Fig. 2: Across-rift age distribution of observed and modelled magmatic activity.
Observed (a) and modelled (b, c) magmatic activity distribution across rift. a The top image represents the topographic profile of the A–A’ across-rift profile (Fig. 1). The middle image shows the ages of the dated samples projected along the A–A’ across-rift profile. The colours identify the samples used to fit the linear regression model (solid lines), purple and pale blue crosses are respectively used for the samples located on the SW and NE side of A–A’ across-rift profile while the black crosses had been used for both sides. The dashed lines identify the 95% confidence interval of the linear regression. The calculated rates are 11.5 ± 1.5 and 26.7 ± 2.3 mm/year, respectively, for the SW and NE sides. The inclination of each one of the shaded areas identifies half of the Central Afar extension rate (~10 mm/year) spanning broadly the Manda Hararo magmatic segment width. The bottom image shows the estimated Moho depths with the errors projected along the A–A’ across-rift profile33,38 (Supplementary Fig. 2). The estimated depths have been fitted by a polynomial curve (red line) to show the crustal thickness variation. b, c Schematic representations of the distribution of the eruptive centres areas for both ocean spreading-like rifting (b) and rift localisation (c). Each coloured box indicates the areas accommodating the extension (i.e., the eruptive centres) during a given time period with the total extension rate being kept the same for all the models and through time (the top boxes represent the initial stage while the bottom boxes represent the final stage). Below each one of the box models, a graph shows the hypothetical spatial distribution of eruptive centres at their final stages (bottom boxes of each model) to compare them with the real case (a). b For the uniform ocean spreading-like rifting the width and position of the magmatic segment are fixed. To have asymmetric ocean spreading-like rifting, different spreading rates for the two sides are needed (in the example, it is greater on the right side with respect to the left side). c For the uniform localisation, the width of the Plate Boundary Zone gets narrower toward its centre throughout time. To have asymmetric localisation of the PBZ, different spreading rates are needed (in the example, it is greater on the right side with respect to the left side). See the text for discussion.
