Oceanic microplate formation and the India-Eurasia collision
From University of Oxford, UK
Mapping of seafloor tectonic fabric in the Indian Ocean, using high-resolution satellite-derived vertical gravity gradient data, reveals an extinct Pacific-style oceanic microplate west of the Ninetyeast Ridge. It is one of the first such microplates to be mapped outside the Pacific basin, and we refer to it as the ‘Mammerickx Microplate’ after seafloor mapping pioneer Dr Jacqueline Mammerickx. The microplate formed at the Indian–Antarctic ridge and is bordered by an extinct ridge in the north and pseudofault in the south, whose conjugate is located north of the Kerguelen Plateau. Independent microplate rotation is indicated by asymmetric pseudofaults and rotated abyssal hill fabric, also seen in multibeam data. Magnetic anomaly picks and age estimates calculated from published spreading rates suggest formation during chron 21o (∼47.3 Ma). Plate reorganizations can trigger ridge propagation and microplate development, and we propose that Mammerickx Microplate formation is linked with the India–Eurasia collision. The collision altered the stress regime at the Indian–Antarctic ridge, leading to a change in segmentation and ridge propagation. Fast Indian–Antarctic spreading that preceded microplate formation, and Kerguelen Plume activity may have facilitated ridge propagation via the production of thin and weak lithosphere. Microplate formation provides a novel means of dating the onset of the India–Eurasia collision and is independent of, yet complementary to timing constraints derived from continental geology and convergence histories.