Abstract
In order to decipher the tectono-metamorphic evolution of shallow crustal levels of the active volcanic arc of the Guadeloupe archipelago (Lesser Antilles) we present new geochemical, geochronological, mineralogical and structural investigations of the so-called Basal Complex, the oldest and most eroded volcanic complex of Basse-Terre in Guadeloupe. Based on geochemical and mineralogical criteria we propose an updated geological map of this northern area of Basse-Terre. Using40Ar–39Ar geochronology we demonstrate first that the eroded “Gros Morne” of Deshaies belong to the Basal Complex, and second that this complex is characterized by 4.3 to 2 Ma old volcanism. Structural analysis reveals a long-lived deformation history with the development through time of N80-N100 schistose zones; N110-N140 and N160-N10 oriented hydrothermal breccias and N140-N150 brittle normal faults. The boundary between the Basal Complex and the southernmost Septentrional Chain corresponds to a series of faults with N 150° and N 50° main directions. Detailed mineralogical and petrological investigations, including thermodynamic modeling, allow the identification of three phases of post-magmatic mineralogical transformations with first a high-temperature stage under Greenschist to sub-Greenschist facies conditions (0.6–2 kbar for 250–300 °C), a re-equilibration under Zeolite facies conditions and finally a sub-surface alteration. The consistency between P–T conditions of metamorphism and the present day measured geothermal gradient demonstrates that the metamorphic pattern is the record of hydrothermal fluids circulation during building and cooling of the Lesser Antilles magmatic arc. The tectono-metamorphic evolution recognized in the Basal Complex enables us to propose a conceptual model for heat and fluid transport within shallow crustal levels of the Guadeloupe active volcanic arc.
Highlights
Elucidating the structural and mineralogical transformations driven by heat and fluid transfers within the crust of magmatic arcs is an important yet tricky problem
The Basal Complex is a key target for deciphering the evolution of shallow crustal levels of the Lesser Antilles arc as it exposes the most eroded part of the Basse-Terre volcanic chain, consisting of the basement of the volcanic chain
We investigate the tectono-metamorphic evolution of this exhumed piece of the upper crustal level of the Lesser Antilles volcanic arc
Summary
Elucidating the structural and mineralogical transformations driven by heat and fluid transfers within the crust of magmatic arcs is an important yet tricky problem. Located at tropical latitudes, Basse-Terre of Guadeloupe is prone to significant weathering and erosion processes (Dessert et al, 2015) where mechanical and chemical erosion rates of around 1–2 mm/yr are effective (Sak et al, 2010, Lloret et al, 2011; Rad et al, 2013; Ricci et al, 2015a, b) In this context, the Basal Complex is a key target for deciphering the evolution of shallow crustal levels of the Lesser Antilles arc as it exposes the most eroded part of the Basse-Terre volcanic chain, consisting of the basement of the volcanic chain. This dataset allows us to discuss the heat and fluid transfers in the Lesser Antilles magmatic arc, so as to propose a conceptual scheme of these transfers and their influence on the strain accommodation and metamorphic evolution, in the framework of the shallow crustal level of an active volcanic arc
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