Ar-40/Ar-39 age of the Cabo de Gata volcanic series and displacements on the Carboneras fault zone, SE Spain

The SW-NE-trending Carboneras fault zone of SE Spain separates a terrain co mprising uplifted massifs of the metamorphic basement of the Betic Cordille ras and intervening Neogene sedimentary basins, from the Cabo de Gata volca nic series. Along the southeastern boundary of the Carboneras fault, Burdig alian marls and tuffs,, mark the beginning of the volcanic episode, rest un conformably on the basement, and were tilted to the vertical during the ear liest stages of movement on the fault zone. Ar-40/Ar-39 dating of hornblend e grains and igneous clasts from the tuffs constrain the onset of the volca nic episode at 21 Ma, some 4 Ma earlier than previously reported. Volcanic rocks higher in the sequence that overstep unconformably onto the southern edge of the fault zone yielded an age of 11 Ma, thus constraining the earli est episode of motion on the fault zone between these age limits. The main phase of left-lateral strike-slip movement on the Carboneras fault may be l ater than this time. Movements on more northerly strands of the fault zone, including the uplift of the Sierra Cabrera basement block to the NW, conti nued at least through Pliocene times. The onset of volcanism is broadly coe val with the unroofing of the orogen by extensional collapse, and supports earlier inferences of very rapid rates of uplift and cooling of the basemen t rocks.