Subsidence analysis on the Sardinian margin and the central Tyrrhenian Basin: Thermal modelling and heat flow control; deep structure implications

The subsidence of the Tyrrhenian Basin is analysed based on numerous MCS reflection data and related seismic velocities, and calibrated using subsidence curves versus time at ODP Leg 107 sites 654 and 652 on the Sardinian margin. Two main phases of rifting are clearly defined for the margin-basin evolution: the first, beginning at 7 Ma, split the Sardinian-Calabrian margins, the second, beginning at 5 Ma formed the Central oceanic subbasins.Thermal models, based on thinned crust geometry from reflection-refraction data, are used which consider both vertical and horizontal conduction over time along a NW-SE transect across the entire Tyrrhenian Basin from Sardinia to Calabria. In general, there is a close agrrement between the predicted and the observed surface heat flow and the rate of subsidence over time. However, within the oceanic domain an initial subsidence must be chosen about 1000 m greater than observed on typical spreading centers, i.e., at about 3500 m as postulated in numerous back-arc basins.Thermal models, constrained by subsidence analysis and gravity observations, imply a large difference for the Moho depth beneath the Sardinian margin as determined after refraction seismic experiments. The upper mantle, hot but with high density, would be situated much higher than is postulated by seismic data and probably includes 7.3–7.4 km/s velocity layers previously interpreted as deep crustal layers.