Distribution of large-scale detachment faults on mid-ocean ridges in relation to spreading rates

Large-scale detachment faults on mid-ocean ridges(MORs)provide a window into the deeper earth.They have megamullion on their corrugated surfaces,with exposed lower crustal and upper mantle rocks,relatively high residual Bouguer gravity anomaly and P-wave velocity,and are commonly associated with oceanic core complex.According to 30 detachment faults identified on MORs,we found that their distances to the axis mostly range from 5 to 50 km,half-spreading rates range from 6.8 to 17 mm/a,and activity time ranges from recent to 3 Ma.Most of the detachment faults are developed on the slow spreading Mid-Atlantic Ridge(MAR)and ultra-slow spreading Southwest Indian Ridge(SWIR),with the dominant half-spreading rates of7–13 mm/a,especially 10–13 mm/a.Furthermore,they mostly occur at the inside corner of one segment end and result in an asymmetric seafloor spreading.The detachment faults on MORs are mainly controlled by the tectonism and influenced by the magmatism.Long-lived detachment faults tend to be formed where the ridge magma supply is at a moderate level,although the tectonism is a first-order controlling factor.At the slow spreading ridges,detachment faults tend to occur where local magma supply is relatively low,whilst at the ultra-slow spreading ridges,they normally occur where local magma supply is relatively high.These faults are accompanied by hydrothermal activities,with their relationships being useful in the study of hydrothermal polymetallic sulfides and their origin.