The Proterozoic granitoids of Finland: Granite types, metallogeny and relation to crustal evolution

Nurmi, Pekka A.; Haapala, Ilmari

doi:10.17741/bgsf/58.1.014

Cited by 99 publications

(40 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The migmatite granites in southern Finland have previously been described by e.g. Eskola (1914), Sederholm (1932Sederholm ( , 1934, Nurmi and Haapala (1986) and Selonen et al (1996). Sta˚lfors and Ehlers (2000a, b, 2001, 2003 have discussed their emplacement mechanisms suggesting that partial melts moved through the crust to form either granitic massifs in the middle and upper crust, or froze as migmatites at greater depths.…”

Section: Introductionmentioning

confidence: 81%

Emplacement mechanisms of late-orogenic granites: structural and geochemical evidence from southern Finland

Stålfors

Ehlers

2005

Int J Earth Sci (Geol Rundsch)

View full text Add to dashboard Cite

The country rock in southern Finland formed mainly during the Svecofennian orogeny ca. 1.9 Ga ago. The middle and lower crust was partially melted 1.83 Ga ago due to crustal thickening and subsequent extension. During this event, S-type migmatites and granites were formed along a 100·500 km zone. This Late Svecofennian Granite-Migmatite zone (LSGM zone) is a large crustal segment characterised by roughly E-W trending sub-horizontal migmatites and granites. Combined ductile E-W shear movements and NNW-SSE compressional movements defined a transpressional tectonic regime during the emplacement. Partial melts that moved through the crust pooled as granite sheets or froze as migmatites. Major transpressive shear zones border the LSGM zone, which forms a tectonic and metamorphic zone that crosscuts the earlier Svecofennian granitoids. Based on field observations and geochemical data from two sets of outcrops, we show that the great volumes of late-orogenic granites and migmatites in southern Finland were transported and emplaced as small chemically variable batches, possibly extracted from different protoliths. These melt batches were transported along repeatedly activated channels and collected at some horizontal level in the crust. In the Nagu area, the melt batches were trapped under a rooflayer of amphibolite and the whole complex was synchronously folded into open folds with steep axial surfaces and E-W trending fold axes. The sheets of microcline granite are, in places, strongly sheared; the microcline phenocrysts are imbricated and subsequent deformation of the microcline phenocrysts indicates syntectonic movements of the layers as well as a syn-tectonic mechanism for the late-magmatic fractionation. Depending on the degree of crystallisation of the individual melt batches during shearing at different intensities, the granites have slightly different appearances. Some sheared zones show a cumulate-like trace element geochemistry, indicating that melt fractions were expelled from the system, producing layers of deformation enhanced fractionated granites and cumulate layers. Our interpretation is that the Nagu area shows shear-assisted fractionation mechanisms in granitic melts, and that similar processes are responsible for the fractionation trends seen in the sub-horizontal sheeted granites in Ha¨meenlinna at higher levels in the crust.

show abstract

Section: Introductionmentioning

confidence: 81%

Emplacement mechanisms of late-orogenic granites: structural and geochemical evidence from southern Finland

Stålfors

Ehlers

2005

Int J Earth Sci (Geol Rundsch)

View full text Add to dashboard Cite

show abstract

“…Thus they are usually described as synorogenic, late orogenic or postorogenic (Simonen 1980, Nurmi & Haapala 1986, although the existence of an intraorogenic group in southern Finland has been proposed (Suominen 1991).…”

Section: Geological Setting and Grani-toid Typesmentioning

confidence: 99%

“…Late orogenic granitoids often exhibit S-type characteristics (Nurmi & Haapala 1986). They consist of pegmatites, quartz monzonites and granites, which often occur as diapiric bodies or form neosomes in migmatites.…”

Section: Geological Setting and Grani-toid Typesmentioning

confidence: 99%

Timing of Palaeoproterozoic crustal shearing in the central Fennoscandian Shield according to U-Pb data from associated granitoids, Finland

Vaasjoki¹,

Kärki²,

Laajoki³

2001

Bull Geol Soc Finland

View full text Add to dashboard Cite

Granitoids in the Finnish part of the Fennoscandian Shield were created by numerous Archaean and Palaeoproterozoic tectonic events. Late phases of Palaeoproterozoic, Svecokarelian deformation created ductile, crustal-scale shear zones, of which the N-S striking Hirvaskoski Shear Zone and the NE-SW striking Oulujärvi Shear Zone were strongly affected by the latest deformation stages, D 3 and D 4 . These shear tectonic events deformed ductilely prekinematic granitoids and caused intrusion of synkinematic igneous rocks, but the D 3 and D 4 fault rocks are also penetrated by postkinematic intrusives.Archaean granitoids behaved mostly as rigid blocks unaffected by Palaeoproterozoic deformation. However, inherited Archaean zircons occur in some obviously Proterozoic granitoids, and others contain heterogeneous zircon populations. Granitoids lacking structures of the earliest deformations, D 1 and D 2 , contain inherited zircon populations partially reset during the Svecokarelian orogeny and have been sheared ductilely during stages D 3 and D 4 . Granitic rocks yielding zircon ages of 1.82-1.80 Ga show no features associated with these shearing events and penetrate the D 4 fault rocks setting a minimum age for these deformation events. This age marks also the end of convergent tectonics in the central Fennoscandian Shield. Monazite data from a variety of rocks demonstrates a regional cooling below the 600°C isotherm at 1.8 Ga.

show abstract

“…The crustal segment displays direct evidence of volcanic arcs, subduction and collision (references in Gaål 1986;Huhma 1986) and the bulk of the epiclastics in the thick volcanicsedimentary sequence was eroded from the recently formed crust (Huhma 1986(Huhma , 1987. The Svecokarelian fold belt was intruded by anorogenic rapakivi granites recording the onset of continental rifting (Nurmi and Haapala 1986), produced some fault-bounded troughs (Kahma 1978) in which the Jotnian arkose-shale redbed association was deposited (Simonen and Kouvo 1955).…”

Section: + -F I Rapakivi Granitesmentioning

confidence: 99%

The Lapland greenstone belt: Stratigraphic and depositional features in northern Finland

Saverikko¹

1987

Bull Geol Soc Finland

View full text Add to dashboard Cite

The Lapland greenstone belt formed in a continental environment, as a result of rifting of the 3.1-3.0 Ga Saamian craton. The basin subsided to a depth of five kilometres between 3.0-2.5 Ga and contains a sequence which is subdivided into Lower, Middle and Upper Lapponian groups, with the Middle Lapponian metasediments separating the Lower Lapponian Salla-Jauratsi and Upper Lapponian Kittilä greenstone successions. After a folding episode the Lapponian supergroup was covered with the Kumpu conglomerate-metasandstone-slate suite, occurring as Karelian, i.e. Sariolan-Jatulian, deposits. A few erosional remnants are capped with Svecofennian rocks 1.9 Ga old.The Lower Lapponian consists of basal arkose, the Möykkelmä greenstones, a cratonic quartzite-carbonate-schist suite and the Salla greenstone complex(es) preserving evidence of a lava plateau. The Salla bimodal metavolcanic rocks and the Middle Lapponian metasediments, which, at their thickest, constitute the Oraniemi arkose-slate-quartzite association (incl. redbeds), evidently indicate cratonic rifting that terminated with the growth of isolated lava fields of Fe-rich tholeiitic basalt. In the Upper Lapponian, euxinic-exhalative metasediments underlie the Sattasvaara, Sotkaselkä and Kummitsoiva komatiite complexes and the Kittilä greenstones, which are present as complicated but distinct eruption centres and contain a varying amount of ejecta and volcaniclastic greywacke-slate intercalations. The komatiite-dominant succession evidently represent mantle-activated rifting and the linear mantle upwelling.The Lapland greenstone belt and adjacent granulitic belt appear to constitute a paired metamorphic terrain, where the overthrusting of the granulites is explained by mutual motions of the distinct cratonic megablocks.

show abstract

The Proterozoic granitoids of Finland: Granite types, metallogeny and relation to crustal evolution

Cited by 99 publications

References 47 publications

Emplacement mechanisms of late-orogenic granites: structural and geochemical evidence from southern Finland

Emplacement mechanisms of late-orogenic granites: structural and geochemical evidence from southern Finland

Timing of Palaeoproterozoic crustal shearing in the central Fennoscandian Shield according to U-Pb data from associated granitoids, Finland

The Lapland greenstone belt: Stratigraphic and depositional features in northern Finland

Contact Info

Product

Resources

About