Constraints on the movement history of the Carboneras Fault Zone (SE Spain) from stratigraphy and 40Ar–39Ar dating of Neogene volcanic rocks

The Carboneras Fault Zone (CFZ) of SE Spain separates the volcanic Cabo de Gata terrain to the SE (accumulated over 18 to 6 Ma BP) from the tract of uplifted Alpine metamorphic basement blocks and post-orogenic basins that comprise the Betic Cordilleras to the NW. The CFZ cuts metamorphic basement and folded post-orogenic sediments and volcanic rocks, and acted as a conduit for upper Miocene calc-alkaline volcanic rocks to the surface. NW of the CFZ, unconformities and deformation episodes affect successive sedimentary formations of upper Miocene age (upper Serravallian through Messinian). CFZ movements are constrained stratigraphically by an unconformity within the volcanic sequence. Older, pre-faulting volcanic rocks are uptilted against the CFZ whilst the youngest volcanic rocks step across it. 40Ar–39Ar age determinations on amphibole crysts from the volcanic rocks show the main CFZ movements began 11–12 Ma BP and ended about 6 Ma. Lesser movement rates continue today. The CFZ is interpreted as part of a transform fault system separating NE–SW stretched and NW–SE shortened crust deformed above a southwestward-retreating subducted slab, from a less deformed terrain lying to the SE. Locally, total offset on the CFZ may be up to 40 km but is at least 15 km.