Magnetic field reversals recorded by partial thermomagnetic remanences of pyrrhotite in low grade metamorphic limestones

低品位变质灰岩中磁黄铁矿的部分热磁剩磁记录的磁场反转

• 批准号: 5251316
• 负责人: Professor Dr. Erwin Appel
• 金额: --
• 依托单位: Arbeitsgruppe Geophysik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2000
• 资助国家: 德国
• 起止时间: 1999-12-31 至 2004-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5251316?language=en
• 关键词: Magnetic; field; reversals; recorded; partial

The Earth`s magnetic field during a reversal is usually studied in lava flows and sediments. Both rock types provide important knowledge but also have their specific uncertainties. This proposal introduces a further recording process: partial thermomagnetic remanences (pTRM) in low grade metamorphic limestones. In many limestones, pyrrhotite with a Curie temperature around 320°C is formed at elevated temperatures and acquires a TRM during cooling. Directional behaviour and palaeointensity of the Earth`s field may be revealed by unblocking of (p) TRM(s) during thermal demagnetization. Our aims are to study non-antipodality and palaeointensity before and after a reversal and - if cooling rates are high enough (superior to 1°/kyr) - also during a reversal. A nearly continuous record may be achieved using temperature intervals of pTRM unblocking as a measure of geological time. Experiments with artificial pTRMs have to be conducted to allow translation of laboratory unblocking into pTRM recording. Samples will be taken from the Tethyan and Lesser Himalaya, where stable pyrrhotite pTRMs with normal and reverse components are proved. Besides the pTRM studies, work on dating and metamorphic temperatures will be also included to get a better insight into the age of remanence acquisition and to confirm that the Curie temperature was exceeded.

地球逆转过程中的磁场通常是在熔岩流和沉积物中研究的。这两种岩石类型都提供了重要的知识，但也有其特定的不确定性。提出了一种进一步的记录过程：低变质灰岩中的部分热磁剩磁(PTRM)。在许多石灰岩中，居里温度在320℃左右的磁黄铁矿是在高温下形成的，并在冷却过程中获得TRM。(P)TRM(S)在热退磁过程中的解堵可以揭示地磁场的方向性行为和古强度。我们的目标是研究反转前后的非对足性和古强度--如果冷却速度足够高(优于1°/KYR)--也在反转期间。利用PTRM解堵的温度间隔作为地质时间的量度，可以获得几乎连续的记录。必须进行人造pTRM的实验，以允许将实验室解锁转换为PTRM记录。样品将从特提斯和小喜马拉雅地区采集，在那里证实了具有正反向成分的稳定的磁黄铁矿pTRM。除了PTRM研究，还将包括测年和变质温度方面的工作，以更好地了解剩磁获取的年龄，并确认超过居里温度。