The Volcano-Tectonic Setting and Mineralization of the Early Proterozoic Kemiö-Orijärvi-Lohja Belt, SW Finland

Colley, H.; Westra, L.

doi:10.1144/gsl.sp.1987.033.01.08

Cited by 16 publications

(11 citation statements)

References 12 publications

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“…The Orijärvi Formation is lowermost, with felsic and mafic metavolcanic rocks and interlayers of marble, metapelite and iron formation; stratigraphic interpretation by Latvalahti (1979) differs from that of Colley & Westra (1987 In the stratigraphic column (Fig. 11) rocks of 1890-1880 Ma age are missing which is somewhat strange considering that this was a period of voluminous crust formation during the Svecofennian orogeny.…”

Section: Stratigraphy and Age Correlationmentioning

confidence: 97%

The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy

Nironen¹,

Mänttäri²,

Väisänen³

2016

Bull Geol Soc Finland

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Because of the relatively low metamorphic grade, low strain and well-preserved early structures in volcanic and volcaniclastic rocks, the Orijärvi triangle (in the center of the larger Orijärvi area) is one of the few locations in the Svecofennian orogen of southern Finland where lithostratigraphy has been determined. The geochemistry of the picriticbasaltic metavolcanic rocks of the Salittu Formation, located in the northeastern part of the Orijärvi area, has been characterized but otherwise the bedrock and structures have been barely touched. After remapping we give an interpretation of structural evolution, provide new age data to constrain duration of volcanism at Salittu, and refine the stratigraphy in the Orijärvi area.The original stratigraphy is visible at Salittu: metabasalt overlies migmatitic gneisses, and metapicrite is on top. The rocks were folded during early Svecofennian D 1 -D 2 deformations, and the large synformal structures developed as D 2 -D 5 interference structures formed during late Svecofennian D 5 deformation. The structural pattern at Salittu is much the same as in the Orijärvi triangle.The new age data, combined with earlier published data, constrains the Salittu volcanism at ca. 1875 Ma. The stratigraphy in the Orijärvi area consists of the early (1.90-1.89 Ga) volcanic Orijärvi Formation, overlain by the sedimentary Vetio Formation, the volcanic Kisko Formation, the volcanic-sedimentary Ahdisto Formation, the volcanic Toija Formation, and on top the Salittu Formation, all emplaced at 1.88-1.87 Ga. We propose a model in which the Orijärvi Formation represents magmatism at the margin of a microcontinent, and the overlying package represents sedimentation and magmatism above a subduction zone during an initial stage of microcontinental accretion. D 1 deformation occurred in an advanced stage of accretion, after emplacement of the volcanic rocks of the Salittu Formation.

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Section: Stratigraphy and Age Correlationmentioning

confidence: 97%

The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy

Nironen¹,

Mänttäri²,

Väisänen³

2016

Bull Geol Soc Finland

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“…Hietanen, 1975;Latvalahti, 1979;Mäkelä, 1989;Gáal, 1990;Ploegsma & Westra, 1990) or a back-arc basin (e.g. Colley & Westra, 1987;Nironen, 1997). described the Orijärvi area as resembling a modern volcanic arc with back-arc basin, and identified the progressive development of geochemical characteristics in the volcanic rocks, starting with bimodal magmatism and evolving to intermediate compositions after 10-15 Ma.…”

Section: Geological Settingmentioning

confidence: 99%

“…Ages for intrusive rocks from the Uusimaa Belt include a quartz diorite at 1891±13 Ma (Huhma, 1986) and granodiorites at Orijärvi at 1898±4 Ma and at 1891±13 Ma (Huhma, 1986), and have been considered synvolcanic (e.g. Colley & Westra, 1987;. A discordantly cutting gabbroidic pegmatite in the southern part of the SSAC is dated at 1885±7 Ma, setting a minimum age for the volcano-sedimentary rocks and a maximum age for the first deformation phase with associated penetrative metamorphic fabric (Hopgood et al, 1983).…”

Section: Introductionmentioning

confidence: 99%

Supracrustal rocks in the Kuovila area, Southern Finland: Structural evolution, geochemical characteristics and the age of volcanism

Skyttä¹,

Käpyaho²,

Mänttäri³

2005

Bull Geol Soc Finland

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The supracrustal rocks of the Kuovila area in the Palaeoproterozoic Svecofennian Uusimaa Belt, southern Finland, consist mainly of volcaniclastic rocks associated with banded iron formations (BIFs) and marbles. Small ZnS and PbS mineralizations are occasionally located within the marbles. Some primary features are well preserved in the sedimentary and volcanic rocks, including lamination in tuffites and banded iron formations.Geochemical results show that the volcanism was bimodal and it mainly had volcanic arc affinity. Specific geochemical indicators suggesting a volcanic arc origin for the Kuovila volcanic rocks include: 1) Enrichment of LILE over the HFSE elements and 2) Distinctly low Nb and Ta contents in relation to Th, Ce and LREE. Geochemistry of the Kuovila area volcanic rocks is very similar to those of the Orijärvi and Kisko formations, located ~15 km NE of Kuovila. Felsic tuff in the Kuovila area was dated at 1891±4 Ma by the U-Pb system on zircons. Consequently volcanism was contemporaneous with magmatism in the adjacent Orijärvi area, thus representing the earliest identified volcanic stage in the southern Svecofennian Uusimaa Belt.Early deformation structures within the Kuovila area are suggested to relate to lowmetamorphic or localized low-angle thrusting during D 1 . F 1 folds were recumbent and the S 1 cleavages are generally weak. Thrusting was followed by approximately N-S contraction with upright, peak-metamorphic F 2 folding overprinting D 1 structures and defining the Kuovila synform. Two separate intrusive phases include a synvolcanic granodiorite-dioritegabbro association and a weakly S 2 -foliated syn-D 2 granodiorite. Anatectic granites and associated migmatizing veins are absent, therefore suggesting that D 2 pre-dates the ~1.84-1.82 Ga metamorphic event in the Southern Svecofennian Arc Complex (SSAC). D 2 structures in the Kuovila area are suggested to correlate with the early structures with associated axial planar cleavages in the Orijärvi area. D 2 strain is localized into axial planar high strain zones and the curvilinear patterns of the B 2 fold axes probably result from vertical stretching during D 2 .

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“…The zone is composed of several elongated lenses of cordierite-anthophyllite rocks; these lenses are tens to hundreds of metres in length and less than 300 m in width. The ores and their host rocks are intensively deformed and metamorphosed (Colley & Westra 1987). The Orijfirvi deposit is located within a zone that is composed of andalusitecordierite-muscovite gneisses, cordierite-muscovite-biotite gneisses with garnet porphyroblasts and cordierite-anthophyllite gneisses.…”

Section: Regional Backgroundmentioning

confidence: 99%

“…Common ore minerals are pyrite, chalcopyrite, sphalerite and galena(M~ikel/i 1989;Colley & Westra 1987;Papunen 1986). The Cu-Zn ore lies 50 m south of the main zone and is hosted in cordierite-anthophyllite rocks.…”

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confidence: 99%

Fluorine in orthoamphibole dominated Zn-Cu-Pb deposits: examples from Finland and Australia

Rajavuori

Kriegsman

2002

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Volcanogenic massive sulphide (VMS) deposits commonly occur within much larger fluorine (F)-bearing hydrothermal systems, where cordierite-orthoamphibole rocks are characteristic pathfinder assemblages. Here we report whole-rock and mineral F contents for orthoamphibole bearing rocks and associated rock types from Zn--Cu-Pb deposits in Finland (Orijtirvi, Iilij~irvi, Pyh~isalmi, Mullikkorgme) and central Australia (Oonagalabi). Textural and mineralogical data suggest that F influx predates peak metamorphism in these deposits.The Mullikkortime whole-rock data show positive correlations between F and XMg = molar Mg/(Mg + Fe) and between F and elements of relatively low mobility (Ti, A1, Mg) and negative correlations between Fe and these elements. This suggests that iron was leached from silicate rocks by F-bearing fluids and was transferred to the Fe-rich sulphide ore. When normalized to immobile elements, F correlates positively with total metal content (Cu + Pb ÷ Zn + Fe), consistent with the commonly observed increase of F content towards ore bodies.Combining all microprobe data, hydrous minerals show the following order of decreasing F/ (F + OH) ratio when coexisting: apatite > chondrodite > biotite > gedrite > (hornblende, muscovite, anthophyllite) > chlorite. The low-to medium-grade Finnish samples (Mullikkor-

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The Volcano-Tectonic Setting and Mineralization of the Early Proterozoic Kemiö-Orijärvi-Lohja Belt, SW Finland

Cited by 16 publications

References 12 publications

The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy

The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy

Supracrustal rocks in the Kuovila area, Southern Finland: Structural evolution, geochemical characteristics and the age of volcanism

Fluorine in orthoamphibole dominated Zn-Cu-Pb deposits: examples from Finland and Australia

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