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See detailIlmenite composition in the Tellnes Fe–Ti deposit, SW Norway: fractional crystallization, postcumulus evolution and ilmenite–zircon relation
Charlier, Bernard ULg; Skar, Oyvind; Korneliussen, Are et al

in Contributions to Mineralogy & Petrology (2007), 154(2), 119-134

Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit, Rogaland Anorthosite Province, SW Norway, constrains a two stage fractional crystallization model of ... [more ▼]

Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit, Rogaland Anorthosite Province, SW Norway, constrains a two stage fractional crystallization model of a ferrodioritic Fe-Ti-P rich melt. Stage 1 is characterized by ilmenite-plagioclase cumulates, partly stored in the lower part of the ore body (Lower Central Zone, LCZ), and stage 2 by ilmenite-plagioclase-orthopyroxene-olivine cumulates (Upper Central Zone, UCZ). The concentration of V and Cr in ilmenite, corrected for the trapped liquid effect, (1) defines the cotectic proportion of ilmenite to be 17.5 wt% during stage 1, and (2) implies an increase of D VIlm during stage 2, most likely related to a shift in fO2. The proportion of 17.5 wt% is lower than the modal proportion of ilmenite (ca. 50 wt%) in the ore body, implying accumulation of ilmenite and flotation of plagioclase. The fraction of residual liquid left after crystallization of Tellnes cumulates is estimated at 0.6 and the flotation of plagioclase at 26 wt% of the initial melt mass. The increasing content of intercumulus magnetite with stratigraphic height, from 0 to ca. 3 wt%, results from differentiation of the trapped liquid towards magnetite saturation. The MgO content of ilmenite (1.4–4.4 wt%) is much lower than the expected cumulus composition. It shows extensive postcumulus re-equilibration with trapped liquid and ferromagnesian silicates, correlated with distance to the host anorthosite. The Zr content of ilmenite, provided by in situ analyses, is low (<114 ppm) and uncorrelated with stratigraphy or Cr content. The data demonstrate that zircon coronas observed around ilmenite formed by subsolidus exsolution of ZrO2 from ilmenite. The U-Pb zircon age of 920 ± 3 Ma probably records this exsolution process. [less ▲]

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See detailIlmenite deposits and their geological environment (with special reference to the Rogaland Anorthosite province, including a geological map at scale 1:75,000)
Duchesne, Jean-Clair ULg; Korneliussen, Are

Book published by NGU (2003)

The Rogaland Anorthosite Province comprises three major massif-type anorthosites, two smaller-sized anorthositic-leuconoritic bodies, as well as a large layered, dominantly noritic intrusion. A mangero ... [more ▼]

The Rogaland Anorthosite Province comprises three major massif-type anorthosites, two smaller-sized anorthositic-leuconoritic bodies, as well as a large layered, dominantly noritic intrusion. A mangero-noritic intrusion is found in the northeastern part of the province and major acidic intrusions are located to the far southeast. The Rogaland Anorthosite Province was emplaced into the Sveconorwegian orogenic belt of southwest Scandinavia at 931±3 Ma. Emplacement took place at around 5.5 kbar producing a thermal aureole with osumilite and pigeonite isograds and evidence for dehydration melting. The early history of the hosting terrane most likely dates back to Gothian or late Pre-Gothian times and contain evidence for numerous episodes of folding and deformation. Contact metamorphism was superimposed on a crustal volume, which had been exposed to Sveconorwegian granulite facies metamorphism between 1024 and 970 Ma. Deformation patterns, mineral compositional considerations and geothermobarometry imply that the Rogaland anorthosites crystallized along a P-T trajectory starting at 10-13 kbar, and were emplaced in a mushy state. The possibility that primitive jotunites may be parental to the andesine anorthosites have recently been substantiated, and experimental data show that these jotunites most likely formed by melting of gabbronoritic sources in the lower crust. The 230 km2 Bjerkreim-Sokndal Layered Intrusion also derive from jotunitic parents, and jotunites form a continuous liquid line of descent filling the gap between basic and acidic rocks in Rogaland. This intrusion contains a >7000 m thick layered cumulate sequence, consisting of virtually all the rock types belonging to the anorthosite kindred. The intrusion morphology, layering and compositional variation result from a variety of magma chamber processes, which are discussed in detail. The Rogaland Anorthosite Province also hosts numerous Fe-Ti oxide deposits of variable size, grade and composition. The oxide deposits have been divided into three basic types based on their oxide-phosphate association; type 1: ilmenite-only, type 2: ilmenite + magnetite and type 3: ilmenite + magnetite + apatite. This excursion guide provides detailed itineraries to most parts of the Rogaland Anorthosite Province, with in-depth descriptions of more than 40 key localities, The itineraries cover the various anorthosites, the Bjerkreim-Sokndal Layered Intrusion, jotunitic and acidic intrusions, the hosting metamorphic complex, as well as Fe-Ti oxide and sulfide deposits. [less ▲]

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