Quantifying magmatism and tectonism along the ultraslow-spreading Southwest Indian Ridge (46-52°E)

Over one-third of mid-ocean ridges exhibit a spreading rate less than 20 mm per year. The process of crustal accretion, which facilitates the expansion of oceanic plates at mid-ocean ridges, is driven by the combined and interactive efforts of magmatic and tectonic processes. The seafloor morphology along ultraslow mid-ocean ridge flanks serves as a record of the accretion on oceanic crust. However, volcanic eruptions, mass wasting and reverse-faulting earthquakes occurring on mid-ocean ridges, which reshape the seafloor, present a significant obstacle for the precise quantification of oceanic crust accretion and seafloor morphology. Due to the temporal and spatial variability of magma supply, particularly in the Indomed-Gallieni supersegment (46-52°E) of the Southwest Indian Ridge (SWIR), magmatic and tectonic processes exhibit pronounced spatiotemporal variations, along with asymmetric crustal accretion, making it rather difficult to conduct quantitative analysis of the geomorphology of the oceanic crust. By utilizing multibeam bathymetry and gravity data of Indomed-Gallieni supersegment, we calculated several parameters such as the fraction of magmatic accretion (M-value), axial valley depth (D-value), magma supply, melt flux, and strain ratio, as well as fault heave and fault throw, thereby quantifying magmatism and tectonism. The majority of parameters indicative of tectonic accretion exhibit a negative correlation with magmatic parameters. Moreover, we compared the two-dimensional Fourier spectra of seafloor on mid-ocean ridge flank with magma supply. The anisotropy of seafloor is positively correlated with magma supply, with morphology becoming increasingly isotropic as magma supply diminishes. Our research suggests that although tectonic processes account for nearly 50% of oceanic crust accretion at ultraslow spreading mid-ocean ridges, the accretion process and the geomorphic features of the young oceanic crust are predominantly influenced by magma supply.