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Consequences of magmatic intraplating: Crustal melting and magma contamination in the Norwegian Caledonides Calvin Barne

Consequences of magmatic intraplating: Crustal melting and magma contamination in the Norwegian Caledonides Calvin Barnes Aaron Yoshinobu Tore Prestvik Greg Dumond Melanie Barnes Øystein Nordgulen. pluton emplacement. zone of crustal melting. and hybridization. mafic underplate.

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Consequences of magmatic intraplating: Crustal melting and magma contamination in the Norwegian Caledonides Calvin Barne

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  1. Consequences of magmatic intraplating: Crustal melting and magma contamination in the Norwegian Caledonides Calvin Barnes Aaron Yoshinobu Tore Prestvik Greg Dumond Melanie Barnes Øystein Nordgulen

  2. pluton emplacement zone of crustal melting and hybridization mafic underplate or intraplate Magmatic intraplating: Emplacement of hot, mafic magma into lower or middle crust. Consequent crustal melting, thought by some to be the principal source of granitic magmas. Possible mafic magma evolution due to: --Fractional crystallization (heat lost to melt host rocks) --Magma mixing --Assimilation

  3. Helgeland Nappe Complex Laurentian affinity. Taconian-style deformation: east-dipping, west- vergent thrust faults. Bindal Batholith: 475 to 430 Ma

  4. TIMING • 500 to 490 Ma. Arc-related • Ophiolites develop between large • continental fragments. Locally- • derived cover sequences. • 2.477 to 468 Ma. Medium-grade • metamorphism of ophiolite • fragments and cover sequences. • High-grade metamorphism of • the shelf sequences. Migmatization • of appropriate lithologies. • 3. 468 to 448 Ma. Imbrication of • alternating thrust slices of • medium- and high-grade rocks. • 4. 448 to 435 Ma. Emplacement • of dioritic to granitic plutons.

  5. VELFJORD 448 to 445 Ma Pluton emplacement at 7 – 8 kbar; liquidus Ts near 1240ºC----- intraplating. Melting of pelitic host rocks within 1 km of contact. Local concentration of “contact granite”.

  6. SAUSFJELLET PLUTON Two intrusive stages. In Stage 2, quartz, hornblende, incompatible elements, δ18O all increase from central to west East side in contact with marble and related refractory metasedimentary rocks. West side in contact with metapelitic diatexites, which are partly melted in the aureole.

  7. amphibole cpx monzodiorite amphibole cpx nepheline diorite

  8. Regional migmatites: muscovite + biotite ± garnet ±sillimanite ±staurolite

  9. Contact diatexites: sillimanite + garnet + biotite

  10. SAUSFJELLET PLUTON Two intrusive stages. In Stage 2, quartz, hornblende, incompatible elements, δ18O all increase from central to west East side in contact with marble and related refractory metasedimentary rocks. West side in contact with metapelitic diatexites, which are partly melted in the aureole.

  11. d O 18 14 Sausfjellet pluton Stage 2. host migmatites 12 and granite 10 western/annular 8 zone central zone 6 0 5 10 15 MgO

  12. δ18O ppm Zr

  13. Medium-grade metamorphism of ophiolites and cover sequences. • High-grade metamorphism of • the shelf sequences. Migmatization of appropriate lithologies. • Arc-related ophiolites develop between large continental fragments. Locally-derived cover sequences. • Imbrication of alternating thrust • slices of medium- and high- • grade rocks. Emplacement of dioritic to granitic plutons. Melting in some pluton aureoles. One tectonic scenario for the Helgeland Nappe Complex

  14. High-K (granitic) leucosomes. Migmatites are refractory. Diatexites are the most refractory. Contact granites: 1. A distinct compositional trend. 2. Felsic part of trend overlaps high-K leucosomes. 3. Mafic part of trend IS NOT co-linear with migmatite trend.

  15. High-K (granitic) leucosomes: isotopically similar to migmatites. Contact granites: Nd and oxygen isotopes are intermediate between leucosomes and diorites.

  16. GEOLOGIC SETTING Caledonian fold belt—collision of Laurentia and Baltica beginning at about 430 Ma and ending at about 400 Ma. Emplacement of four allochthons on the Baltic craton. Uppermost Allochthon Exotic to Baltica. Geologic history distinct from allochthons formed near the Baltic craton. Amalgamated during Ordovician time, probably close to Laurentia. Consists of ophiolite-floored metasedimentary units and high-grade shelf sequences.

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