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  • 1
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    PANGAEA
    In:  Supplement to: Devey, Colin W; Ackermand, Dietrich; Binard, Nicolas; Chmarzynski, P; Franke-Bruckmaier, B; Geldmacher, Jörg; Graupner, T; Haake, F W; Haase, Karsten M; Hemond, Christophe; Krüger, O; Mühlhan, Norbert; O'Connor, John; Ott, S; Peucker-Ehrenbrink, Bernhard; Pototzki, Frank; Segl, Monika; Tichomirov, W (1993): Cruise report SO-84: The St Helena hotspot - Las Palmas-Cape Town 02.01.93-20.02.93. Berichte - Reports, Geologisch-Paläontologisches Institut und Museum, Christian-Albrechts-Universität, Kiel; 64; 1-103; ISSN 0175-9302, TIB - Technische Informationsbibliothek Universitätsbibliothek Hannover, Berichte-Reports, Geologisch-Paläontologisches Institut der Universität Kiel, 64, 103 pp, https://doi.org/10.2312/reports-gpi.1993.64
    Publication Date: 2024-02-03
    Description: The SO-84 cruise from Las Palmas to Cape Town studied the underwater volcanism associated with the St Helena hotspot. Wide-spaced grid mapping of a region south and west of St Helena island identified three previously unknown hotspot volcanoes (which we named Josephine 16°27'S-9°W, Jade 16°13'S-7°46'W and Benjamin 16°12'S-8°31'W) and several older, probably near-ridge-generated seamounts. The newly discovered hotspot seamounts, and the previously-known seamounts of Bagration, Bonaparte and Kutuzov were mapped and sampled. Onboard geochemical studies confirm that they all show trace-element (Rb, Nb, Y, Zr, Sr) enriched, hotspot magma-type compositions. Morphological studies and the state of the samples collected from the seamounts (all have at least 1 mm-thick Mn crusts) suggest that none of the volcanoes is presently active, and that the St Helena hotspot is probably extinct at the present time. Josephine appears to be the youngest volcano, and one dredge here yielded fossil hydrothermal material (Fe-hydroxides). To test the hypothesis that the extinction of the hotspot is due to its magmas being channelled to the Mid-Atlantic Ridge, several dredges were taken on the ridge opposite St Helena. Furthermore, in the proposed influence zone of the St Helena plume head, Grattan seamount (9°44'S-12°48'W) was also sampled to examine whether its composition has been affected by the St Helena plume. During the transit from Las Palmas to St Helena, several sediment cores were taken in 3000 m water depth close to the ridge axis for palaeoclimatological work.
    Keywords: 12DS; 13DS; 14DS; 1DS; 20DS; 21DS; 22DS; 23DS; 24DS; 25DS; 26DS; 27DS; 31DS; 35DS; 37DS; 42DS; 43DS; 44DS; 47DS; 49DS; 53DS; 54DS; 55DS; 59DS; 60DS; 63DS; 64DS; 65DS; 68DS; 69DS; 71DS; 72DS; 74DS; 7DS; 83DS; Comment; Deposit type; DEPTH, sediment/rock; Description; Dredge; DRG; Event label; GIK/IfG; GIK17835-1; GIK17841-1; GIK17846-1; GIK17847-1; GIK17848-1; GIK17854-1; GIK17855-1; GIK17856-1; GIK17857-1; GIK17858-1; GIK17859-1; GIK17860-1; GIK17861-1; GIK17865-1; GIK17869-1; GIK17871-1; GIK17876-1; GIK17877-1; GIK17878-1; GIK17881-1; GIK17883-1; GIK17887-1; GIK17888-1; GIK17889-1; GIK17893-1; GIK17894-1; GIK17897-1; GIK17898-1; GIK17899-1; GIK17902-1; GIK17903-1; GIK17905-1; GIK17906-1; GIK17908-1; GIK17917-1; Identification; Institute for Geosciences, Christian Albrechts University, Kiel; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; Position; Quantity of deposit; Sediment type; Size; SO84; Sonne; South Atlantic; ST. HELENA HOTSPOT; Substrate type; Visual description
    Type: Dataset
    Format: text/tab-separated-values, 725 data points
    Location Call Number Limitation Availability
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  • 2
    Publication Date: 2018-05-04
    Description: Vesteris Seamount is a solitary alkaline volcano in the Greenland Basin some 280 km NW of Jan Mayen. Topographic and geophysical studies have shown no sign of an associated plume trace. Evidence from ash layers in sediment cores around the volcano and dating of dredged samples show that it has been active in Quaternary times. The lavas from Vesteris studied here consist of basanites, tephrites, mugearite, and alkali basalts. Crystal fractionation models are consistent with the generation of the tephrites and mugearite from a basanitic parent. Extensive kaersutite fractionation is required late in the fractionation sequence to produce the extreme mugearite composition. Na-Al-Fe-rich green cores to many clinopyroxene phenocrysts at Vesteris suggest a fractionation history beginning at high pressure in the mantle. Differences between Vesteris and Jan Mayen in the ratios of highly incompatible trace elements such as Ce/Pb and Rb/Cs, which will not normally be fractionated from one another during mantle melting, suggest that the two are not derived from the same source. Relatively unradiogenic Sr isotope ratios (compared with Bulk Earth), and highly incompatible trace element patterns similar to those for St. Helena, suggest that Vesteris magmas are derived from a depleted, asthenospheric source. We propose that the Vesteris basanites are very low degree partial melts (˜1%) of this source, most probably those which give rise to the seismic low-velocity zone (LVZ). Such small-degree melts may preferentially tap small-scale heterogeneities in the asthenosphere. Vesteris lies at the intersection of two major structural trends in the Greenland Basin—(1) a zone of major reorientation of spreading direction on the Mohns Ridge north of Jan Mayen and (2) the extension of the Kolbeinsey Ridge axis. We propose that a combination of the extensional stress fields related to these two lineaments produces sufficient dilation of the lithosphere at Vesteris to allow magmas from the LVZ to reach the surface.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Limitation Availability
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