T11E-2946
Birth of an island arc : Stuctural and Kinematics records of upper plate deformation. Example of St Barthelemy, Lesser Antilles (French West Indies).

Monday, 14 December 2015
Poster Hall (Moscone South)
Lucie Legendre1, Mélody Maéva Philippon2, Yves Mazabraud2 and Lebrun Jean-Frederic2, (1)University of the French West Indies and Guiana, Fouillole, Finland, (2)UMR 5243 Geosciences Montpellier, Antilles University, Pointe à Pitre, France
Abstract:
The Lesser Antilles subduction initiated in Lower Cretaceous at the eastern tip of the Caribbean plate where Atlantic is subducting westward bellow Caribbean plate. The associated island arc extends from St Martin (to the north) to Grenada Island (to the south). The northern half of the volcanic arc presents a peculiar morphology with (i) an eastern outer arc that was active from Eocene to Oligocene from St Martin to Martinique and (ii) a western inner one from Saba to Martinique which is active since the Miocene attesting for a westward jump of the volcanic arc at that time. The long-term deformation pattern and kinematics affecting the Lesser Antilles arcand its evolution from Eocene to Miocene, before its westward jump, remain poorly constrained.

This study aims at constraining the deformation pattern expressed in the eastern outer arc of the Lesser Antilles during Eocene time, which is contemporaneous with arc formation. To achieve this goal, St Barthelemy Isand (St Barth) is a key target as it consists of Eocene volcanites inter layered with carbonate platform sequences, intruded by Oligocene dykes and pipes. During fieldwork, we accurately mapped the main tectonic features that affect the island, and characterized the mineralogy of the gouges and fluid circulation along the main faults. The kinematics data were used to perform inversions in order to recover the paleostate of stress and datable minerals found in fault gouge will be further used to constrain the timing of fault activity.

We discuss the observed deformations within the regional tectonic framework and the birth of the Lesser Antilles volcanic arc. Firstly, we recover the Eocene local paleostress in St Barth corresponding to the first stages of island arc building. Secondly, we discuss the Eo-Oligocene evolution of the stress field at the island scale. Thirdly, thanks to the observed mineralogy we decipher the different deformation stages that occurred at distinct structural levels.