The subduction reference framework

Plate tectonic reconstructions are essential for determining the spatial and temporal context for geological and geophysical data and help distinguish competing models for regional plate kinematic histories and the relationships between tectonic features and events. Plate reconstructions, a series of relative plate motions anchored to an absolute reference frame via a plate circuit, can act as surface boundary constraints for mantle convection models, allowing us to link surface processes to the deep earth. One of the limitations in global plate motion models has been to accurately determine the positions of plates through time. Traditionally, this has been based on either palaeomagnetic or hotspot reference frames, however both these methodologies have some shortcomings. Palaeomagnetic reference frames can determine latitudes but not longitudes, with additional inaccuracies due to true polar wander. Hotspot reference frames can only be confidently tied back to about 130 Ma and there is evidence that mantle plumes have moved relative to each other. New “hybrid” reference frames are emerging, which consist of fixed or moving hotspot reference frames merged with true polar wander (TPW) corrected palaeomagnetic reference frames. We have devised a methodology to link plate reconstructions to mantle convection back to Pangaea breakup time to converge on a solution that correctly aligns slab material in the mantle to the locations of subduction zones in the past. We aim to construct a “Subduction Reference Frame” for plate motions since 200 Ma by iteratively matching forward geodynamic models with tomographically imaged slabs in the mantle. Our forward models involve coupling global plate kinematics, the thermal structure of the oceanic lithosphere and slab assimilation to a spherical mantle convection code, CitcomS. Preliminary results have been obtained for a plate motion model using a moving hotspot reference frame to 100 Ma and a TPW corrected reference frame for times prior to 100 Ma. Focussing on the Farallon slab and the palaeo-subduction east of Australia, we find that our models reasonably reproduce the present-day location of the Farallon slab. However, there is a mismatch between the slab east of Australia and the predicted location of subduction based on the TPW-corrected reference frame. Further models will allow us to test new alternative reference frames to achieve a correct alignment with the location of slabs imaged in the mantle and the location of subduction along continental margins in the past.