GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.2 GNGTS 2024 The presence of decimetric lava lithics and bombs in the hydromagmatc deposits associated with the Martgnano actvity and the outcrop of a scoria cone deposit on the lake southern border (Sotli et al., 2012), suggests the presence of a highly magnetzed lava plateau that was partly fragmented by the onset of the maar eruptve actvity at Martgnano. Anomaly D in Fig. 2 can represent the magnetc efect of the scoria cone deposits. The existence of a pre-eruptve 10- meter thick lava plateau is also documented for the nearby Stracciacappa maar crater (Moscatelli et al., 2021) (Fig. 1). The negatve magnetzaton contrast between Martgnano and surrounding SVD products is testfy by the two aeromagnetc profles reported in fgure 2, where a intense positve anomaly is observed along profle L1 and L2 at the northern border of the lake, mirroring the positve anomaly B of fgure 2 and indicatng the presence of higher magnetzed material separatng Martgnano and Straccicappa maars (fgure 1); this magnetc anomaly is not compatble with the presence of the low magnetzed hydromagmatc products outcropping in the northern rim of the Martgnano crater. Magnetc anomaly B in Figure 2 is therefore interpreted as the result of subsurface lava and pyroclastc products from the SVD which previously formed the topography of the pre-maar actvity. The geometry of magnetc anomaly B suggests a thinning of the magnetzed material and an inclined surface that deepens toward the center of the lake marking the contact surface between maar’s diatrema and the pre-maar products; The negatve intensity sub-circular magnetc anomaly observed in the central region of the crater lake (G in Fig. 2) represents the efect of low magnetzaton material; this zone can be interpreted as the area where the magnetzed pre-maar volcanic pile disappears due to the presence of the maar diatrema and inflling products.