Evaluation of the multispecimen parallel differential pTRM method: a test on historical lavas from Iceland and Mexico
Evaluation of the multispecimen parallel differential pTRM method: a test on historical lavas from Iceland and Mexico
复制标题
DOI：
10.1111/j.1365-246x.2008.03740.x
复制
发表时间：
2008-05
影响因子：
2.8
通讯作者：
D. Michalk;A. Muxworthy;H. Böhnel;J. Maclennan;N. Nowaczyk
中科院分区：
文献类型：
--
作者：
D. Michalk;A. Muxworthy;H. Böhnel;J. Maclennan;N. Nowaczyk
摘要 获得可靠的地磁古强度（PI）估计值仍然是一个困难的目标。 PI 研究中最常见的技术是基于 Thellier 方法的各种修改，但失败率高且不确定性大。此外，只有遵守严格标准的岩石才能产生忠实的 PI 估计值。一般来说，磁性颗粒必须具有单畴尺寸，磁化必须是热剩磁，并且在实验室实验期间必须避免磁性载体的化学改变。最近，提出了一种获取 PI 的新方法，该方法基于两个历史熔岩和三个模拟实验的结果，假设该方法与磁畴状态无关。该方法使用多个样品，在中等温度下仅进行一次加热步骤。在这里，我们对来自冰岛和墨西哥的 11 个历史熔岩进行了多样本并行微分 pTRM 方法的测试，从中可以通过磁力观测数据或磁场模型获知实际磁场强度。我们的结果表明，多样本平行微分 pTRM 方法后的大多数 PI 估计产生的结果在与预期强度的误差范围内非常接近或无法区分，从而在很大程度上证实了最初研究的结果，然而，总体上存在小的高估，我们表明这与多域材料有关。与对来自五个冰岛熔岩流的姊妹样本进行的泰勒型 PI 实验相比，平均多样本 PI 更接近实际场强。由于实验室引起的改变，来自一个熔岩的样本以低居里温度为特征，未能通过泰利尔方法，但这里的多样本方法返回了合理的 PI。尽管有证据表明该方法并不完全独立于磁域状态，如之前提出的，我们认为该方法是未来 PI 研究中的一个有价值的替代方法。
SUMMARY Obtaining reliable geomagnetic palaeointensity (PI) estimates is still a difficult objective. Most common techniques in PI studies are based on various modifications of the Thellier method, but high failure rates and large uncertainties are common. Furthermore, only rocks which obey stringent criteria are assumed to yield faithful PI estimates. In general, magnetic particles must be of single domain size, the magnetization must be a thermoremanent magnetization and chemical alteration of magnetic carriers must be avoided during the laboratory experiment. Recently, a new method for obtaining PIs was proposed, which, on the grounds of results from two historic lavas and three simulated experiments, is assumed to be independent of magnetic domain state. This method uses multiple samples subjected to only one heating step at moderate temperatures. Here we present a test of the multispecimen parallel differential pTRM method on 11 historical lavas from Iceland and Mexico, from which the actual field intensity is known, either from magnetic observatory data, or from magnetic field models. Our results show, that the majority of PI estimates after the multispecimen parallel differential pTRM method yielded results that are very close or indistinguishable within the range of error from the expected intensity and thus largely confirm the findings from the initial study, however, there is in general a small overestimate, which we show is associated with multidomain material. When compared to a Thellier-type PI experiment, carried out on sister samples from five Icelandic lava flows, the average multispecimen PI is closer to the actual field intensity. Samples from one lava, characterized by low Curie temperatures, failed the Thellier approach due to laboratory-induced alteration, but here the multispecimen method returned a reasonable PI. Even though there is evidence that the method is not entirely independent of magnetic domain state, as previously proposed, we regard this method as a valuable alternative in future PI studies.