Effects of axially variable diking rates on faulting at slow spreading mid-ocean ridges
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Earth and Planetary Science Letters
Magma supply for dike injection can be highly variable within a segment of a slow-spreading mid-ocean ridge but the tectonic impact of this variability is not fully understood. Here, we use three-dimensional numerical models to quantify the effects of variable diking rates on the faulting mode at a 20 km-long slow spreading ridge segment. In addition to end-member faulting modes in which long-lived detachment faults or short-lived normal faults form along the whole segment, we newly identify a transitional mode in which a detachment and a short-lived normal fault form simultaneously but in respective domains separated by a transfer fault. Different faulting modes can be better correlated with the average dike intrusion rate, rather than the highest or lowest rate along the segment. Along-axis stress coupling tends to homogenize fault offset along the segment, inhibiting the domination of a particular faulting mode associated with an extreme local diking rate. This homogenizing effect explains why detachment faults can sometimes form even in the regions previously considered as unfavorable. Our results further suggest that a long (>15 km) and continuous detachment, partially overlain by younger faults, can create an oceanic core complex when faults weaken fast and diking rate is low. When faults weaken slow and diking rate is moderate, however, faulting occurs in the transitional mode, producing a detachment over only a part of the segment length.