Insights on the spreading of Tyrrhenian Sea from the magnetic anomaly pattern

We analyse the pattern of magnetic anomalies in the Tyrrhenian back-arc basin by a simple and objective method that is able to simplify the readability of the maps and to safely identify reversely magnetized sources. This analysis is useful to better understand the reliability of recent studies indicating the presence of striped, ‘mid-ocean like’, magnetic anomalies in this small basin, from which spreading velocities have been calculated. Our results show that in the Vavilov and Marsili sub-basins reversely magnetized bodies are actually present, but their areal distribution is rather irregular. The resulting pattern of normally and reversely magnetized bodies does not fit with an ocean-like central expansion model. Instead, the distribution of magnetic sources may suggest that the crustal tearing induced by extension processes is not concentrated only beneath the seamounts, but may have in different times involved different areas of these sub-basins.