Alexandre Kounov

Denudation along the Atlantic passive margin: new insights from apatite fission-track analysis on the western coast of South Africa

Abstract Apatite fission-track (AFT) data from two traverses across the Great Escarpment of the western coast of South Africa are used to reconstruct the tectonic evolution and denudation history of this sector of the Atlantic passive margin. Fission-track ages range between 180 and 86 Ma. Modelling of this data identifies two distinct cooling events. The first event, between 160 and 138 Ma, is recorded only by the rocks above the escarpment in the Karoo area, and is tentatively linked to post-Karoo magmatism (c. 180 Ma) thermal relaxation. The second, between 115 and 90 Ma, results instead from a tectonically induced denudation episode responsible for the removal of up to 2.5 km of crust across the coastal zone in front of the escarpment and less than 1 km on the elevated interior plateau. Based on these results, it is suggested that the Cretaceous is the time when most of the elevated topography of Southern Africa was generated, with only a minor Cenozoic contribution.

Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone

blocks along its southern margin. New U/Pb, 40 Ar/ 39 Ar, apatite fission track, and apatite (U‐Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ∼90 to ∼87Ma and crops out onAruba. Subsequent structural displacements resulted in >80°C of cooling on Aruba during 70–60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85–80 Ma and 55–45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ∼65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian‐Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene–early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ≤1 km. Late Miocene–recent transpression caused inversion and ≤1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block. Citation: van der Lelij, R., R. A. Spikings, A. C. Kerr, A. Kounov, M. Cosca, D. Chew, and D. Villagomez (2010), Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone, Tectonics, 29, TC6003, doi:10.1029/2009TC002654.