Missing Basement
Apart from the controversial situation described below the M. Alburno massif (i.e., interpretations of Menardi Noguera and Rea, 2000 vs. Mazzotti et al., 2000), there is a wide agreement that the sedimentary covers belonging to the Apennine Carbonate Platform and to the Lagonegro-Molise basin are completely detached from their original basement.
To quantitatively assess the amount of missing crystalline basement, the pre-deformational width of the Apennine platform and of the Lagonegro basin has been estimated assuming that an equivalent amount of crystalline basement was originally situated below these domains (Scrocca et al., 2005)
To get this result, line lengths of key-bed, which show little penetrative deformation and preserved hanging wall and footwall cutoffs, have been computed for the Apennine Carbonate Platform (i.e., top Jurassic) and the Lagonegro basinal units (i.e., top Late Triassic corresponding to the top of the” Calcari con Selce” Formation) on the cross-section proposed in figure 4.
This simplified approach is obviously affected by some approximation (e.g., pressure solution phenomena, strike slip tectonics or polyphase deformation have not been considered) but it provides a useful first order estimate. The resulting total length of the missing crystalline basement could be estimated in the range of 190-210 km (Fig. 8), with about 70-80 km originally located below the Apennine carbonate platform and 120-130 km below the Lagonegro basin (in agreement with the result of the detailed tectonic modelling of the Lagonegro units).
Figure 8. Missing basement
Available well and seismic data show that the sedimentary covers belonging to the Apennine Carbonate Platform and to the Lagonegro-Molise basin are completely detached from their original basement. The amount of missing crystalline basement, originally located below these domains, has been approximately evaluated along our regional cross-section applying key-bed balancing techniques to derive the pre-deformational width of the sedimentary cover. By means of key-bed balancing techniques applied to the regional cross section, the amount of missing crystalline basement is estimated to be about 190-210 km (modified after Scrocca et al., 2005).
This piece of evidence implies that during the eastward roll-back of the subduction hinge the sedimentary covers of both the Apennine Carbonate Platform and the Lagonegro-Molise basin have been off-scraped from the subducting Apulo-Adriatic lithosphere (e.g., Roure et al., 1991; Doglioni et al., 1996]. Moreover, the same tectonic process, together with the absence of documented basement slice in the accretionary prism, requires that the crystalline basement originally underlying these sedimentary cover must have disappeared in the subduction zone.