SW Norway Research Articles

The aquatic glacial relict fauna of Norway – an update of distribution and conservation status

The aquatic “glacial relict” fauna in Norway comprises a group of predominantly cold-water animals, mainly crustaceans, which immigrated during or immediately after the deglaciation when some of the territory was still inundated by water. Their distribution is mainly confined to lakes in the SE corner of the country, east of the Glomma River in the counties of Akershus, Østfold and Hedmark. We review the history and current status of the knowledge on this assemblage and of two further similarly distributed copepod species, adding new observations from the last decades, and notes on taxonomical changes and conservation status. By now records of original populations of these taxa have been made in 42 Norwegian lakes. Seven different species are known from Lake Store Le/Foxen on the Swedish border, whereas six species inhabit lakes Femsjøen, Øymarksjøen and Rødenessjøen, and five are found in Aspern, Aremarksjøen and in the largest Norwegian lake, Mjøsa. From half of the localities only one of the species is known. The most common species are Mysis relicta (s.str.), Pallaseopsis quadrispinosa and Limnocalanus macrurus. Some populations may have become extirpated recently due to eutrophication, acidification or increased fish predation. Apart from the main SE Norwegian distribution, some lakes of Jæren, SW Norway, also harbour relict crustaceans, which is puzzling. The region is disjunct from any current fresh- or brackish-water sources, whereas following the early deglaciation it bordered the large, dry landmass of Doggerland, now the submerged bottom of the North Sea. While the Jæren Mysis population indeed is found to represent a different, plausibly more salt-tolerant species than that in SE Norway, the recent discovery of the freshwater amphipod Pallaseopsis quadrispinosa from the same lake upholds the zoogeographical enigma.

Asymmetrical magnetic fabrics in the Egersund doleritic dike swarm (SW Norway) reveal sinistral oblique rifting before the opening of the Iapetus

The 616 ± 3 Ma (Ediacaran) Egersund doleritic dike swarm cuts across the Rogaland anorthosite province and its granulitic country rocks, in SW Norway. The structure of eight out of eleven main dikes of the swarm was investigated using the anisotropy of magnetic susceptibility (AMS) technique. Thermomagnetic data and values of the bulk magnetic susceptibility reveal a magnetic mineralogy dominated by Ti-poor titanomagnetite. Magnetic fabric and global petrofabric are coaxial, except in sites strongly affected by hydrothermal alteration, as demonstrated through image analysis. Asymmetrical dispositions of the magnetic foliation and lineation support the existence of a syn-emplacement, sinistral strike-slip shearing resolved on dike walls. Such asymmetrical fabrics are attributed to a transtension tectonic regime, in a context of oblique extension during the continental rifting phase which preceded the opening of the Iapetus Ocean along the SW margin (present-day orientation) of Baltica.

Heavy-mineral and garnet compositions of stream sediments and HP–UHP basement rocks from the Western Gneiss Region, SW Norway

Heavy-mineral and garnet compositions of stream sediments and HP–UHP basement rocks from the Western Gneiss Region, SW Norway

A major re-growth of the Scandinavian Ice Sheet in western Norway during Allerød-Younger Dryas

Distinct Younger Dryas (YD) moraines are mapped more-or-less continuously around the Scandinavian Ice Sheet. In most areas there is no evidence to suggest that a glacial re-advance took place during the YD, either because it did not happen or because older deposits have been removed by glacial erosion. In contrast we here present 90 radiocarbon dates from 36 different sites that were overrun by a major ice sheet advance in the area between Hardangerfjorden and Sognefjorden, SW Norway. Thus this region is exceptional for examining the glacial response to the climate shifts across Allerød-YD. The re-growth of the ice sheet in this sector commenced during the Allerød Interstadial. It expanded along 600–800 m deep fjords reaching a thickness of up to 2000 m. We produce time–distance diagrams for two lobes; for both the outermost coast became ice free close to 15 cal ka BP, i.e. at the onset of the Bølling. The Hardangerfjorden Lobe re-advanced during the Older Dryas (14 cal ka BP), an event that was not replicated for the Herdla Lobe farther north. Both lobes reached their most landward position before re-advancing at 13.5–13.0 cal ka and obtained their maximum extent at the very end of the YD, 11.5 cal ka. The late culmination of the advance is accurately dated and differs from most of the Scandinavian Ice Sheet margin where the maximum was reached during early or middle YD. We also present a time–distance diagram from the Last Glacial Maximum to the ice divide showing two-step retreat; fast retreat occurs 21–20 and 11.5–10 cal ka BP separated by a period of almost no net retreat 20–11.5 cal ka BP, which contrasts with much more even retreat in other parts of the Scandinavian Ice Sheet.

Heavy minerals and garnet geochemistry of stream sediments and bedrocks from the Almklovdalen area, Western Gneiss Region, SW Norway: Implications for provenance analysis

Detrital heavy minerals commonly document the geological setting in the source area, hence they are widely used in sedimentary provenance analysis. In heavy mineral studies, the 63–125 and 63–250μm grain size fractions are most commonly used. Heavy mineral data and garnet geochemistry of stream sediments and bedrocks from the catchment area draining the Almklovdalen peridotite massif in SW Norway reveal that a wider grain size spectrum needs to be considered to avoid misleading interpretations. The Almklovdalen peridotite massif consists mainly of dunite and harzburgite, as testified by the heavy mineral suite. At the outlet of the main river, the heavy mineral spectrum is very monotonous due to dilution by a strong influx of olivine. Heavy minerals like apatite and epidote characterising the host gneisses have almost disappeared. MgO-rich almandine garnets are more frequent in the coarser grain size fractions, whereas MnO-rich almandine garnets are more frequent in the finer grain size fractions. Garnets with pyrope content exceeding 50% are only found in the 500–1000μm grain size fraction. Therefore, the sample location and the selected grain size fraction are of paramount importance when dealing with heavy minerals and mineral geochemical data; otherwise, provenance-sensitive information may be missed.

The Late Mesoproterozoic Sirdal Magmatic Belt, SW Norway: Relationships between magmatism and metamorphism and implications for Sveconorwegian orogenesis

The Late Mesoproterozoic Sveconorwegian Province is commonly correlated with the continent-collision related Grenville Province in eastern Canada. Recently, however, the evolution of the Sveconorwegian Province in SW Norway has been strongly debated, casting doubt on a direct correlation between these provinces.Metamorphism in SW Norway has traditionally been interpreted as representing a main collisional event between ca. 1030 and 970Ma, followed by a contact metamorphic event at 930Ma. Magmatism has been grouped into a ‘syn-collisional’ suite at 1050–1035Ma, a ‘post-collisional’ suite at 980–930Ma, and an anorthosite–mangerite–charnockite–granite (AMCG) suite at 930Ma. New detailed mapping and geochronology in the area reveal a very different and much more complex evolution, and require re-evaluation of previously presented models. In this paper, we focus on the introduction and description of a newly discovered, ca. 200km×50km magmatic belt, the Sirdal Magmatic Belt (SMB). Previously mapped as granitic gneisses in many areas, the existence of this large, commonly undeformed and unmetamorphosed granitoid batholith was only recognized a few years ago (Slagstad et al., 2013a). Magmatism in this belt between 1060 and 1020Ma precedes and overlaps the main Sveconorwegian metamorphic event(s) that affected the region.Our observations of cross-cutting relationships between previously metamorphosed gneisses and SMB rocks indicate that at least one episode of amphibolite- to granulite-facies metamorphism occurred in the region during or prior to emplacement. A lack of widespread metamorphic overprinting and common preservation of igneous textures in most of the SMB indicate that high-grade Sveconorwegian metamorphism after ca. 1020Ma was local rather than regional in SW Norway.The orogenic evolution of SW Norway is characterized by emplacement of large volumes of granitic magma and more localized UHT metamorphism, which is quite different from the widespread, long-lasting metamorphic evolution observed in the Grenville Province, and may point to different tectonic regimes for the two provinces.

Evidence of plaggen soils in SW Norway

AbstractThis study aimed at clarifying whether a notable group of soils of the Jæren region, SW Norway, with deep humus‐rich top soils support a man‐made genesis. Four sites were investigated. The soils are characterized by thick top soils of 45, 70, 80, and 90 cm, which are enriched in soil organic matter and often also in artifacts, like fragments of potter's clay, indicating an anthropogenic origin. Soil pH ranges from 5.4 to 6.2 (H2O) and 4.4 to 5.3 (CaCl2), respectively. Soil organic C (SOC) contents range from 6.4 to 51.6 g kg−1 and N contents vary between 0 and 2.9 g kg−1. Increased P contents of up to 2,924.3 mg kg−1 total P (Pt) and 1,166.4 mg kg−1 citric acid‐soluble phosphorus (Pc) in the humus‐rich top soils support the assumption of an anthropogenic influence. Although many characteristics indicate an anthropogenic genesis, one soil lacks the required depth of 50 cm of a plaggen horizon and cannot be classified as Plaggic Anthrosol (WRB) and Plagganthrept (US Soil Taxonomy). As the requirement is 40 cm in the German system, all soils can be classified as Plaggenesch. The formation of these soils is related to human activity aiming at increasing soil fertility and overcoming the need of bedding material, the basic aims of the plaggen management in Europe. Highest P contents ever found for this kind of soils and references from the literature indicate that the formation of the soils in Norway started at Viking time, hence, being older than most other Plaggic Anthrosols.

Source-derived heterogeneities in the composite (charnockite-granite) ferroan Farsund intrusion (SW Norway)

The Sveconorwegian late-orogenic magmatism of southern Norway (970–916Ma) consists of two magmatic suites: the Hornblende–Biotite–Granitoids (HBG) suite and the Anorthosite–Mangerite–Charnockite (AMC) suite of the Rogaland Anorthosite Province (RAP), characterized by opx-bearing lithologies. The Farsund body comprises elements of both suites that display mingling relationships. The main facies, mostly charnockitic, contains orthopyroxene whereas a subordinate granitic facies comprises hornblende and biotite. U–Pb (zircon) isotopic data show overlapping ages of 931±2Ma for the charnockitic facies and 926±4Ma for the granitic facies. Both facies display similar extent of differentiation demonstrating that the granitic facies was not derived by fractionation from the charnockitic one. Mineralogical, geochemical and petrological data indicate that the charnockitic facies belongs to the AMC suite and the granitic facies, to the HBG suite. Strontium, Nd and Pb isotopic data show that the Farsund intrusion was emplaced at the boundary between two different lithotectonic units that are separated by the Farsund-RAP shear zone. This shear zone likely favored the emplacement of the magmas. Most of the assimilation occurred in the lower crust whereas limited differentiation likely took place in the upper crust.

Provenance and rift basin architecture of the Neoproterozoic Hedmark Basin, South Norway inferred from U–Pb ages and Lu–Hf isotopes of conglomerate clasts and detrital zircons

AbstractThe Neoproterozoic Hedmark Basin in the Caledonides of South Norway was formed at the western margin of the continent Baltica by rifting 750–600 Ma ago. The margin was destroyed in the Caledonian Orogeny and sedimentary basins translated eastwards. This study uses provenance analysis to map the crustal architecture of the pre-Caledonian SW Baltican margin. Conglomerate clasts and sandstones were sampled from submarine fan, alluvial fan and terrestrial glacigenic sedimentary rocks. Samples were analysed for U–Pb isotopes and clast samples additionally for Lu–Hf isotopes. The clasts are mainly granitesc. 960 Ma and 1680 Ma old, coeval with the Sveconorwegian Orogeny and formation of the Palaeoproterozoic Transscandinavian Igneous Belt (TIB). Mesoproterozoic (Sveconorwegian) ages are abundant in the western part of the basin, whereas Palaeoproterozoic ages are common in the east. Lu–Hf isotopes support crustally contaminated source for all clasts linking them to Fennoscandia. Detrital zircon ages of the sandstones can be matched with those from the granitic clasts except for ages within the range 1200–1500 Ma. These ages are typically found in the present-day Telemark, SW Norway. The sandstones and conglomerate clasts in the western part of the Hedmark Basin were sourced from the Sveconorwegian domain in the present SW Norway or its continuation to the present-day NW. The conglomerate clasts in the eastern part of the Hedmark Basin were sourced mainly from the TIB domain or its northwesterly continuation. The Hedmark Basin was initiated within the boundary of two domains in the basement: the TIB and the Sveconorwegian domains.

From orogen to passive margin: constraints from fission track and (U–Th)/He analyses on Mesozoic uplift and fault reactivation in SW Norway

Abstract The post-Caledonian tectonic history and landscape evolution of southwestern Norway are poorly understood, primarily owing to the lack of onshore post-Devonian sediments. To bridge this knowledge gap, low-temperature thermochronological techniques were applied to investigate vertical movements in the upper crust. New apatite fission track and apatite and zircon (U–Th)/He analyses on samples from southwestern Norway yielded Permian to Jurassic, Triassic to Cretaceous and Carboniferous to Triassic ages, respectively. Thermal history modelling indicates relatively high cooling rates (2–3 °C Ma −1 ) throughout Permian to early Jurassic times. Since the Jurassic, samples from coastal areas have remained close to the surface and were reheated to 30–50 °C during sedimentary burial in the Cretaceous. Inland samples experienced lesser amounts of Permo-Triassic exhumation, continued to cool slowly (<1 °C Ma −1 ) throughout the Jurassic–Cretaceous and did not reach the surface until the Cenozoic. Both fission track and (U–Th)/He ages are offset across faults, highlighting the importance of fault activity throughout the Mesozoic. In combination with previously published results, the new data suggest that the geomorphological evolution of southwestern Norway is closely connected to rift- and post-rift tectonics related to North Sea and North Atlantic rifting. The topographic relief was most likely repeatedly rejuvenated during periods of tectonic activity.

Transtensional folding

Strain modeling shows that folds can form in transtension, particularly in simple shear-dominated transtension. Folds that develop in transtension do not rotate toward the shear zone boundary, as they do in transpression; instead they rotate toward the divergence vector, a useful feature for determining past relative plate motions. Transtension folds can only accumulate a fixed amount of horizontal shortening and tightness that are prescribed by the angle of oblique divergence, regardless of finite strain. Hinge-parallel stretching of transtensional folds always exceeds hinge-perpendicular shortening, causing constrictional fabrics and hinge-parallel boudinage to develop.These theoretical results are applied to structures that developed during oblique continental rifting in the upper crust (seismic/brittle) and the ductile crust. Examples include (1) oblique opening of the Gulf of California, where folds and normal faults developed simultaneously in syn-divergence basins; (2) incipient continental break-up in the Eastern California-Walker Lane shear zone, where earthquake focal mechanisms reflect bulk constrictional strain; and (3) exhumation of the ultrahigh-pressure terrain in SW Norway in which transtensional folds and large magnitude stretching developed in the footwall of detachment shear zones, consistent with constrictional strain. More generally, folds may be misinterpreted as indicating convergence when they can form readily in oblique divergence.

Sveconorwegian Mid-crustal Ultrahigh-temperature Metamorphism in Rogaland, Norway: U-Pb LA-ICP-MS Geochronology and Pseudosections of Sapphirine Granulites and Associated Paragneisses

MgAl-rich sapphirine granulites (bulk X Mg 0·71–0·75) occur as boudinaged layers in migmatitic garnet–orthopyroxene–cordierite–spinel gneisses and migmatitic garnet–sillimanite metapelites in the vicinity of the c. 930–920 Ma Rogaland anorthosite–mangerite–charnockite complex, SW Norway. Investigation of the mineral reaction history of the sapphirine granulites and the surrounding paragneisses, combined with geothermobarometric calculations and constraints from pseudosections calculated in the Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–TiO 2 (NCKFMASHT) system, indicates a clockwise P–T path that reached peak-metamorphic ultrahigh-temperature (UHT) conditions of c. 1000°C at c. 7·5 kbar by prograde heating. UHT peak metamorphism is followed by near-isothermal (ultra)high-temperature decompression to P 850–940°C as estimated from Ti-in-zircon thermometry, suggesting that UHT metamorphism and the deduced clockwise P–T evolution is linked to regional Sveconorwegian metamorphism at c. 1010 Ma. Most of the metamorphic zircon surrounds largely resorbed inherited oscillatory zoned zircon cores ( 207 Pb/ 206 Pb apparent ages 1220–1841 Ma), testifying to the sedimentary origin of the sapphirine granulites. Epitactic growth of xenotime on metamorphic zircon at 933 ± 5 Ma is suggested to be related to crystallization of anatectic melt during post-decompressional cooling. The clockwise P–T path culminating at mid-crustal UHT conditions at c. 1010 Ma followed by (U)HT decompression is interpreted to result from collisional tectonics during the early stages of the Sveconorwegian Orogeny, followed by gravitational collapse of the mountain plateau.

Sedimentary recycling in arc magmas: geochemical and U–Pb–Hf–O constraints on the Mesoproterozoic Suldal Arc, SW Norway

The Hardangervidda-Rogaland Block within southwest Norway is host to ~1.52 to 1.48 Ga continental building and variable reworking during the ~1.1 to 0.9 Ga Sveconorwegian orogeny. Due to the lack of geochronological and geochemical data, the timing and tectonic setting of early Mesoproterozoic magmatism has long been ambiguous. This paper presents zircon U–Pb–Hf–O isotope data combined with whole-rock geochemistry to address the age and petrogenesis of basement units within the Suldal region, located in the centre of the Hardangervidda-Rogaland Block. The basement comprises variably deformed grey gneisses and granitoids that petrologically and geochemically resemble mature volcanic arc lithologies. U–Pb ages confirm that magmatism occurred from ~1,521 to 1,485 Ma, and conspicuously lack any xenocrystic inheritance of distinctly older crust. Hafnium isotope data range from eHf(initial) +1 to +11, suggesting a rather juvenile magmatic source, but with possible involvement of late Palaeoproterozoic crust. Oxygen isotope data range from mantle-like (δ18O ~5 ‰) to elevated (~10 ‰) suggesting involvement of low-temperature altered material (e.g., supracrustal rocks) in the magma source. The Hf–O isotope array is compatible with mixing between mantle-derived material with young low-temperature altered material (oceanic crust/sediments) and older low-temperature altered material (continent-derived sediments). This, combined with a lack of xenoliths and xenocrysts, exposed older crust, AFC trends and S-type geochemistry, all point to mixing within a deep-crustal magma-generation zone. A proposed model comprises accretion of altered oceanic crust and the overlying sediments to a pre-existing continental margin, underthrusting to the magma-generation zone and remobilisation during arc magmatism. The geodynamic setting for this arc magmatism is comparable with that seen in the Phanerozoic (e.g., the Sierra Nevada and Coast Range batholiths), with compositions in the Suldal Sector reaching those of average upper continental crust. As within these younger examples, factors that drive magmatism towards the composition of the average continental crust include the addition of sedimentary material to magma source regions, and delamination of cumulate material. Underthrusting of sedimentary materials and their subsequent involvement in arc magmatism is perhaps a more widespread mechanism involved in continental growth than is currently recognised. Finally, the Suldal Arc magmatism represents a significant juvenile crustal addition to SW Fennoscandia.

Thermal structure of supra-detachment basins: a case study of the Devonian basins of western Norway

We investigate the peak temperatures of the Devonian Hornelen, Kvamshesten and Solund basins in SW Norway to constrain their thermal history. These basins are the three largest Devonian units exposed in Norway and were formed as supra-detachment basins in the hangingwall of the Nordfjord Sogn Detachment Zone. The peak temperatures of the basins were obtained using a geothermometer based on Raman spectroscopy of carbonaceous material on detrital carbonaceous plant fossils. The data confirm an anchizone to low greenschist-facies metamorphism with temperatures (±30 °C) of 284–301 °C in the Hornelen and Solund basins and a significantly higher temperature, 345 °C in the Kvamshesten basin. The temperature increases toward the detachment fault and cannot be explained by ordinary burial alone. In the Kvamshesten basin this temperature increase is close to 100 °C. The new data demonstrate that exhumation of high-grade rocks in the footwall in the Nordfjord Sogn Detachment Zone played an important role in controlling temperatures in the hangingwall. We conclude that the dynamic evolution along large-scale detachments may introduce heat at the base of the hangingwall and thereby control the thermal state of supra-detachment basins formed during extension.

Poa pratensis or Lolium perenne for establishment and overseeding of Scandinavian football (soccer) pitches

Scandinavian football pitches are sometimes sodded because of slow establishment of Kentucky bluegrass (KB, Poa pratensis) from seed. Sodding is fast but expensive and brings with it thatch and sometimes annual bluegrass (AB, Poa annua). Perennial ryegrass (PR, Lolium perenne) is used for overseeding and often becomes an important component of the turf. Triggered by experiences in SW Norway and predictions for milder winters, our objectives were (1) to compare KB sod and PR seed for establishment of football pitches in three climatic regions; and (2) for both types of turf to document the effect of overseeding PR or KB in spring, summer or fall on turf cover, botanical composition, and wear tolerance. Field trials with sodded KB and seeded PR on main plots and overseeding on subplots were conducted from June 2008 to Nov. 2011 at the Bioforsk units Landvik (58 °N, coast), Apelsvoll (61 °N, inland) and Kvithamar (64 °N, coast). Seeded PR plots could be opened to play one month after sodded KB plots. KB survived well at all sites, but complete winterkill of PR occurred in two out of three years at Kvithamar and one out of three years at Apelsvoll. At Landvik one of two main plots with PR died during the last winter. The fact that winterkill was not caused by snow mold but long-lasting ice covers or low freezing temperatures combined with little or no snow cover, shows that a milder but more unstable winter climate will not allow for pure PR pitches in the future. Pitches still ought to have KB in the base, but PR is recommended for overseeding, preferably in spring, to reduce AB ingress and improve turf quality. Overseeding of PR into KB did not outcompete KB, but overseeding of KB into PR or KB was mostly not successful.

Social behaviour of wintering Great Northern Divers <em>Gavia immer</em> in relation to age categories

Focal-animal studies of Great Northern Divers Gavia immer wintering on the coast of Jaeren, SW Norway, showed social behaviour to vary over the season. Groups consisting of two adults and one or two juveniles arrived in autumn. The adults of such groups were aggressive toward neighbouring divers including other adults. In early winter juveniles as well as adults adopted a solitary and dispersed existence and adults showed aggressiveness also toward juveniles. Second winter birds were solitary throughout the winter, and they were intermediate between adults and juveniles in dominance level. Juveniles associated with two adults spent more time feeding and less time in comfort activities than the accompanying adults. The social groups containing adults and juveniles are interpreted as family groups in which parents perform prolonged parental care presumably allowing juveniles to gain experience with marine food and habitat. Some twosome adults without juvenile company are seen after arrival in autumn, and again in late winter some time before departure, suggesting that pair members might accompany one another on migration. Differences in social behaviour of birds wintering in Europe and in North America are briefly discussed.

Provenance and exhumation of an exotic eclogite-bearing nappe in the Caledonides: a U–Pb and Rb–Sr study of the Jæren nappe, SW Norway

Abstract: The provenance and exhumation history of paragneisses that enclose the 471–458 Ma eclogites in the Caledonian Jæren nappe, SW Norway, were constrained by performing U–Pb analysis on detrital zircon and Rb–Sr dating of mica. Zircon grains from four samples were analysed by laser ablation inductively coupled plasma mass spectrometry, providing detrital U–Pb ages between 3130 and 620 Ma. These data suggest Laurentian provenance, implying the existence of an early Caledonian (Taconian) HP fragment of Laurentian crust in the southern Scandinavian Caledonides. Several rims and recrystallized zircon patches yielded U–Pb ages averaging at 469 ± 6 Ma (2σ). These are identical to the Lu–Hf ages of the eclogites and underscore the importance of Taconian metamorphism in this part of the Caledonides. The main phengite Rb–Sr age cluster at 424.4 ± 4.6 Ma provides time constraints on the amphibolite-facies recrystallization of former high-Si phengite. Five out of seven biotite Rb–Sr ages were identical, yielding a weighted mean age of 413.6 ± 2.6 Ma. Low-Si phengite and biotite in three samples gave c . 400 Ma ages. The Rb–Sr data record the mid-crustal emplacement of the exotic Jæren nappe and its subsequent unroofing along the western edge of Baltica during the backsliding and collapse of the Scandian orogenic front. Supplementary material: The sample locations, U–Pb isotope data and ages for zircon, and the phengite and biotite major element data are available at http://www.geolsoc.org.uk/SUP18448 .

Polybaric Fractional Crystallization of High-alumina Basalt Parental Magmas in the Egersund–Ogna Massif-type Anorthosite (Rogaland, SW Norway) Constrained by Plagioclase and High-alumina Orthopyroxene Megacrysts

Bulk analyses of plagioclase and high-alumina orthopyroxene megacrysts (decimetreto metre-sized crystals with plagioclase lamellae) from the late Proterozoic Egersund^Ogna massif-type anorthosite (Rogaland anorthosite province, SWNorway) are used to constrain the parental magma compositions and differentiation processes within this 30 km diameter diapir. Spatial compositional variations show that two types of anorthosite occur: high-Sr (720^1090 ppm) andesine anorthosite (An48 4) in the centre of the intrusion and low-Sr (320^620 ppm) labradorite anorthosite (An59 6) in the margin. Two populations of orthopyroxene megacrysts are clearly discriminated by their Mn and Cr contents, but display similar ranges of Mg-number (55^79). Interpretation of trace element data and comparison with inversion models suggest that the two types of anorthosite result from crystallization of different parental magma compositions with high-alumina basalt affinities and similar Mg-numbers, but different wollastonite, Sr, Mn and Cr contents. A Rayleigh fractional crystallization model of the trace element concentrations vs MgO content in orthopyroxene constrains the cotectic orthopyroxene:plagioclase proportions to 0·33:0·67 in both magma types before the appearance of Fe^Ti oxide minerals on the liquidus at F 0·7 (where F is melt fraction). Polybaric crystallization is recorded by variable alumina contents in the orthopyroxene megacrysts (2·3^8·5 wt %), corresponding to crystallization pressures in the 3^13 kbar range as shown by experimental data. This implies that the high-alumina orthopyroxene megacrysts mainly crystallized en route during diapiric rise of the anorthositic mush. Modelling the plagioclase compositions with experimentally determined partition coefficients for Ca, K, Sr and Ba confirms that pressure variation during polybaric crystallization is the main controlling factor on compositional variations in the anorthosite pluton.

A simulation model of carrying capacity for mussel culture in a Norwegian fjord: Role of induced upwelling

Shellfish carrying capacity is determined by the interaction of cultured species with the ecosystem, principally constrained by environmental characteristics, especially food availability. A recent experiment carried out in Lysefjord (SW Norway) has shown that induced upwelling of nutrient-rich deeper water stimulated phytoplankton growth, potentially increasing the carrying capacity for mussel cultivation. With the aim of assisting in development of sustainable mussel culture in Lysefjord, an object-oriented model of aquaculture–environment interactions and mussel carrying capacity was constructed. A multiple box ecosystem model was developed within the visual simulation environment of Simile software allowing explicit coupling between boxes, which represent regions of the fjord. Once the box model was developed and calibrated, subsequent application of PEST (Parameter ESTimation) allowed optimization of different parameters of the model in order to manage mussel production according to carrying capacity criteria. The Simile model and the simultaneous application of PEST allowed several scenarios taking into account different stocking densities, upwelling alternatives, and the creation of new cultivation areas.

Magma flow and feeder chamber location inferred from magnetic fabrics in jotunitic dykes (Rogaland anorthosite province, SW Norway)

The ca. 930–920 Ma Rogaland anorthosite province of Southwest Norway is cross cutted by up to several-km-long dykes of the jotunite kindred. The fabric of three major jotunitic dykes from this igneous complex (the Vetteland, Varberg and Lomland dykes) is investigated here, using measurements of the anisotropy of magnetic susceptibility (AMS) made along transversal sampling sections. The petrofabric in the three studied dykes has an overall magmatic character and it is shown, through image analysis, that the AMS, which is controlled by the shape-preferred orientation of low-Ti titanomagnetite grains, can be used as a proxy for its orientation. The average magnetic fabrics, taken as flow markers, give valuable information on the geometry of the dykes and enable to locate the feeder magma chambers. It appears that each dyke is connected to its own chamber, in agreement with the conclusions of published geochemical studies. A model of emplacement along a set, probably two conjugate sets, of active shear zones is proposed. This model takes into account, in particular, the local occurrence of asymmetrical distributions of magnetic fabrics.