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Spatial variability of Quaternary denudation rates across a volcanic ocean island (Santo Antão, Cape Verde) from cosmogenic 3He

Litty, C. ; Charreau, J. ; Blard, P.H. ; Pik, R. ; Nomade, S. ; Geomorphology

Spatial variability of Quaternary denudation rates across a volcanic ocean island (Santo Antão, Cape Verde) from cosmogenic 3He

Litty, C. ; Charreau, J. ; Blard, P.H. ; Pik, R. ; Nomade, S.

Geomorphology, 2020, 375, 107557

Denudation of volcanic ocean islands creates remarkable landscapes and contributes to Earth’s carbon cycle, since the chemical alteration of basalts is a CO2 sink. Because many volcanic islands have large climate gradients and relatively lowvariations in lithology and tectonic history, they represent excellent natural laboratories for studying climatic effects on landscape evolution. However, little is known about the control of denudation rates in ocean islands and the respective influences of climatic gradients andmorphological parameters. Here,we present new measurements of long-term denudation rates from Santo Antão Island, Cape Verde (17°N). In this 779 km2 island, mean annual precipitation ranges from 40 mm·yr−1 in the southwest to 1100 mm·yr−1 in the north. To constrain the spatial distribution of denudation rates, we measured the cosmogenic 3He concentration in river transported pyroxene grains from 23 river bedload samples. We obtained basin wide denudation rates ranging from 2.7±0.1 to 57.5±0.3 m/Ma. The denudation rates display a significant spatial variability, with the highest rates in catchments located in the northeast side of the island where modern precipitation are the highest and lowdenudation rates in the southern andwestern dry basins. Our study shows that precipitation is themain control on denudation and landscape development of the Santo Antão volcanic island. This study provides for the first time the spatial distribution of denudation rates across a volcanic island located in a tropical zone.

Voir en ligne : https://doi.org/10.1016/j.geomorph....




publié vendredi 18 décembre 2020