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Contributions to Mineralogy and Petrology

, Volume 123, Issue 3, pp 223–237 | Cite as

Geochemistry of lavas from Mohns Ridge, Norwegian-Greenland Sea: implications for melting conditions and magma sources near Jan Mayen

  • K. M. Haase
  • Colin W. Devey
  • Dieter F. Mertz
  • Peter Stoffers
  • Dieter Garbe-Schönberg

Abstract

 Mohns Ridge lavas between 71 and 72°30′N (∼360 km) have heterogeneous compositions varying between alkali basalts and incompatible-element-depleted tholeiites. On a large scale there is a continuity of incompatible element and isotopic compositions between the alkali basalts from the island Jan Mayen and Mohns Ridge tholeiites. The variation in isotopes suggests a heterogeneous mantle which appears to be tapped preferentially by low degree melts (∼5%) close to Jan Mayen but also shows its signature much further north on Mohns Ridge. Three lava types with different incompatible element compositions [e.g. chondrite-normalized (La/Sm)N<1 to >2] occur in the area at 72°N and were generated from this heterogeneous mantle. The relatively depleted tholeiitic melts were mixed with a small degree melt from an enriched source. The elements Ba, Rb and K of the enriched melt were probably buffered in the mantle by residual amphibole or phlogopite. That such a residual phase is stable in this region of oceanic mantle suggests both high water contents and low mantle temperatures, at odds with a hotspot origin for Jan Mayen. Instead we suggest that the melting may be induced by the lowered solidus temperature of a “wet” mantle. Mohns MORB (mid ocean ridge basalt) and Jan Mayen area alkali basalts have high contents of Ba and Rb compared to other incompatible elements (e.g. Ba/La >10). These ratios reflect the signature of the mantle source. Ratios of Ce/Pb and Rb/Cs are normal MORB mantle ratios of 25 and 80, respectively, thus the enrichments of Ba and Rb are not indicative of a sedimentary component added to the mantle source but were probably generated by the influence of a metasomatizing fluid, as supported by the presence of hydrous phases during the petrogenesis of the alkali basalts. Geophysical and petrological models suggest that Jan Mayen is not the product of hotspot activity above a mantle plume, and suggest instead that it owes its existence to the unique juxtaposition of a continental fragment, a fracture zone and a spreading axis in this part of the North Atlantic.

Keywords

Mantle Source Mantle Plume Incompatible Element Alkali Basalt Heterogeneous Mantle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1996

Authors and Affiliations

  • K. M. Haase
    • 1
  • Colin W. Devey
    • 1
  • Dieter F. Mertz
    • 2
  • Peter Stoffers
    • 1
  • Dieter Garbe-Schönberg
    • 1
  1. 1.Geologisch-Paläontologisches Institut der Universität Kiel, Olshausenstr. 40, D-24118 Kiel, GermanyDE
  2. 2.Institut für Geowissenschaften der Universität, D-55099 Mainz, GermanyDE

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