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The Trans‐Atlantic Geotraverse (TAG) hydrothermal field on the Mid‐Atlantic Ridge is one of the best‐studied hydrothermal systems to date. However, high‐resolution bathymetric data obtained in 2016 by an autonomous underwater vehicle (AUV) reveal new information about the distribution of active and inactive hydrothermal deposits, and their relation to structural features. The discovery of previously undocumented inactive vent sites contributes to a better understanding of the accumulation rates and the resource potential of seafloor massive sulfide deposits at slow‐spreading ridges. The interpretation of ship‐based and high‐resolution AUV‐based data sets allowed for the determination of the main tectonic stress regimes that have a first‐order control on the location and distribution of past and present hydrothermal activity. The data reveal the importance of cross‐cutting lineament populations and temporal variations in the prevalent stress regime. A dozen sulfide mounds contribute to a substantial accumulation of hydrothermal material (~29 Mt). The accumulation rate of ~1,500 t/yr is comparable to those of other modern seafloor vent fields. However, our observations suggest that the TAG segment is different from many other slow‐spreading ridge segments in its tectonic complexity, which confines sulfide formation into a relatively small area and is responsible for the longevity of the hydrothermal system and substantial mineral accumulation. The inactive and weakly active mounds contain almost 10 times the amount of material as the active high‐temperature mound, providing an important indication of the global resource potential for inactive seafloor massive sulfide deposits.

At slow to ultraslow spreading rates along mid-ocean ridges, thicker lithosphere typically impedes magma generation and tectonic extension can play a more significant role in crustal production (Dick et al., 2003). The source of anomalously high magma supply thus remains unclear along ridges with ultraslow-spreading rates adjacent to Jan Mayen Island in the North Atlantic (Neumann and Schilling, 1984;Mertz et al., 1991; Haase et al., 1996;Schilling et al., 1999;Trønnes et al., 1999; Haase et al., 2003;Mertz et al., 2004;Blichert-Toft et al., 2005; Debaille et al., 2009). Here we show that Jan Mayen volcanism is likely the surface expression of a small mantle plume, which exerts significant influence on nearby mid-ocean ridge tectonics and volcanism. Progressive dilution of Jan Mayen geochemical signatures with distance from the hotspot is observed in lava samples from the immediately adjacent Mohns Ridge, and morphological indicators of enhanced magma supply are observed on both the Mohns Ridge and the nearby Kolbeinsey Ridge, which additionally locally overlies a highly heterogeneous, eclogite-bearing mantle source. These morphological and geochemical influences underscore the importance of heterogeneous mantle sources in modifying melt supply and thus the local expression of tectonic boundaries. LetterThe normal accretion process along divergent plate boundaries can be notably altered in hotspot-ridge interaction settings, where elevated mantle temperature anomalies enhance mantle melting, generating unusually thick oceanic crust (e.g., Schilling et al., 1985;Schilling, 1991; Gale et al., 2013 Gale et al., , 2014. Jan Mayen and its immediate environs in the North Atlantic (Fig. 1) include an intraplate, volcanically-active island or hotspot (Jan Mayen Island), positioned at the northern terminus of a small, rifted microcontinent (Jan Mayen Ridge; Johnson and Heezen, 1967; Kodaira et al., 1997; Gaina et al., 2009) and adjacent to two second-order ultraslow-spreading (Dick et al., 2003) ridge segments, the Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR), and the Jan Mayen Fracture Zone, a major fracture zone with ~200 km of transform offset. Although different in key ways, broad geochemical similarities between Jan Mayen Island and Icelandic lavas have suggested the influence of a mantle plume (either a unique Jan Mayen plume or emplaced Icelandic material) on mantle melting beneath Jan Mayen Island (Schilling et al., 1999;Trønnes et al., 1999; Debaille et al., 2009). The absence of a clear hotspot track has led to conflicting, alternate interpretations for Jan Mayen's high magma production rate and enriched chemistry (Imsland, 1986;Maaløe et al., 1986;Thy et al., 1991): cold edge effects near the fracture zone (Mertz et al., 1991; Haase et al., 1996), variably melting source heterogeneities (Mertz et al., 1991; Haase et al., 2003;Mertz et al., 2004), upwelling along a mantle chemical discontinuity (Blichert-Toft et al., 2005), or a locally wet mantle (Haase et al., 2003;Mertz et al., 2004)....

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