Fig. 6: Relative motion between the East Pacific Rise and the Easter hotspot.

A Magnetic anomaly ages versus longitude using the time scale in GEEK2007¹⁰⁷. The blue and black trendlines are fitted to Nazca anomaly picks flanking the SYGR to the south and north, respectively. The similar length of the red bands signifies a constant offset between the hotspot (Fig. 3 & S1) and the axis south of the SYGR. The dashed version of this blue trendline and the short vertical black line show that north of the microplate the current position of the EPR agrees with consistent EPR migration relative to the hotspot. The assigned numbers correspond to the half-spreading rates in mm/yr. The diagonal solid blue line represents the inferred propagation of the SW Rift based on SO80 Ar/Ar dates discussed in the text (Fig. 3). The ⁴⁰Ar/³⁹Ar dates defining the ‘Pacific’ trend (red diamonds and black dashed line) align with the migration of the EPR (West Rift) crust (circle symbols and black regression line). The distance between these trends implies that the ‘Pacific’ trend volcanism erupted about 170 km west of the EPR (West Rift). Asymmetric crustal accretion to the Nazca Plate at the latitude of the hotspot amounts to ~21%, while to the south, it is ~6% (Asymmetry Percentage = [(difference in spreading rates / total spreading) * 100]). The long vertical back line denotes the resulting current location of EPR at the latitude of the hotspot. The ⁴⁰Ar/³⁹Ar ages defining the SYGR age progression¹³ are indicated by the red triangles (see also Fig. S1). B The map shows the location of magnetic anomaly picks since anomaly C5AAn (13.065 Ma) from ref. ¹⁰⁸, http://www.soest.hawaii.edu/PT/GSFML/. The box and circle symbols represent isochron picks on the Nazca and Pacific plates, respectively. Yellow shading indicates picks south of the Easter hotspot system. Symbols for picks on the Easter microplate are explained in Fig. 7.