Fluorine-bearing hydrogarnets from Blengsvatn,Bamble Sector,south Norway

Summary Hydrograndites (grossular-andradite) with up to 1.60 weight percent fluorine occur in altered parts of andesine-garnet-biotite-cummingtonite-hornblende rocks, Blengsvatn, Bamble Sector, south Norway. The garnets occur intergrown with secondary prehnite, pumpellyite, epidote and chlorite along biotite cleavage planes and formed through retrogradation of nearby plagioclase, almandine-rich garnet and hornblende. The conditions of formation are estimated at about 300°C and 1–2 kbar. The observed F/OH distribution at 300°C and calculated relatively low fHF/fH₂O ratios of 10^–5.84 to 10^–7.32 indicates that fluorine is more strongly partitioned relative to OH in hydrogarnet than coexisting biotite and cummingtonite. The low fHF/fH₂O ratios suggest that fluorinebearing hydrogarnets could be very common.

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Fluorhaltige Hydrogranate von Blengsvatn, Bezirk Bamble, Südnorwegen

Zusammenfassung Fluorhaltige Hydrograndite (Grossular-Andradit) mit bis zu 1,60 Gew.% Fluor kommen in umgewandelten Teilen von Andesin-Granat-Biotit-Cummingtonit-HornblendeGesteinen von Blengsvatn, Bezirk Bamble, Südnorwegen, vor. Die Granate treten verwachsen mit sekundärem Prehnit, Pumpellyit, Epidot und Chlorit längs Biotitspaltflächen auf und bildeten sich durch retrograden Abbav von benachbartem Plagioklas, Almandin-reichem Granat und Hornblende. Die Bildungsbedingungen werden auf ungefähr 300°C und 1–2 kbar geschätzt. Die beobachtete F/OH-Verteilung und die relativ niedrigen berechneten fHF/fH₂OQuotienten von 10^–5.84 bis 10^–7.32 weisen darauf hin, daß Fluor relativ zu OH stärker in Hydrogranat als in koexistierendem Biotit und Cummingtonit angereichert ist. Die fHF/fH₂O-Verhältnisse lassen vermuten, daß fluorhaltige Hydrogranate sehr verbreitet sein könnten.

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With 5 Figures     

A radiometric study of polymetamorphism in the Bamble region,Norway

Metamorphism-induced parent-daughter isotopic rearrangement yields information concerning the nature and duration of metamorphism in the Bamble Area, Southern Norway. The thermal maximum of the Bamble Sveconorwegian metamorphism was reached at 1160–1200 m.y. ago, according to zircon and sphene U-Pb, and Rb-Sr whole rock results. Dating of post-kinematic pegmatites suggests that the major kinematic episodes took place not much more than 100 m.y. and that not until more than 200 m.y. after the thermal maximum had uplift and cooling resulted in closure of the K-Ar system in micas. Petrological considerations together with radiometric data on the Levang Gneiss Dome suggest that Rb-Sr whole rock samples show open and closed system behaviour under similar temperatures but possibly different . Variable recrystallization of zircon in the Levang Gneiss Dome (when taken with accompanying radiometric U-Pb data) appears to substantiate the idea that when = P _solid, resetting of both the U-Pb systems in zircon and Rb-Sr whole rock systems is greatly facilitated.     

Hydrothermal dolomite marbles associated with charnockitic magmatism in the Proterozoic Bamble Shear Belt,south Norway

Deformed and metamorphosed dolomite marbles in the Kragerø area of the Bamble Shear Belt occur as lenses within metasupracrustal sequences, as matrix in bodies resembling magmatic breccias, and as veins/dykes cutting amphibolites and metagabbros. A common origin is not evident from the field relationships, but is nevertherless probable due to great geochemical similarities between dolomite from the different occurrences. They are characterized by higher REE, Ni, Co, Cr and Sc, and lower Ba and Sr contents relative to metasedimentary marbles occurring nearby. Sm-Nd isotope data shows that the dolomites are of Sveconorwegian age (1175±37 Ma). The dolomite marbles are very weakly LREE-enriched and display in most cases positive Eu anomalies. Their stable isotope compositions are uniform (¹⁸O=+9.6 to +10.7; ¹³C=-8.5 to-6.2), their initial ⁸⁷Sr/⁸⁶Sr ratios are high (0.706–0.709), whereas their age corrected _Nd varies from +0.7 to-1.5. Geochemically the dolomitic marbles differ considerably from sedimentary or metasedimentary marbles as well as from carbonatites. The Kragerø dolomite marbles represent deformed and metamorphosed hydrothermal veins or vein-complexes deposited in tensional fractures in the deep crust. Although the dolomitic marbles regionally are of minor volume, the dolomite deposition represents a specific and important event in the geological evolution of the Bamble Shear Belt. Their geochemical and isotopic homogeneity on a regional scale suggest that the hydrothermal solutions were supplied from a very large, homogeneous reservoir. Trace elements, stable and radiogenic isotopes, and field and isotopic age relationships are consistent with a deposition from hydrothermal solutions which were exsolved from crystallizing charnockitic intrusions and subsequently interacted with the crust. The parental magma to these intrusions underplated the crust and raised the geotherm of a carbonated ultramafic uppermost mantle, and imposed decarbonation and fluid release. These fluids were channelled into a large degassing zone now found as a deformed, regional zone with hydrothermal dolomite deposits, albitites, apatite-veins and widespread scapolitization. Whether the CO₂-rich fluids, which precipitated the Kragerø dolomites, pervasively infiltrated crustal rocks at a deeper level and caused granulitization is ambiguous, but possible.     

Aluminous reaction textures in orthoamphibole-bearing rocks: the pressure–temperature evolution of the high-grade Proterozoic of the Bamble sector, south Norway

Aluminous reaction textures in orthoamphibole-bearing rocks from the Froland area, Bamble, south Norway, record the prograde pressure–temperature path of the high-grade Kongsbergian Orogeny (c. 1600–1500 Ma) and the low–mid amphibolite facies overprint during the Sveconorwegian Orogeny (c. 1100–1000 Ma). The rocks contain anthophyllite/gedrite, garnet, cordierite, biotite, quartz, andalusite, kyanite, Cr-rich staurolite, tourmaline, ilmenite, rutile and corundum in a variety of parageneses. The P–T path is deduced from petrographic observations, mineral chemistry and zoning, geothermometry and (N)FMASH equilibria. The results indicate the sequence of metamorphic stages outlined below. (a) An M₁ phase characterized by the presence of strongly deformed andalusite, gedrite and tourmaline. (b) An M₂ phase with the development of kyanite after andalusite and the growth of staurolite associated with strong Na–Al–Mg zoning in orthoamphibole, indicating an increase in pressure (4 8 kbar) and temperature (500° 650°C). (c) Pressure decrease at high P (6–7 kbar) and high T (600–700 °C) during M_3a with the production of cordierite ° Corundum between kyanite, staurolite and orthoamphibole and cordierite growth between corundum and orthoamphibole. (d) Temperature increase to 740 ± 60 °C and 7 kbar; static growth of garnet (M_3b) at the metamorphic climax (peak T). The heat supply necessary to explain the temperature increase between the M_3a and M_3b phases is correlated with synkinematic enderbitic–charnockitic and basic intrusions in the Arendal granulite facies terrain. (e) M_3b metamorphic conditions were followed by an initial isobaric cooling path (early M₄) and late-stage pressure decrease (late M₄). Early M₄ conditions of 6–7 kbar and 550–600 °C, assuming P_H2O < P_total are indicated by a retrograde talc–kyanite–quartz assemblage in late quartz–cordierite veins. Late M₄ conditions of 3–4 kbar and 420–530 °C are inferred from a kyanite–andalusite–chlorite–quartz assemblage in vein-cordierite. The M₁–M₃ stages are interpreted as being the result of the same metamorphic P–T path, which was caused by both tectonic and magmatic thickening. A prolonged crustal residence time is proposed for the Bamble sector before uplift during the later stages of M₄ occurred.     

Orthopyroxene–sillimanite–sapphirine granulites from the Bamble granulite terrane, southern Norway

Silica-deficient sapphirine-bearing rocks occur as an enclave within granulite facies Proterozoic gneisses and migmatites near Grimstad in the Bamble sector of south-east Norway (Hasleholmen locality). The rocks contain peraluminous sapphirine, orthopyroxene, gedrite, anthophyllite, sillimanite, sapphirine, corundum, cordierite, spinel, quartz and biotite in a variety of assemblages. Feldspar is absent.
Fe²⁺/(Fe²⁺+ Mg) in the analysed minerals varies in the order: spinel > gedrite ≥ anthophyllite ≥ biotite > sapphirine>orthopyroxene > cordierite.
Characteristic pseudomorph textures indicate coexistence of orthopyroxene and sillimanite during early stages of the reaction history. Assemblages containing orthopyroxene-sillimanite-sapphirine-cordierite-corundum developed during a high-pressure phase of metamorphism and are consistent with equilibration pressures of about 9 kbar at temperatures of 750–800°C. Decompression towards medium-pressure granulite facies generated various sapphirine-bearing assemblages. The diagnostic assemblage of this stage is sapphirine-cordierite. Sapphirine occurs in characteristic symplectite textures. The major mineralogical changes can be described by the discontinuous FMAS reaction: orthopyroxene + sillimanite → sapphirine + cordierite + corundum.
The disequilibrium textures found in the Hasleholmen rocks are characteristic for reactions which have been in progress but then ceased before they run to completion. Textures such as reaction rims, symplectites, partial replacement, corrosion and dissolution of earlier minerals are characteristic of granulite facies rocks. They indicate that, despite relatively high temperatures (700–800° C), equilibrium domains were small and chemical communication and transport was hampered as a result of dry or H₂O-poor conditions.     

Radioelement geochemistry of alkali granites of the Kerala region,south-west India

Th, U and K abundances in four alkali granites of the Kerala region, south-west India, are presented. The plutons show high radioelement levels, correlatable with those of alkali granites in other regions. The nature of variation is consistent with the correlation of Th and U with accessory phases like sphene, zircon, allanite, apatite and monazite. A geochronologic correlation is also observed between the alkali granites and the Th-bearing beach placers of the region. The petrogenetic features of the alkali plutons, their taphrogenic association, Pan-African affiliation and high Th/U levels suggest that the alkali plutons are favourable locales for radioelement exploration.     

Late Weichselian deglaciation in the Oslofjord area, south Norway

The older 'moraine lines' outside the Ra Moraine in the outer Oslofjord area have been correlated with events in Bohuslän, Sweden. Recent radiocarbon datings in the vicinity of the Ra Moraine and a radiocarbon dated sea-level curve for the Ski area show that the Ra Moraine was formed during the Early Younger Dryas, whereas the Ski Moraine was formed at the end of the Younger Dryas chronozone. An equidistant shoreline diagram together with a large number of marine limit observations have been used to establish the position of the glacier front during Late Younger Dryas and Early Preboreal chronozones. Reconnaissance mapping indicates a fairly regular recession with many short stops during the Bølling, Older Dryas and Allerød chronozones; at least two readvances to the Ra Moraine before 10,600 years B.P.; a rapid recession during the Middle Younger Dryas and a number of ice-front oscillations at the end of the Younger Dryas chronozone.     

Uplift and cooling magnetisation record in the Bamble and Telemark terranes,Sveconorwegian orogenic belt,SE Norway,and the Grenville-Sveconorwegian loop

The ~ 1100 Ma Sveconorwegian orogenic belt comprises allochthonous terranes juxtaposed by major fault zones and emplaced against, and onto, the south-western margin of the Fennoscandian Shield. To resolve the magnetic signature acquired during post-orogenic uplift and cooling and evaluate wider correlations with the contemporaneous Grenville belt of North America, this study reports a regional palaeomagnetic study on a range of rock types from sectors of the medium-high metamorphic grade Bamble terrane (48 sites and 390 cores) and the adjoining medium-low grade Telemark terrane (33 and 240 cores) juxtaposed by an orogen-parallel (Porsgrunn- Kristiansand) fault zone with major vertical displacement. Magnetite and ilmeno-hematites are magnetic carriers with the latter more significant in the higher metamorphic grades. Magnetic intensities are stronger in the higher-grade terrane presumably due to the growth of metamorphic ferromagnets, but are an order lower than values predicted for the lower continental crust and indicate that an additional mechanism is responsible for high magnetisations in deep crust. Anisotropy of magnetic susceptibility (AMS) largely reflects the NE–SW tectonic grain of the last stage of Sveconorwegian ductile deformation. The magnetisation record is filtered by excluding magnetisations possibly acquired during regional Mesozoic dyke emplacement, development of the Permo-Carboniferous Oslo Rift and Late Proterozoic magmatism. The remaining record is a dual polarity signature summarised by mean poles at 31.9°N, 50.9°E, (N = 191 components) in the Bamble terrane and at 34.2°N, 58.9°E (N = 151 components) in the Telemark terrane. However these means are non-Fisherian and embrace arcuate distributions of magnetic components acquired during protracted exhumation cooling of the orogen with the best-defined parts comprising clockwise trajectories correlating with each another but indicating that cooling in Telemark was more protracted; in each case directions of more shallow NW-direction tend to be derived from lower unblocking temperature components. The geochronological evidence indicates that regional temperatures had fallen to permit acquisition of magnetisation by ~ 950–900 Ma and the two swathes define the younger limb of a clockwise (Grenville-Sveconorwegian) APW loop embracing the approximate interval 940–850 Ma; the outward path of this loop (~ 1020–940 Ma) is probably at present recorded only in dyke swarms from the Finnish sector of the shield. Correlation of APW between Laurentia and Fennoscandia confirms that the two shields broke apart shortly after culmination of the Sveconorwegian orogeny when Fennoscandia rotated rapidly clockwise into a secondary configuration adjacent to the eastern margin of Laurentia; the Grenville and Sveconorwegian orogenic frontal zones formed in alignment were reoriented at a high angle to one another in a coupling that appears to have persisted during most of the remainder of Neoproterozoic times.     

Formation of monazite and xenotime inclusions in fluorapatite megacrysts, Gloserheia Granite Pegmatite, Froland, Bamble Sector, southern Norway

Xenotime and monazite inclusions in fluorapatite megacrysts from a granitic pegmatite, Gloserheia, Froland, Bamble Sector, southern Norway are described utilizing high contrast backscattered electron imaging of cross sections of a selection of fluorapatite crystals. Electron microprobe analysis is then used to further characterize the xenotime and monazite, as well as (Y+REE) normal and depleted regions in the fluorapatite. In the (Y+REE) normal regions Y₂O₃ ranges from 0.4 to 1.3 whereas it ranges from below the electron microprobe detection limit to around 0.4 in the depleted regions. Low Y values in monazite (X_Y?=?0.01?0.05) co-existing with xenotime indicates that inclusion formation in the originally (Y+REE)-enriched fluorapatite must have occurred below 300°C. Formation of the xenotime and monazite inclusions is attributed to fluid-aided coupled dissolution-reprecipitation processes during the later stages of subsolidus cooling of the pegmatite. The fluorapatite megacrysts are hypothesized to have under gone two major fluid-induced alteration events. The first occurred sometime after crystallization was complete at temperatures below 300°C and resulted in the initial formation of the xenotime and monazite inclusions. The second occurred at some later time as the product of a relatively limited fluid infiltration, also under T?<?300°C. This resulted in the formation of (Y+REE)-depleted regions along lattice and cleavage planes while at the same time promoting Ostwald ripening of the xenotime inclusions resulting in larger grains in the (Y+REE)-depleted areas.     

Petrology and geothermobarometry of granulite facies metapelites from the Hisøy-Torungen area, south Norway: new data on the Sveconorvegian P–T–t path of the Bamble sector

ABSTRACT The high-grade rocks (metapelite, quartzite, metagabbro) of the Hisøy-Torungen area represent the south-westernmost exposures of granulites in the Proterozoic Bamble sector, south Norway. The area is isoclinally folded and a metamorphic P–T–t path through four successive stages (M1-M4) is recognized. Petrological evidence for a prograde metamorphic event (M1) is obtained from relict staurolite + chlorite + albite, staurolite + hercynite + ilmenite, cordierite + sillimanite, fine-grained felsic material + quartz and hercynite + biotite ± sillimanite within metapelitic garnet. The phase relations are consistent with a pressure of 3.6 ± 0.5 kbar and temperatures up to 750–850°C. M1 is connected to the thermal effect of the gabbroic intrusions prior to the main (M2) Sveconorwegian granulite facies metamorphism. The main M2 granulite facies mineral assemblages (quartz+ plagioclase + K-feldspar + garnet + biotite ± sillimanite) are best preserved in the several-metre-wide Al-rich metapelites, which represent conditions of 5.9–9.1 kbar and 790–884°C. These P–T conditions are consistent with a temperature increase of 80–100°C relative to the adjacent amphibolite facies terranes. No accompanying pressure variations are recorded. Up to 1-mm-wide fine-grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction: Bt + Sil + Qtz→Grt + lq. This dehydration reaction, together with the absence of large-scale migmatites in the area, suggests a very reduced water activity in the rocks and XH₂O = 0.25 in the C–O–H fluid system was calculated for a metapelitic unit. A low but variable water activity can best explain the presence or absence of fine-grained felsic material representing a former melt in the different granulitic metapelites. The strongly peraluminous composition of the felsic veinlets is due to the reaction: Grt +former melt ± Sil→Crd + Bt ± Qtz + H₂O, which has given poorly crystalline cordierite aggregates intergrown with well-crystalline biotite. The cordierite- and biotite-producing reaction constrains a steep first-stage retrograde (relative to M2) uplift path. Decimetre- to metre-wide, strongly banded metapelites (quartz + plagioclase + biotite + garnet ± sillimanite) inter-layered with quartzites are retrograded to (M3) amphibolite facies assemblages. A P–T estimate of 1.7–5.6 kbar, 516–581°C is obtained from geothermobarometry based on rim-rim analyses of garnet–biotite–plagioclase–sillimanite–quartz assemblages, and can be related to the isoclinal folding of the rocks. M4 greenschist facies conditions are most extensively developed in millimetre-wide chlorite-rich, calcite-bearing veins cutting the foliation.     

Boron isotopes in tourmaline as a tracer of metasomatic processes in the Bamble sector of Southern Norway

The Bamble sector of southern Norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the Sveconorwegian orogeny (~1.06 Ga). The infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of Fe–Ti oxides. Typical secondary mineral assemblages include either scapolite + apatite + amphibole + phlogopite + tourmaline, or albite + epidote + calcite + chlorite + white mica, indicating that the fluids introduced large amounts of Na, Cl, Mg, Ca, K, P, and B to the system. Metasomatic tourmalines associated with different alteration stages as identified by variations in major-element composition and initial ⁸⁷Sr/⁸⁶Sr were analyzed for B isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid(s). Measured δ¹¹B values range from ?5 to +27 ‰ relative to SRM-951, suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible B source reservoir. The influence of a seawater-derived component is clearly indicated by the heavy B isotope signature of tourmaline related to Al–Mg-rich metapelites. In contrast, negative δ¹¹B values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites. On a regional scale (i.e., several km), δ¹¹B values in tourmaline vary widely, whereas variations within a single outcrop (tens of m) are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses.     

Subglacial plant remains from the Omnsbreen glacier area, south Norway

Plant remains have been found on ground recently deglaciated from the Omnsbreen glacier. They consist of Salix herbacea, Salix spp., Silene acaulis, Polytrichum norvegicum, Kiaeria of. starkei, and some unidentified species. Their age has been determined by the radiocarbon method to approx. 550 years, indicating that the present Omnsbreen glacier emerged as late as the clima deterioration in the late Middle Ages. The past vegetation was similar to the present, but slightly more thermophilous, indicating a rapid clima deterioration in the fourteenth century.     

Rb-Sr isotope systematics in metamorphic rocks,Kongsberg sector,south Norway

Rb-Sr isotope data are presented for gneisses, migmatite neosome material and granitic and gabbroic intrusive rocks from the southern part of the Kongsberg sector, south Norway. The maximum age of the crust in this area appears to be ～1.6 AE. Two metamorphic episodes at ～1.5–1.6 AE and at ～1.1–1.2 AE are recognized. Initial ⁸⁷Sr/⁸⁶Sr ratios for the granitic rocks give evidence for reworking of sialic crust and indicate that approximately 1.6 AE old crust repeatedly acted as a source for granitic magmas for a timespan of ～0.5 AE.     

Fluid-controlled quartz recovery in granulite as revealed by cathodoluminescence and trace element analysis (Bamble sector,Norway)

Dispersed quartz veinlets in Proterozoic enderbitic charnockite from Tromøy, Bamble sector (southern Norway), with Ti-concentrations of mostly 80–180 ppm, produce bright blue cathodoluminescence (CL), against contrasting micro-textures of secondary pure quartz with low CL intensity. The textures comprise grain boundary alteration, healed micro-fractures, patches of secondary quartz, and euhedral quartz nuclei. The secondary quartz locally makes up 50% of the total quartz. Trace element analysis has been done by electron-probe micro-analysis (EPMA), laser-induced coupled plasma mass spectrometry (LA-ICPMS), and additional electron-paramagnetic resonance (EPR) spectroscopy. These studies testify systematic trace element reduction and extensive quartz recovery during retrograde metamorphism. We assume healing of a part of the aqueous fluid inclusions during a late thermal event, possible correlated with Paleozoic magmatic activity in the Oslo-Rift. During final cooling, aqueous fluids were largely retrapped in patches of secondary quartz associated with healed fractures, whereas carbonic inclusions (without secondary quartz) may have survived retrograde metamorphism. The variable but generally high salinity of fluid inclusions is assumed to be in part the result of quartz recovery by which ion concentrations were increased in the percentage range.Editorial Responsibility: J. Touret     

Fluid inclusions in quartz from deep-seated granitic intrusions,south Norway

H₂O, CO₂, and H₂OCO₂ inclusions were observed in quatz from deep-seated granitic intrusions belonging to the Precambrian Farsund plutonic complex, south Norway. These inclusions represent solidus and/or sub-solidus fluids that were present in these rocks at some period between the initial melt and the present. Early CO₂ and H₂OCO₂ inclusions with about 20 mole% CO₂ contain up to 10 mole% CH₄ in the CO₂ phase and have densities from 0.96 to 0.85 g/cc. These inclusions are considered to most nearly approximate solidus vapour phases and suggest conditions of final solidification of the magma at 5 to 6 Kb and 700°C to 800°C. The H₂O inclusions have salinities between 2 and 60 wt%; the majority contain 5 to 20 equivalent wt.% NaCl and have densities from 1.05 to 0.85 g/cc. Microthermometry indicates that other cations such as K⁺, Ca²⁺ and / or Mg²⁺ are present in these aqueous fluids. The H₂O inclusions primarily represent fluids present at a post-magmatic stage of fracturing and healing of these rocks during uplift.     

The Precambrian Telemark area in south central Norway

A brief review of the geology of south eastern Norway is given just to emplace the Precambrian Telemark area in the general geological picture. Field work carried out during 20 years has enabled the author and his coworkers to establish a “Telemark suite” which is composed of three groups of supracrustal rocks separated by angular unconformities. Its total thickness exceeds 4000 metres. Granitization has everywhere obliterated the base of the supracrustals and granite domes have penetrated even the youngest known member of the sequence. Copper, molybdenum, galena and other ore deposits of the quartz vein type are most probably connected with the granitization, whereas the deposits of native copper and silver in quartzite are regarded as syngenetic products, formed when a basaltic lava overflowed a bed of sand. It is pointed out that this area although being of Precambrian age, locally contains more well preserved features (e.g. ripplemarks, mudcracks, fossils [?] etc) than is usual in basement complexes.     

Rare-earth and LIL element fractionation in high-grade charnockitic gneisses,south Norway

High-Fe, intermediate-acid, charnockitic gneisses in the Arendal-Tromøy area of the Svecofennian terrain of southeast Norway comprise two chemically contrasting zones - one with normal large-ion-lithophile (LIL) element characteristics, and the other IIL-deficint. The noramal -LiLL-deficient varitties also have low ΣEEE, commonly with positive Eu anomalies. The normal-LIL rocks are enriched in ?REE, exhibit fractionated patterns and have negative Eu anomalies. Modelling shows that both the LIL and REE patterns are consistent with an essentially primary fractionation process involving the separation of cumulus (LIL-deficient) phases from andesitic-dacitic magma emplaced directly under the high-grade conditions, with the normal-LIL rocks crystallising from the residual melt. This process is interpreted as a deep-seated component of the magma system which culminated in the emplacement of some higher level rapakivi granite late in the Svecofennian event. The model presented does not require anorthosite to be part of the same magma system.     

Distribution and genesis of tills in central south Norway

The morphogenesis of tills below the culmination zones of the Weichsclian inland ice has been studied an an upland area with a relief of 1500 m. The thickness of the tills varies considerably, depending principally on gee-morphology, ice-movement directions, and glaciofluvial drainage during the last deglaciation period. The thickest tills, found in valleys, accumulated in three ways. Glaciofluvial/lacustrine sediments of prcsumed Mid-Weichselian age have been discovered beneath the tills at niorc than 10 localities. The overlying tills are correlated with different phases of ice movement reconstructed on the basis of detailed studies of stt-iae. The till stratigraphy of one locality, Stenseng, is described in detail. Based upon combined analyses of texture, structure, and fabric, four different hasal tills are recognized, each corresponding to a particular ice direction. A characteristic boulder layer represents a change in thc direction of glacial movement. Boulder layers in till are thought to he essential for the development of earth pillars.