Magmatism, tectonism, and segmentation of ultraslow spreading ridges
Ultraslow spreading ridges, which account for ~20% of the global Mid-Ocean Ridge (MOR) system, are the least surveyed part of the MOR system, because they are mostly in hard-to-access oceans. The longest (~7000 km), the Southwest Indian Ridge (SWIR), is in a remote location with the Roaring Forties, and the second longest (~2000 km), the Gakkel Ridge, is in the ice-covered Arctic Ocean. There is a challenge to state-of-the-art models of seafloor spreading from recent observations on ultraslow spreading ridges: the seafloor at the SWIR 64.5°E (an extreme case with nearly zero magma supply) is almost entirely (>90%) covered by ultramafic mantle rocks that are exhumed by successive flip-flop detachment faults, so-called detachment-detachment spreading mode (Sauter et al., 2013; Cannat et al., 2019); this mode is completely new relative to faster spreading ridges. Moreover, magma supply at ultraslow spreading ridges is not overall low as expected, but extremely variable in space and time (Cannat et al., 2008; Grevemeyer et al. 2018). This magma supply varies from nearly zero at the SWIR 64.5°E to the other extreme at the SWIR 50.5°E (and also at Gakkel 100°E detected by the recent JASMInE cruise), where the crust is 9.5 thick (Li et al., 2015; Jian et al., 2017), far more than expected (3-6 km). Seafloor spreading at the SWIR 50.5°E is dominated by magmatism with few faults, almost comparable to fast spreading EPR 9°N (Chen et al., 2021). Thus, it is timely to build a more comprehensive, global-scale model for seafloor spreading by studying the missing ultraslow spreading ridges.
Related publications:
Chen Jie, Crawford Wayne, Cannat Mathilde (2023). Microseismicity and lithosphere thickness at a nearly-amagmatic oceanic detachment fault system. Nature Communications.
Chen Jie, Cannat Mathilde, Tao Chunhui, Sauter Daniel, Munschy Marc (2021). 780 thousand years of upper-crustal construction at a melt-rich segment of the ultraslow spreading Southwest Indian Ridge 50°28’E. Journal of Geophysical Research:Solid Earth.
Chen, J., Zhang, T., Li, H., Tao, C., Cannat, M., Sauter, D. (2023). Evolution of enhanced magmatism at the ultraslow spreading Southwest Indian Ridge between 46°E and 53.5°E. Tectonophysics.
Yan Kaixuan, Chen Jie, Zhang Tao. (2024). Teleseismic Indication of Magmatic and Tectonic Activities at Slow- and Ultraslow-Spreading Ridges. J. Mar. Sci. Eng.
