Geomagnetic Paleointensity During Anomolous Field Behavior (Mid-Jurassic)

在太平洋侏罗纪大洋玄武岩中发现了一个令人兴奋的地磁场行为。在400米的玄武岩序列中，观测到了地磁极性的连续变化。观测到了六个极性“间隔”，大致相当于每50000年一次的地磁场反转。如此快速、持续的反转行为以前从未被观察到。约170 Ma的洋壳未发生明显变化(类似于0~20 Ma的大洋玄武岩)。对于未改变的洋壳，玄武岩的磁场强度正常到略高，微观探测工作表明，这不是钛磁铁矿剩磁载体不寻常化学作用的结果。在400米的海面上有大量的玻璃，通常保存着原始的钛磁铁矿。在这种不同寻常的磁场行为中，丰富的玻璃提供了检测地磁场强度的机会。在不断变化的极性记录中，还存在许多中间方向的间隔，包括预计地磁场强度最低的零倾角间隔。在连续变化的磁场行为和中间和零倾斜方向的记录中的玻璃丰度允许在这种不寻常的定向行为期间询问地磁场的强度。将测量每个“极性”状态和存在玻璃的所有中间方向间隔的古强度。这一结果有望提供有关地磁场在如此快速的时间尺度上变化的能力的信息。这些结果应该会为约束地磁发电机理论提供数据。

EAR-0126561Maureen B. SteinerAn exciting discovery of geomagnetic field behavior was made in Jurassic oceanic basalts of the Pacific Ocean. Continuous change of geomagnetic polarity was observed in a four hundred meter basalt sequence. Six polarity "intervals" were observed, corresponding to geomagnetic field reversals roughly once every 50,000 years. Such fast, continuously reversing behavior has never before been observed. The ~170 Ma oceanic crust is remarkably unaltered (similar to 0-20 Ma age oceanic basalt). Magnetic intensities of the basalt are normal to slightly high for unaltered oceanic crust, and microprobe work shows that this is not the result of an unusual chemistry of the titanomagnetite remanence carriers. An abundance of glass, which commonly preserves pristine titanomagnetite is present throughout the 400 m. The glass abundance provides the opportunity to examine geomagnetic field intensity during this unusual field behavior. In the record of constantly changing polarity, numerous intervals of intermediate directions also are present, including intervals of zero inclination at which geomagnetic field intensity would be expected to be lowest. The glass abundance in a record of continuously changing field behavior and the intermediate and zero-inclination directions allow interrogation of the intensity of the geomagnetic field during this unusual directional behavior. Paleointensities will be measured for each "polarity" state and for all intermediate-direction intervals for which glass is present. The result is expected to provide information about the geomagnetic field's ability to change on such a fast time scale. The results should provide data to help constrain geomagnetic dynamo theory.