Origin of the Pacific Jurassic quiet zone
Origin of the Pacific Jurassic quiet zone
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DOI：
10.1130/g22894.1
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发表时间：
2006-09
期刊：
影响因子：
5.8
通讯作者：
M. Tivey;W. Sager;Sang‐Mook Lee;M. Tominaga
中科院分区：
文献类型：
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作者：
M. Tivey;W. Sager;Sang‐Mook Lee;M. Tominaga
了解海洋磁异常记录对于构建全球地磁场、极性反转机制和长期地磁场行为的真实地球发电机模型至关重要。海洋磁异常记录中最不为人所知的部分之一，也是记录中最古老的部分，侏罗纪静区（JQZ），异常变得很弱，很难相互关联。JQZ存在的原因尚不清楚。有人认为，JQZ是一个真正的极性超时，类似于白垩纪正常超时。大陆磁性地层学研究表明，JQZ是一个快速极性反转，低场强，或两者兼而有之的时期。我们展示了太平洋侏罗纪地壳深拖调查的结果，证实了JQZ内存在磁异常。我们配合大洋钻探计划孔801 C（167.4马）的记录，并表明海底扩展磁异常存在于孔周围，并延伸到170马地壳。我们发现逆转率随着年龄的增加而增加，逆转率超过10转/百万年。在160 Ma和167 Ma。异常振幅减少记录从155 Ma，直到162 Ma，低振幅异常是很难相关。在167 Ma之前，异常恢复振幅并保持强劲，直到我们记录的170 Ma结束。因此，JQZ似乎是低振幅磁异常与快速场波动的组合，这可能是由于强度或极性变化。
Understanding the marine magnetic anomaly record is critical for constructing realistic geodynamo models of global geomagnetic field, polarity reversal mechanisms, and long-term geomagnetic field behavior. One of the least understood portions of the marine magnetic anomaly record is also the oldest part of the record, the Jurassic quiet zone (JQZ), where anomalies become weak and difficult to correlate. The reason for the existence of the JQZ is unclear. It has been suggested that the JQZ is a true polarity superchron, similar to the Cretaceous normal superchron. Continental magnetostratigraphic studies have suggested that the JQZ is a period of rapid polarity reversal, of low field intensity, or both. We show results of a deep-tow survey of Pacific Jurassic crust that confirms the existence of magnetic anomalies within the JQZ. We tie Ocean Drilling Program Hole 801C (167.4 Ma) into the record and show that seafloor-spreading magnetic anomalies are present around the hole and extend to 170 Ma crust. We find a rise in reversal rate with increasing age with reversal rates over 10 rev/m.y. at 160 Ma and at 167 Ma. Anomaly amplitudes decrease in the record from 155 Ma until 162 Ma, where low-amplitude anomalies are difficult to correlate. Prior to 167 Ma, anomalies regain amplitude and remain strong until the end of our record at 170 Ma. The JQZ thus appears to be a combination of low-amplitude magnetic anomalies combined with rapid field fluctuations, which could be due to either intensity or polarity changes.