Sveconorwegian massif-type anorthosites and related granitoids result from post-collisional melting of a continental arc root

• Published in: Earth-science reviews Vol. 107; no. 3; pp. 375 - 397
• Main Authors: Vander Auwera, J., Bolle, O., Bingen, B., Liégeois, J.-P., Bogaerts, M., Duchesne, J.C., De Waele, B., Longhi, J.
• Format: Journal Article Web Resource
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2011; Elsevier Sequoia S.A; Elsevier Science
• Subjects: Anorthosite; Chemical compounds; Differentiation; Earth sciences & physical geography; Electric arc melting; Evolution; Ferroan granites; Geochemistry; High temperature; Igneous rocks; Jotunites; Lower continental crust; Magma; Melting; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Post-collisional magmatism; Proterozoic massif-type anorthosites; Roots; Sciences de la terre & géographie physique; Sveconorwegian orogen; Trends; Proterozoic massif-type anorthosites; Post-collisional magmatism; Jotunites; Ferroan granites; Lower continental crust; Sveconorwegian orogen
• ISSN: 0012-8252; 1872-6828; 1872-6828
• DOI: 10.1016/j.earscirev.2011.04.005

Two magmatic suites were emplaced during the post-collisional evolution of the Sveconorwegian orogeny: an Anorthosite–Mangerite–Charnockite suite (AMC suite), and an hornblende- and biotite-bearing granitoids suite (HBG suite). The AMC suite is exclusively located in the westernmost and warmest part of the orogen, in granulite facies gneisses, whereas the HBG suite intruded in the rest of the orogen, but not in the granulite domain. New U–Pb zircon geochronological data confirm previous age determinations: 970–932 Ma (HBG suite) and 933–916 Ma (AMC suite). The mafic facies of the two post-collisional magmatic suites have similar geochemical compositions but the HBG differentiation trend displays higher CaO, Sr, U and Th as well as lower K 2O and FeO t/MgO than the AMC differentiation trend. The HBG suite is hydrous and has a broadly higher fO 2 whereas the AMC suite is anhydrous. The inferred parent magmas of both suites have overlapping initial Sr, Nd and Pb isotopic compositions. With increasing differentiation, the two trends point towards two different crustal contaminants. Together with the recent recognition of a major crustal shear zone located just east of the AMC suite, this difference suggests that the suites were emplaced in two different lithotectonic units. Using published experimental constraints and geochemical modeling, we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated, probably during the evolution of a long-lasting convergent margin. Later, these lower crustal sources were modified by the regional granulite facies metamorphism (1.035 to 0.97 Ga) prevailing in the westernmost part of the orogen, thus producing an anhydrous lower crustal source for the AMC suite. Accordingly, we conclude that the Sveconorwegian massif-type anorthosites result from partial melting of the continental arc root. This process, if accepted for other AMCG (Anorthosite–Mangerite–Charnockite–Granite) complexes, was possible in the Proterozoic because of a sufficiently high temperature, but not in the Archean because in subduction zones the main transfer to the crust was then felsic (tonalites, granodiorites) and not basaltic. We thus further suggest that the onset of massif-type anorthosites at the beginning of the Proterozoic may mark the time when plate tectonics began to operate in a similar way as today. ► We compare the geochemistry and petrology of the two post-collisional sveconorwegian (0.97 – 0.92 Ga) magmatic suites. ► New geochronological data (U-Pb zircon) confirm previous age determinations. ► The two post-collisional sveconorwegian magmatic suites were emplaced in two different lithotectonic units. ► The parent magmas of bothmagmatic suitesresult from partial melting of a continental arc root. ► The regional granulite metamorphism produced an anhydrous crustal source for the Anorthosite-Mangerite-Charnockite suite.