Qiang Maa*, Huaiyang Zhoua,b*, Henry J.B. Dicka,c
a State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
b Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
c Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
Abstract：Tectonic extension at slow- to ultraslow-spreading mid-ocean ridges is predominantly accommodated by large-offset detachment faults. Nonetheless, the interplay between these detachment faults and melt supply remains an area of active research. In our study, we undertook a comprehensive analysis of a narrow shear zone and its wall rock, both retrieved from the International Ocean Discovery Program (IODP) Hole U1473A at the Atlantis Bank Oceanic Core Complex (OCC) on the Southwest Indian Ridge. Our methodology encompassed microstructural observations, electron probe analysis, and electron backscatter diffraction. Our findings indicate that an oxide-saturated melt permeated the semi-brittle lithosphere and the fault plane, acting as a lubricant and significantly diminishing the fault's frictional strength. Subsequent deformation-triggered melt segregation led to a 3–4-fold reduction in the viscosity of the footwall gabbros. This reduction likely induced a listric geometry, driven by the reorientation of local stress fields and unusually elevated melt pressure. In contrast to numerical model predictions, our results suggest that the development of oceanic detachment faults is chiefly controlled by syn-magmatic strain localization, potentially linked to the rate of melt emplacement and the thickness of the axial lithosphere.
Full article: https://doi.org/10.1016/j.epsl.2024.118892
