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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 V Ilm during stage 2, most likely related to a shift in fO 2 . 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 ZrO 2 from ilmenite. The U-Pb zircon age of 920 ± 3 Ma probably records this exsolution process.

Widespread metasomatism affected the 100 km long and 25 km wide Proterozoic Bamble and ModumKongsberg sectors, South Norway, resulting in the chemical and mineralogical transformation of wide segments of continental crust. Scapolitization was associated with veining, and was followed by albitization, transforming metagabbros pervasively over large areas. Fluids played an active role in these reactions, forming H 2 O-, CO 2 -and Cl-bearing phases at the expense of the primary volatile-free minerals, causing depletion in Fe and infiltration of K, Mg, Na, B and P. The transformation of gabbro to scapolite metagabbro is observed as a fluid front replacing the primary magmatic mineral assemblage in three stages: during an incipient amphibolitization stage, the primary mafic minerals were replaced by anthophyllite or hastingsite, followed by pargasitic and edenitic Ca-amphibole. Magnetite was dissolved, while rutile formed by the breakdown of ilmenite. Plagioclase was replaced by Cl-rich scapolite (Me 19-42 ) reflecting Cl-saturation, while K-and Mg-saturation produced phlogopite, enstatite, sapphirine and rare corundum. The high modal contents of chlorapatite and tourmaline in the scapolite metagabbro imply infiltration of B and P. The albitites consist dominantly of albite (Ab 95-98 ) with varying, generally small, amounts of chlorite, calcite, rutile, epidote and pumpellyite. They formed from a H 2 O-CO 2 -fluid rich in Na. The gabbro yields a zircon U-Pb age of 1149 ± 7 Ma and tonalite 1294 ± 38 Ma, whereas rutile from scapolite metagabbro and albitite has U-Pb ages of 1090-1084 Ma, and phlogopite produced during scapolitization Rb-Sr ages of 1070-1040 Ma. Temperature conditions for the scapolitization are inferred to have been 600-700°C. The reported ages, combined with mineralogical and petrographic observations and inferred P-T conditions, indicate that the metasomatism was a part of the regional Sveconorwegian amphibolite facies metamorphic phase. Initial 87 Sr ⁄ 86 Sr of the scapolite ranges from 0.704 to 0.709. The Sr-signature, the Cl-and B-rich environment and regional distribution of lithologies suggest that the fluid may have originated from evaporites that were mobilized during the regional metamorphism.

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