Mixing and Progressive Melting of Deep and Shallow Mantle Sources in the NE Atlantic and Arctic

• Published in: Mineralogical Magazine
• Main Authors: Trønnes, Reidar, Debaille, Vincianne, Erambert, M., Waight, Tod Earle
• Format: Conference Object
• Language: English
• Published: 2013
• Subjects: Arctic; Gakkel Ridge; Jan Mayen; Kolbeinsey; Reykjanes; Iceland; Spitsbergen
• Online Access: https://curis.ku.dk/portal/da/publications/mixing-and-progressive-melting-of-deep-and-shallow-mantle-sources-in-the-ne-atlantic-and-arctic(f993aab2-f493-49aa-a246-3b7248b6ef06).html; https://doi.org/10.1180/minmag.2013.077.5.20; https://curis.ku.dk/ws/files/122446791/2357.pdf

NE Atlantic and Arctic MORB and primitive off-rift basalts in Iceland, Jan Mayen and Spitsbergen (late Quaternary alkaline basalts) record variable geochemical interaction between the asthenospheric mantle (AM), material supplied by the Iceland plume and subcontinental lithospheric mantle (SCLM). The SCLM-component was mixed with the local asthenosphere during and shortly after the continental rifting and ocean basin opening. Using combined Sr-Nd-Pb- Os-He-isotope systematics, the Iceland plume can be modelled as a mixture of 70% refractory/primordial lower mantle (LM) and 30% recycled oceanic crust (ROC). Low-degree melts are preferentially from the enriched ROC and SCLM components, before progressive melting gradually consumes more of the the LM and AM components. The modelled ROC/SCLM-ratio decreases markedly from a maximum of about 2.3 at the Reykjanes Ridge, Reykjanes Peninsula and the Southern Volcanic Flank Zone in Iceland, via 1.2 at the Snæfellsnes peninsula, Western Rift Zone and Mid-Icelandic Belt and 0.7 at Jan Mayen and the Kolbeinsey, Mohns and Knipovich Ridges to less than 0.2 in Spitsbergen and along the Gakkel Ridge. These ratios might be slightly overestimated due to a general background level of ROC (HIMU-component) in an otherwise depleted asthenosphere. The minor element composition of olivine phenocrysts in primitive off-rift basalts in Iceland and Jan Mayen, sampling preferentially the enriched source components, indicates that the SCLM-lithologies are dominantly peridotitic, in contrast to the ROC-lithologies, recording a higher proportion of eclogites and hybridized pyroxenites. The combined Hf-Ndisotope systematics also discriminate between these two enriched source components. The high proportion of the SCLM-component in the asthenosphere along the Kolbeinsey, Mohns, Knipovich and Gakkel Ridges reflects the young, narrow and slow-spreading character of the corresponding oceanic basins. These ridges appear to sample mantle sources with higher proportions of locally derived SCLM-material than other mid-ocean ridges.