Formation of sulfide deposits and its relation to sodic and potassic alteration of Proterozoic metabasites in the Sax� rift basin, Bergslagen, Sweden

Hellingwerf, Rob H.

doi:10.1007/bf00204245

Cited by 10 publications

(4 citation statements)

References 30 publications

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“…The early gabbros and diorites from Askaoun have compositions similar to those of oceanic and intraplate basalts. Such rocks, commonly encountered in continental rift settings (Harper & Link 1986;Hellingwerf 1987), have been reported from a number of sites in the Anti-Atlas belt. In the Bou-Azzer inlier (Central Anti-Atlas), affinities with MORB and within-plate basalts have been found (Leblanc & Moussine-Pouchkine 1994) for basaltic rocks from the volcanoclastic BleidaTachdamt, which is an equivalent of the Siroua series.…”

Section: Discussionmentioning

confidence: 98%

Petrology and geochemistry of the Neoproterozoic Siroua granitoids (central Anti-Atlas, Morocco): evolution from subduction-related to within-plate magmatism

Touil¹,

Hafid²,

Moutte

et al. 2008

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The Siroua massif includes many plutons of Neoproterozoic age. The mineralogical and geochemical character of the plutons allows us to describe an evolution of the magmatism, in space and time, from a subduction-related type in the northern part, to a within-plate subalkaline type in the southern part. The first magmatic activity coeval with the closing of the Khzama oceanic basin in the north is little evolved and of oceanic type (dominantly gabbros and basalts). It is followed by a low potassic calc-alkaline magmatism (gabbro-diorites, tonalites and trondhjemites of Nebdas pluton) and by a voluminous highly potassic calcalkaline magmatism (Askaoun and Ifouachguel plutons) that marks the collisional period. The end of crustal uplift and the beginning of the extension is marked in the south by a sub-alkaline magmatism corresponding to the Ida ou Illoun, Imdghar and Affela N'ouassif granites. Magmatic activity, in the Siroua massif, is marked at the end of the Neoproterozoic (PIII) by a continental tholeiite with an alkaline affinity, which occurs as dykes crosscutting the Neoproterozoic granites, and later by dominantly alkaline granites.

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Section: Discussionmentioning

confidence: 98%

Petrology and geochemistry of the Neoproterozoic Siroua granitoids (central Anti-Atlas, Morocco): evolution from subduction-related to within-plate magmatism

Touil¹,

Hafid²,

Moutte

et al. 2008

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“…Heat from the GDG suite intrusions and cooling volcanic rocks initiated sub-seafloor hydrothermal circulation, giving rise to the innumerable polymetallic sulphide and iron-oxide deposits with associated synvolcanic hydrothermal Na-and K-alteration and Mgmetasomatism of the volcano-sedimentary rocks (Hellingwerf 1987;Oen 1987). The supracrustal series was subsequently metamorphosed, deformed and intruded by the alkali-calcic granitoid-syenitoid-dioritoid-gabbroid suite during several stages of the c. 1.87 -1.8 Ga Svecokarelian orogeny (Stephens et al 2009).…”

Section: Regional Geologymentioning

confidence: 99%

An epigenetic magnesite deposit in the Bergslagen area, central Sweden

Högmalm

Hellingwerf

Cornell

et al. 2012

GFF

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A Palaeoproterozoic magnesite deposit in the Bergslagen ore province in Sweden is characterized in terms of petrography and major element, trace element and stable isotope compositions. The magnesite horizons are situated at the contact between a metamorphosed gabbro intrusion and felsic metavolcanic rocks, in association with iron-oxide mineralizations and intense Mg-metasomatism. The alteration of the surrounding rocks is used to explain the formation of the magnesite, and chemical dating of hydrothermal monazite constrains the timing of Mg-alteration to a pre-metamorphic age of 1911^16 Ma (2s). High Y contents in hydrothermal monazite in both metavolcanic and magnesite samples indicate a temperature of . 4008C for the hydrothermal alteration. C and O isotopic composition of the magnesite points to interaction with seawater at 200-2508C. We conclude that the magnesite was formed by replacement of a carbonate precursor through hydrothermal alteration, induced by the emplacement of the gabbro intrusion.

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“…Although our emphasis herein is on the Grythyttan Slate Belt, we concur with Sundius' (1923) interpretation that the Grythyttan and the Saxån Slate Belts originally formed a single lithostratigraphic unit. Hellingwerf (1984Hellingwerf ( , 1986Hellingwerf ( , 1987 and Hellingwerf & Oen (1986) have shown that the SSB was affected by a synsedimentary hydrothermal system, fed by seawater, by analogy with widespread Na/K exchange reactions and Mg-metasomatism superimposed onto many of the volcanic rocks in western Bergslagen. The obvious consequence that most or all of the Grythyttan Slate Formation was deposited in a marine environment will be discussed later on.…”

Section: Grythyttan Slate Formationmentioning

confidence: 99%

The Palaeoproterozoic Grythyttan Field in the Svecofennian Orogen, West Bergslagen, Central Sweden: structure, stratigraphy and age

Beunk

Kuipers²,

et al. 2018

NJG

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A number of discrete slate belts of limited size occur in the Palaeoproterozoic volcano-sedimentary Bergslagen Group of western Bergslagen in the Fennoscandian Shield of south-central Sweden. The Grythyttan Slate Belt (GSB), studied for more than a century, forms a single basin with the nearby Saxån Slate Belt (SSB). We use the lithostratigraphy of the Grythyttan Slate Formation of the Grythyttan belt, based on basin-scale sedimentary facies associations of the volcaniclastic sediments in time and space, as a method to interpret overall tectonic structure. Contrary to traditional views, we reconstruct the GSB as a single overturned limb of a km-scale anticline with horizontal axis in the hanging wall of an east-vergent thrust fault, reactivating a listric extensional fault. The fold connects the GSB to the neighboring SSB. Folding and thrusting were related to tectonic closure of a volcanic back-arc or intra-arc basin. The early folds were subsequently affected by strike-slip shearing and folding around vertical fold axes, which partitioned preferentially into the least competent lithologies (slates and marbles), significantly modifying the map appearance of the slate belt. The late shearing and folding resulted from accretion of Bergslagen onto the Fennoscandian continental margin during the late, Svecobaltic phase of the Svecofennian orogeny. The GSB forms a thin, intraformational wedge in the Bergslagen Group and represents a relatively short interlude with a conglomeratic alluvial fan and turbiditic volcaniclastics followed by more felsic volcanic rocks resembling those of the Bergslagen Group. We suggest that the GSB, and by inference the other slate belts, stem from calderas, as either terrestrial volcanic lakes or shallow submarine eruption centres. The conglomerates are pre-orogenic, not a post-orogenic molasse as traditionally conceived, and their clast fabric has resulted from sedimentary processes only. Newly determined SIMS U-Pb zircon ages constrain the age of the GSB at c. 1895 Ma.

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Formation of sulfide deposits and its relation to sodic and potassic alteration of Proterozoic metabasites in the Sax� rift basin, Bergslagen, Sweden

Cited by 10 publications

References 30 publications

Petrology and geochemistry of the Neoproterozoic Siroua granitoids (central Anti-Atlas, Morocco): evolution from subduction-related to within-plate magmatism

Petrology and geochemistry of the Neoproterozoic Siroua granitoids (central Anti-Atlas, Morocco): evolution from subduction-related to within-plate magmatism

An epigenetic magnesite deposit in the Bergslagen area, central Sweden

The Palaeoproterozoic Grythyttan Field in the Svecofennian Orogen, West Bergslagen, Central Sweden: structure, stratigraphy and age

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