Towards a Reconstruction of the Magmatic and Tectonic Evolution of the Demise of the Antarctic Peninsula Subduction Zone

The Antarctic Peninsula preserves the life cycle of a subduction zone from initiation to demise. The Antarctic-Phoenix subduction zone was active from the Late Jurassic till the initiation of its demise, 53Ma¹. This demise was triggered by the collision of the Antarctic-Phoenix spreading ridge with the subduction zone trench, leading to the development of a slab window. This ridge crest-trench interaction occurred segmentally from the southern end of the arc to the northern end. Today three segments of the mid-ocean ridge exist west of the South Shetland Islands, but there is no longer any subduction, leaving a paleo-subduction zone. The progressive shut down and subsequent lack of overprinting or tectonic events, allows an assessment of the stages of collision and slab-window formation, and the impact this has had on the magma generation and volcanism.

Limited work has been conducted on linking the evolution of the volcanism with the evolution of the subduction zone, however, recent efforts have worked to classify different geochemical groups within the subduction volcanism and to assess the spread of geochronological data^2,3. From this, it has been possible to highlight some key questions which warrant further data collection and analysis.

This work focusses on the assessment of a potential migration of the volcanic axis trench-wards in response to the approaching mid-ocean ridge. It also works to marry the spatial and temporal assessment with a geochemical analysis. With the aim to observe changes in mantle conditions and magma generation through the evolving geochemistry of the volcanic activity and link it to the changing tectonic setting.

To achieve this, 64 additional major and trace element analysis, and 14 new U-Pb dates have been collected. Which have been applied to a spatial analysis and detailed tectonic/coastal reconstruction. From this a new look at the structure, evolution and impact of subduction demise and slab-window formation within the Antarctic Peninsula can be gleaned.

References:
[1] Smellie, et al. (2021), Geological Society of London, Memoirs, https://doi.org/10.1144/M55-2020-14
[2] Leat and Riley (2021a), Geological Society of London, Memoirs, https://doi.org/10.1144/m55-2018-68
[3] Leat and Riley (2021b), Geological Society of London, Memoirs, https://doi.org/10.1144/m55-2018-52