Trench Bending Initiation: Upper Plate Strain Pattern and Volcanism. Insights From the Lesser Antilles Arc, St. Barthelemy Island, French West Indies

Abstract

The upper plate deformation pattern reflects the mechanical behavior of subduction zones. Here we focus on the consequences of the entrance of a buoyant bank into the Caribbean subduction zone during the Eocene by studying the oldest exposed rocks belonging to the Lesser Antilles volcanic arc. Using a novel geochronological data set, we show that the volcanic arc activity on the island of St. Barthelemy spanned over the mid‐Eocene to early Miocene with a westward migration of the tectono‐volcanic activity, which is comparable to what has already been observed on other volcanic islands in the Lesser Antilles. The kinematics analysis allows us to identify a switch in the stress field from pure to radial extension at the Oligo‐Miocene hinge with a subhorizontal σ3 that has a mean trend of N20°. A three‐step restoration of the regional deformation indicates that this switch from pure parallel‐to‐the‐trench extension to radial extension may reflect a strain partitioning initiation affecting the upper Caribbean Plate in response to trench bending that followed the entrance of the Bahamas Bank into the subduction zone. We show that the northern end of the Lesser Antilles arc shows a tectono‐volcanic evolution which is similar to the southern one. The north‐south dichotomy in the perpendicular‐to‐the‐trench extension, 15% in the north versus 30% in the south, may reflect different slab ends that are highly curved to the north (restraining the extension in the upper plate) versus a tear to the south (allowing a larger amount of extension within the upper plate).

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

“…Finally, similar trends, observed in brittle, semi-brittle and ductile tectonic structures suggest strong inheritances within the crust of the volcanic arc of the Lesser Antilles and corroborates observations from previous workers along the Lesser Antilles volcanic arc (Corsini et al, 2011;Lardeaux et al, 2013;De Min et al, 2015;Legendre et al, 2018). In such a framework, the boundaries between volcanic complexes are possibly controlled by brittle normal faults, developed under recent to active extensional tectonic regimes, as it is the case for the geometric relation between the Basal Complex and the Northern Chain (Fig.…”

The Bunce Fault and Strain Partitioning in the Northern Lesser Antilles

“…Mann et al () summarize these tectonic studies at the PRVI microplate between southward underthrusting along the Puerto Rico Trench and northward underthrusting along the Muertos Trough. The collision of the Bahamas Bank with the northern Caribbean margin since the late Paleogene (e.g., Pindell & Kennan, ) led to inception of the North Caribbean strike‐slip Plate boundary and motion partitioning along the NLA‐PRVI margins as the trench curvature initiated (Legendre et al, ). During the Miocene, the Anegada Passage possibly accommodated transtensive relative motion between Caribbean and PRVI block in response to this collision (e.g., Jany et al, ; Mann et al, ).…”

Paleogene V-shaped basins and Neogene subsidence of the Northern Lesser Antilles Forearc

“…At St Barthélemy and in the backarc, compressional tectonic structures are sealed by a late Priabonian unconformity (Church and Allison, 2004;Philippon et al, 2019). Following this compression, the Kalinago Basin opening and extensive evidences in the northern Anguilla Bank attest for a regional extension during the early Oligocene (Cornée et al, 2019;Legendre et al, 2018). Syntectonic deposits of Unit U1 in the Saint-Barthelemy Valley suggest that the oldest sediments in the V-shaped basin postdates the late Priabonian unconformity.…”

“…The NLA Subduction Zone has generated three distinct volcanic arcs: 1/ the late Cretaceous -Paleocene arc at the Aves Ridge (Bouysse et al, 1985;Neill et al, 2011), 2/ the remnant middle Eoceneearliest Miocene Lesser Antilles Arc in the current forearc to the north of Martinique Island (Bouysse and Westercamp, 1990;Legendre et al, 2018;Martin-Kaye, 1969) and 3/ the early Pliocene -present day Lesser Antilles active Arc, located to the west of the previous arc (Lindsay et al, 2005) (Figure 1). The NLA forearc basins developed, at least partly, during the post early Miocene landward migration of the volcanic Lesser Antilles Arc recording the tectonic evolution for this time period.…”