Abstract
We analyze a wide gravity low in the Campania Active Volcanic Area and interpret it by a large and deep source distribution of partially molten, low-density material from about 8 to 30 km depth. Given the complex spatial-temporal distribution of explosive volcanism in the area, we model the gravity data consistently with several volcanological and petrological constraints. We propose two possible models: one accounts for the coexistence, within the lower/intermediate crust, of large amounts of melts and cumulates besides country rocks. It implies a layered distribution of densities and, thus, a variation with depth of percentages of silicate liquids, cumulates and country rocks. The other reflects a fractal density distribution, based on the scaling exponent estimated from the gravity data. According to this model, the gravity low would be related to a distribution of melt pockets within solid rocks. Both density distributions account for the available volcanological and seismic constraints and can be considered as end-members of possible models compatible with gravity data. Such results agree with the general views about the roots of large areas of ignimbritic volcanism worldwide. Given the prolonged history of magmatism in the Campania area since Pliocene times, we interpret the detected low-density body as a developing batholith.
Highlights
The Campania Plain, Southern Italy, is a Plio-Quaternary, NW–Sorrento Peninsula (SE) trending, 2000 km[2] wide graben, bordered by Mesozoic limestone/dolostone mountains (Fig. 1a)
The wide gravity low (Fig. 2a) denotes the existence of a mass defect within the deep crustal volume beneath the onshore and offshore areas of the Gulf of Naples. The source of this gravity low imaged by Depth from Extreme Points (DEXP) (Fig. 2b) is distributed from 7–8 km to depths below the Moho, the latter estimated at 20–25 km beneath the Campania Active Volcanic Area[22]
We have here proposed two different models for the gravity low of the investigated area, which try to honor the current volcanological and petrological knowledge. Both density distributions can be considered as end-members of possible models compatible with gravity data
Summary
We use the gravity data derived from the Bouguer Gravity Anomaly Map of Italy published by the CNR21 with 1 km data spacing. Using such volcanological and petrological evidences, potassic primary magmas should have generated not less than 5,400 km[3] of ultramafic and mafic cumulates, together with residual shoshonitic liquids that migrate upward through the lower crust (Table 1, Methods) All this information provide a number of constraints to the gravity modeling, summarized as follows (see Methods): (i) the regional geotherm; (ii) the volume of cumulates generated by magma segregation within the body source; (iii) the composition of the country rocks and their density vertical profile within the intruded crust; (iv) the concentration of fluids based on recent studies. The wide gravity low (Fig. 2a) denotes the existence of a mass defect within the deep crustal volume beneath the onshore and offshore areas of the Gulf of Naples The source of this gravity low imaged by DEXP (Fig. 2b) is distributed from 7–8 km to depths below the Moho, the latter estimated at 20–25 km beneath the Campania Active Volcanic Area[22]. This body has a volume of about 40,000 km[3] and a negative density contrast (varying from −0.26 to −0.06 g/cm3) with respect to the country rocks
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