Abstract

40Ar/39Ar step heating experiments were performed on biotites from seven andesites/dacites/rhyolites which represent the entire volcano‐stratigraphic range in a c. 125 km2 area in Sierra de Gata. Each sample rendered well defined plateau shaped incremental 39Ar release spectra which define a time span of c. 12–10.5 Ma for the volcanic activity. There appears to have been a time gap in the volcanism, separating a basal section of c. 12–11.5 Ma from a cover section of c. 11–10.5 Ma. The two samples from the basal section constrain a weighed average age of 11.75 ± 0.15(2σ) Ma and the five samples from the cover section of 10.70 ± 0.15(2σ) Ma. This contrasts with earlier claims of c. 15–7 Ma for the whole spectrum, based mainly on K–Ar whole rock and ‘groundmass’ experiments. The c. 12–10.5 Ma age for 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 Alborán volcanic province, which connects magma generation not to an active subduction zone of the collisional stage, but rather to a late stage anatectic event in the Betic–Ligurian lithosphere under influence of post‐collisional lithospheric slab detachment.

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