Further evidence for low intensity of the geomagnetic field during the early Cretaceous time: using the modified Shaw method and microwave technique
Further evidence for low intensity of the geomagnetic field during the early Cretaceous time: using the modified Shaw method and microwave technique
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DOI：
10.1111/j.1365-246x.2004.02253.x
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发表时间：
2004-05
影响因子：
2.8
通讯作者：
Yongxin Pan;M. Hill;R. Zhu;J. Shaw
中科院分区：
文献类型：
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作者：
Yongxin Pan;M. Hill;R. Zhu;J. Shaw
我们报告了使用中国东北玄武岩（K/Ar年龄，125 - 120 Ma），使用改进的Shaw方法结合微波技术进行的新的绝对古强度估计。古强度实验样品的选择主要是基于其良好的热磁曲线可逆性和单一的主磁化特征。用改进的Shaw法测得10台制冷机组的45个样品中有28个样品的虚偶极矩为（3.1 ± 1.0）× 1022 Am 2，用微波法测得20个样品中14个样品的虚偶极矩平均值为（2.9 ± 0.9）× 1022 Am 2。用改进的Shaw方法和微波技术的结果表明，这些熔岩记录的地磁场强度很低。这是在协议与以前的结果相同的时间间隔获得的Thellier方法与部分热剩磁（p-TRM）检查。事实上，不同的技术提供了定性兼容的低古强度的结果提供了更大的信心，弱字段功能之前看到的白垩纪正常超时（CNS）是由玄武岩记录的实际字段的结果，而不是人工制品的方法/分析。这项研究还表明，微波技术可以用于非常古老的玄武岩。
SUMMARY We report new absolute palaeointensity estimates using basalts from northeastern China (K/Ar age, 125‐120 Ma) using the modified Shaw method in conjunction with the microwave technique. Samples for the palaeointensity experiments were selected mainly based on their good reversibility of thermomagnetic curves and single primary magnetization characteristics. Using the modified Shaw method, 28 out of 45 measured samples from 10 cooling units give a virtual dipole moment of (3.1 ± 1.0) × 10 22 Am 2 , and the microwave technique using 14 acceptable determinations (out of 20 measured) give an average value of (2.9 ± 0.9) × 10 22 Am 2 . Results using both the modified Shaw method and the microwave technique demonstrate that the geomagnetic field strength recorded by these lavas was low. This is in agreement with previous results of the same time interval obtained by the Thellier method with partial thermal remanence (p-TRM) checks. The fact that different techniques give qualitatively compatible low palaeointensity results provides greater confidence that the weak field features seen just prior to the Cretaceous normal superchron (CNS) are the result of the actual field recorded by the basalts as opposed to artefacts of the method/analysis. This study also demonstrates that the microwave technique can be used for very old basalts.