Formation of volcanic ash soils in the Matese Mountains of southern Italy

Over the past 40 ka, there have been many explosive eruptions in southern Italy from Campi Flegrei that have dispersed pyroclastic material in the southern Apennines surrounding the Matese Massif . A detailed mineralogical study was conducted on 5 pedons sampled on the Matese Massif to study volcanic ash soil genesis. All pedons contained vermiculite, mica, kaolinite and some interstratified mica-kaolinite. The diffraction patterns presented weak peaks, indicating a low mineral content and the presence of materials that did not diffract strongly, most likely allophane and unweathered volcanic glass and sanidine. The mica was most likely primary mica that crystallized along with the sanidine. The vermiculite was a weathering product of the mica. We assume that the finest ash cools faster, resulting in a glass, whereas the larger particles cool slower, resulting in sanidine and mica. Sanidine and mica weathering released K and Na ions, which leached from the profile, resulting in halloysite crystallization. We also identified gibbsite in the deepest horizons of 2 profiles. The sequence of pyroclastic deposits and the mineralogical evidence demonstrate the important contribution of the Campi Flegrei pyroclastic products on volcanic ash soil genesis in the southern Apennines.