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

Abstract

The SW–NE-trending Carboneras fault zone of SE Spain separates a terrain comprising uplifted massifs of the metamorphic basement of the Betic Cordilleras and intervening Neogene sedimentary basins, from the Cabo de Gata volcanic series. Along the southeastern boundary of the Carboneras fault, Burdigalian marls and tuffs, mark the beginning of the volcanic episode, rest unconformably on the basement, and were tilted to the vertical during the earliest stages of movement on the fault zone. 40 Ar/ 39 Ar dating of hornblende grains and igneous clasts from the tuffs constrain the onset of the volcanic 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 earliest 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 later than this time. Movements on more northerly strands of the fault zone, including the uplift of the Sierra Cabrera basement block to the NW, continued at least through Pliocene times. The onset of volcanism is broadly coeval with the unroofing of the orogen by extensional collapse, and supports earlier inferences of very rapid rates of uplift and cooling of the basement rocks.