High resolution volcanology and geochemistry of mid ocean ridge segments flanking the 9°40'S melt anomaly and the Ascension hot spot
Zusammenfassung der Projektergebnisse
This project was part of the multidisciplinary Special Research Program (SPP) 1144: „Mantle to Ocean“ that was active from 2003 to 2009. This SPP investigated the central portion of the Mid-Atlantic Ridge system with a southern working area including Ascension Island (7° to 12° S) and a northern area focused on the Logatchev seafloor hydrothermal system (14° to 15° N). The principal aim of this project was to investigate the small-scale geochemical heterogeneities along the section of the Mid-Atlantic Ridge in the southern working area and Ascension Island, using high-resolution analyses of high field strength elements (isotope dilution) and radiogenic isotope ratios (Sr, Nd, Hf, Pb). Since Ascension Island is an integral part of this petrogenetic system, we conducted two field seasons on the island in order to investigate the volcanological evolution, the chronology of explosive eruptions, and isotopic systematics. In addition, cooperations with colleagues from IFM-GEOMAR resulted in the investigations of interrelationships between volcanism, tectonics and hydrothermal activity and a study of fluid interaction processes at the ultra-mafic hosted Logatchev hydrothermal field. The principal results of these work packages can be summarized as follows. Mid-ocean ridge hydrothermal processes: During the course of the SPP, three new hydrothermal systems have been discovered on MAR segments with variable crustal thickness, ridge morphology, and local tectonic framework. Systematic changes in hydrothermal processes have been observed and interpreted as a consequence of differing magma supply rates. Volcanology and chronology of pyroclastic successions on Ascension Island: The island consists of a two distincive parts with felsic volcanism (lava domes and pydroclastic deposits) restricted to the mountainous Central Volcanic Complex (CVC). The results of Ar-Ar dating show that plinean eruptions date back to 920 ka ±20 ka with the youngest eruption at 50 ka ± 12 ka. The lava plains adjacent to the CVC are devoid of felsic pyroclastic deposits and inferred to be a recent addition to the subaerial portion of Ascension Island. High resolution geochemistry and petrogenetic models for Ascension Island and the adjacent segment of the Mid-Atlantic Ridge: Using trace element and isotopic evidence, it can be demonstrated that the submarine portion of Ascension (drill hole samples) has a different mantle source signature than the subaerial portion. Combining these data and data from the adjacent MAR prompted the development of a new petrogenetic model for the area involving small-scale (10 to <50 km along axis) mixing of distinctive mantle materials and an on-axis origin of the submarine portion of Ascension. Sub-1-km-scale sampling of individual MAR lava flows demonstrated that geochemical heterogeneities can be developed even in individual magma batches feeding on-axis fissure eruptions. The high-precision trace element data generated during this study were also used in a global scale investigation which revised the age of Earth’s core formation and showed strong similarities in the Hf-W composition between the silicate earth and the silicate portion of the Moon.
Projektbezogene Publikationen (Auswahl)
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(2007): Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge.- Geochemistry, Geophysics, Geosystems (G cubed); Volume 8, Number 11, Q11002
Haase, K.M., Petersen, S., Koschinsky, A., and 31 others including Paulick, H.
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(2008) First evidence for hightemperature off-axis venting of deep crustal/mantle heat: The Nibelungen Hydrothermal Field, southern Mid-Atlantic Ridge.- Earth and Planetary Science Letters, 275, 61-69
Melchert, B, Devey C.W., German, C.R., Lackschewitz, K.S., Seifert, R., Walter, M., Mertens, C., Yoerger, D.R., Baker, E.T., Paulick, H., Nakamura, K.
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(2008) Hydrothermale Alterationsprozesse am mittelatlantischen Rücken und im Manus back-arc Becken (Papua Neuguinea).- Steinmann Institut für Geologie, Mineralogie und Paläontologie, Rheinische Friedrich-Wilhelms-Universität Bonn
Paulick, H.
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Scientific Parties (2009): Diking, young volcanism and diffuse hydrothermal activity on the southern Mid-Atlantic Ridge: The Lilliput field at 9°33′S.- Marine Geology, 266, 52-64
Haase, K.M., Koschinsky, A., Petersen, S., Devey, C.W., German, C., Lackschewitz, K.S., Melchert, B., Seifert, R., Borowski, C., Giere, O., Paulick, H.
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(2010) The influence of small-scale mantle heterogeneities on Mid Ocean Ridge volcanism: Evidence from the southern Mid-Atlantic Ridge (7°30’S to 11°30’S) and Ascension Island.- Earth and Planetary Science Letters, 296, 299-130
Paulick, H., Münker, C., Schuth, S.
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(2011): The Earth’s tungsten budget during mantle melting and crust formation. Geochimica et Cosmochimica Acta, 75, 2119-2136
König, S., Münker, C., Hohl, S., Paulick, H., Barth, A.R., Lagos, R., Pfänder, J., Büchl A.
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(2012): Alteration at the ultramafic-hosted Logatchev hydrothermal field: Constraints from trace element and Sr-O isotope data.- Geochemistry, Geophysics, Geosystems (G cubed), 13
Augustin, N., Paulick, H., Lackschewitz, K. S., Eisenhauer, A., Garbe-Schönberg, D., Kuhn, T., Botz, R., Schmidt, M.
