Evaluating Rifean Corridor Closure using Detrital Zircon Sediment Provenance of the Taza-Guercif Basin, Morocco

In the late Miocene, the connection between the Mediterranean Sea and Atlantic Ocean was tectonically severed leading to severe evaporative draw down of Mediterranean sea level such that the entire basin was desiccated or near desiccated in an event from ~5.96-5.33 Ma known as the Messinian Salinity Crisis (MSC). The MSC sequestered 6% of global ocean salinity into evaporite deposits, created a deep, dry and hot basin that altered global atmospheric circulation, opened passageways for mammal migration between Europe, Africa and Arabia and ended in the largest flood observed in the geologic record. The combined effects of the Messinian Salinity Crisis make it the most important oceanic event in the last 20 million years, yet despite the dramatic ramifications of the MSC, the exact nature of its cause has remained both elusive and controversial. By examining the sedimentary provenance of Rifean Corridor, this research evaluates the progression of corridor closure and the tectonic context of the initiation of the Messinian Salinity Crisis. The difficulty in evaluating the progression of closure is due to the tectonic complexity of the Africa-Eurasia convergent plate boundary in north-central Morocco. The shortening associated with the tectonic convergence is accommodated by two genetically and tectonically distinct orogenic systems, the Rif and Atlas mountain belts, which lie in juxtaposition to the slab-rollback dominated Alboran Sea. The basins of the Rifean corridor lie between these two orogens and as such shortening and uplift associated with either or both ranges could be the cause of the corridor closure. Several hypotheses have been posited for the tectonic controls on basin emergence including slab-rollback related delamination on the Alboran margin, domal uplift of the Middle Atlas as well as a more traditional propagation of the Rifean orogenic wedge. This research provides the first quantitative provenance data for the Taza-Guercif basin in the form of LA-ICP-MS detrital zircon analysis of 10 samples from the basin-fill and 3 samples from two separate domains within the Rif. The new data reveal a lack of dramatic shifts in provenance within the basin-fill tied to corridor closure but instead reveal more subtle changes in peak zircon ages. Peak age shifts from 600 Ma to 700 Ma periodically within the strata in both open marine marls and within turbidites derived from the Middle Atlas in a pattern consistent with changes in basin bathymetry. Basin samples show an age-distribution consistent with the Rifean samples, which acquire an slight overprinting of Middle Atlas ages in the latter half of the succession. The data point to a progressive closure of the corridor through the advancement of the Rifean orogenic wedge with minor influence from uplift within the core of the Middle Atlas without a major shift in provenance during rapid basin emergence.