Derivation of the 1.0-0.9 Ga ferro-potassic A-type granitoids of southern Norway by extreme differentiation from basic magmas

in Precambrian Research (2003), 124

Major and trace elements, Sr and Nd isotopic data as well as mineral compositions are presented for a selection of the 1.0 - 0.9 ferro-potassic A-type granitoids (Bessefjellet, Rustfjellet ... [more ▼]

Major and trace elements, Sr and Nd isotopic data as well as mineral compositions are presented for a selection of the 1.0 - 0.9 ferro-potassic A-type granitoids (Bessefjellet, Rustfjellet, Verhuskjerringi, Valle, Holum, Svöfjell, Handeland-Tveit, Åseral, Lyngdal gabbronorites) that occur close to the Mandal-Ustaoset Line of southern Norway. These hornblende biotite granitoids (HBG) define an extensive differentiation trend ranging from gabbronorites (50 wt % SiO2) to granites (77 wt % SiO2). This trend is interpreted as resulting from extreme fractional crystallization of several basaltic magma batches with similar major and trace elements compositions. At 930 Ma, the HBG suite displays a narrower range in ISr (0.7027 - 0.7056) than in Nd(t) (+1.97 down to -4.90) suggesting some assimilation of a Rb-depleted lower crust (AFC process) or/and source variability. An age of 929 ± 47 Ma is given by a Rb-Sr isochron on the Holum granite (Sri = 0.7046 ±0.0006, MSWD = 1.7). Geothermobarometers indicate a low pressure of emplacement (1.3-2.7 kbar) and an oxygen fugacity close to NNO. High liquidus temperatures are given by the apatite saturation thermometer (1005°C to 1054 °C) and are in agreement with results from other studies. The basaltic parent magmas of the HBG suite are partial melts of an hydrous mafic, potassic source lying either in the lithospheric upper mantle or in the mafic lower crust derived from it. This contrasts with the 930 Ma anorthosite-mangerite-charnockite suite (AMC) of the Rogaland Province for which a depleted lower crustal anhydrous gabbronoritic source has been indicated. The present data imply the penecontemporaneous melting of two contrasting sources in southern Norway. The source duality could result from an increasing degree of metamorphism (amphibolite to granulite) from East to West, an horizontal stratification of the lower crust or from the stratification of the lithosphere (melting of the lower crust or upper mantle). It may also indicate that the AMC and HBG suites formed in two distinct crustal segments. The linear alignment of the HBG suite along the Mandal-Ustaoset shear zone suggests that a linear uprise of the asthenosphere, following a lithospheric delamination under this structure, could be the vector of the mantle heat. [less ▲]

Petrogenesis of jotunitic and acidic members of an AMC suite (Rogaland anorthosite province, SW Norway): a Sr and Nd isotopic assessment

in Precambrian Research (2003), 124(2-4), 185-214

Sr and Nd isotopic data from the anorthosite-mangerite-charnockite (AMC) suite of the Late-Sveconorwegian (ca. 0.93 Ga) Rogaland anorthosite province of SW Norway are discussed. The study focuses on new ... [more ▼]

Sr and Nd isotopic data from the anorthosite-mangerite-charnockite (AMC) suite of the Late-Sveconorwegian (ca. 0.93 Ga) Rogaland anorthosite province of SW Norway are discussed. The study focuses on new data obtained from three distinct rock occurrences: (1) primitive (=MgO-rich and K2O-poor)jotunites that represent the parental magmas of leuconorite and mafic plutons (Sr-87/Sr-86(0.93Ga) = ca. 0.704-0.707, epsilon(Nd)(0.93 Ga) = +3.6 down to +1.2); (2) evolved jotunites that differentiated from the primitive jotunites and constitute the starting components of dyke-scale fractionation trends (Sr-87/Sr-86(0.93Ga) = ca. 0.705-0.713, epsilon(Nd)(0.93 Ga) = +0.4 down to -2.0); and (3) felsic plutons (Sr-87/Sr-86(0.93Ga) = ca. 0.707-0.723, epsilon(Nd)(0.93Ga) = +1.4 down to -1.7). A comparison of the Sr and Nd isotopic compositions with available geochemical data (major and trace elements) is also made. Fractionation of the primitive to the evolved jotunites, below the intrusion level of the anorthosite province, is shown to have involved crustal contamination. A case of fractional crystallization and simultaneous contamination/assimilation is substantiated in the felsic cap of a layered intrusion (the Bjerkreim-Sokndal intrusion). It is further proposed that the Sr and Nd isotopic compositions of the various felsic occurrences result from fractional crystallization of primitive jotunitic melts, with or without contamination/assimilation; this strengthens the possibility for large volumes of silica-rich magmas to have been produced by fractionation, through evolved jotunites, of primitive jotunites. The entire range in Sr and Nd isotopic compositions of the Rogaland anorthosite province is interpreted as reflecting a mixing of crustal contaminants, having variable Sr-87/Sr-86(0.93Ga) ratios and (negative) epsilon(Nd)(0.93 Ga) values, with a more isotopically primitive source. The crustal end members of that mixing array are represented by moderatey to strongly LILE-enriched high-grade gneisses from the Pre-Sveconorwegian basement of southernmost Norway, that have a crustal history extending back to 1.5-1.9 Ga in the surroundings of the anorthosite province. The primitive end member is either an unusual LREE-depleted and Rb-enriched component, possibly corresponding to an originally depleted source subsequently modified by metasomatic fluids, or a more classical depleted component; it corresponds to a gabbronoritic rock of the deep crust, as shown by recent experimental data, with a quite short crustal residence time (<0.4-0.2 Ga). If that mafic end member is the lower granulitic crust itself, this would imply the presence in the deep continental crust of southwesternmost Norway of a crustal material strongly different from the 1.7- to 1.9-Gyr-old, moderately LILE-enriched component that is supposed to constitute the largest volume of the present deep continental crust in southern Norway. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Dyke swarms in the Pan-African basement from the Alpine Danubian window : new field and geochemical investigation in southern Carpathians (Romania)

in Journal of Conference Abstracts (2001), 6

Geochemistry of granitoids from the south Carpathians: A review

in Anuarul Institutului Geologic al României (2000), 71

Pan-african acidic magmatism in the south Carpathians (Romania): from calc-alkaline to shoshonitic and back

in Documents du BRGM (1999), 290

Post-collisional granitoids in the south Carpathians danubian nappes (Romania) : a multi-source origin

in Terra Abstracts (1997), 9

Geochemical constraints on the genesis of the Tellnes Ilmenite deposit, southwest Norway

in Economic Geology & the Bulletin of the Society of Economic Geologists (1989), 84

The Rogaland intrusive masses

in Maijer, C.; Padget, P. (Eds.) The Geology of southernmost Norway: an excursion guide (1987)

A series of papers providing comments and description of itineraries in the Rogaland anorthosite province. A revised and amplified version is now available (published in 2003) under reference http://hdl ... [more ▼]

A series of papers providing comments and description of itineraries in the Rogaland anorthosite province. A revised and amplified version is now available (published in 2003) under reference http://hdl.handle.net/2268/265 [less ▲]

The Rogaland anorthosites: facts and speculations

in Tobi, A. C.; Touret, J. L. R. (Eds.) The deep Proterozoic crust in the North Atlantic Provinces (1985)

The massif-type anorthosites of the province were emplaced as crystal mushes of plagioclase, lubricated by noritic liquids crystallizing along a P-T gradient, and containing aggregates of plagioclase and ... [more ▼]

The massif-type anorthosites of the province were emplaced as crystal mushes of plagioclase, lubricated by noritic liquids crystallizing along a P-T gradient, and containing aggregates of plagioclase and/or Al-rich orthopyroxene megacrysts, formed in a magma chamber at the base of a thickened crust. Synemplacement deformations were produced in the envelope and within the plutons, where they started in the magmatic stage and ended in the solid stage. The anorthositic suite can be accounted for by three magma types, the composition of which are basaltic, jotunitic and charnockitic. Each magma generates part of the suite, with some overlapping. The basaltic magma is mantle-derived in an undefined geodynamic environment. The alkali to alkali-calcic jotunitic magma is generated as distinct batches with variable crustal signatures, due to contamination by deep-crustal material or direct partial melting of this material. The charnockitic magma can be produced by fractionation of the jotunites but can also result from direct partial melting in granulite facies conditions. For both magma types partial melting is triggered by the hot anorthosite diapirs en route to their final level of emplacement. [less ▲]

Trace element variations and isotopic composition of charnockitic acidic rocks related to anorthosites (Rogaland, S.W. Norway)

Part of book (1979)