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Uncertain Age Complexes
The Lovnozero norite, hypersthene gabbro and websterite complex unites numerous small bodies within the Lapland Granulite Belt. The bodies are lens-like, flattened, sigar- and ribbon-like. Most of elongated massifs are parallel to lineation in the country rocks. Their dimensions do not exceed first dozens of meters along a long axis. The largest differentiated bodies of 1.5 km long and 600 m thick are found in the Lovnozero Lake and Laukku Mountain areas. Norite is a predominant rock. The rocks are related to rocks that are undersaturated and slightly oversaturated with Si. Ultramafites are slightly enriched in Cr and Ti, and mafites - in Ni. These intrusives have been folded and metamorphosed under granulite and amphibolite facies conditions. They are characterized by the economic content of sulphide Cu-Ni ores in the Lovnozero Lake area.

There are bodies of gabbro-amphibolites and metaultrabasites whose link with the above rock associations is unknown. Their age is taken to be late Archaean-early Proterozoic. Into this group included are numerous and widely spread gabbro-amphibolites as well as ultrabasites of the Kanozero Lake area. Most basic bodies are within the western Kola region and the largest - in the Terskaya Zone.

Proterozoic Erathem
The Notozero and Severokarel'sky (Northern Karelia) dunite and harzburgite complexes are spread in the western Kola peninsula. Some massifs of identical rocks are known to be found in the southern framing of the Imandra-Varzuga Zone in the Falaley Stream area and one massif is situated northwards of the Salny Tundra Mountains in the Pecha River area. The Sumian magmatic cycle starts with these complexes [42] though this conclusion was made on the basis of indirect indications, in particular, on a petrochemical similarity with early differentiates of the basic layered intrusions. The basement gneisses and the Archaean TTG plutonic rocks are the country rocks for the harzburgites in the most part of the territory. The form of the massifs is plate- and lens-like, the contacts are tectonic, concordant with foliation in the country rocks. The internal structure of the massifs is autonomous, the largest of them are differentiated. A rock association of the massifs includes dunite, olivinite, harzburgite and pyroxenite, harzburgites being predominant. The main chemical feature of the rocks is the high Mg, Ni and Cr content. The rocks are deformed, they have undergone autometamorphic reworking and regional metamorphism. Anthophyllite-asbestos mineralization is observed in the massifs.

The rocks of the complex of layered peridotite-pyroxenite-hypersthene-gabbro intrusions and the Alakurtti Complex of lherzolite, hypersthene gabbros compose a lateral suite. The first ones are mainly spread along the north and the south boundaries of the Pechenga-Varzuga and Northern Karelia Zones, respectively. The Pansky and Fedorova Tundra, Monchegora massifs as well as the intrusions of the Olanga complex are the largest. Their analogues are established southwards of the Pechenga Structure. The massifs of the Karik-Yavr Lake area in the eastern framing of the Pechenga Zone are regarded to these plutonic rocks because their geological setting, rock and mineral composition, ore mineralization and secondary reworking are similar to those of the above intrusives. Earlier these massifs were related to a Late Archaean gabbro-hyperbasite association [42]. Based on a petrographic and petrochemical similarity, to the layered intrusions related are basite massifs in areas of the upper flow of the Strel'na and Chapoma rivers and Ondomozero Lakes (the Ondomozero Complex) in the Terskaya Zone.

Most intrusives are characterized by the lopolith-like form, autonomous internal structure, and intrusive contacts with gneissic units. They cross-cut also Early Proterozoic sedimentary-volcanic formations. The rocks of the massifs are very different ranging from olivinite to anorthosite. Mostly spread are hypersthene gabbro. Ultramafites and mafites are related to the rock suites with the low and moderate Fe and alkali content. As a whole, they are characterized by Cu-Ni and Pt ore mineralization. The ages of the Lukkulaisvaara, Kivakka (the Olanga Complex), Monchegora and Pansky-and-Fedorova Tundra massifs are 2437+/-11, 2445+/-2, 2493+/-7 and 2470+/-9 Ma, respectively [8, 10].

The Alakurtti lherzolite and hypersthene gabbro complex unites numerous small massifs characterized by an areal extension in the Belomorian Zone. Separate bodies of these rocks are found to the north-east of the Salny and Kolvitsa Tundra Mountains and in the southern framing of the Pechenga Zone.

The massifs are of a lens-and circle-like form and have distinct cross-cutting contacts. Their dimensions vary from some dozens of meters to some kilometers. The largest of them are differentiated. The composition ranges from lherzolitic to leucogabbroic. Their peculiar feature is drusitic (coronitic) rims. These mafites and ultramafites are chemically similar to those of the basic layered intrusions.

The gabbro, gabbro-anorthosite and diorite massifs of the Kolvitsa-Laplandian Zone and of the Glavny Khrebet (Main Ridge) are widespread in the western region. They are represented by the Kandalaksha, Kolvitsa, Pyrshin, Vulvara, Yavrozero, Vuim-Elgoras massifs as well as massifs of the Anis Tundra Complex. Until recently, all these massifs have been considered to be Late Archaean. At present, this suite has been added by some massifs in the Belomorian Zone, i.e. by the Zhemchuzhny, Tolstik and Voley ones related earlier to the pre-Lopian anorthosite-hypersthene-norite association [64].

The massifs are lens-, plate-, and lopolith-like bodies concordant to the country rocks. The intrusive relationships with gneisses have been established only for the Main Ridge massif, which has tectonic contacts with the Monchegora Massif. The geological relationship between these two massifs is unknown, so their position in the Legend is determined by geochronological data. Most massifs are differentiated. The Main Ridge Massif is the largest in the region and is characterised by the most representative syngenetic rock suite - from plagioclase-bearing peridotite to anorthosite. Leucogabbro and gabbro-anorthosite dominate in most massifs with the exception of the Zhemchuzhny and Anis Tundra complex massifs containing diorite.

The rocks considered differ from the late Archaean gabbro-anorthosite association in the low alkali and silica content and show Ti-Fe mineralisation with the high V content. The ages of the Main Ridge, Kolvitsa and Pyrshin massifs are 2453+/-4, 2450+/-10 and 2452+/-7 Ma, respectively [45], and those of the Tolstik and Zhemchuzhny ones - are in the age range of 2400-2500 Ma [39, 68].

The Imandra lopolith of norite, hypersthene gabbro and diorite unites separate massifs in the western part of the Imandra-Varzuga zone. Till now, these rocks have been included into a peridotite-pyroxenite-hypersthene gabbro association. The massifs of the north group are located in lower Proterozoic volcanic-sedimentary rocks or in the contact zone between these rocks and the ancient gneisses; those of the south group - in Archaean gneisses and an amphibolite unit where these rocks tectonically contact with the Tominga Group rocks. The contacts are intrusive. The rocks vary in composition from plagioclase-bearing pyroxenite to gabbro-diorite. They are oversaturated with Si and have the high Fe and alkali content. The content of Cr is higher at the bottom of the massifs and that of Ti and V - at the top. The age of zircon from hypersthene gabbro is 2396+/-7 Ma [10].

The Zasteid gabbro, lherzolite and websterite complex is represented by small massifs in the north-western part of the Kolvitsa-Laplandian Zone. The massifs of the same composition were mapped to the south-east of Kolvitsa Lake within the same zone. The configuration of the bodies is sheet-and lens-like, sometimes close to an isometric one, the bodies lie conformably to the strike of the country rocks. Their contacts are tectonized. The largest massifs are intrusive into the ancient gneisses, are differentiated and composed of olivinite, lherzolite, websterite, and hypersthene gabbro. Websterites are mostly widespread. The massifs of the Kolvitsa-Kandalaksha area are composed of hornblende peridotites. The peculiar chemical features of ultramafites, mafites are their being undersaturated with silica, and the moderate Fe and alkali content. They feature the higher Cr, Ti, and Ni content. The Suenlagash massif has an Sm-Nd isochrone age of 1890+/-60 Ma, which most likely corresponds to a metamorphic event [72].

The Rainenchorr and Por'ya Guba pyroxenite and wehrlite complexes include small massifs and sometimes dykes in the southern part of the Main Ridge Massif and in the Kolvitsa-Laplandian Zone. In the Salny Tundra Mountains, the massifs are mainly located in marginal zones of the easternmost part of the Lapland Granulite Belt. All the massifs with the exception of the Por'ya Guba Complex are linked spatially with gabbro-anorthosites. The shape of massifs is mainly lens-like. The contacts with the country gneisses and gabbro-anorthosites are concordant, the rocks being foliated near them. The massifs have intrusive relationships with the country rocks in the Kolvitsa area. Most massifs are composed of olivinite and pyroxenite, the latter being predominant. The largest ones are differentiated from ultramafites to leucogabbros (the Por'ya Guba Complex). The rocks feature the higher alkali and Ti content, and are undersaturated with Si. The pyroxenite and wehrlites contain an economic concentration of Ti-Fe ores with the high V content. The alkali granites intrude these rocks, which indicates their upper age limit.

The Sumian magmatic cycle is completed by complexes of charnockites and granites (i), monzodiorites and granites (ii), and alkali granites and syenites (iii). These three groups of granitoids form an evolutionary suite, the higher the alkali content is, the higher the colour index is.

The Umba charnockite and granite complex is a representative one for the Kola peninsula. Its analogues are the Yarva-Varaka Massif in the Moncha Gora area as well as massifs in the Sokolozero and Notozero Lakes areas in the Northern Karelian Zone. The form of the massifs is sheet- and lopolith-like. The contacts with Archaean rocks are both concordant and cross-cutting; there are hornfels and breccia zones along them. The massifs are multiphase and differentiated. In the Umba complex, the early phase rocks belong to an enderbite suite, the intermediate ones - to a charnockites suite and the third ones - to a granite suite. The most spread are granites. In the Yarva-Varaka massif granodiorites and granites predominate. In the northern Karelia the massifs are composed of granites and leucogranites. The characteristic chemical features of the rocks are their being oversaturated with Si and Al, and the lower alkali content. The age of the Topozero charnockites in northern Karelia that are considered to be as old as the Umba Complex charnockites is 2370 Ma [62].

The Koigera and Kukhtozero monzodiorite and granite massifs are multiphase intrusions in the Northern Karelia Zone.The country rocks for them are the TTG rocks of the Pyaozero Complex. In the Koigera massif, the early phase is biotite-amphibole-diopside monzodiorites, the late one is represented by quartz syenites, granosyenites, leucogranites and granite-porphyry. The Kukhtozero massif is composed of biotite-amphibole monzodiorites. The Si content varies within a large range; the alkali-content is relatively high. There are no reliable isotope age determinations.

Alkali granite and syenite intrusions are the most spread among the Proterozoic granitoids, it is most characteristic of them to occur in the eastern part of the region - in the Keivy Zone and southwards of the Imandra-Varzuga Zone. Many the intrusions, for instance, the Western Keivy, Ponoy, Purnach, Belaya Tundra, Lavrent'evsky, Kanozero, and Gremyakha-Vyrmes massifs, have a sheet-like shape and intrusive contacts with the country rocks. Lineation and foliation formed by dark-coloured minerals are characteristic of the granites. A vertical zonation is established - subalkali varieties are exposed in the most eroded areas (the Kanozero massif). Aegirine-arfvedsonite granites dominate among the granitoids. Granosyenites and syenites occupy about 5% of the territory composed of these rocks; they are represented by lepidomelan-ferrohastingsite varieties. The granitoids are characterized by the higher Fe/(Fe+Mg) ratio and the higher agpaitic coefficient. Their peculiar geochemical feature is the higher rare and REE content against their clarkes of concentration. The alkali granites are supposed to form a single volcano-plutonic association with rhyolites and basalts of the Strel'na Group. The isochrone Rb-Sr age of the Western Keivy alkali granites is 2350+/-71 Ma [66], model Rb-Sr and isochrone Pb-Pb ages of the Kanozero Massif are 2270+/-80 and 2365+/-15 Ma, respectively [53, 72].

The Strel'na and Vochelambina peridotite and pyroxenite complexes comprise small massifs in western and south-western parts of the Imandra-Varzuga Zone as well as in its south subzone. Their analogues are established in the Kuolajarvi Zone [59]. These complexes correspond to the Jatulian level in the Imandra-Varzuga Zone and to the Ludikovian one in the Kuolajarvi Zone [33]. In fact, these massifs are dykes and sheet-like bodies, their thickness does not exceed 100 m, they are up to 3.5 km long. The contacts are both cross-cutting and concordant. The massifs are mainly composed of one variety of rocks with the exception only of differentiated bodies composed of harzburgites, lherzolites, wehrlites, pyroxenites, and sometimes gabbroids. The rocks were intensively reworked during the autometamorphic stage and then during a regional metamorphism one. The peculiar chemical features of ultramafites is the high Mg, Ca, and Cr content and the low Ni and Ti content. These rocks form a single volcano-plutonic association with the high-Mg basalts in the Kuolajarvi Zone.

The Kuksha gabbro-pyroxenite complex includes sheet-like subconcordant bodies in the central and eastern parts of the Imandra-Varzuga Zone, where they are located in the Strel'na Group rocks, massifs located in the basement of the southern subzone (the Fomkin Stream area) as well as the Podzemel'ny Massif. The thickest bodies are differentiated. The rocks are similar in composition to the Polisarka volcanic rocks [59], they are characterized by the higher Mg and Si content and by the low Ti, Ni, and Cr content.

The Tominga gabbro-diabase complex unites sills and dykes in the Pechenga and Imandra-Varzuga Zones (in the south subzone of the latter, in particular) and in the Monchegorsk area. The maximum concentration of them is related to the Umbarechka-Vilmuaiv Fault. In the western Imandra-Varzuga Zone, the gabbro-diabase bodies cross-cut the Polisarka Formation rocks and the Imandra Lopolith basites. The gabbro and gabbro-diabase are widely spread in the rocks of the third and fourth units of the Pechenga Karelian succession.

Some massifs are differentiated. To the petrochemical features of the rocks related may be the high Ti, Fe, V and P content. The gabbro-diabase is supposed to be comagmatic to the volcanics of the Pil'gujarvi and Tominga Groups.

The Pechenga and Solyonoye Ozero (Salty Lake) gabbro, pyroxenite and wehrlite complexes are spread in the Pechenga-Varzuga Zone. The first one is represented by numerous massifs in the Pechenga ore area. and the second one - by single bodies in the western Imandra-Varzuga Zone. To the group of rocks under consideration related are dykes of the Nyasyukka Complex, the Panarechka Massif is conditionally related to this group, too. The intrusions of first two complexes are mainly located within Lower Proterozoic pyroclastic-sedimentary formations, they have a sheet-and phacolith-like form and are differentiated. These dykes are characterized by both concordant and cross-cutting contacts, with the dykes cross-cutting the Tominga gabbro-diabase sills. There are foliation and breccia zones along the contacts. All the mafites and ultramafites are intensively reworked; from petrochemical reconstructions, they correspond to an olivinite-wehrlite-pyroxenite-gabbro-subalkali gabbro suite.

The rock association under consideration is related to a high-Fe and high-Ti subalkali type with the high Ni, Cr, and P content. It is correlated with the ferropicritic volcanics of the Pil'gujarvi Formation and the South Pechenga Group. Gabbro-wehrlites of the Pechenga ore area are related to the deposits of sulphide Cu-Ni ores. The age of the Pechenga Complex massifs is 1970+/-70 Ma [59].

The following complexes of dioritic porphyrites (i) and quartz diorites and TTG granitoids (ii) are coeval formations as suggested by preliminary geochronological data [22].

The Por'itash dioritic porphyrite complex is represented by subvolcanic bodies in the South Pechenga Subzone. Their analogues are single massifs in the south part of the Imandra-Varzuga Zone. The intrusions have a simple structure and form a volcano-plutonic association with pyroclastic rocks similar to them in composition in the South Pechenga Group. The rocks feature the higher Ti and K concentration and the high Fe₂O₃ content.

The massifs of the Kaskel'javr diorite and TTG rocks complex are spread within the southern framing of the Pechenga Zone. Their contours are close to isometric. The boundaries with the country rocks are everywhere tectonic and are accompanied by migmatization zones. The massifs are considered to be multiphase rootless plutons. All the granitoids feature distinct gneissic textures, which are concordant to pluton contours. Primary structures and textures are rare in them.

In the largest Kaskel'javr Massif dominate the first phase rocks, i.e. quartz diorites, in other massifs - the TTG granitoids. Chemically, the granitoids of the complex are close to a Late Archaean diorite association. They are related to the Na suite rocks of the normal alkali content. By some data, the granitoids were formed 1940+/-40 Ma ago [53].

The massifs formed at the final stage of the Jatulian-Kalevian magmatic cycle are typical for the Imandra-Varzuga Belt, they are also located out of the belt in the NW-SE trending fault zones. They are composed of different rocks that form three groups: (i) peridotites, pyroxenites, gabbro and gabbro-anorthosites, (2) subalkali gabbro, akerites and (3) alkali and nepheline syenites, foidites. Each group is related to an independent intrusive phase.

The massifs have intrusive contacts and most of them are multiphase. These rock associations are mostly fully observed in the Gremyakha-Vyrmes Massif, in which gabbro, subalkali gabbro and gabbro-anorthosites dominate. In the Peschanozerskiy Massif, ultramafites dominate, and foidites are 10% of the whole square of the massif. The Sakhar'jok, Kul'jok and Soustov intrusions are mainly composed of alkali and nepheline syenites, in the first one also established are alkali gabbros. The ultramafites are mostly chemically close to rocks of a pyroxenite-wehrlite association. In the Gremyakha-Vyrmes massif, with the ultramafites connected are complex P-Fe-Ti ore deposits. Zr, Nb, REE, Li and P are specific element-admixtures for the rocks, which form a single volcano-plutonic association with the alkali volcanics of the Tominga Group. The age of two earliest rock groups in the Gremyakha-Vyrmes Massif is 1865+/-100 Ma [53]; the reliable age determinations are still absent.

Of later age are massifs of granodiorites, granites and leucogranites formed at the initial stage of the Karelian tectogenesis and located in extension zones [33].

The Litsa-Ara Guba and Juovoaivskiy granodiorite and diorite complexes are spread in the western part of the Kola peninsula. The massifs have intrusive contacts with the country rocks. The north-eastern group of the massifs is of a dyke-and sheet-like form, the rest ones are of a laccolith-, harpolith- and stock-like shape.

The granitoid complexes are multiphase. The massifs of the Litsa-Ara Guba complex are composed of rocks of monzodiorite, granodiorite-granite and granosyenite suites. Mostly spread are porphyric granites and granodiorites. The Juovoaivskiy Complex consists of granites and granite-porphyry. The decrease in rock crystallization depth from the NE to the SW is established. The colour index of the rocks decreases in the same direction, whereas the SiO₂ content in final differentiates increases. The granitoids chemically corresponds to granitic rocks of the normal and low alkali content, they feature the higher content of rare elements. Mo mineralization is linked with the granites. The age of the Litsa-Ara Complex granitoids determined by the Rb-Sr and U-Pb methods corresponds to 1720+/-85 and 1850+/-130 Ma [53].

The leucogranite massifs are mainly spread through the Terskaya Zone, two small bodies being known in the Kontozero and Lyavozero Lakes area. All the massifs are spatially linked with deep NE-SW and N-S trending faults and have the intrusive contacts with the country Archaean rocks. The largest one, Strel'na Massif is characterized by a sheet-like form and the autonomous internal structure, which is concordant to the contact surface. The massifs are mainly composed of granites among which distinguished are leucogranites and granite-pegmatite. Peculiar chemical features are the high SiO₂ and alkali content and the higher Fe/(Fe+Mg) ratio. Muscovite ore deposits are connected with the Strel'na Massif pegmatites. The age of the granites is 1780-1830 Ma ago [53].

The mafic dykes d₂ unite early Proterozoic dyke complexes (the Sumian-Vepsian stage) which are widely spread through the region and mainly have the NE-SW and NS strike. Their extent rarely exceeds first kilometers except for the Keivy Zone dykes. The development of the dyke complexes is related to the evolution of the Pechenga-Varzuga Zone [40, 55]. Four dyke complexes are distinguished: (i) hypersthene gabbro - gabbros; (ii) quartz metadolerites and (iii) olivine gabbro - ferrous metadolerites - kaersutite gabbros; and (iv) picrite dolerites. This line corresponds to the succession of the complexes development. The first and third ones are widely spread through the Kola Peninsula, the second and fourth ones are mainly spread through its north-eastern part. The oldest complex is correlated with the layered peridotite-pyroxenite-hypersthene gabbro intrusions. The quartz metadolerite complex shows a similarity with the andesitic basalts of the Akhmalakhta Formation, the third complex is correlated with gabbro-wehrlite intrusions to which related are the Nyasyukka dykes. The rocks of many dykes, in the Keivy Zone, in particular, are transformed into gabbro-amphibolites.

The late Proterozoic dolerite sills and dykes d₃ complete the Precambrian magmatism in the region; they are typical platform intrusive rocks. The dolerite bodies are mostly spread along the Barents Sea coast from the Kola Fjord to the St.Nose Cape and are unified into the Barents Sea Complex.

The location of the bodies is conditioned by en-echelon faults that are splays of the Karpinsky deep fault. Their country rocks are both the Archaean granitogneisses and the Riphean sediments [58]. The NE-SW and N-S trending dolerite dykes are observed in the Keivy Zone [55]. Large gently dipping intrusions and dykes are differentiated. In the Barents Sea Complex dominate dolerites and quartz dolerites. The rocks chemically are homogeneous and belong to a normal tholeiite-basalt suite. They have undergone only autometamorphism.

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