Identification and tectonic implications of a tear in the South American plate at the southern end of the Lesser Antilles

Abstract

In the southeast corner of the Caribbean, westward subduction of (Atlantic) oceanic South America beneath the Lesser Antilles transitions to east‐west transform motion between continental South America and the Caribbean plate. This geometry requires negatively buoyant, subducting, oceanic South American lithosphere to progressively detach from positively buoyant, continental South American lithosphere. The most widely accepted model is slab break‐off, with oblique arc‐continent collision and northwest dipping, continental subduction precipitating narrow rifting in the subducting slab. In contrast, the subduction‐transform edge propagator (STEP) model conceptualizes progressive detachment along a vertical, dip‐slip tear through the lithosphere, with stress focused at the edge of the propagating transform boundary. We present four types of seismic data to resolve the ongoing lithospheric detachment: local seismicity, receiver functions, wide‐angle seismic velocity inversion, and a regional, balanced cross section constrained by petroleum industry data. These four data sets image a near‐vertical tear extending through the entire lithosphere, revealing a key mechanism for the structural evolution of Venezuela.

Keywords

• lithospheric detachment
• mantle dynamics
• STEP
• jelly sandwich
• slab break‐off
• tear