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Romain Meyer romain@mit

Mantle-crust interactions during different zonal and temporal evolutionary stages of VRM formation. Romain Meyer romain@mit.edu. The importance of crust-mantle interactions for the final break-up.

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Romain Meyer romain@mit

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  1. Mantle-crust interactions during different zonal and temporal evolutionary stages ofVRM formation. Romain Meyer romain@mit.edu

  2. The importance of crust-mantle interactions for the final break-up The contribution of the continental crust to either the production of melt or to the contamination of mantle melts during the magmatic episodes accompanying continental break-up is still a matter of debate. • I choose two case study areas that are examples for the importance of crustal anatexis during the rift-to-drift transition.

  3. North Atlantic Igneous Province Meyer, van Wijk, Gernigon (2007)

  4. VRM tectono-magmatic crustal zones Modified after Meyer et al (2009)

  5. VRM tectono-magmatic crustal zones Potential analogues? Modified after Meyer et al (2009)

  6. VRM tectono-magmatic crustal zones Vøring Modified after Meyer et al (2009)

  7. The Vøring margin After Eldholm et al. 1987

  8. Example of the heterogeneous LS

  9. Glassy (blueish) perlitic dacite. Glass partly altered (brown)

  10. Leg 104 isotope geology Depleted mantle Crustal melts Upper Continental crust Meyer et al. (in press)

  11. Cs as a new geochemical tool to investigate mantle-crust interactions Meyer et al. (in press)

  12. VRM tectono-magmatic crustal zones Rum Modified after Meyer et al (2009)

  13. Why study the magmas of Rum? . • The magmas on Rum are similar to the Vøring margin melts: with a broad range of rocks from mafic basalts to evolved rhyolites • Few other places have deep plutons (possible analogues for the HVLC bodies) and erupted rocks so well exposed in such a small area Modified after Meyer et al (2009)

  14. Isle of Rum • Rum is probably best known for its spectacular “Layered Suite”. • An earlier felsic caldera episode is preserved in two marginal zones.

  15. The layered suite (analogue for HVLC?): crystal-liquid separation • If crystals are removed, more Si-rich magmascan be produced forming the start of a magma series. Ultramafic rocks of Rum modelled as adcumulates after 50% fractional crystallisation of a liquid similar to picrite Meyer et al. (2009)

  16. Two different petrogenetic models could explain the isotope geology of Rum magmas Meyer et al. (2009)

  17. Rum (Rhyo)dacites anatectic melts of local Lewisian amphibolite gneiss Meyer et al. (2009)

  18. Summary • In both presented VRM areas the felsic magmas are dominantly crustal melts. • No alkaline (RIFT) basalts have been sampled • In both cases the mafic magmas are MORB

  19. Mixtures between crustal melts and MORB SCLM gone @ rift-to-drift transition SCLM Meyer et al. (2009)

  20. Dichotomy in isotope geology UCC MCC LCC Meyer et al. (in press)

  21. Why this dichotomy in isotope geology? Meyer et al. (in press)

  22. IODP proposal: Excess magmatism on VRM

  23. Model for mantle crust interactions at VRM Meyer et al. (in press)

  24. Conclusions • Crustal anatexis is an important geological process at the rift-to-drift transition. • Asymmetry in crust-mantle melt interactions in the NE Atlantic (Jan Mayen Fracture zone) • The mafic magmas at the rift-to-drift transition are already MORBs (SCLM gone) • Layered suits could be used as analogues to study HVLC bodies

  25. No alkaline basalts at the rift-to-drift transition Meyer et al. (in press)

  26. Dichotomy in isotope geology Mainly UCC – mantle interactions Jan Mayen FZ Mainly LCC to MCC– mantle interactions

  27. NAIP isotope geology Meyer et al. (in press)

  28. Conceptual model of Sr-isotopic evaluation of amphibolite gneiss that underwent variable degree of Rb (Cs) depletion in the past The change back in time of the 87Sr/86Sr ratio of two amphibolite gneiss formations, having 87Rb/86Sr = 1 (a common value for Hebridean amphibolites) and 87Sr/86Sr ratios of 0.717 and 0.715 at 60 Ma ago (as for the analysed samples from Rum). The range of estimated percentage loss of Rb is based on the observed (ca. 1.4) and expected (ca. 2.3) enrichment of Rb in rhyodacites relative to average amphibolite gneiss

  29. Mantle-crust interactions interactions Lithosphere Asthenosphere melting Components a) Asthenosphere (depleted mantle and/or enriched mantle) b) Lithosphere (Sub-continental lithospheric mantle and/or continental crust)

  30. The geodynamic history of the NAIP Meyer, van Wijk, Gernigon (2007)

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