Lithospheric response to volcanic loading by the Canary Islands: constraints from seismic reflection data in their flexural moat

We use multichannel seismic reflection profiles to determine the seismic stratigraphy of the flexural moat that flanks the Canary Islands. The moat stratigraphy has been divided into 5 units on the basis of internal character and correlation of distinctive reflections. The deepest units, I and II, which well-ties indicate are Eocene and older, thicken towards the east suggesting they are the consequence of sediment loading at the Moroccan continental margin. Units III, IV and V, which are Oligocene and younger and highly reflective, thicken concentrically around individual islands suggesting they are dominantly the result of volcanic loading. Distinct stratigraphic patterns of onlap at the base and offlap at the top of individual flexural units are seen on the across-moat profiles but they were not easily identified on our limited along-moat profiles. The thickness of the upper three units is in accord with the predictions of flexural loading models. Moreover, a model in which the volcanoes that make up the Canary Islands progressively load the underlying lithosphere from east to west generally accounts for the thickness variations that are observed in the region of individual islands. We date the shield building stages of the Fuerteventura, Gran Canaria and La Gomera as Oligocene to Early Miocene, that of Tenerife as Middle Miocene to Late Miocene and those of La Palma and El Hierro as Pliocene to Quaternary. The best overall fit to stratigraphic data in the northern moat is for an elastic thickness of the lithosphere, Te, of 35 km, which is similar to the 30–40 km which would be expected for Oligocene and Neogene loading of Jurassic oceanic lithosphere. There is evidence that a contribution from the margin is required to explain the divergence of Units III, IV and V along the Moroccan margin. Detailed modelling of an along-strike seismic profile of the moat north of Tenerife and Gran Canaria, however, suggests that flexure due to island loading fully explains the stratigraphic patterns that are observed and does not require an additional contribution from the margin. The most likely explanation for this observation is that a ‘barrier’ had developed by the Oligocene, along the present trend of Fuerteventura and Lanzarote, which prevented sediments from the Moroccan margin infilling the northern parts of the moats caused by volcanic loading. Furthermore, there is evidence from differences in the thickness of Units I and II that a barrier may also have existed prior to the Oligocene which protected the northern basin from corrosive bottom currents that removed large amounts of late Cretaceous and Palaeogene age material from the southern basin.