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

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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.