Palaeointensity study of the Hawaiian 1960 lava: implications for possible causes of erroneously high intensities
Palaeointensity study of the Hawaiian 1960 lava: implications for possible causes of erroneously high intensities
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DOI：
10.1046/j.1365-246x.2003.01909.x
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发表时间：
2003-04
影响因子：
2.8
通讯作者：
Y. Yamamoto;H. Tsunakawa;H. Shibuya
中科院分区：
文献类型：
--
作者：
Y. Yamamoto;H. Tsunakawa;H. Shibuya
摘要
已知1960年夏威夷熔岩有时产生的古强度比国际地磁参考场（36.2微特斯拉）更高。为了阐明原因，我们对来自该熔岩的19个岩芯进行了古强度测量的综合研究。根据各种岩石磁学分析，它们依据热液氧化程度被分为三组。在科埃版本的泰利耶方法中，观测到平均古强度显著更高，为49.0±9.6微特斯拉（N = 17），这与先前的研究相似。这些古强度显示出对氧化指数的依赖性，这可以通过熔岩自然冷却阶段热化学剩磁（TCRM）的获得来解释。尽管通常很难区分热化学剩磁和热剩磁（TRM），但在泰利耶实验中对天然剩磁（NRM）和热剩磁进行低温退磁（LTD）处理似乎使我们能够检测到热化学剩磁对天然剩磁的影响。另一种用于检测热化学剩磁的可能工具是肖方法的双加热技术（DHT）与低温退磁相结合（低温退磁 - 双加热技术肖方法）。它给出了更好的平均值39.4±7.9微特斯拉（N = 9），尽管成功率低得多。大多数不合适的结果通过双加热测试、非滞后剩磁（ARM）校正和低温退磁处理的组合被筛选出来。如果进一步排除两个异常值，平均值提高到35.7±3.3微特斯拉（N = 7），这与预期强度非常吻合。两种方法的结果都强调了从熔岩流中不同氧化程度的部分采集和测量样本的重要性。
SUMMARY It is known that the Hawaiian 1960 lava sometimes yields higher palaeointensities than the IGRF (36.2 µT). In order to clarify the causes, we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava. According to various rock magnetic analyses, they are classified into three groups with degrees of the deuteric oxidation. In Coe’s version of the Thellier method, a significantly larger mean palaeointensity of 49.0 ± 9.6 µ T( N = 17) was observed similar to previous studies. These palaeointensities showed a dependence on the oxidation indices, which can be explained by thermochemical remanent magnetization (TCRM) acquisition during the natural cooling stage of the lava. Although it is generally difficult to distinguish the TCRM from thermoremanent magnetization (TRM), a lowtemperature demagnetization (LTD) treatment on NRM and TRM in the Thellier experiment seems to allow us to detect the influence of the TCRM on NRM. Another possible tool for TCRM detection is the double-heating technique (DHT) of the Shaw method combined with LTD (LTD‐DHT Shaw method). It gave a better average of 39.4 ± 7.9 µ T( N = 9), though the success rate was much lower. Most of the inappropriate results were screened by a combination of the double-heating test, the ARM correction and the LTD treatment. If two outliers are further excluded, the average is improved to be 35.7 ± 3.3 µ T( N = 7), which agrees well with the expected intensity. The results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow.