Active tectonics, fault patterns, and stress field of Deception Island: A response to oblique convergence between the Pacific and Antarctic plates

Abstract

Palaeostress results derived from brittle mesoscopic structures on Deception Island (Bransfield Trough, Western Antarctica) show a recent stress field characterized by an extensional regime, with local compressional stress states. The maximum horizontal stress ( σ y ) shows NW–SE and NNE–SSW to NE–SW orientations and horizontal extension ( σ 3) in NE–SW and WNW–ESE to NW–SE directions. Alignments of mesofractures show a maximum of NNE–SSW orientation and several relative maxima striking N030-050E, N060-080E, N110-120E, and N160-170E. Subaerial and submarine macrofaults of Deception Island show six main systems controlling the morphology of the island: N–S, NNE–SSW, NE–SW, ENE–WSW to E–W, WNW–ESE, and NNW–SSE. Geochemical patterns related to submarine hydrothermally influenced fault and fissure pathways also share the same trends. The orientation of these fault systems is compared to Riedel shear fractures. Following this model, we propose two evolutionary stages from geometrical relationships between the location and orientation of joints and faults. These stages imply a counter-clockwise rotation of Deception Island, which may be linked to a regional left-lateral strike-slip. In addition, the simple shear zone could be a response to oblique convergence between the Antarctic and Pacific plates. This stress direction is consistent with the present-day movements between the Antarctic, Scotia, and Pacific plates. Nevertheless, present basalt-andesitic volcanism and deep earthquake focal mechanisms may indicate rollback of the former Phoenix subducted slab, which is presently amalgamated with the Pacific plate. We postulate that both mechanisms could occur simultaneously.