caption: Network of plates in the Scotia Arc, showing the type of constraints on plate motion available from each boundary. SCT, Southern Chile Trench; SAAR, South American--Antarctic Ridge; NSR, North Scotia Ridge; SSR, South Scotia Ridge; SST, South Sandwich Trench. Solid lines show the availability of spreading rate and azimuth data, dotted lines represent boundaries for which only azimuth data (slip vectors) are available.