Molybdenite Re-Os dating constrains gravitational collapse of the Sveconorwegian orogen, SW Scandinavia

in Lithos (2006), 87(3-4), 328-346

Re-Os dating of molybdenite constrains late-orogenic gneiss dome formation in the Sveconorwegian orogen, SW Scandinavia

Conference (2004)

Magnetic fabrics in the Holum granite (Vest-Agder, southernmost Norway): implications for the late evolution of the Sveconorwegian (Grenvillian) orogen of SW Scandinavia

in Geophysical Research Abstracts (2003), 5

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 ▲]

The Tellnes ilmenite deposit (Rogaland, South Norway): magnetic and petrofabric evidence for emplacement of a Ti-enriched noritic crystal mush in a fracture zone

in Journal of Structural Geology (2003), 25(4), 481-501

The Tellnes ilmenite deposit, a world class titanium deposit, occurs in the Ana-Sira anorthosite (Rogaland anorthosite province, South Norway). It is mainly made up of an ilmenite-rich norite that has ... [more ▼]

The Tellnes ilmenite deposit, a world class titanium deposit, occurs in the Ana-Sira anorthosite (Rogaland anorthosite province, South Norway). It is mainly made up of an ilmenite-rich norite that has been previously interpreted as injected in a crystal mush state, in a weakness zone of the enclosing anorthosite. This emplacement mechanism has produced a faint orientation in the ore due to the flow of the mush. The internal flow structure of the orebody is studied here using the low-field anisotropy of magnetic susceptibility (AMS) method. Partial anhysteretic remanent magnetization (pAARM) indicates that coarse magnetite is the main mineral responsible for the magnetic fabric. Parallelism of the magnetic fabric with the shape-preferred orientation of the ore-forming minerals is checked using image analysis (IA) from oriented sections (intercept method). Interpretation of the AMS data verified by pAARM and IA, provides information on the magmatic foliation and lineation. Emplacement flow of the ilmenite norite crystal mush occurred in the direction of the orebody, parallel to its walls, and with an average SE 18degrees plunge. The feeder zone was likely situated below a network of veins on the SE end of the orebody. The sickle-shaped outcrop of the deposit suggests a transcurrent, dextral opening of a WNW-ESE-striking weakness zone across the anorthosite pluton. (C) 2002 Elsevier Science Ltd. All rights reserved. [less ▲]

Imaging downward granitic magma transport in the Rogaland Igneous Complex, SW norway

in Terra Nova (2002), 14(2), 87-92

Combining geological mapping and petrological, structural and geophysical (gravity and seismic) data already available for the late Proterozoic Rogaland Igneous Complex of Norway allows the 3D shape of ... [more ▼]

Combining geological mapping and petrological, structural and geophysical (gravity and seismic) data already available for the late Proterozoic Rogaland Igneous Complex of Norway allows the 3D shape of the Bjerkreim-Sokndal layered intrusion to be modelled as a thick cumulate series capped by massive granitic rocks. Using the latter data, along with the spectacular convergent linear flow pattern that covers both the cumulates and the felsic rocks of this chamber, evidence is presented to show that the granitic material was down-dragged through the sinking of its high-density mafic floor into lower density anorthosites and granulitic gneisses. This example illustrates that downward gravity-driven flows of rocks were active, in addition to upward flows, in the building of the early crust up to late-Proterozoic times, helping to explain the geochemical and structural complexities of the old crust. [less ▲]

Remanence anisotropy: methodological analysis and examples from plutonic rocks

in Geophysical Research Abstracts (2001), 3

The jotunitic and the acidic igneous rocks

in Duchesne, Jean-Clair (Ed.) The Rogaland Intrusive Massifs: an excursion guide (2001)

Secondary fabrics revealed by remanence anisotropy: methodological study and examples from plutonic rocks

in Geophysical Journal International (2001), 147(2), 310-318

Magnetic fabric and deformation in charnockitic igneous rocks of the Bjerkreim-Sokndal layered intrusion (Rogaland, Soutwest Norway)

in Journal of Structural Geology (2000), 22