Clinopyroxene geobarometry of pyroxenitic xenoliths from Hyblean Plateau (SE Sicily, Italy)

Using density estimates for the sedimentary cover, crustal basement and mantle, and assuming that the crustal basement is essentially granitic, it is possible to estimate a maximum range of 34-55 km for the depth of magmatic segregation of coarse-grained pyroxenites. The medium-grained pyroxenites may have formed at shallower depths, in some cases perhaps as monomineralic clinopyroxenites. The most reliable P estimate (8 kbar) corresponds with a depth of approximately 28 km, matching the depth of the Moho discontinuity under this region of SE Sicily. Combination of clinopyroxene P estimates with T data based on two-pyroxene geothermometry suggests the existence of a high geothermal gradient comparable with those defined for environments dominated by advective heat-transfer mechanisms. The proposed P-T profile is consistent with petrological constraints (absence of garnet, presence of spinel) and with the palaeodynamic setting of the region.