Consequences of magmatic intraplating: Crustal melting and magma contamination in the Norwegian Caledonides Calvin Barnes Aaron Yoshinobu Tore Prestvik.

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Presentation transcript:

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

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 mafic underplate or intraplate pluton emplacement zone of crustal melting and hybridization

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

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

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”.

SAUSFJELLET PLUTON Two intrusive stages. In Stage 2, quartz, hornblende, incompatible elements, δ 18 O all increase from central to west West side in contact with metapelitic diatexites, which are partly melted in the aureole. East side in contact with marble and related refractory metasedimentary rocks.

amphibole cpx monzodioriteamphibole cpx nepheline diorite

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

Contact diatexites: sillimanite + garnet + biotite

SAUSFJELLET PLUTON Two intrusive stages. In Stage 2, quartz, hornblende, incompatible elements, δ 18 O all increase from central to west West side in contact with metapelitic diatexites, which are partly melted in the aureole. East side in contact with marble and related refractory metasedimentary rocks.

 18 O MgO western/annular zone central zone host migmatites and granite Sausfjellet pluton Stage 2.

δ 18 O ppm Zr

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

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.

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

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.