Seismological constraints on the thermal structure along the Lucky Strike segment (Mid-Atlantic Ridge) and interaction of tectonic and magmatic processes around the magma chamber

The crust at mid-ocean ridges is formed through a combination of magmatic and tectonic processes. Along slow-spreading ridges, magmatism is inferred to be discontinuous and episodic, and lithospheric faulting may strongly interact with the melt supply system. These interactions can be studied for the first time at the Lucky Strike segment along the Mid-Atlantic Ridge (MAR), where a 3.4 km deep magma chamber (AMC) extending ∼6 km along-axis is found at its centre (Singh et al. in Earth Planet Sci Lett 246:353-366, 2006). With an array of ocean bottom seismometers we have detected along this ridge segment approximately 400 microseismic events during a total of 6 days, and located 71 of them, whose local magnitudes ranged from 0.2 to 1.8. While most of the events were concentrated at non-transform offset and inside corners, three events with well-constrained locations were detected beneath the central volcano and at the edges of the AMC. Two of the microearthquakes, which occur in a brittle lithosphere and therefore at temperatures lower than 750°C, are deeper than the AMC and therefore very steep thermal gradients both along- and across-axis. Regionally seismicity deepens from ∼6 km at the segment center to >10 km towards the ends.