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magmas (Kathol & Martinsson 1999). The main
magmatic event can probably be set at 1.87–1.88 Ga
with the emplacement of the composite monzoniticsyenitic-granitic
intrusions, whereas some granites
formed as late as at c. 1.86 Ga (Skiöld 1981, Skiöld
& Öhlander 1989, Martinsson et al. 1999).
Intrusions of the Perthite Monzonite Suite are
suggested to be comagmatic with the Kiirunavaara
Group volcanic rocks. Both display a compositional
variation from mafic to felsic combined with a relatively
high content of alkali and HFS-elements. The
intra-plate setting suggested for the Kiirunavaara
Group is indicated by the chemical characteristics
of the Perthite Monzonite Suite intrusions. Mantle
plume origin is supported by the abundant occurrence
of mafic-ultramafic complexes northwest of
Kiruna, which possibly define the plume centre.
Lina Suite
Intrusions of the Lina Suite are extensive in northern
Norrbotten where they typically occur as granite,
pegmatite and aplite of mainly minimum melt
composition generated by crustal melting. In Finland,
they appear to form most of the volume of the
Central Lapland Granitoid Complex (Fig. 1), and
are also present as smaller intrusions in many areas
across northern Finland (Lehtonen et al. 1998). However,
the seismic appearance of the Central Lapland
Granitoid Complex is inconsistent with this area as
an intrusion-rich belt, and it may have a composition
comparable with the supracrustal belts to the north
and south (Patison et al. 2006a). The Lina Suite is
composed of monzo-, syeno-granites, and adamellite,
and is characterised by its restricted SiO 2 range
at 72–76 wt. %. It is peraluminous and a high content
of Rb and depletion of Eu are characteristic.
The heat source generating the magmas
might be the continent-continent collision events to
the south and west (Öhlander et al. 1987b, Öhlander
& Skiöld 1994, Lahtinen et al. 2005) or the contemporaneous
TIB 1 magmatism. Age determinations
indicate a relatively large span in the emplacement
age at 1.81–1.78 Ga for the Lina Suite (Huhma 1986,
Wikström & Persson 1997b, Perttunen & Vaasjoki
2001, Rastas et al. 2001, Väänänen & Lehtonen
2001, Bergman et al. 2002).
A- and I-type intrusions
This is the youngest of the described intrusive suites
and, in the west, it forms part of the Transcandinavian
Igneous Belt (TIB). Two generations (c. 1.8
and 1.7 Ga) of intrusions belonging to the TIB exist
in northern Sweden and adjacent areas of Norway.
They commonly show quartz-poor monzonitic
trends, and gabbroic-dioritic-granitic components
are relatively common. (Romer et al. 1994, Öhlander
& Skiöld 1994)
Across northern Finland, the suite is represented
by the Nattanen-type granitic intrusions dated
at 1.80–1.77 Ga (Huhma 1986, Rastas et al. 2001).
They form undeformed and unmetamorphosed, multiphase,
peraluminous, F-rich plutons which sharply
cut across their country rocks. Their Nd and Hf isotopic
ratios indicate a substantial Archaean component
in their source.
In northern Norrbotten, monzonitic to syenitic
rocks give ages between 1.80 and 1.79 (Romer
et al 1994, Bergman et al. 2001), whereas granites
range from 1.78–1.77 and 1.72–1.70 Ga (Romer et
al. 1994). Further south, the age of the granitic Ale
massif in the Luleå area is 1802±3 Ma and 1796±2
Ma for the core and the rim of the massif, respectively
(Öhlander & Schöberg 1991). This is similar
to the 1.80 Ga age of Edefors type monzonitic to granitic
rocks (Öhlander & Skiöld 1994).
This suite can be classified as a quartz
monzodiorite–quartz monzonite–adamellite–granite
suite and shows a metaluminous to peraluminous
trend with alkaline affinity (Ahl et al. 2001). Lithophile
elements are enriched in this suite, e.g. Zr is
strongly enriched in the Edefors granitoids (Öhlander
& Skiöld 1994).
Characteristic for the 1.8 Ga monzonitic to
syenitic rocks is the occurrence of augite and locally
also orthopyroxene and olivine demonstrating an
origin from dry magmas (Ödman 1957, Öhlander
& Skiöld 1994, Bergman et al. 2001). The Transscandinavian
Igneous Belt (TIB) has been suggested
to have formed in response to eastward subduction
(Nyström 1982, Andersson 1991, Weihed et al.
2002), possibly during a period of extensional conditions
(Wilson et al. 1986, Åhäll & Larsson 2000).
The Edefors granitoids are interpreted as products of
plate convergence and a mantle source is suggested
for these rocks based on Sm-Nd isotopic characteristics.
Mafic magmas may have formed by mantle
melting in an extensional setting caused by a 1.8 Ga
collisional event following northward subduction.
These magmas were subsequently contaminated
with continental crust and crystallised as monzonitic
to granitic rocks (Öhlander & Skiöld 1994).
The related plate-tectonic setting may also
be that of the final orogenic collapse, decompression
and/or thermal resetting in the terminal stages of the
orogenic development, following the continent-continent
collisional stage (Lahtinen et al. 2005).
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