Extended Data Fig. 1: Latitudinal variations in CO₂ flux and R_A values (³He/⁴He) with respect to the modelled lithosphere structure.

a, R_A versus latitude along the Eastern Rift from −1.5° to −4.5°. Air-contaminated samples (TZ18-C16) were removed from the analysis. The Tanzanian craton boundary (light grey) is interpreted using the sharp density (c) and velocity (d) contrasts near the northern Manyara and southern Natron basins. It is marked as a broad region to account for location uncertainties and the overall three-dimensional nature of the boundary in the region. b, Diffuse CO₂ flux versus latitude along the Eastern Rift from −1.5° to −4.5° for sample sites presented in Fig. 1a and the Oldoinyo Lengai volcano. c, Lithosphere density model from Tiberi et al.²¹. d, Lithosphere velocity model from Tiberi et al.²¹ (model resolution discussed in Methods). The density and velocity contrasts are relative to the IASP91 model⁴⁹. The position of the cross-section is shown in Fig. 1a.