3-D numerical modelling of the feedback between deformation and thermal structure during subduction initiation for the French Lesser Antilles

Abstract

We used 3-D thermomechanical modelling to investigate conditions during subduction-zone initiation and early thermal development with focus on the Lesser Antilles. Our model imposes a convergence velocity of 2 cm per year and incorporates heating caused by irreversible deformation of mantle and crustal rocks, using elasticity, creep, and non-associative plastic flow laws. Our results show that deformational heating before slab development is unexpectedly strong. After several million years, buckling and heating due to irreversible deformation create distinctive patterns of topography and surface heat flow that resemble present-day observations, despite the slab and subduction interface being incompletely developed. Within the Caribbean plate, plate buckling produces a high topographic ridge underlain by a large positive thermal anomaly of approximately 200 K, centred just below the Moho. The conductive thermal boundary layer transporting this heat to the surface thins from about 100 km to 10 km beneath the topographic maximum, allowing the ridge to rise above sea level. This thermal structure suggests the potential initiation of a volcanic arc approximately 180 km from the inter-plate contact. A hot zone at 30-50 km depth has pressures consistent with those inferred from Lesser Antilles primitive magmas and represents the most plausible location for partial melting of Caribbean mantle if volatiles are present. The thick Caribbean crust, approximately 20-25 km, is also heated sufficiently for possible silicic melt generation. The inferred lithospheric thickness of 50-100 km aligns with tomography studies. Thus, subduction thermal structure is strongly influenced by several million years of initiation processes.