Revised geochronology of the Neogene calc-alkaline volcanic suite in Sierra de Gata, Alboran volcanic province, SE Spain

Ar-40/Ar-39 step heating experiments were performed on biotites from seven andesites/dacites/rhyolites which represent the entire volcano-stratigraphi c range in a c. 125 km(2) area in Sierra de Gata. Each sample rendered well defined plateau shaped incremental Ar-39 release spectra which define a ti me span of c. 12-10.5 Ma for the volcanic activity. There appears to have b een a time gap in the volcanism, separating a basal section of c. 12-11.5 M a from a cover section of c. 11-10.5 Ma. The two samples from the basal sec tion constrain a weighed average age of 11.75 +/- 0.15(2 sigma) Ma and the five samples from the cover section of 10.70 +/- 0.15(2 sigma) Ma. This con trasts with earlier claims of c. 15-7 Ma for the whole spectrum, based main ly on K-Ar whole rock and 'groundmass' experiments. The c. 12-10.5 Ma age f or the calc-alkaline volcanism places it unequivocally after the late stage extensional tectonics (c. 24-17 Ma). This supports the currently available model for the Alboran volcanic province, which connects magma generation n ot to an active subduction zone of the collisional stage, but rather to a l ate stage anatectic event in the Betic-Ligurian lithosphere under influence of post-collisional lithospheric slab detachment.