Unveiling the hotspot-driven magmatic plumbing system of the Center track, Walvis Ridge (South Atlantic Ocean): Insights from mineral geochemistry and isotopic heterogeneity in basalts from IODP Expedition 391

The Tristan-Gough-Walvis Ridge volcanic chain, located in the South Atlantic Ocean on the African plate, is one of Earth’s longest linear seafloor features. However, the origin of its magmatism remains poorly understood. To better understand its formation, temporal evolution, and geochemical characteristics, six sites were drilled along the Tristan-Gough-Walvis Ridge chain by International Ocean Discovery Program (IODP) Expeditions 391 and 397T: three sites on Valdivia Bank (U1575, U1576, and U1577) and three sites in the Guyot Province (U1578, U1584, and U1585). Among these, Site U1578, located on the deep northwestern flank of a “Center track” seamount, represents the deepest basement penetration (>300 m) of both expeditions. According to preliminary geophysical and biostratigraphic constraints, the stratigraphic sections recovered from Site U1578 span >2.0 m.y. of the Paleocene (ca. 64.8−62.3 Ma). Here, we present an integrated study of major and trace element concentrations in minerals, combined with in situ Sr isotopes of plagioclase (Pl) from Site U1578 basalts. Based on the olivine-spinel (Ol-Sp) thermometry and pyMelt modeling, the calculated mantle potential temperature of the Center track is ≥1400 °C, which is ∼50 °C higher than that of mid-ocean-ridge basalts (MORBs), most likely reflecting the influence of a mantle plume. Based on geochemical compositions and crystal textures, we identified three distinct clinopyroxene (Cpx) groups: Group 1 is characterized by high Mg# (>83.4) and elevated Ni (>200 ppm) and Cr (>5000 ppm) contents; Group 2 has intermediate Mg# (76.6−83.4), Ni (100−200 ppm), and Cr (1000−5000 ppm); and Group 3 exhibits low Mg# (<76.6) and depleted Ni (<70 ppm) and Cr (<30 ppm) contents. Multiple episodes of magma recharge and mixing in the plumbing system beneath the Center track produced a diversity of mineral textures, including normal, reverse, sector, and oscillatory zoning. Additionally, Pl from this site is isotopically heterogeneous (87Sr/86Sr of 0.7038 ± 0.0001 to 0.7046 ± 0.0001) and broadly similar to basalts from the northern Tristan track in the Guyot Province. A shift to more radiogenic Sr isotopic signatures from the lower to the upper igneous units suggests the increasing incorporation of radiogenic materials into the mantle source with time, potentially derived from enriched mantle typically associated with basalts of the southern Gough track. These findings indicate that basaltic lavas from the Center track originate from an anomalously hot and geochemically enriched mantle source associated with a mantle plume or hotspot activity. Diverse mineral textures and chemistry record complex fractional crystallization and mixing processes during magma storage prior to eruption.