Garnet–clinopyroxene mafic rocks have been investigated in the outer coastal area of the northwestern‐most part of the Western Gneiss Region (WGR), South Norway. The garnet–clinopyroxene rocks occur as lenses with amphibolitized and deformed margins ranging in size from 1 m2 up to 2–3 km2. They are regionally widespread and included in migmatitic gneisses, mica schists and amphibolites. The mafic lenses vary from fine‐ to coarse‐grained with a strain variation from massive to coaxial S > L tectonite fabric. Garnet is Alm42‐53Prp17‐35Grs20‐33Sps0‐3. Clinopyroxene is a Na–Al diopside (En34‐43Fs8‐17Wo48‐52) with Al up to 0.50 a.p.f.u. and Na content up to Jd24. Garnet and clinopyroxene occur in an assemblage with edenitic‐pargasitic amphibole (Ti < 0.32 a.p.f.u.), plagioclase (An16‐43Ab57‐71), quartz, locally biotite (Mg# = 0.0.46–0.56; Ti = 0.51–0.59 a.p.f.u.), calcite, epidote and accessory rutile, ilmenite, zircon and apatite. Garnet porphyroblasts occur commonly as euhedral crystals, and locally with corroded rims surrounded by a corona of plagioclase or amphibole–plagioclase. Growth of secondary garnet is locally observed in S > L tectonite rock. Clinopyroxene occurs as elongated subhedral crystals forming a strong fabric, or as a coarse symplectite with plagioclase. Amphibole is present as matrix grains in the garnet–clinopyroxene assemblage, but occurs also in coronas on garnet as symplectite with plagioclase, or as replacement textures on clinopyroxene. Secondary titanite is produced on rutile, and spinel+plagioclase on ilmenite. The P–T evolution is modelled by P–T pseudosections (TheriakDomino software), thermobarometry and by mapping of garnet chemistry. Garnet porphyroblasts show a decrease in CaO and MnO, an increase in MgO and variable FeO with resulting increasing Mg# from core to rim, indicating growth under increasing temperatures and decompression. Calculation of garnet+clinopyroxene+plagioclase+quartz+rutile stability combined with garnet and clinopyroxene isopleths of grossular and Mg# composition yields a maximum temperature metamorphism of 1.4–1.8 GPa and >900°C. The P–T modelling supports high‐P granulite facies conditions for the equilibration of the garnet–clinopyroxene‐dominated mafic lenses. The maximum temperature metamorphism is associated with partial melting. In addition, an outermost small Mn increase, and local reversal of the Mg# ratio and CaO‐flattening in garnet of the mafic lenses are interpreted as retrogression into amphibolite facies. This is in accordance of mineral replacement of clinopyroxene to amphibole and titanite growth on rutile. The data support an evolution where the eclogite facies crust in the northwestern‐most coastal part of WGR underwent decompression during heating into high‐P granulite facies conditions, followed by cooling and amphibolitization. Our investigation gives a regional petrological documentation and illustrates an extensive high‐T equilibration in the Caledonian root zone subsequent to the deep crustal burial.

Petrological studies of staurolite-garnet-kyanite-biotite schist and garnet-muscovite schist of the Gula Complex, central Norway, provide constraints on metamorphic evolution during Scandian continent -continent collision, burial and exhumation of the Caledonian Upper Allochthon. The biotite schist contains conspicuous porphyroblasts of Fe-rich staurolite, garnet and kyanite, set in a fine-grained, well-foliated matrix of biotite, quartz, minor plagioclase and muscovite. The muscovite schist is fine-to medium-grained with a muscovite-quartz-dominated matrix, including garnet, biotite, minor plagioclase and clinozoisite. Pressure-temperature (P -T ) modelling based on thermobarometric calculations and construction of P-T pseudo-sections illustrate that metamorphism reached 680 8C with pressures estimated up to 1.01 + 0.11 GPa. Retrogression and decompression are constrained by secondary mineral reactions: local replacement of kyanite to fibrous sillimanite indicates decompression below 0.7 GPa. Growth of foliation-parallel chlorite reflects cooling below 640 8C and the chlorite formation proceeded during cooling and decompression towards 550 8C and 0.4 GPa. The metamorphism is associated with a strong north-southtrending regional foliation, and retrogression and decompression apparently continued within the same strain regime. The P-T modelling shows that even small variations in whole-rock chemistry and P-T conditions can explain heterogeneity and significant shifts in mineralogy and modal concentration of the index minerals of metapelites.

A helicopter geophysical survey of about [Formula: see text] was flown over an area of [Formula: see text] in southern Norway to aid in determining which route a proposed railroad should follow. Along any route chosen, extensive tunnelling would be necessary. The aerial geophysical survey aided geologists in mapping the area and provided information on the presence of geological structures, particularly faults and fractures, which could hinder tunnel construction if they are major water conduits. The helicopter survey collected magnetic, electromagnetic, radiometric, and very low frequency (VLF) electromagnetic data, and mapped a number of geophysical lineations and other structures. Most lineaments appear to be related to dikes, faults and fractures. Known major faults appear on all data sets, and minor faults appear on one or more of the individual data sets. Magnetic measurements proved to be the most useful geophysical tool for locating dikes in the area. Contacts between dikes and surrounding rock have been shown to be major water conduits, so the locations of dikes were as important as fault and fracture location. The combination of data sets proved valuable for corroborating the findings from any given data set. From the geophysical data, it appears that the western half of the survey area is more intensely fractured than the eastern half, although a few large lineations, presumably fractures of faults, appear in both areas. Ground follow up in selected areas confirmed the reliability of the airborne data.

Background: We have made an attempt to understand the main mechanism which controls the conductive heat transfer in the Årvollskogen borehole. This has been done in order to determine the 2D subsurface temperature distribution within the deep-seated crystalline rocks and, therefore, to estimate the geothermal potential in the Moss area near Oslo.

No abstract