What can island isostasy tell us about hotspot dynamics?
The Cape Verde Archipelago - the type-example of a hotspot in a stationary plate environment with respect to its melting source - exhibits ubiquitous evidence for quaternary uplift. This uplift is possibly associated to a regional growth pulse of the Cape Verde Rise, the largest bathymetric anomally in the Earth's oceans. This project aims to date quaternary uplift tracers across the Cape Verde Islands and test a regional vs local mechanism for the uplift in orther to gain insight on the origins of the Cape Verde Rise and processes of island growth. If considerable uplift trends occur at a regional scale, a mechanism associated with hotspot swell development and dynamics (i.e. dynamic topography) must be invoqued as the source of isostatic imbalance. Conversely, if highly differential uplift trends occur at a more local scale, affecting nearby islands differently, local intrusion-related mechanisms are the most likely source of uplift.
Quaternary uplift tracers in the Cape Verdes consist essentially of relative sea-level markers such as marine terraces (wavecut surfaces and raised beach deposits) and lava deltas, which are potentially dateable. In this project we plan to use cutting-edge surface exposure dating techniques, as well as U-Th (on corals) and Ar-Ar (on lava deltas), to date uplift features. The application of surface exposure geochronology to date other features - such as young volcanic landforms and tsunami and storm deposits - will also be attempted.
This project is linked to R. Ramalho's FP7-PEOPLE-2011 Marie Curie International Outgoing Fellowship, with Lamont-Doherty Earth Observatory at Columbia University as Outgoing Host and Joerg Schaefer and Gisela Winckler as PI's, and the School of Earth Sciences of Bristol University (UK) as a Return Host and with George Helffrich as PI.