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

地球磁场在逆转期间通常在熔岩流和沉积物中进行研究。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。该建议介绍了进一步的记录过程：部分热磁剩磁（pTRM）在低级变质石灰岩。在许多石灰岩中，居里温度约为320°C的磁黄铁矿在高温下形成，并在冷却过程中获得TRM。地球磁场的方向性和古强度可以通过热退磁过程中（p）TRM（s）的解除阻塞来揭示。我们的目标是研究反转前后的非对跖性和古强度，如果冷却速率足够高（上级达到1°/kyr），也研究反转期间的非对跖性和古强度。使用pTRM解阻塞的温度间隔作为地质时间的量度，可以实现几乎连续的记录。必须进行人工pTRM的实验，以允许将实验室解除封闭转化为pTRM记录。样品将取自特提斯和小喜马拉雅，在那里证明了具有正向和反向分量的稳定磁黄铁矿pTRM。除了pTRM研究外，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得的年龄，并确认居里温度被超过。

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.