Holocene tectonic uplift of the St Peter and St Paul Rocks (Equatorial Atlantic) consistent with emplacement by extrusion

Abstract

St Peter and St Paul Rocks (SPSPR) are emergent portions of a peridotitic mass within the St Paul fracture zone of the Equatorial Mid-Atlantic Ridge, where local seismicity is dominated by strike-slip mechanisms. We used subtidal red algae in living position, death assemblages in intertidal conglomerates, and marine terraces as sea-level markers. The highest deposits correspond to a marine terrace with a shoreline angle at 8 ± 1 m asl that formed ca. 6400–6200 cal. yr BP. After correction for the sea-level changes derived by glacioisostatic modelling, AMS and radiometric 14C age measurements on the Holocene sea-level markers indicate emergence during the last 6600 a at a minimum average rate of ∼ 1.5 mm/a. We propose that uplift resulted from peridotite emplacement by extrusion, rather than volcanic activity or fault slip, with the implication that the ridge has been subject to compression during the Holocene.