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1. Site U1575

   https://doi.org/10.14379/iodp.proc.391.103.2023  

   Sager, W.; Hoernle, K.; Höfig, T.W.; Avery, A.J.; Bhutani, R.; Buchs, D.M.; Carvallo, C.A.; Class, C.; Dai, Y.; Dalla Valle, G.; et al (October 2023, Proceedings of the International Ocean Discovery Program Expedition reports)

   The strategy for International Ocean Discovery Program (IODP) Expedition 391 (Walvis Ridge Hotspot) was to drill at three general locations on Walvis Ridge and one in Guyot Province, providing an age transect along the Tristan-Gough-Walvis (TGW) hotspot track. Site U1575 (proposed Site FR-1B), located on the lower Walvis Ridge between Valdivia Bank and Frio Ridge (Figure F1), is the easternmost and presumably the oldest site. Both hotspot models and the age progression of Homrighausen et al. (2019) predict an age of ~100 Ma (Figures F2, F3). Site U1575 is thus an important sample of the early TGW track shortly after it transitioned from the continental flood basalt to the submarine hotspot track setting. 

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2. Expedition 397T Scientific Prospectus: Transit and Return to Walvis Ridge Hotspot

   https://doi.org/10.14379/iodp.sp.397T.2022  

   Sager, W.W.; Hoernle, K.; Blum, P. (July 2022, Scientific prospectus)

   During International Ocean Discovery Program (IODP) Expedition 391, the Tristan-Gough-Walvis Ridge (TGW) hotspot track was cored in December 2021–February 2022. Its overarching objective was to recover basaltic rock from TGW edifices to understand the evolution of Walvis Ridge and related guyots. Significant cuts to the Expedition 391 operational plan were necessary as a result of lost time due to COVID-19 mitigation procedures. Because the R/V JOIDES Resolution will pass over Walvis Ridge during the transit from Cape Town, South Africa, to Lisbon, Portugal, prior to IODP Expedition 397, the 3 week transit provides an opportunity to drill one or two holes that were planned but not cored during Expedition 391. The transit schedule indicates that ~7 days of ship time will be available for this effort. Coring will be attempted at one or two sites, depending on weather and operational difficulties. The first site to be cored will be proposed Site GT-6A on the flank of the Gough track ridge. If time permits, coring will also be done at proposed Site TT-3A on the Tristan track, completing the proposed transect across the three chains of the Walvis Ridge guyot province. Two operational strategies are planned to address the limited time available. First, the ~164 m thick (Site GT-6A) and ~146 m thick (Site TT-3A) sediment sections will be drilled without coring to ~20 m above basement. Primary Site GT-6A, which is ~1.1 km upslope from alternate Site GT-4A, was specifically proposed because of its reduced sediment thickness. 

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3. Site U1576

   https://doi.org/10.14379/iodp.proc.391.104.2023  

   Sager, W.; Hoernle, K.; Höfig, T.W.; Avery, A.J.; Bhutani, R.; Buchs, D.M.; Carvallo, C.A.; Class, C.; Dai, Y.; Dalla Valle, G.; et al (October 2023, Proceedings of the International Ocean Discovery Program Expedition reports)

   The strategy for International Ocean Discovery Program (IODP) Expedition 391 was to drill at three distributed locations on Walvis Ridge and one in Guyot Province, providing an age transect along the Tristan-Gough-Walvis (TGW) hotspot track. Site U1576 (proposed Site VB-14A), located on the western flank of Valdivia Bank (Figure F1), is one of two sites on this edifice selected to investigate the type of volcanism, possible plume-ridge interaction, the older extent of hotspot track geochemical zonation, and the age progression. Both hotspot models and the age progression of Homrighausen et al. (2019) predict an age of ~80–85 Ma (Figures F2, F3). A magnetic anomaly map indicates that Site U1576 is located on a prominent negative anomaly (Figure F4) that is thought to be Chron 33r (79.9–83.6 Ma; Ogg, 2020). 

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4. Site U1585

    Sager, W.; Blum, P.; Carvallo, C.A.; Heaton, D.; Nelson, W.R.; Tshiningayamwe, M.; Widdowson, M. (October 2023, Proceedings of the International Ocean Discovery Program Expedition reports)

   The strategy of Expedition 391 was to core at six distributed locations on the Tristan-Gough-Walvis (TGW) hotspot track, providing new insights into the temporal, volcanologic, petrologic, geochemical and paleomagnetic evolution of the hotspot track (see Scientific objectives in the Expedition 391 summary chapter [Sager et al., 2023c]). At the youngest and westernmost of these locations, three sites were proposed as a transect across the northern Guyot Province seamounts and ridges immediately southwest of the morphologic split that occurs at about 2°E (Figure F1). Because of severe cuts to operational time on that expedition caused by COVID-19 mitigation, two proposed sites (GT-4A and TT-4A) were omitted (see Introduction in the Expedition 391 summary chapter [Sager et al., 2023c]). Only the middle site (U1578) was cored (Figures F1, F2). This omission was a major deficiency for Expedition 391, because the three holes were positioned to sample the isotopic split that first occurs farther northeast, at the location of the DSDP Leg 74 transect (Hoernle et al., 2015). By omitting the ends of the transect, only dredge samples are available to characterize the isotopic end-members, which correspond to the Tristan track (northern seamounts that connect Walvis Ridge with the Tristan Island group) and the Gough track (southern seamounts that connect Walvis Ridge to the Gough Island group). 

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5. Site U1577

   https://doi.org/10.14379/iodp.proc.391.105.2023  

   Sager, W.; Hoernle, K.; Höfig, T.W.; Avery, A.J.; Bhutani, R.; Buchs, D.M.; Carvallo, C.A.; Class, C.; Dai, Y.; Dalla Valle, G.; et al (October 2023, Proceedings of the International Ocean Discovery Program Expedition reports)

   The strategy for International Ocean Discovery Program (IODP) Expedition 391 was to drill at three distributed locations on Walvis Ridge and one in Guyot Province, providing an age transect along the Tristan-Gough-Walvis (TGW) hotspot track. Site U1577 (proposed Site VB-13A) is located on the eastern flank of Valdivia Bank (Figure F1). The purpose of this site and Site U1576 (on the west side of Valdivia Bank) is to investigate the type of volcanism, possible plume-ridge interaction, geochemical heterogeneity, and the age progression of the hotspot track. Both hotspot models and the age progression of Homrighausen et al. (2019) predict an age of ~80–85 Ma (Figures F2, F3). A magnetic anomaly map indicates that Site U1577 is located on a prominent positive anomaly (Figure F4) that is thought to be the young end of Chron 34n (83.7 Ma; Ogg, 2020). 

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