Crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes, with magmatic accretion possibly involving short-lived crustal magma chambers1. The reflections of seismic waves from crustal magma chambers have been observed beneath intermediate2,3 and fast-spreading centres4,5, but it has been difficult to image such magma chambers beneath slow-spreading centres6,7, owing to rough seafloor topography and associated seafloor scattering7,8. In the absence of any images of magma chambers6 or of subsurface near-axis faults, it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow-spreading ridges. Here we report the presence of a crustal magma chamber beneath the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge. The reflection from the top of the magma chamber, centred beneath the Lucky Strike volcano and hydrothermal field, is approximately 3 km beneath the sea floor, 3–4 km wide and extends up to 7 km along-axis. We suggest that this magma chamber provides the heat for the active hydrothermal vent field above it. We also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward-dipping faults cutting through the volcanic edifice, suggesting continuous interactions between tectonic and magmatic processes.
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Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
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We thank the captain (J.-R. Glehen) and the crew of the RV l'Atalante for providing support during the SISMOMAR cruise, and the seismic team of GENAVIR for acquiring the seismic data. The INSU MOMAR programme funded the acquisition of SISMOMAR project. This is an Institut de Physique du Globe de Paris contribution.
Flattened Seismic reflection images: Seismic sections for lines 8, 20 and 37 flattened using smooth seafloor topography to obtain a more accurate crustal geometry. The AMC reflections are bounded by red circles, layer 2A is indicated by blue squares and the fault reflector ends are indicated by arrows. No vertical exaggeration for a crustal velocity of 5 km/s. (PDF 18920 kb)
Seismic reflection images of the AMC and faults: The same seismic sections as in Figure 2, but without highlights and labels (interpretive curves). The fault reflectors are indicated by arrows at their ends. (PDF 21730 kb)
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Multi-scale Quantitative Risk Analysis of Seabed Minerals: Principles and Application to Seafloor Massive Sulfide Prospects
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