Beschreibung: At the present, the geochemical influence of the Galápagos hotspot (offshore South America) can be seen only along the Galápagos spreading center, north of the hotspot. It is possible, however, that Galápagos plume material also reached the East Pacific Rise in the past. Detecting such influence would be of particular importance for the interpretation of geochemical data from oceanic crust at Ocean Drilling Program (ODP) Site 1256, which formed ∼15 m.y. ago at the East Pacific Rise during a Miocene period of superfast spreading, and is considered to be a reference site for oceanic crust produced at fast-spreading ridges. Here we present geochemical data from Miocene basaltic crust (23–7 Ma) drilled at several Deep Sea Drilling Project (DSDP), ODP, and Integrated Ocean Drilling Program (IODP) sites that formed along the East Pacific Rise between 3°S and 7°N. Lavas formed between ca. 22.5 and ca. 11 Ma show enriched, Galápagos plume–like Pb and Nd isotope ratios (with a peak in enrichment between ≥18 and 12 Ma) compared to lavas created shortly before or after this time interval. Despite their enriched isotope composition, these samples generally show depletion in more-incompatible, relative to less-incompatible, trace elements. Derivation from an enriched Galápagos plume source that had experienced recent melt extraction before it melted further beneath the East Pacific Rise can explain the combined incompatible-trace-element depletion and isotopic enrichment of the 22.5–11 Ma lavas. The influence of plume material correlates with the interval of superfast spreading along the equatorial East Pacific Rise, suggesting a causal relationship. Enhanced ridge-plume interaction ("ridge suction") due to superfast spreading could have facilitated the flow of Galápagos plume material to the ridge. On the other hand, the arrival of Galápagos-type signatures took place immediately after formation of the Galápagos spreading center, which could have provided a pathway for hot plume material to spread into the main ridge network.

Beschreibung: The goal of R/V METEOR expedition M168 was to investigate the origin and geodynamic evolution of the enigmatic King’s Trough Complex, surrounding seamounts and the AzoresBiscay Rise in the North Atlantic Ocean northeast of the Azores. Before M168, these structures were still largely unexplored and their origin has been debated for decades. Investigation of the structures was conducted by extensive rock sampling with chain bag dredges, by bathymetric mapping with the ship’s own multi-beam echo-sounding system (KONGSBERG EM 122) and by sub-bottom profiling (ATLAS PARASOUND P70). A total of 48 dredge hauls in water depths between 5,340 and 1,340 m were carried out at Palmer Ridge and associated Freen and Peake Troughs, at King’s Trough, at the Gnitsevich Seamounts northwest of King’s Trough and at the northernmost Azores-Biscay Rise including the North Charcot Seamount Complex directly in the east. Of these dredge hauls, 36 (= 76.6 %) yielded a variety of magmatic rocks comprising lava fragments and pillow lava occasionally containing fresh glass, gabbroic/dioritic and doleritic rocks, ultramafic rocks possibly of harzburgitic composition and volcaniclastic rocks. Bathymetric mapping revealed that King’s Trough is much more complex than it appeared from previously available maps based on low resolution satellite altimetry. It seems to be composed of individual segments striking in slightly different directions and could possibly formed by a series of strike-slip faults.

Beschreibung: Despite their large number and in contrast to seamount chains, small solitary seamounts/seamount groups have rarely been sampled and therefore their origins remain enigmatic. Here we present 40Ar/39Ar, trace element and Nd‐Pb‐Hf isotope data from the solitary Demenitskoy Seamount, the isolated Tolkien seamount group and the Krylov Seamount and Ridge in the Canary Basin. Their chemical compositions range from intraplate ocean‐island‐basalt (Demenitskoy) to normal‐ and enriched‐mid‐ocean‐ridge‐basalt types (Tolkien and Krylov system, respectively). Lavas from all three seamount groups, however, show geochemical evidence for involvement of enriched (Canary/Cape Verde) plume material. Seismic tomography shows that large areas around these mantle plumes are affected by dispersal of presumably low‐velocity material, which also could have fed nearby isolated seamounts with diffusely‐upwelling plume material. This process may be extremely widespread but has been poorly studied to date.

Beschreibung: Understanding the opening of the Bay of Biscay and the associated kinematics of the Iberian plate during the late Cretaceous is fundamental for reconstructing the opening and evolution of the North Atlantic Ocean. A key region for unraveling the opening history of the Atlantic Ocean basin is the intersection of the former Biscay spreading axis with the early Mid-Atlantic Ridge, offshore of the NW corner of present-day Iberia. At this site, the intersection merges with the ~750 km long Azores-Biscay Rise, a prominent feature in the East Atlantic of unknown origin. Models for the origin of the Azores-Biscay Riserange from formation as intraplate hotspot track to shallow tectonic causes. The R/V METEOR expedition M176 conducted multi-beam mapping and hard rocksampling of the following structures: 1) Charcot and La Coruña seamount complexes (the presumed former Biscay spreading center), 2) seamounts north of the Azores-Biscay Rise, and 3) the entire Azores-Biscay Rise. Despite technical challenges, 78 dredge hauls were carried out and 2,404 nm were swath-mapped. Age determinations and geochemical investigations of the recovered rock samples will allow us to test the different models regarding the opening of the Bay of Biscay and the origin of the Azores-Biscay Riseas well as the possible role of a mantle plume in this area during the opening of the North Atlantic.

Beschreibung: Although previous findings support an origin of the Shatsky Rise igneous plateau (Northwest Pacific) through interaction of a mantle plume with a mid-ocean ridge triple junction, the evidence for the involvement of a mantle plume is equivocal. The identification of an intraplate hotspot track emanating from the plateau could solve this controversy. Here we present major and trace element geochemical data from two different bathymetric features that emanate from the youngest end of Shatsky Rise: Papanin Ridge and the Ojin Rise Seamount province. Combining our results with plate tectonic reconstructions, we conclude that Papanin Ridge represents a hotspot track formed by plume-ridge interaction. Whereas the southwestern part was formed along the path of the retreating Pacific-Farallon-Izanagi triple junction, the northeastern part was built by preferential drainage into its Pacific-Farallon branch. In contrast, the Ojin Rise Seamounts formed as a true intraplate hotspot track of the Shatsky plume tail. Our wide-ranging study reveals systematic spatial geochemical variations, consistent with a lithospheric thickness control on magma composition derived from melting a heterogeneous plume source. The recognition of two hotspot tracks and in particular of the Ojin Rise Seamounts as an intraplate hotspot track that is directly linked to Shatsky plateau volcanism both in terms of geochemistry and plate tectonic reconstructions confirms the long-disputed involvement of a mantle plume for the formation of Shatsky Rise.

Beschreibung: Rio Grande Rise: microcontinent, mantle plume, or both? The origin of the Rio Grande Rise (RGR) is debated. It could represent a continental sliver, or a large igneous province that was emplaced in the late Cretaceous after the opening of the South Atlantic Ocean. The interplay between the RGR and the nearby Jean Charcot Seamount Chain (JCSC) is also not understood. Cruise MSM82 dredge sampled rocks from the JCSC and the RGR and measured two seismic refraction profiles across the RGR where it is bisected by a long rift graben. A range of geophysical data were also collected during much of the expedition, including magnetics, gravity, bathymetry (Kongsberg EM 122), sub-bottom profiling (ATLAS PARASOUND DS P70) and ADCP data. The combination of geochronological, geochemical and geophysical information will provide a unique window on the relation between mantle plumes, continental fragments and the evolution of large igneous provinces.