Vertical movements of ocean island volcanoes: insights from a stationary plate environment

Abstract

Uplift reconstructions based on the Cape Verde's geological record provide a unique opportunity to study the long-term isostatic movements associated with hotspot activity on a stationary plate environment. The archipelago is considered stationary with respect to its melting source so the hotspot-driven isostatic effects affecting the ocean islands are expected to be enhanced. In this study, Ar–Ar and U–Th geochronology techniques were used to date a set of palaeo-markers of sea-level from Santiago's and São Nicolau's edifices, two of the main Cape Verde Islands. A comparison between relative sea-level and eustatic sea-level (from a modern eustatic curve) was established to extract the vertical displacement undergone by the markers, and to reconstruct the uplift/subsidence history of each island. The resulting uplift reconstructions confirm that both Santiago and São Nicolau experienced a general uplift trend over the last 6 Ma, seemingly synchronous with the vigorous volcanic activity that built their exposed edifices. These islands, however, exhibit different uplift histories despite their common uplift trend. Several uplift mechanisms were tested and a local rather than regional mechanism is proposed as the main cause of uplift, generally unrelated with far-field effects of surface loading. This mechanism is probably associated with magmatic additions at crustal level.