The Sattasvaara komatiite complex is part of an extensive zone of explosive komatiitic volcanism which may have been a significant stage in the Lapponian evolution regarded as Archean. This volcanism took place at the latest 2.43 Ga ago and appears to have been connected with cratonic rifting in the Baltic Shield. The complex was formed by fissure eruptions rather than central-vent eruptions, at the margin of a restricted depositional basin. Effusive, explosive and mixed eruption phases were separated by erosional periods and the komatiitic volcanism was succeeded by mafic effusions and explosive eruptions.The Sattasvaara complex is composed of interchanging amphibole rocks, or komatiitic basalts, and amphibole-chlorite rocks or (basaltic)komatiites, and encloses minor serpentinitic and peridotitic rocks as terminal komatiite flows and picrite plugs. However, main part of the komatiites has discharged earlier and is present as intercalations in graphitic slate zone beneath the Sattasvaara complex.The komatiitic rocks were originally co-magmatic according to their gradual rock suite. The komatiitic basalt (MgO 9-18 wt.% anhydrous basis) shows signs of fractional crystallization of pyroxene and plagioclase, whereas the (basaltic)komatiite (MgO 18-29 wt.% anhydrous basis) contains pyroxene and olivine phenocrysts and the komatiite (MgO>29 wt.% anhydrous basis) is olivinepyroxene cumulate both in distinct flows and lower parts of the (basaltic)komatiite flows. The erupting lavas differed physically and discharged in unlike manner: eruptions of the fluid komatiitic basalt were Hawaiian-type and the ones of the viscous (basaltic)komatiite were Strombolian-type. The initial komatiite flows were most fluidal and flowed after the manner of flood eruptions.Pyroclasticity is associated with the (basaltic)komatiite that is dominantly fragmentary, consisting of lithic, vitric and crystal ejecta; subordinate lava flows are largely block lavas. The voluminous explosive eruptions appear to have been magmatic in origin. Also, a minor pyroclastic breccia is formed by the komatiitic basalt that is usually present in massive or pillowed lava flows; these exceptional volcanic explosions have possibly caused by hydromagmatic eruptions.The komatiitic rocks may have been source of the gold contained in chromian marbles and quartzite-conglomerates nearby the Sattasvaara complex and the komatiitic volcanism seems to have caused iron-manganoferrous emanations in its periphery.

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.

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The variously explosive komatiitic volcanism in Finland was virtually confined to the Archaean continental segment, where it occurred in the Lapland and Kuhmo-Suomussalmi greenstone belts between 3.0 Ga and 2.5 Ga, in the continental borderland at 1.97 Ga, and in the continental shelf break 1.91-1.88 Ga ago. The Archaean continent comprised the Saamian craton, which stabilized at 3.1-3.0 Ga before splitting into an array of sialic megablocks. Except for the NWtrending rifts, the linear crustal openings of the Fennoscandian greenstone belts constituted a radial swarm of aulacogens caused by domal uplift in connection with shield-wide mantle upwelling. Diapirism resulted in the Lapponian pyroclastic komatiite zone of mantle-activated rifting and in the large Solovetski mantle plume in the USSR, along which continental breakup reached no more than an embryonic stage of divergence. The Finnish greenstone belts underwent three periods of supracrustal evolution from cratonic deposition and/or continental rifting to oceanic or mantle-activated rifting. The extensional stage of the greenstone-belt genesis is recognizable in Lapland but not in the Kuhmo-Suomussalmi area, in the ductile? periphery of the continental plate, where sagduction obscured the geological history. In Lapland, the komatiitic central-vents opened at rift-aulacogen intersections. Some signs of volcanic bursting, albeit obscure, can be traced in the earlier ultramafics, namely in the initial komatiitic greenstones beneath the cratonic metasediments and in those associated with bimodal metavolcanics. Pyroclastics formed in all the komatiitic rock types but the pyroxene peridotitic komatiite (MgO 18-30 wt%, anhydrous basis) was the predominant substance to extrude in enormous magmatic explosions during the terminal stage of mantle upwelling. After the Karelian anorogenic period, mantle activity produced two ophiolitic suites from the mantle plumes 1.97-1.96 Ga ago. The one at Outokumpu brought about volcaniclastic komatiites under shallow-water to terrestrial conditions. The preferred environment was the Raahe-Ladoga marginal rift, of basin-range nature. At the peak of the Svecofennian orogeny (1.90-1.87 Ga), some minor komatiites with negligible ejecta discharged at the continental edge, forming the extreme member of Bothnian volcanism.