Tectono-metamorphic evolution of shallow crustal levels within active volcanic arcs. Insights from the exhumed Basal Complex of Basse-Terre (Guadeloupe, French West Indies)

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. Using 40 Ar-39 Ar 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.Keywords: arc-related metamorphism / Lesser Antilles / Guadeloupe / Basal Complex / tectono-metamorphic evolution / hydrothermal fluids Résumé -Évolution tectono-métamorphique des niveaux superficiels de la croûte dans les arcs volcaniques actifs. Exemple du Complexe Basal exhumé de Basse-Terre (Guadeloupe, Antilles françaises). Afin de décrypter l'évolution tectono-métamorphique des niveaux crustaux peu profonds de l'arc volcanique actif de l'archipel de la Guadeloupe (Petites Antilles), nous présentons de nouvelles investigations géochimiques, géochronologiques, minéralogiques et structurales du Complexe Basal, le plus ancien et le plus érodé des complexes volcaniques de Basse-Terre en Guadeloupe. Sur la base de critères géochimiques et minéralogiques, nous proposons une carte géologique actualisée de cette zone nord de la Basse-Terre. En utilisant la géochronologie 40 Ar-39 Ar nous démontrons d'abord que le « Gros Morne »

Genetic patterns of Magnolia in the Lesser Antilles: Stepwise colonisation leading to highly inbred island ‘populations’

“…The rocks of Dominica have been estimated to be not older than 7 mya (Bellon, 1988; Monjaret, 1985). Basse‐Terre of Guadeloupe has been estimated to be younger than 5 mya (Favier et al, 2019; Wadge, 1994). Most are K‐Ar dating estimates of the oldest surface rocks, which correlate with, yet outdate, the shield emergence and can hence lead to an underestimation of the true island ages (Obbard et al, 2012).…”

Metamorphic Facies and Deformation Fabrics Diagnostic of Subduction: Insights From 2D Numerical Models

“…Traditionally three metamorphic series with different P/T ratios have been identified from petro‐structural analysis of orogenic belts, and they are usually associated with different stages of evolution of a convergent margin (e.g., Ernst, 1976, 1977; Kornprobst, 2002; Spear, 1993; Yardley & Warren, 2020): Metamorphic series with high P/T ratios, deduced by regional scale distribution of dominant metamorphic imprints (e.g., Ernst, 1973; Miyashiro, 1961), are generally associated with Pressure‐Temperature (P‐T) conditions interpreted as peculiar of subduction and are referred to as Franciscan (or Sanbagawa) metamorphic sequences. Barrovian (or Dalradian) metamorphic series, which are characterized by intermediate P/T ratios, are traditionally interpreted as the effect of crustal thickening during continental collision both by mountain belt tectono‐metamorphic analyzes and by thermo‐mechanical modeling predictions (e.g., Barrow, 1912; Bohlen, 1987; England & Richardson, 1977; England & Thompson, 1984; Jamieson et al., 1998; Sandiford & Powell, 1991; Thompson, 1981; Thompson & England, 1984). Metamorphic facies series characterized by low P/T ratios (Abukuma or Buchan‐type metamorphism) have been generally associated with abnormally high geothermal gradients such as those of the island arc or ridge settings (Cloos, 1993; Fagan et al., 2001; Favier et al., 2019; Mevel et al., 1978; Oxburgh & Turcotte, 1970; Verati et al., 2018), slab rollback or increase of the slab dip after continental collision (Ji et al., 2019; Li et al., 2013; Menant et al., 2016; Schliffke et al., 2019; Sizova et al., 2019), post‐collisional extension (Carmignani & Kligfield, 1990; Vanderhaeghe, 2012), melt migration through the crust (Depine et al., 2008), local effects of contact metamorphism (Rothstein & Manning, 2003). …”

“…Metamorphic facies series characterized by low P/T ratios (Abukuma or Buchan‐type metamorphism) have been generally associated with abnormally high geothermal gradients such as those of the island arc or ridge settings (Cloos, 1993; Fagan et al., 2001; Favier et al., 2019; Mevel et al., 1978; Oxburgh & Turcotte, 1970; Verati et al., 2018), slab rollback or increase of the slab dip after continental collision (Ji et al., 2019; Li et al., 2013; Menant et al., 2016; Schliffke et al., 2019; Sizova et al., 2019), post‐collisional extension (Carmignani & Kligfield, 1990; Vanderhaeghe, 2012), melt migration through the crust (Depine et al., 2008), local effects of contact metamorphism (Rothstein & Manning, 2003).…”

“…have been generally associated with abnormally high geothermal gradients such as those of the island arc or ridge settings (Cloos, 1993;Fagan et al, 2001;Favier et al, 2019;Mevel et al, 1978;Oxburgh & Turcotte, 1970;Verati et al, 2018), slab rollback or increase of the slab dip after continental collision (Ji et al, 2019;Li et al, 2013;Menant et al, 2016;Schliffke et al, 2019;Sizova et al, 2019), post-collisional extension (Carmignani & Kligfield, 1990;Vanderhaeghe, 2012), melt migration through the crust (Depine et al, 2008), local effects of contact metamorphism (Rothstein & Manning, 2003). Miyashiro (1961Miyashiro ( , 1973 promoted the concept of paired metamorphic belts, revisited by Brown (2010), and based on the juxtaposition along orogenic crustal sections of tectonic complexes characterized by Franciscan-and Abukuma-type metamorphic facies series.…”

Evolution of a Shallow Volcanic Arc Pluton During Arc Migration: A Tectono‐Thermal Integrated Study of the St. Martin Granodiorites (Northern Lesser Antilles)

“…For example, along the Hikurangi margin (New Zealand) thermochronometry allowed determining rapid phases of magmatic thickening and burial (lasting 6 Myrs) followed by contrasting slow unroofing (lasting 40 Myrs) (e.g., Flowers et al., 2005). Along many volcanic arcs it has been demonstrated that active volcanoes were emplaced in their own metamorphosed magmatic basement that was promptly exhumed (Kuril: De Grave et al., 2016; Lesser Antilles: Favier et al., 2019). It is noteworthy that during arc migration, cooling of an arc pluton might be interpreted to record its exhumation, whereas it might be associated with a drop in the paleo‐geothermal gradient due to volcanic arc cessation (Kohút & Danišík, 2017).…”