Evidence for off-ridge thermal interaction along the Carlsberg and Central Indian ridges and its tectonic significance

Seafloor spreading along the Carlsberg and Central Indian ridges has steered the tectonic evolution of the western Indian Ocean. These spreading ridges display variations in spreading rate, segmentation, and morphological characteristics, providing clues to the long-term evolution of the oceanic lithosphere in this region. To assess the influence of two notable off-axis thermal sources, the Réunion plume and the Indian Ocean Diffuse Boundary Zone, on factors such as rigidity and seafloor subsidence along these ridges, we computed the effective elastic thickness (Te), residual geoid-age slopes, and residual depth anomalies (RDA) of the region using gravity and geoid data. The results reveal a weaker lithosphere at the northern Central Indian Ridge (Te: ~ 8.5–8.9 km) compared to the neighboring segments of the southern Central Indian Ridge (Te: ~ 10.5–12.7 km) and the Carlsberg Ridge (Te: ~ 10.5–14.7 km). Residual geoid and RDA variations suggest asymmetric seafloor spreading and subsidence along the entire ridge system. The asymmetric subsidence across the Central Indian Ridge is largely due to upper mantle contamination from the Réunion plume, while across the Carlsberg Ridge, it may be linked to its complex tectonic history. The rigidity and seafloor spreading patterns along the northern Central Indian Ridge are notably affected by thermal perturbations from the regional heat flow anomaly of the ongoing diffuse deformation zone. Moreover, the Te and segmentation patterns roughly correlate along the ridge system, suggesting a causal relationship between the two or the presence of underlying factors such as regional thermal structure influencing both.