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  • 1
    Publication Date: 2018-01-10
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 2
    ISSN: 0016-7835
    Keywords: Key words Costa Rica ; Ophiolites ; Oceanic crust ; Hotspot ; Galápagos islands ; Volcanology ; Petrology ; Geochemistry ; Isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The Quepos, Nicoya and Herradura oceanic igneous terranes in Costa Rica are conspicuous features of a Mid to Late Cretaceous regional magmatic event that encompasses similar terranes in Central America, Colombia, Ecuador and the Caribbean. The Quepos terrane (66 Ma), which consists of ol-cpx phyric, tholeiitic pillow lavas overlain by highly vesicular hyaloclastites, breccias and conglomerates, is interpreted as an uplifted seamount/ocean island complex. The Nicoya (∼90 Ma) and Herradura terranes consist of fault-bounded sequences of sediments, tholeiitic volcanics (pillow lavas and massive sheet flows) and plutonic rocks. The volcanic rocks were emplaced at relatively high eruption rates in moderate to deep water, possibly forming part of an oceanic plateau. Major and trace element data from Nicoya/Herradura tholeiites indicate higher melting temperatures than inferred for normal mid-ocean-ridge basalts (MORB) and/or a different source composition. Sr–Nd–Pb isotopic ratios from all three terranes are distinct from MORB but resemble those from the Galápagos hotspot. The volcanological, petrological and geochemical data from Costa Rican volcanic terranes, combined with published age data, paleomagnetic results and plate tectonic reconstructions of this region, provide strong evidence for a Mid Cretaceous (∼90Ma) age for the Galápagos hotspot, making it one of the oldest known, active hotspots on Earth. Our results also support an origin of the Caribbean Plate through melting of the head of the Galápagos starting plume.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2006
    Keywords: TF III ; Task Force III ; Lithosphere-Astenosphere Interactions
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  • 4
    Publication Date: 2017-12-19
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
    Publication Date: 2015-06-03
    Description: Ocean islands, seamounts and volcanic ridges are thought to form above mantle plumes.Yet, this mechanism cannot explain many volcanic features on the Pacific Ocean floor1 and some might instead be caused by cracks in the oceanic crust linked to the reorganization of plate motions1–3. A distinctive bend in the Hawaiian–Emperor volcanic chain has been linked to changes in the direction of motion of the Pacific Plate4,5, movement of the Hawaiian plume6–8, or a combination of both9. However, these links are uncertain because there is no independent record that precisely dates tectonic events that a�ected the Pacific Plate. Here we analyse the geochemical characteristics of lava samples collected from the Musicians Ridges, lines of volcanic seamounts formed close to the Hawaiian–Emperor bend. We find that the geochemical signature of these lavas is unlike typical ocean island basalts and instead resembles mid-ocean ridge basalts. We infer that the seamounts are unrelated to mantle plume activity and instead formed in an extensional setting, due to deformation of the Pacific Plate. 40Ar/39Ar dating reveals that the Musicians Ridges formed during two time windows that bracket the time of formation of the Hawaiian–Emperor bend, 53–52 and 48–47 million years ago.We conclude that the Hawaiian–Emperor bendwas formed by plate–mantle reorganization, potentially triggered by a series of subduction events at the Pacific Plate margins.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    Publication Date: 2019-07-17
    Description: Die Marie Byrd Seamounts sind eine submarine Intraplattenvulkanprovinz, die sich im Norden des Schelfs von Marie Byrd Land über 800 km von Osten nach Westen erstreckt. Die einzelnen Seamounts sind bis zu 3.000 m hoch und messen bis zu 75 x 50 km an ihrer Basis in ca. 3.500 bis 4.000 m Wassertiefe. Da bisher nur wenig über diese bedeutende Vulkanprovinz, die nicht allein mit den herkömmlichen Modellen zur Entstehung von Intraplattenvulkanismus erklärt werden kann, bekannt war, wurden auf der F.S. Polarstern-Expedition ANT-XXIII/4 2006 sowohl neue bathymetrische Daten als auch erstmals magmatische Gesteine der Marie Byrd Seamounts gewonnen. Ziel der Untersuchungen an den Marie Byrd Seamounts ist es, die Magmenquellen, Petrogenese und die zeitlich-räumliche Entwicklung dieser Vulkane zu rekonstruieren. In Kombination mit geophysikalischen Modellen soll so zur Rekonstruktion der tektonischen Entwicklung des Südwestpazifiks und der Ursachen von Intraplattenvulkanismus (Great Plume Debate) beigetragen werden.Alle kartierten großen Marie Byrd Seamounts sind Guyots, d.h. ehemalige Inselvulkane, die an der Meeresoberfläche erodiert wurden und abgesunken sind, wobei die Absenkungsraten im Westen der Seamountprovinz mit 1.600 m niedriger sind als im Osten (2.400 m). Ferner zeigt die Bathymetrie mindestens zwei Aktivitätsphasen dieser Vulkane (Schildphase, Posterosionsphase). Ar/Ar-Laserdatierungen ergaben känozoische Alter (Eozänen bis Paläozän) für die Marie Byrd Seamounts, die demnach deutlich nach dem Gondwana-Aufbruch und der Ausbildung des pazifisch-antarktischen Rückens entstanden sind. Erste, vorläufige Ergebnisse der geochemischen Analytik zeigen, dass die Marie Byrd Seamounts von relativ hoch entwickelten, Si-unterstättigten Magmen (ne-normative Alkalibasalte bis hy-normative Trachybasalte) gebildet wurden. Diese wurden aus einer isotopisch angereicherten Quelle generiert, bei der wahrscheinlich eine verarmte Komponente (DUM =depleted upper mantle) und mindestens zwei angereicherte Komponenten beteiligt waren, darunter möglicherweise EMII (kontinentales Material oder Sedimente). Die heterogene Kristallinität der Magmen verweist auf Magmenmischung als wichtigen Prozess während der Magmengenese. Insgesamt deuten die ersten Daten von den Marie Byrd Seamounts auf komplexe tektonische und magmatische Prozesse im Gebiet der südwestlichen Amundsensee während des Paläogen hin.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 7
    Publication Date: 2019-07-16
    Description: The crudely linear trend and apparent age progression of the Walvis Track (Walvis aseismic volcanic ridge and Guyot Province to the SW) is commonly believed to reflect a mantle-plume-related hotspot track connecting the Etendeka Flood Basalts with Tristan and Gough Islands. The validity of the few age data and thus age progression for the Tristan/Gough hotspot track, however, are severely questioned. The plume hypothesis itself is also increasingly challenged by The Great Plume Debate and requires critical field tests. In addition, the Walvis Ridge is considered a type locality for the enriched mantle (EM) I endmember of intraplate basalts. The project WALVIS I conducts an integrated Ar/Ar geochronological and geochemical study (major and trace element and Sr-Nd-Pb-Hf-O isotopes) on existing samples from the Walvis Track and Rio Grande Rise. Our sample collection includes 〉100 samples from 34 sites of various international cruises and from five DSDP sites. These samples are used to test for age progressive magmatism along the Walvis Track, to evaluate changes in chemical composition through time, particularly to see if there is a geochemical zonation along this volcanic lineament, and to constrain further the ultimate origin of the EM-I mantle endmember. Due to logistical reasons the appointment of Mrs. Joana Deppe as Ph D student has been delayed until summer 2009. Nevertheless initial screening of the entire sample suite, making of thin sections as well as preparation of 22 samples from the Guyot Province for XRF (major elements), ICPMS (trace elements) and TIMS (Sr-Nd-Pb isotopes) has been carried out since January 2009. This geochemical work serves as a critical test for a possible zonation of the Tristan-Gough mantle source region through time and first results will be presented at the SPP1375 workshop. Available data from both island groups possess distinct trace element and Pb isotopic compositions (e.g. Ba/Th and 207 Pb/204Pb), which could reflect a zoned plume. Still the longevity of these components has not been established yet, because the Gough component can presently only be tracked to McNish seamount (8 Ma), to the east of Gough, and RSA (19 Ma) seamount. Therefore, the dredge samples collected by R/V Polarstern in 2006 at the morphological termination of the Gough track play a crucial role. Full scale preparation of key samples for Ar-Ar geochronological work will take place this summer and a first batch of mineral separates will be irradiated this fall so that age dates will become available early 2010. Overall our study also serves as the basis for a more detailed survey along the Walvis Ridge with R/V Meteor; a proposal of our workgroup that has been positively reviewed recently by the Senatskommission für Ozeanographie.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
    Publication Date: 2015-12-10
    Description: A suite of 48 samples, including both historical and prehistoric lavas and some plutonic rocks, have been analysed from the Cumbre Vieja rift, La Palma, Canary Islands. Additionally, mineral–melt partition coefficients have been measured for clinopyroxene, plagioclase, amphibole, titanite and apatite in selected rocks. The lavas range from basanite to phonolite (SiO 2 = 41·2–57·5 wt % and MgO = 10–0·8 wt %) in composition and form coherent, curvilinear major and trace element arrays in variation diagrams, irrespective of eruption age. The mafic lavas have typical ocean island incompatible trace element patterns and Sr, Nd and Pb isotope compositions show little variation but have a HIMU-type character. Generation of the parental magmas is inferred to have involved ~4% dynamic melting of a garnet lherzolite source that may have previously been metasomatized by melts derived from a recycled mafic component containing residual phlogopite. The major process of differentiation to phonotephrite involved fractional crystallization of basanitic magmas that evolved along the same liquid line of descent under similar pressure–temperature conditions. Numerical simulations using the MELTS algorithm suggest that this occurred across a temperature interval from c. 1320 to 950°C at 400 MPa and an oxygen fugacity equivalent to quartz–fayalite–magnetite (QFM), with an initial H 2 O content of 0·3 wt %. The later stages of differentiation (〈5 wt % MgO) were dominated by mixing with partial melts of young syenites formed from earlier magma batches. All of the lavas are characterized by 230 Th and 226 Ra excesses and ( 230 Th/ 238 U) decreases with decreasing Nb/U and increasing SiO 2 , with no accompanying change in ( 226 Ra/ 230 Th). To explain the observations, we propose a model in which there was a significant role for amphibole, and more importantly accessory titanite, in decre'asing Nb/U, Ce/Pb and Th/U ratios and increasing or buffering ( 226 Ra/ 230 Th) ratios during the later stages of differentiation and magma mixing. These processes all occurred over a few millennia in small magma batches that were repeatedly emplaced within the mid-crust of the Cumbre Vieja rift system prior to rapid transport to the surface.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
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  • 9
    Publication Date: 2011-07-01
    Description: The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), 176Hf/177Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (176Hf/177Hf_m up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over 〉 10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component of Hanan and Graham ( 1996 ). In contrast, all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hf_m = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is believed to represent subducted, 〈1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower 176Hf/177Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat older recycling ages of ≥1 Ga. ©2010 The Author(s)〈br /〉〈br /〉〈a href="http://doi.org/10.1007/s00410-010-0580-5" target="_blank"〉〈img src="http://bib.telegrafenberg.de/typo3temp/pics/f2f773b55e.png" border="0"〉〈/a〉
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
    Topics: Geosciences
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  • 10
    Publication Date: 2008-04-20
    Description: We present new major and trace element and O–Sr–Nd-isotope data for igneous rocks from the western Mediterranean Alborán Sea, collected during the METEOR 51/1 cruise, and for high-grade schists and gneisses from the continental Alborán basement, drilled during the Ocean Drilling Programme (ODP Leg 161, Site 976). The geochemical data allow a detailed examination of crustal and mantle processes involved in the petrogenesis of the lavas and for the first time reveal a zonation of the Miocene Alborán Sea volcanism: (1) a keel-shaped area of LREE-depleted (mainly tholeiitic series) lavas in the central Alborán Sea, generated by high degrees of partial melting of a depleted mantle source and involving hydrous fluids from subducted marine sediments, that is surrounded by (2) a horseshoe-shaped zone with LREE-enriched (mainly calc-alkaline series) lavas subparallel to the arcuate Betic-Gibraltar-Rif mountain belt. We propose that the geochemical zonation of the Miocene Alborán Basin volcanism results from eastward subduction of Tethys oceanic lithosphere coupled with increasing lithospheric thickness between the central Alborán Sea and the continental margins of Iberia and Africa. ©2008 Springer-Verlag
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
    Topics: Geosciences
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