The chemistry and origins of Proterozoic low-potash, high-iron, charnockitic gneisses from Tromøy, south Norway

doi:10.1016/0012-821X(77)90033-4

Earth and Planetary Science Letters

Volume 35, Issue 1, May 1977, Pages 105-115

https://doi.org/10.1016/0012-821X(77)90033-4 Get rights and content

Abstract

New major and trace element data for 79 acid-intermediate charnockitic gneisses (the Tromøy gneisses) and 16 associated metabasites from the island of Tromøy show that this part of the 1200–900-m.y. Sveconorwegian zone is occupied by rocks of unusual composition. Overall values for K and Rb are the lowest yet reported for any granulites, and K/Rb ratios are very high. Cs and Th are also low and, abnormally for granulites, so are Ba, Sr and Zr. Ba/Sr ratios are similar to those in other suites, but K/Ba and K/Sr are higher. These features may partially be reflecting unusual pre-metamorphic lithologies, but it is considered more likely that they are largely the product of metamorphically induced depletion processes involving metasomatism. There is some indication that the Na₂O/CaO and normative Ab/An ratios may also have been modified during metamorphism.

Data for the presumed relatively immobile elements Cr, Co, Ni and V support an igneous origin for the Tromøy gneisses, but the presence of a paragneiss component cannot be ruled out. A characteristic of the gneisses is their high iron content, and spatial and temporal considerations point towards a genetic link with the iron-rich, intrusive rapakivi suites of Finland, Sweden and south Greenland. If the Tromøy gneisses do represent material of this type, it would seem to follow that potash fractionation has been extreme.

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The Sveconorwegian orogeny
2021, Gondwana Research
Citation Excerpt :
Zircon and monazite U–Pb data constrain the peak of amphibolite- and granulite-facies metamorphism between 1147 ±12 and 1122 ± 8 Ma in both the Bamble and Kongsberg lithotectonic units (Bingen et al. 2008b; Bingen and Viola 2018; Cosca et al. 1998; Engvik et al. 2016; Knudsen et al. 1997). In coastal Bamble, the granulite-facies Tromøy complex (Fig. 6) consists of low-K calc-alkaline enderbitic gneisses depleted in large ion-lithophile elements (LILE) (Cooper and Field 1977; Field et al. 1980; Knudsen and Andersen 1999). Zircon U–Pb data demonstrate that the protoliths formed between 1575 ± 44 and 1544 ± 14 Ma while the granulite facies overprint took place between 1147 ± 12 and 1132 ± 6 Ma (Bingen and Viola 2018).
This article reviews the geology of the Sveconorwegian orogen in south Scandinavia and existing tectonic models for the Mesoproterozoic to Neoproterozoic Sveconorwegian orogeny. It proposes an updated geodynamic scenario of large, hot, long-duration continental collision starting at c. 1065 Ma between proto-Baltica and another plate, presumably Amazonia, in a Rodinia-forming context. An orogenic plateau formed at 1280 Ma as a back-arc Cordillera-style plateau, and then grew further stepwise after 1065 Ma, as a collisional Tibetan-style plateau. Voluminous mantle- and crustal-derived Sveconorwegian magmatism took place in the hinterland in the west of the orogen, mainly: (i) bimodal magmatism at 1280–1145 Ma, overlapping with extensional intramontane basin sedimentation, (ii) the calc-alkaline Sirdal magmatic belt at 1065–1020 Ma, (iii) the hydrous ferroan hornblende-biotite granite (HBG) suite at 985–925 Ma and (iv) the anhydrous ferroan massif-type anorthosite-mangerite-charnockite (AMC) suite at 935–915 Ma. High-alumina orthopyroxene megacrysts in anorthosite imply mafic underplating at 1040 Ma and remelting of the underplates at 930 Ma. Overlapping with magmatism, protracted low-pressure, granulite-facies metamorphism reached twice ultra-high temperature conditions of 0.6 GPa-920 °C at 1030–1005 Ma and 0.4 GPa-920 °C at 930 Ma, respectively. These features imply shallow asthenosphere under the crust. Towards the foreland in the east, metamorphism shows an increasing high-pressure signature eastwards with time, with peak P-T values of 1.15 GPa-850 °C at 1150–1120 Ma in the Bamble-Kongsberg lithotectonic units, 1.5 GPa-740 °C at c. 1050 Ma in the Idefjorden lithotectonic unit, and 1.8 GPa-870 °C at c. 990 Ma in the Eastern Segment under eclogite-facies conditions. These are attributed to retreating delamination of the dense sub-continental lithospheric mantle and growth of the orogenic plateau towards the foreland. After c. 930 Ma, convergence came to a halt, the orogenic plateau collapsed, and 16 km of overburden was removed by extension and erosion.
The early-Sveconorwegian orogeny in southern Norway: Tectonic model involving delamination of the sub-continental lithospheric mantle
2018, Precambrian Research
Citation Excerpt :
It is tailing other estimates of the age of metamorphism inside the Kongsberg Unit. In this study, we specifically address the controversial geochronology of the enderbitic Tromøy Complex, located in the core of the granulite-facies domain on the Island of Tromøy in coastal Bamble (Andersen et al., 2004a; Cooper and Field, 1977; Field et al., 1980; Knudsen and Andersen, 1999). The Tromøy Complex (Fig. 3; Fig. 7) consists of noritic, enderbitic and trondhjemitic gneisses characterized by low-K calc-alkaline signature and depletion in large ion-lithophile elements (LILE) and other incompatible elements (Cooper and Field, 1977; Field et al., 1980; Knudsen and Andersen, 1999).
The Sveconorwegian orogeny is a more than 250 Myr-long multiphase orogenic event that contributed to the amalgamation of Fennoscandia into Rodinia at the end of the Mesoproterozoic. We propose a new lithospheric-scale tectonic model for the pre- to early Sveconorwegian orogenic evolution between 1280 and 1080 Ma. This evolution is recorded in southern Norway by two c. 25 km wide belts of up to granulite-facies rocks, the Bamble and Kongsberg Lithotectonic Units, and a c. 80 km belt in the Telemarkia Lithotectonic Unit, which contains lower-grade rocks and evidence of widespread plutonism. New zircon U–Pb geochronological data from 54 samples confirm magmatic activity between 1575 and 1485 Ma, and 1210 and 1140 Ma. The new data constrain peak amphibolite to granulite-facies metamorphism in Bamble and Kongsberg to between 1145 and 1130 Ma. New geological mapping shows that the Kongsberg Lithotectonic Unit is characterized by a regional, N–S trending highly transposed lithological banding reflecting E–W orthogonal shortening as expressed by tight to isoclinal folds, and a penetrative subvertical foliation bearing a steep peak-metamorphic lineation. Telemarkia is instead characterized by crustal extension-related bimodal magmatism and intermontane basin sedimentation between 1280 and 1080 Ma. Paired and in part coeval extension and compression are interpreted as reflecting asthenospheric upwelling, orogenic plateau development and delamination of the sub-continental lithospheric mantle beneath Telemarkia, followed by foundering (dripping-off) of the lithospheric mantle slab under the Kongsberg and Bamble Lithotectonic Units. This model stresses the pull effect of a foundering mantle slab in an actively shortening orogen to facilitate highly localised compression and granulite-facies metamorphism in the crust. It accounts for the well-known, first-order geological characteristics of the orogen and does not require the accretion of exotic terranes to explain the early-Sveconorwegian orogenic evolution.
Variations of sulfur isotopes in metamorphic rocks from Bamble Sector, Southern Norway: A laser probe study
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Citation Excerpt :
A sedimentary origin was also considered as an alternative by Andreae (1974). More recent studies, however, support an igneous origin based on mineral assemblages and whole rock geochemistry (Cooper and Field, 1977; Field et al., 1980; Smalley and Field, 1985; Knudsen and Andersen, 1999). Depletion of LILE and LREE have alternatively been attributed to magmatic differentiation and crystallization at deep crustal levels (Field et al., 1980, 1985), metamorphic processes (Cooper and Field, 1977; Cameron, 1989; Touret, 1996), or primary features inherited from the source region (Knudsen and Andersen, 1999).
Variations of sulfur isotopes in metamorphic rocks from Bamble Sector, southern Norway, are investigated using a Q-switched, pulsed mode, laser combustion technique. The results indicate that laser-related fractionations are reproducible (1σ=0.2‰), provided uniform conditions are maintained during analysis.
Bamble is a Precambrian high-grade metamorphic terrain. A transition from amphibolite- to granulite-facies occurs across the 25-km width of the Sector. Supracrustal rocks of mid-Proterozoic ages were intruded by felsic and mafic magmas and metamorphosed during the Sveconorwegian orogenic episode. Earlier studies indicated that Bamble rocks equilibrated under a relatively high f_O₂, 2–3 log units above QFM buffer, during peak metamorphism [J. Geochemical Exploration 31 (1989) 149; J. Geology 100 (1992) 447; Contrib. Mineral Petrol. 1139 (2000) 180], which led to phase changes in sulfides. Pyrrhotite, or Po_mss, has variably been replaced by pyrite±magnetite. Mantling of pyrite by magnetite is common.
Metasupracrustal rocks display a large variation in δ³⁴S_CDT (−1‰ to +12‰), consistent with data from sedimentary rocks of similar age. No distinction can be made between amphibolite, transition, and granulite zones. The isotopic signature of sulfides was determined by bacteriogenic reduction of seawater sulfate with an initial δ³⁴S value of 20–30‰.
Tonalitic–trondhjemitic gneisses from granulite zone show a large scatter in δ³⁴S_CDT (0‰ to +8‰), implying that the parent magmas were contaminated by sedimentary materials. This is supported by S/Se ratios. Mafic rocks from various metamorphic zones display a clustering of δ³⁴S_CDT values around 0‰, and S/Se ratios in the range 3×10³ to 6×10³. This is consistent with a mantle source for S. Ni–Cu sulfide ores locally associated with the mafic rocks, however, are enriched in ³⁴S, indicating the involvement of sedimentary S in the formation of the ores.
Mass and isotopic balance calculations indicate that oxidation of pyrrhotite, or Po_mss, proceeded without significant addition or removal of S. Sulfur liberated during mantling of Fe–sulfides by magnetite was in a reduced form and reprecipitated in short distances as secondary overgrowth and fracture filling pyrite. The large variation of δ³⁴S values for the supracrustal rocks, and the preservation of the original isotopic features for various rock units suggest that no isotopic homogenization occurred in spite of the high-grade metamorphism.
Petrologic evidence for K-feldspar metasomatism in granulite facies rocks
1998, Chemical Geology
We present evidence for K-feldspar metasomatism in charnockitic granulites from two well-known terranes: the Shevaroy Hills Massif, S. India (750°C, 8 kbars) and the Bamble Sector, S.E. Norway (790°C, 7.5 kbars) in the form of K-feldspar veins principally along plagioclase and quartz grain boundaries and in the form of highly variable antiperthitic patches of K-feldspar in an uneven scattering of plagioclase grains. With one exception, orthopyroxene or amphibole grains in contact with these K-feldspar veins show no alteration to secondary biotite, indicating that the H₂O activity of the fluids responsible for these veins must have been relatively low. A high Ba concentration in these veins also suggests a metasomatic origin. Point counted, back-scattered electron photomicrographs, along with microprobe analyses, provide reintegrated K-feldspar and plagioclase compositions for 8 to 12 predetermined random areas per thin section for three samples from Bamble and three samples from the Shevaroy Hills. These reintegrated feldspar compositions plot over a range of temperatures on the feldspar ternary for each sample, and indicate saturation temperatures above the mean temperature for either region with a few reintegrated compositions above the 1000°C isotherm and with the lower cut-off temperatures at 700°C and 600°C for the Shevaroy and Bamble samples, respectively. These patterns suggest that exsolution alone could not have been responsible for the formation of the K-feldspar veins and patches in these rocks. We suggest that these veins are due to the influx of complex, supercritical, low H₂O activity brines shortly after peak metamorphic conditions, that this influx continued during the initial phases of post-peak metamorphic uplift and that these fluids represent the first stage in a series of fluid influxes in which the H₂O activity increased as uplift continued. Reaction of these brines with potassium-undersaturated plagioclase grains formed K-feldspar veins along grain boundaries and fractures, as well as diffusing into the plagioclase, which became supersaturated, and exsolved K-feldspar as antiperthite patches during uplift and cooling. Formation of secondary biotite halos around orthopyroxene in one sample associated with these K-feldspar veins can be explained by heightened H₂O activity in the brines due to enrichment in H₂O, emplacement of the veins at lower pressure during uplift or both compared to the other Shevaroy and Bamble samples.
Trace-element characteristics and Pb isotopic evolution of metasediments and associated Proterozoic rocks from the amphibolite- To granulite-facies Bamble sector, southern Norway
1997, Chemical Geology
A study of trace-element distribution and Rb/Sr, Sm/Nd, and Pb isotopic compositions has been performed on amphibolite- and granulite-facies metasediments, mafic granulites, dioritic gneiss, intrusive enderbitic veins and calc-alkaline tonalitic gneisses from the Proterozoic Bamble sector, southern Norway. The LILE content of the granulite-facies metapelites is similar to the average of the upper crust and post-Archaean average shales. The K/Rb ratios of the amphibolite- and granulite-facies semipelites and impure quartzites are similar, and the K/Rb ratios of the metapelites show overall similarities to the ratios of undepleted metapelites (< 300). There is evidence of incomplete Sveconorwegian correlations in the RbSr isotopic system, and a poor correlation in the SmNd system. The calculated t_DM model ages for the metasediments can represent crustal residence times of 1.67 to 2.05 Ga. The present-day lead isotopic data can be reproduced by a three-stage model of Pb evolution in which (t₀ = 4.57 Ga, t₁ = 1.9 or 1.5 Ga, t2 = 1.1 Ga, μ₁ (²³⁸U/²⁰⁴Pb) = 7.9, κ₁ (²³²Th/²³⁸U) = 2.5, κ₂ ≤ 4.15), where t₁ and t₂ are related to separation from the mantle and the Sveconorwegian orogeny, respectively. The protolith of the metasediments, the dioritic gneiss and the mafic granulites evolved in high-U/Pb environments prior to Sveconorwegian times (μ₂ = 16−32, 19,and18−45, respectively). Most of these rock units experienced conditions ofμ₂ > μ₃ andκ₂ < κ₃, suggesting a large-scale fractionation in the UThPb system connected to U-mobility during the medium- to high-grade metamorphism. There are no unambiguous differences in the Pb isotopic composition between the amphibolite- and granulite-facies rocks, but the mafic granulites from the classical ‘depleted granulite’ area of Tromøy island evolved in overall lowerμ₂ (²³⁸U/²⁰⁴Pb) environments than similar rocks from the neighbouring Hisøy island. This suggests that the similar U content of these rocks largely can be due to local pre-Sveconorwegian ²³⁸U/²⁰⁴Pb variations. Sveconorwegian intrusive enderbitic dykes and veins crystallized with low LILE and Nb concentrations at granulite-facies PTaCO₂ conditions. Pre-Sveconorwegian granulite-facies tonalitic gneisses show a less depleted trace-element pattern and low Nb concentrations and the hornblende-free tonalitic gneisses have significantly lower U content than their hornblende-bearing counterparts. The investigated metasediments have very low contents of the less mobile elements Nb, Sr, Cu and P₂O₅, which probably represent characteristics of the pre-sedimentary protolith.
Precambrian multi-stage crustal evolution in the Bamble sector of south Norway: Pb isotopic evidence from a Sveconorwegian deep-seated granitic intrusion
1994, Chemical Geology
The Precambrian Ubergsmoen augen gneiss in the Bamble sector of south Norway is a dry, syntectonic charnockitic intrusion, which was emplaced at amphibolite- to granulite-facies conditions in the Sveconorwegian orogeny (∼ 1120 Ma). The present-day $^{206} Pb^{204} Pb$ and $^{207} Pb^{204} Pb$ ratios show restricted variation ( $^{206} Pb^{204} Pb = 17.566−17.938$ , $^{207} Pb^{204} Pb = 15.459−15.590$ in whole rocks; and $^{206} Pb^{204} Pb = 17.159−17.350$ , $^{207} Pb^{204} Pb = 15.451−15.487$ in feldspar), whereas the $^{208} Pb^{204} Pb$ ratio has a wider range of variation in whole rocks (36.571–42.200), but not in feldspars (36.487–37.054). These values reflect a $^{238} U^{204} Pb$ (μ) of 2–6 since the Sveconorwegian, and a variable Th/U ratio (2–20). At the time of final U-Pb differentiation, homogenization of the Pb isotopes was imperfect. The data therefore do not allow Pb-Pb isochron dating, but are well suited for model calculations. The isotopic evolution of Pb can be reproduced by a three-stage model, involving: (1) a mantle stage ending at 1.9-1.6 Ga; (2) extraction of a crustal precursor at 1.9-1.6 Ga, and differentiation of a LILE-enriched component (μ = 14−22); and (3) anatexis, igneous differentiation, emplacement and subsequent metamorphism at ≈ 1.12 Ga. The granitic intrusion acquired its low U/Pb ratio by magmatic differentiation processes, rather than by fluid-induced U loss at high-grade metamorphic conditions.

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¹: Present address: Institute of Geological Sciences, 154 Clerkenwell Rd., London, EC1R 5DU, U.K.

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The chemistry and origins of Proterozoic low-potash, high-iron, charnockitic gneisses from Tromøy, south Norway

Abstract

Lithos

Chem. Geol.

Chem. Geol.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Lithos

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Phys. Chem. Earth

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Neues Jahrb. Mineral., Monatsh.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Tectonophysics

Precambrian Res.

Geological and petrographical investigations in the Arendal district

Nor. Geol. Tidsskr.

K/Rb ratios and metasomatism in metabasites from a Precambrian amphibolite-granulite transition zone

J. Geol. Soc. Lond.

The geology of the area around Eydehavn, south Norway

A radiometric study of polymetamorphism in the Bamble region, Norway

Contrib. Mineral. Petrol.

Skarn iron ore deposits in the Arendal district

Structures ge´ochimiques et zone´ographie metamorphique dans la Pre´cambrien catazonal du Sud de la Norve`ge (Region d'Arendal)

Sci. Terre

The metamorphic evolution of Tromøy (Arendal area - South Norway)

Tschermaks Mineral. Petrogr. Mitt.

Polyphase metamorphism in the granulite facies terrain of the Riso¨r area, south Norway

Nor. Geol. Tidsskr.

The Pre-Cambrian metamorphic rocks around the Lake Vega˚r (Aust Agder, Southern Norway)

Nor. Geol. Unders.

The Sveconorwegian regeneration and earlier orogenic events in the Bamble series, south Norway

Nor. Geol. Unders.

Rapid analysis of silicate rocks

U.S. Geol. Surv., Bull.