Condor seamount (Azores, NE Atlantic): A morpho-tectonic interpretation

Abstract

High-resolution datasets collected by multibeam and acoustic backscatter surveys were used to produce fine-scale seafloor nature and morpho-tectonic interpretations of the Condor seamount. Condor constitutes an elongated volcanic ridge that extends for 39km and rises more than 1800m from the surrounding seafloor. Constructive morphologies include (i) linear eruptive centres, (ii) volcanic cones with or without summit depressions, (iii) lava flows and (iv) hummocky sectors. Eruptive type is interpreted to vary with depth. On the deeper seamount extremities, the predominance of highly acoustically backscattering volcanic cones and hummocky terrain is interpreted to result from effusive eruptions not yet covered by sediment deposits. In contrast, the smoother relief of the central seamount flanks is interpreted as draping and infilling of the underlying effusive relief by (i) primary volcaniclastic deposits produced by explosive eruptions on the shallowest parts of the ridge, together with (ii) secondary volcanigenic sediments resulting from truncation of the seamount top by swell erosion and (iii) sediments resulting from biogenic production.A set of WNW–ESE to NW–SE trending volcano-tectonic structures are shown to control most of the fissural volcanism that formed the ridge. A network of NNW–SSE trending faults is identified on the sea-floor around Condor but they show little relation with the distribution of volcanic edifices or with post-emplacement dismantling of the seamount. These fault sets are related to the transtensional regime acting on the Azorean segment of the Eurasia–Nubia plate boundary.Erosional features include (i) palaeo wave-cut platforms on the seamount summit, (ii) landslide scars produced by lateral collapses of the NE and SW-facing flanks, (iii) gullies and turbidity current channels and (iv) mass-wasting deposits. Iceberg drag and bump marks are also identified on the seamount upper flanks, representing the first reference to such features in the Azores and an additional low latitude record.Given the lack of major erosional and tectonic dismantling, Condor is suggested to be a relatively young seamount. A revised factoring of eustatic, erosional and isostatic processes does not exclude that the summit may have been eroded as late as the Last Glacial Maximum.