rates and effects of oxidation, the magnetic intensity of unaltered and oxidized rocks, and the idea that perhaps older basalts may have a natural remanent magnetization that consists of two anti-parallel components, which were acquired during successive normal and reversed polarity intervals. The methods to be employed include paleomagnetic and rock magnetic techniques and electron microscopy of the oxides. This project will show whether the causes for magnetic degradation warrant a re-evaluation of the details of the global polarity time scale, or whether magnetic intensity variations are a function of the global geomagnetic field. The latter possibility would create new insights into the origins of the geomagnetic field that are currently the subject of much debate.