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Northern cordillera Eocene Plutonic Rocks. The Granite Problem? 18 th century: Plutonists versus Neptunists igneous/metamorphic sedimentary Early 20 th.

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Presentation on theme: "Northern cordillera Eocene Plutonic Rocks. The Granite Problem? 18 th century: Plutonists versus Neptunists igneous/metamorphic sedimentary Early 20 th."— Presentation transcript:

1 Northern cordillera Eocene Plutonic Rocks

2 The Granite Problem? 18 th century: Plutonists versus Neptunists igneous/metamorphic sedimentary Early 20 th century: Magmatists versus Transformists igneous metasomatic Now: Mantle versus Crust Crystal fractionation Melting

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5 Granite Plutons in Niger

6 Archean Granite – Greestone Terranes granitoid dome greenstone belt granitoid dome granitoid dome granitoid dome

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9 Classification Liquidus Projection

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11 Melt Inclusion Data Are andesite magmas mixtures of mantle-derived basaltic magmas and rhyolitic partial melts of the continental crust?

12 Eocene Sr - Nd

13 SiO TiO Al 2 O MgO FeO CaO Na 2 O K 2 O Total Cations normalized to 100 cations Si Ti Al Mg Fe Ca Na K O Mineralogy (oxygen units, XFe 3+ = 0.10) Quartz Feldspar Clinopyroxene Orthopyroxene Olivine Oxides Mantle Ocean Continent crust crust Oceanic crust - MORB basalt p Continental crust - granite e Spectrum of Igneous liquids Francis, Igneous Petrology EPSC 423A, 2011

14 Continental Crustal Granitoids Second Stage Melting of Basalt The majority of crustal granitoids are, however, thought to be liquids produced at the eutectic point e by the second stage melting of silica- saturated basaltic/gabbroic mafic crust, consisting largely of pyroxene and plagioclase. e Francis, Igneous Petrology EPSC 423A, 2011

15 M A S H M ixing - A ssimilation - S torage - H omogenization

16 Feature A ‑ Type I ‑ Type S ‑ Type Rock Types : granite tonalite to granodiorite granodiorite to to granite to granite Mafic Na-amphibole hornblende muscovite Minerals: Na ‑ pyroxene biotite biotite Accessories: fluoritegarnet topazAl-silicates tourmalinecordierite corundum Oxide: ilmenite magnetite ilmenite Feldspar : perthite K ‑ spar K ‑ spar & Plag and plag hypersolvus subsolvussubsolvus (Na+K)/Al: > 1 <1 << 1 per ‑ alkaline (Na+K+Ca×2)/Al: >> 1 > 1 < 1 meta ‑ aluminous per ‑ aluminous HFSE elements: high low low (Zr,Nb, REE) Restite/ few amphibolite biotite ‑ cordierite Enclaves: sillimanite ‑ garnet gneiss Source granulitic mafic igneous sedimentary Regions: lower crust rocks rocks with halogen mantle ‑ derived pelite volatile flux magmas (M) greywacke Tectonic extensional compressional compressional Setting: within ‑ plate volcanic arcs, continental extensional collisions interplate Granitoids Classified According Interpretted to Source Region


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