Petrologie, Geochemie und Genese diamantführender alkalischer Magmatite am Rande des Labrador-Meeres
Final Report Abstract
This project on the petrological and geochemical characteristics of alkaline rocks on the margins of the Labrador Sea has greatly improved our understanding of the spatial and temporal characteristics of the alkaline rocks and the processes of their origin. Thorough dating of perovskites has established that the magmas were emplaced in three major episodes, which can be thought of as two failed and one successful rifting attempts. Each episode has its own characteristic magma types, which can be related to the state of the lithosphere beneath the North Atlantic craton. The first (1300-1200Ma) produced lamproites which require reduced thick lithosphere; the second (605-570Ma) produced aillikitic ultramafic lamprophyres, which were produced by thinning and oxidation of the cratonic lithosphere, involving carbonate-bearing veins that were produced immediately before magma emplacement. The third episode (ca 120Ma) shortly preceded the opening of the Labrador Sea, and concerns the production of nephelinite and melilitite at much shallower depths than the earlier episodes. After this, voluminous basalts accompanied the onset of ocean crust production and the establishment of the Labrador Sea through an original thick craton. The processes detailed in this project may find general application in other areas where cratons have been thinned and split. This includes East Africa, where kamafugites are influenced by carbonates in the mantle. These processes also offer insights into the production and preservation of diamonds in the cratonic lithosphere. The paucity of diamonds in ultramafic lamprophyres is probably related to oxidation during magma production, and not to intrinsic paucity of diamonds in the original lithosphere. The project has produced five hefty publications in top international journals (ca. 150 printed pages) and a young post-doctoral researcher with an excellent international reputation in his field.
Publications
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(2003) Ultramafic lamprophyre dyke swarm, Torngat Mountains, Quebec and Labrador: mineralogy and geochemistry. 8th International Kimberlite Conference. Victoria, Canada
S. Tappe, S.F.Foley, G.A. Jenner, A.B. Ryan, D. Besserer & B.A. Kjarsgaard
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(2004) Torngat ultramafic lamprophyres and their relation to the North Atlantic Province. Proc. 8th international Kimberlite Conf. Lithos 76, 491-518
S. Tappe, G Jenner, SF Foley, L Heaman, D. Besserer, B. Kjarsgaard, AB Ryan
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(2005) Integrating ultramafic lamprophyres into the IUGS classification of igneous rocks: rationale and implications. Journal of Petrology. 46, 1893-1900
S.Tappe, S.F. Foley, G.A. Jenner, B.A. Kjarsgaard
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Melting of minority assemblages in the mantle and the generation of alkaline melts. PERALK conference. Tübingen, March 2005
S.F. Foley
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(2006) Genesis of ultramafic lamprophyres and carbonatites at Aillik Bay, Labrador: a consequence of incipient lithospheric thinning beneath the North Atlantic craton. Journal of Petrology 47. 1261-1315
S. Tappe, S.F. Foley, G.A. Jenner, L.M. Heaman, B.A. Kjarsgaard, R.L. Romer, A. Stracke, N. Joyce & J. Hoefs
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(2006) Tracking changes in the North Atlantic craton lithosphere structure through time: Sr-Nd-Hf-Pb isotope evidence from alkaline and carbonatitic magmatism. IAVCEI 2006. Guangzhou, May 2006
S. Tappe, S.F. Foley, A. Stracke, R.L. Romer, L.M. Heaman, B.A. Kjargaard, N. Joyce, G.A. Jenner
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(2006): Sr-Nd-Hf-Pb isotope evidence from alkaline magmatism on the Labrador Sea margins for the temporal evolution of a rift in the North Atlantic cratonic mantle lithosphere. European Geosciences Union. Vienna, April 2006
S. Tappe, S.F. Foley, A. Stracke, R.L. Romer, L.M. Heaman, B.A. Kjargaard, N. Joyce, G.A. Jenner
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Alkaline magmatism and the rifting of cratonic lithosphere: behaviour of mantle solidi during sub-rift metasomatism and lithosphere erosion. European Geosciences Union. Vienna, April 2006
S.F. Foley
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(2007) Interactions between carbonate magmas and MARID metasomes: The case of diamondiferous aillikites from the Torngat Mountains, Canada. Geochimica et Cosmochimica Acta 71. (15), A1003. Goldschmidt Conference, Cologne, August 2007
S. Tappe, S.F. Foley, L.M. Heaman, R.L. Romer, A. Stracke, B.A. Kjarsgaard, G.A. Jenner
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Craton reactivation on the Labrador Sea margins: 40Ar/39Ar age and Sr-Nd-Hf-Pb isotope constraints from alkaline and carbonatite intrusives. Earth and Planetary Science Letters 256, 433-454
S. Tappe, S.F. Foley, A. Stracke, R.L. Romer, L.M. Heaman, B.A. Kjarsgaard, N. Joyce
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Between carbonatite and lamproite - diamondiferous Torngat ultramafic lamprophyres formed by carbonate fusion melting of cratonic MARID-type metasomes. Geochimica et Cosmochimica Acta. November 2007
S. Tappe, S.F.Foley, B.A.Kjarsgaard, R.L.Romer, L.M.Heaman, A. Stracke & G.A.Jenner
