Professor of Marine Geology and Geophysics
The Aboran Sea is an extensional basin of Neogene age that is surrounded by highly arcuate thrust belts. Multichannel Seismic (MCS) reflection profile data suggest the basin has a complex tectonic fabric which includes extensional, compressional and strike-slip structures. The early Miocene history appears to be dominated by graben formation with border faults which are in large part contemporaneous with thrust movements in the external zones of the Betic and Rif mountains. Extensional tectonics appear to continue into the late Miocene although the main movements were probably completed by the time of the Messinian Ňsalinity crisisÓ. The Pliocene and younger history of the basin is dominated by infilling of the Messinian landscape, gentle subsidence and, extensional, compressional and strike-slip movements. There is evidence from the sea-floor morphology and seismicity patterns that the basin is actively deforming in response to present day plate motions. Backstripping of well data suggest that the initial extensional event was accompanied by crustal and lithospheric thinning. However, the depth to Moho infered from backstripping is greater than the depth expected based on seismic and gravity modelling suggesting that the well data underestimates the true amount of thinning. One explanation is that some of the thinning occured while the crust was above sea-level due, say to crustal thickening or lithospheric heating and thinning prior to rifting. We found that a model with a "normal" crustal thickness thickness of 31.2 Km, b = 1.4 and a lithospheric thickness of 50 km predicts 0.8 km of uplift fits the well data and, brings the backstrip Moho into good agreement with the seismic and gravity Moho. The origin of such thin lithosphere is not clear but, we believe that it is related to a regional heating event that followed detachment of a cold, overthickened, crustal and lithospheric "root" that formed during the preceeding the Betic, Rif and Tell orogeny.
Watts, A. B., J. Platt and P. Buhl, Basin Research., 5, 153-177, 1993