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Kara, J., Väisänen, M., Johansson, Å., Lahaye, Y., O’Brien, H., Eklund, O., 2018. 1.90-1.88Ga arc magmatism of central Fennoscandia: geochemistry, U-Pb geochronology, Sm-Nd and Lu-Hf isotope systematics of plutonic-volcanic rocks from southern Finland. Geologica Acta, 16(1), 1-23, I-XIV. DOI: 10.1344/GeologicaActa2018.16.1.1

INTRODUCTION

Major crust-forming processes occurred in connection with the amalgamation of the supercontinent Columbia a.k.a. Nuna during Paleoproterozoic time (e.g. Rogers and Santosh, 2002). One of its components, the Svecofennian Orogen (SO) in the Fennoscandian shield (Fig. 1A), was mainly formed between ca. 1.96 and 1.77Ga through accretionary (Gorbatschev and Bogdanova, 1993; Hermansson et al., 2008; Stephens and Andersson, 2015) or combined accretionary and collisional (Lahtinen, 1994; Lahtinen et al., 2005) processes. The orogen also forms a part of the Great Proterozoic Accretionary Orogens, which in places have experienced the longest duration of subduction in the Earth’s history, up to 900Ma (Condie, 2013). The SO covers large areas in Finland and Sweden, and smaller areas in Norway and Russia. Much of it is covered by Paleozoic sediments in the South and southeast (Fig. 1A).

The oldest recognised magmatism in the SO is related to subduction which formed almost juvenile volcanic arcs in a continental margin setting (1.96–1.88Ga; e.g.Kähkönen, 2005; Stephens et al., 2009 and references therein). The volcanic arcs in the SO are mainly composed of extrusive igneous rocks, but magma chambers or subvolcanic intrusions are also present. Such magma chambers have long been recognised in Sweden (Stephens et al., 2009 and references therein) but only occasionally considered in Finland (Colley and Westra, 1987; Ehlers and Lindroos, 1990; Väisänen and Mänttäri, 2002; Talikka and Mänttäri, 2005). It has been recognised that some parts of the SO have initial ε_Nd values close to zero and depleted mantle model ages older than 2.1Ga, indicating an older contribution to the source region (e.g. Huhma, 1986; Patchett et al., 1987; Andersson, 1997; Lahtinen and Huhma, 1997). Single zircon U-Pb dating has also revealed inherited older zircons in the oldest plutonic rocks (e.g.Ehlers et al., 2004). These findings have evoked models where ca. 2.2–2.0Ga small continental fragments, microcratons or pieces of Svecofennian “proto-crust” are hidden under the present crust (Lahtinen et al., 2005; Andersson et al., 2011). However, no direct observations of these microcratons have been made.

In this study, we present whole rock geochemical, U-Pb, Sm-Nd, and Lu-Hf isotope data from two 1.90–1.88Ga magmatic centres in southern Finland: the Orijärvi and Enklinge areas. They comprise plutonic centres surrounded by extrusive volcanic rocks of corresponding ages and chemical compositions. The focus here is on the plutonic and dyke rocks since they have not been previously studied as extensively as their extrusive counterparts. Our aim is to study the magma source/s and the nature of the oldest magmatic rocks of central Fennoscandia. In addition, we evaluate the existence of the proposed proto-crust below the central Fennoscandian bedrock in the light of new Lu-Hf isotope data.

REGIONAL GEOLOGICAL SETTING

The Svecofennian orogen in Finland and Sweden is composed of several large units defined as terranes or lithotectonic units. The oldest volcanic arc-type igneous rocks are found in northern Sweden (1.96-1.92Ga Knaften arc; Wasström, 1993, 2005) and the youngest in southern Sweden (1.83-1.82Ga Oskarshamn-Jönköping Belt; Mansfeld et al., 2005). In the central part, three main terranes are recognised in Finland: the Savo arc (S), Central Svecofennia (CS) and Southern Svecofennia (SS, Fig. 1A) (Korsman et al., 1997; Kähkönen, 2005).

The Savo arc exposes the oldest Svecofennian igneous rocks in Finland (ca. 1.92Ga; Lahtinen, 1994; Vaasjoki et al., 2003) and it is considered an equivalent to the Knaften arc (KN) in Sweden with roughly similar ages (Wasström, 1993; Eliasson et al., 2001; Guitreau et al., 2014). The ages of the volcanic arc-related igneous rocks in central and southern Svecofennia fall between 1.90 and 1.88Ga (e.g.Kähkönen, 2005). A few slightly older (1.91Ga; Johansson and Stephens, 2017) and younger (1.85Ga; e.g.Stephens and Andersson, 2015) rocks also occur. It is traditionally considered that southern Svecofennia and the Bergslagen area (BS) in South-central Sweden belong to the same unit (e.g.Valbracht et al., 1994; Nironen, 1997; Lahtinen et al., 2005), although the presence of large intervening shear zones such as the Singö shear zone along the coast in East-central Sweden and the South Finland shear zone makes such correlations somewhat problematic (cf. Torvela and Ehlers, 2010; Bogdanova et al., 2015).

Southern Svecofennia

Southern Svecofennia comprises two parallel volcanic-sedimentary belts: the Häme and Uusimaa belts (Fig. 1B; Kähkönen, 2005 and references therein). The zircon ages in volcanic rocks in both belts are ca. 1.90-1.88Ga (e.g. Väisänen and Mänttäri, 2002; Ehlers et al., 2004; Skyttä et al., 2005; Väisänen and Kirkland, 2008; Saalmann et al., 2009). Both belts show arc-type geochemical affinities, and the Häme belt is apparently less mature than the bulk of the Uusimaa belt (Lahtinen, 1996; Kähkönen, 2005).

The relationship between the two volcanic belts is ambiguous (cf. Kähkönen. 2005). Korja et al. (2006) regarded the Häme and Uusimaa belts as separate terranes, whereas Väisänen and Mänttäri (2002) suggested that the belts belonged to the same arc system but were rifted apart. The rift basin was filled with felsic volcanic rocks, tholeiitic mafic/ultramafic lavas with E-MORB affinity (ca. 1.88-1.87Ga), sedimentary carbonates (now marbles) and detrital sediments (now mica gneisses; e.g. Nironen et al., 2016 and references therein).

The Häme belt includes several mafic/ultramafic plutonic rocks, which often show layered structures. The largest of these is the Hyvinkää layered intrusion, which Peltonen (2005) regarded as synplutonic to the volcanic rocks of the area (see also Eerola, 2002). The interpretation is supported by the U-Pb zircon ages of the gabbro (1880±5Ma, Patchett and Kouvo, 1986) and the plagioclase-phyric mafic volcanic rock (1880±3Ma, Suominen, 1988). Such synvolcanic plutonism is described for central Svecofennia as well (e.g. Talikka and Mänttäri, 2005), and it is widespread in the Bergslagen area in Sweden (Lundström et al., 1998; Andersson et al., 2006b; Hermansson et al., 2008; Stephens et al., 2009).

The volcanic rocks in the Uusimaa belt show continental margin and rifting type lithological associations and geochemical affinities (Kähkönen, 2005; Weihed et al., 2005). The belt has indications of an older, ca. 2.1–1.91Ga contribution to the magmatism as indicated by initial ε_Nd values around zero (Huhma, 1986; Patchett and Kouvo, 1986; Lahtinen and Huhma, 1997; this study) as well as detrital zircons of that age in metasediments and inherited zircons in igneous rocks (e.g. Claesson et al., 1993; Lahtinen et al., 2002; Ehlers et al., 2004; Bergman et al., 2008; Lahtinen and Nironen, 2010).

Enklinge and Orijärvi are both well-preserved non-migmatitic mega-enclaves surrounded by higher-grade and more deformed areas. Therefore, Enklinge and Orijärvi make excellent targets to study the earliest events in southern Svecofennia (Ehlers and Lindroos, 1990; Ploegsma and Westra, 1990; Skyttä et al., 2006). The Orijärvi area is situated in the middle of the Uusimaa belt and is a type example of it (e.g. Kähkönen, 2005). The Enklinge area, however, is situated in the archipelago to the West of the continuous Häme and Uusimaa belts, and it remains unclear whether it is part of any of them.

Study areas

Orijärvi area

The bedrock in the Orijärvi area (Fig. 2A) in the middle of the Uusimaa belt mainly consists of apparently bimodal volcanic rocks with sedimentary intercalations (Eskola, 1914; Väisänen and Mänttäri, 2002; Kähkönen, 2005; Skyttä et al., 2005). The volcanic rocks are divided into four formations (fms.): the lowermost Orijärvi Formation (Fm.) is a volcanic arc-type bimodal unit with marble and iron formation intercalations as well as Cu- Zn-Pb mineralizations (Eskola, 1914; Latvalahti, 1979; Väisänen and Mänttäri, 2002). The overlying Kisko Fm. is geochemically more evolved, and volcanic rocks range from basalts to rhyolites. The arc rifting started with the Toija Fm. which once again comprises bimodal volcanic rocks. The rifting continued with the Salittu Fm., which mainly consists of E-MORB type basalts and picrites. Age results of the volcanic rocks fall between 1895±3Ma (Orijärvi Fm.) and 1878±4Ma (for both the Kisko and Toija fms.; Väisänen and Mänttäri, 2002; Väisänen and Kirkland, 2008), with the uppermost Salittu Fm. being undated.

The Orijärvi batholith is a composite pluton, where mafic and felsic rocks apparently alternate. Magma mingling between felsic and mafic components is also common (Fig. 3A; B). Mafic rocks are more common in the core, and felsic rocks dominate at the fringes of the pluton. However, a complex structural evolution (Ploegsma and Westra, 1990; Skyttä et al., 2006) might have disrupted the original order of rock types within the pluton. The mafic plutonic rocks show locally a layered structure (Sarapää et al., 2005).

The U-Pb zircon age of the Orijärvi granodiorite (outer border of the batholith) has been determined to 1891±13Ma (Huhma, 1986) and 1898±9Ma (Väisänen et al., 2002; cf. this study). Within errors, this is the same as the age of the felsic volcanic rock from the lowest stratigraphic level, and the Orijärvi batholith is regarded as a magma chamber that fed the surrounding volcanic rocks (Colley and Westra, 1987; Väisänen and Mänttäri, 2002).

Enklinge area

The well-preserved Enklinge volcanic-plutonic centre in the Åland archipelago in SW Finland consists of subaqueous felsic and mafic volcanic rocks with sedimentary intercalations (Fig. 2B; Sederholm, 1934; Rancken, 1953; Ehlers, 1976). The bedrock was divided into upper and lower strata (Ehlers and Lindroos, 1990).

The lower strata consist of felsic schists, graywackes and the lower rhyolitic series which are capped by thin marble layers. The upper strata are composed of mafic and intermediate volcanics, including pillow lavas and lava flows. The upper series of rhyolites is on top of the stratigraphy.

The lower volcanic rocks are intruded and surrounded by syntectonic granodiorite-tonalite and related dacitic quartz porphyric dykes (Ehlers and Lindroos, 1990). Both granodiorite and dacitic dykes contain mafic enclaves, up to 50% of the volume of the bedrock in the northern side of Enklinge (Fig. 3C; D; Impola, 2004). Most of the dykes are bordered by basalts indicating coeval bimodal magmatism. Chemically, the dykes and the surrounding granodiorite are identical but they both differ slightly from the extrusive rhyolites (Ehlers and Lindroos, 1990).

The upper rhyolite and syntectonic granodiorite have been dated to 1885±6Ma and 1882±15Ma, respectively (Suominen, 1987; Ehlers et al., 2004). Ehlers et al. (2004) also determined ages for three similar gneissic granodiorites a few kilometres North of Enklinge, from Sottunga (30km South from Enklinge) and from Kökar (50km SE from Enklinge), and obtained identical ages of 1884±5Ma for all of them. This supports the coeval nature of the Enklinge rhyolite and surrounding granodiorite, although they are different in geochemistry.

ANALYTICAL METHODS

A total of 75 whole rock samples were studied, of which 34 were from Orijärvi and 41 from Enklinge. The data include plutonic, dyke and volcanic rock samples. Analyses were done by Inductively Coupled Plasma- Optical Emission Spectrometry (ICP-OES) and by Inductively Coupled Plasma-Mass Spectrometry (ICP- MS) at three different laboratories.

Two granodiorite samples, one from each study area, were selected for U-Pb spot analyses on zircon in order to determine their crystallization ages, and to perform Lu-Hf analyses on the same zircon grains. The Orijärvi granodiorite U-Pb dating analyses were performed using a Nu Plasma AttoM single collector ICP-MS, whereas the Enklinge granodiorite zircon U-Pb dating analyses were performed using a Nu Plasma HR multicollector ICP-MS, both at the Geological Survey of Finland in Espoo. With the latter instrument, in-situ zircon Lu-Hf isotope analyses were performed on the same or adjacent domains of the grains on which the U-Pb dating was done.

The Sm-Nd analyses were performed on nine samples, of which four were from Orijärvi and five from Enklinge, by a Finnigan MAT261 multicollector mass spectrometer at the Department of Geosciences, Swedish Museum of Natural History.

The full description of the analytical methods used in this study and the whole rock geochemical data (Table I), U-Pb isotopic data (Table II), Sm-Nd isotopic data (Table III) and Lu-Hf isotopic data (Table IV) are provided in the ELECTRONIC APPENDIX.

RESULTS

Whole rock geochemistry

Major elements

The compositions of the Orijärvi and Enklinge samples range from gabbroic to granitic in the Total Alkali vs. Silica (TAS) diagram (Fig. 4A). The classification of the samples (mafic-felsic) was done merely based on silica content of the rocks using 65wt.% of SiO₂ as a threshold value. The plutonic-dyke-volcanic-cumulate division was defined according to field observations. On the K₂O vs. SiO₂ diagram (Fig. 5) the mafic rocks from Orijärvi are calc-alkaline but those from Enklinge fall both in the calc-alkaline and tholeiitic fields. One high-K and one shoshonitic outlier can also be found within the Enklinge mafic rocks. The majority of the rocks follow a similar chemical evolution in the major elements in both study areas and the only slight difference can be found in the P₂O₅ contents; most of the Orijärvi mafic rocks are enriched in P₂O₅ compared to the Enklinge ones (Fig. 5). The felsic rocks follow similar trends as the mafic rocks in most of the major element diagrams; only Na₂O content shows a drop towards lower values between mafic and felsic rocks, and K₂O content shows a large spread between 0.24 and 7.7wt.%.

Two subgroups can be distinguished as separate from this ‘main trend’ based on major element compositions: Orijärvi (six samples) and Enklinge (five samples). The five acumulations of Enklinge are characterized by ferro- magnesian minerals and resulting high MgO and Mg# values, slightly elevated Fe₂O₃ and correspondingly low Na₂O, Al₂O₃ and P₂O₅ contents (Fig. 5). Orijärvi contains five samples of layered intrusions and one separate gabbro (65-MAV-02). The rocks from the Orijärvi layered intrusion are poor in silica (SiO₂ 39-54wt.%). Four of the samples, taken from the gabbroic and the hornblende-rich parts, are enriched in TiO₂ and Fe₂O₃ but rather depleted in MgO. One of these samples (45-MAV-02; gabbro) shows anomalously high P₂O₅ content. The sample taken from the plagioclase part (TKJ-13-10-4; anorthosite) shows high Al₂O₃ and Na₂O contents but is depleted in MgO and Fe₂O₃. The contents, high Mg# value and very low Na₂O, TiO₂ and P₂O₅ contents compared to the other mafic rocks from Orijärvi (Fig. 5). One rhyolite sample from Orijärvi (23- MJV-06) is hydrothermally altered, which can be seen in high silica (85wt.% SiO₂), very low alkalis (0.8wt.% Na₂O and 0.4wt.% K₂O) and low mobile trace element concentrations (below), so it was excluded from the major element examination but included in the trace element diagrams. The mafic rocks from both study areas are metaluminous except one peraluminious sample from Enklinge. The felsic rocks are metaluminous to peraluminious with Alumina Saturation Index (ASI, molar A/CNK: (Al₂O₃/CaO+Na₂O+K₂O)) between 0.95 and 1.18 (Fig. 5).

Trace elements

The log Zr/Ti vs. log Nb/Y classification diagram (Winchester and Floyd, 1977, modified by Pearce, 1996) was used to study the degree of alteration of the samples (Fig. 4B). All the samples form a rather tight and continuous trend from basalts to rhyolites, as in the TAS diagram (Fig. 4A), which supports their unaltered nature. The altered rhyolite sample from Orijärvi plots in the same group as its plutonic counterparts.

The Orijärvi mafic rocks tend to show higher Ba, Sr and Th concentrations compared to those from Enklinge (Fig. 6). Although the trace element data from the mafic rocks from both localities are a little scattered, the majority exhibit similar trace element characteristics in the multi- element diagram showing elevated (relative enrichment) Rb, Ba, Th, U, K and Pb concentrations and distinct negative anomalies (relative depletion) of Nb, Ta and P (Fig. 7). This trend is shared with mafic dykes and volcanics. All the mafic rocks are enriched in LREEs and depleted in HREEs but the rocks from Orijärvi generally show higher LREE concentrations, whereas the Enklinge mafics exhibit flatter REE spectra with higher HREE (Fig. 7). The samples PENK-25 (gabbro), PENK-46 (gabbro), 6-JPI-00 (gabbro dyke) and 12-JPI-00 (gabbro) from Enklinge show a flat, almost MORB-like REE pattern with a relative HREE enrichment. The gabbro sample 31-MJV-06 from Orijärvi differs from the other mafic rocks by its anomalously low HREE concentration. The majority of the mafic samples have AN Eu/Eu* ratio under 1.3.

The trace element data on all the felsic rocks from both localities show large variation in certain Large Ion Lithophile Elements (LILEs) such as Rb, Ba, Sr, Th and Zr. The Orijärvi felsic rocks exhibit lower Cr concentrations than those from Enklinge (Fig. 6). In the multi-element diagram, the felsic plutonic rocks from both localities show very similar trace element patterns with Rb, Ba, Th, U, K and Pb enrichment and depletion of High Field Strength Elements (HFSE) such as Nb and Ta (Fig. 7). The felsic plutonic rocks from both localities are enriched in LREEs and relatively depleted in HREEs. The rocks show mostly negative Eu anomalies and Eu/ Eu* ratios under 1.15, except one tonalite sample from Enklinge (21-JPI-00) and two granodiorite samples from Orijärvi (37.2-MAV-02 and 50-MAV-02) which exhibit more positive Eu peaks. The two felsic dykes from Enklinge show very similar characteristics as the felsic plutonics. The two felsic volcanic rocks from Enklinge exhibit slightly different trace element compositions compared to the other felsic rocks from Enklinge with higher HFSE and REE concentrations but low Cr and Pb concentration (Figs. 6 and 7). The rhyolite sample from Orijärvi (23-MJV-06) shows a similar composition in HFSEs compared to the other felsic rocks but it is depleted in LILEs due to hydrothermal alteration.

The mafic cumulates from Enklinge also stand out in the trace element data. They show very low LILE values as well as low Th, Sr, Zr and Nb concentrations but very high Cr and Ni concentrations. In the multi-element diagram, the cumulate group has similar pattern as the other mafic rocks but their REE pattern is fairly flat (Fig. 7). The Enklinge cumulates also show small Eu anomalies, with Eu/Eu* ratios varying from 0.8 to 1.52.

The Orijärvi layered intrusion rocks show very low Rb, Ba, Zr and Nb concentrations, relatively low Ni and Cr concentrations but rather high Sr and P concentration, and in part very high Pb, compared to the other mafic rocks from both localities (Figs. 6 and 7). The REE concentrations are generally low but the rocks are relatively enriched in the LREEs, depleted in the HREEs, with Eu showing a positive peak in the REE diagram (Fig. 7). Eu/Eu* ratios are higher than in other samples, showing values between 1.36 and 3.51. The sample 65-MAV-02 from Orijärvi exhibits similar trace element characteristics as the Orijärvi layered intrusion rocks except it shows negative Eu anomaly.

U-Pb zircon analyses

The zircons from the Orijärvi granodiorite (29a-MJV-06) range from euhedral to more rounded, subhedral grains (Fig. 8A; B) and their colour varies from transparent to light brown. The grains are mainly elongated, 50-150µm in length and 20-100µm in width. The inner structure of the grains is mostly very homogeneous and few crystals show any distinct oscillatory zoning. Cracks and metamict rims are common. The BSE-images show a few cores (Fig. 8B) but they were too small to be analysed with a 25µm spot size so that possible xenocrystic cores were not verified. A total of 12 analyses were performed on 12 grains. Nine of them yielded a concordia age of 1892±4Ma (2σ; MSWD=0.42) and 10 analyses showed an almost identical weighted average ²⁰⁷Pb/²⁰⁶Pb age of 1892±5Ma (2σ; MSWD=0.81; Fig. 9A).

The Enklinge granodiorite (3-MJV-06) shows a wide range of zircon shapes but two main types are distinguished based on the degree of metamictization: a group of “euhedral” grains and a group of very heterogeneous grains. The euhedral grains are also quite metamictic and have cracks, inclusions and inherited cores/domains (Fig. 8C; D). They are only slightly elongated, about 100-200µm in length. The euhedral zircons show oscillatory zoning and metamictization have advanced following the growing pattern of the grain. The “heterogeneous” group includes large, rounded, about 100-300µm-long grains with a wide variety of shapes, which are full of inclusions and almost completely metamicted. All the 42 U-Pb analyses were performed on the euhedral group of zircons. Several different age populations were found (Fig. 9B; C) out of which a group with a Concordia age of 1882±6Ma (2σ; MSWD=4.2; n=9/15) and a ²⁰⁷Pb/²⁰⁶Pb age of 1880±4 (2σ; MSWD=0.89; n=15/15) are regarded to represent the age of magma crystallisation (Fig. 9C; D). The older zircons probably represent several different inherited populations. The six oldest analyses show ²⁰⁷Pb/²⁰⁶Pb ages between 2247Ma and 2049Ma. Two younger inherited populations yielded ²⁰⁷Pb/²⁰⁶Pb ages of 1952±16Ma (2σ; MSWD=0.0063; n=3; Fig. 9C) and 1988±13Ma (2σ; MSWD=0.32; n=4; Fig. 9C). The youngest 14 zircons (younger than crystallisation) show a continuous ²⁰⁷Pb/²⁰⁶Pb age trend between 1859 and 1802Ma. Nine analyses yielded a concordia age of 1849±9Ma (95%; MSWD=0.78; n=9/14; Fig. 9E) and a weighted average ²⁰⁷Pb/²⁰⁶Pb age of 1848±6Ma (2σ; MSWD=1.14; n=11/14) was obtained on 11 analyses. An upper intercept age of 1850±6Ma (MSWD=0.6) were obtained using 12 analyses. The 1.85Ga age may indicate metamorphic resetting, although the younger zircons or zircon domains do not stand out as texturally different from the magmatic zircon. The three youngest analyses were omitted from the age calculations due to discordancy and/or slightly younger ²⁰⁷Pb/²⁰⁶Pb ages between 1818 and 1802Ma.

Sm-Nd whole rock analyses

The mafic rocks from Enklinge have initial ε_Nd values (at 1882Ma) from +1.9 to +2.9 whereas the felsic rocks exhibit values of +1.1 and +1.2. The depleted mantle model (T_DM) ages for the Enklinge samples fall between 2.15 and 2.12Ga except for the sample 5-MJV06 (gabbro dyke) which shows a T_DM age of 2.0Ga. The two mafic samples from Orijärvi have initial ε_Nd values (at 1892Ma) of +1.1 and +2.0. The felsic rocks have values of -0.4 and +0.2. The T_DM ages for the Orijärvi samples are 2.35 and 2.16Ga for the mafic rocks and 2.21 and 2.16Ga for the felsic rocks. The Sm-Nd isotopic data are compared to previously published Nd-data from central Fennoscandian rocks in Figure 10.

Lu-Hf zircon analyses

In total, 37 analyses were performed on the Orijärvi granodiorite zircons. They show variation in the initial ¹⁷⁶Hf/¹⁷⁷Hf values between 0.28144 and 0.28165 corresponding to ε_Hf values between -4.7 and +2.6 with an average of -1.1 (at 1892Ma).

A total of 21 Lu-Hf analyses were performed on the Enklinge granodiorite zircons. Eleven analyses were performed on zircons representing the age of crystallization, five on inherited zircons or inherited domains in zircons and five on zircons representing the younger ages. The magmatic zircons yielded initial ¹⁷⁶Hf/¹⁷⁷Hf values between 0.28150 and 0.28171 corresponding to initial ε_Hf values between -3.0 and +4.4 with an average value of 0 (at 1882Ma). The individual ²⁰⁷Pb/²⁰⁶Pb age was used for the inherited and young zircon grains (ages varying from 2247 to 1951Ma and 1859 and 1802Ma, respectively) for the calculation of initial ε_Hf values.

The inherited zircons exhibit initial ¹⁷⁶Hf/¹⁷⁷Hf values between 0.28156 and 0.28164, corresponding to initial ε_Hf values between +3.5 and +7.6. The initial ¹⁷⁶Hf/¹⁷⁷Hf values for the young zircons fall in the range 0.28150 to 0.28166, which translates into initial ε_Hf of -4.1 to +1.6. The Lu-Hf isotopic data are compared to previously published Hf-data from central Fennoscandian rocks in Figure 11.

DISCUSSION

Whole rock geochemistry

The Enklinge and Orijärvi igneous rocks have formed in a subduction-related volcanic arc environment (e.g. Colley and Westra, 1987; Ehlers and Lindroos, 1990; Kähkönen, 2005). The distinct subduction component can be seen in all the samples with pronounced troughs at Nb and Ta, and peaks at the subduction-mobile elements such as Ba, Th, U, Pb and Sr in the multi-element diagrams (Fig. 7). This feature is emphasised by fractionated REE pattern for the mafic rocks, as well as the felsic ones (Fig. 7). On the Th/Yb vs. Nb/Yb diagram all the mafic samples plot above the MORB-OIB array (Pearce and Peate, 1995; Pearce, 2008) and show Nb/Yb ratios ≥1.0, suggesting an Active Continental Margin (ACM) setting rather than oceanic arc type magmatism (Fig. 12A). The same feature can be observed on the Th/Ta vs. Yb diagram (Schandl and Gorton, 2002), which shows ACM affinity for the felsic rocks (Fig. 12B). The wide range of rocks with intermediate and felsic compositions also support a continental setting as these form more easily from pre-existing continental crust (e.g. Tatsumi and Takahashi, 2006). However, part of the intermediate rocks is supposed to result from magma mixing (Fig. 3). The Nb/Zr vs. Nb/Ba diagram (Fig. 12C) indicates a SubContinental Lithospheric Mantle (SCLM) source for the mafic magmas.

The Orijärvi and the Enklinge rocks, especially the mafic ones, display some minor differences. The Enklinge rocks are slightly more enriched in HREEs and Cr, and depleted in LILEs, K₂O and P₂O₅. This feature can be explained in different ways, for example: i) mantle heterogeneity (i.e. depleted or enriched magma sources), ii) variations in the materials being contributed by the subducting slab to the mantle wedge, iii) different degrees of partial melting in the mantle wedge, or iv) assimilation of the surrounding crust during magma ascent. These processes are difficult to distinguish from each other. However, different element ratios can give a hint on the petrogenesis of the mafic rocks. A ratio of highly fluid- mobile to less fluid-mobile or fluid-immobile elements (e.g. Sr/Ce, Ba/Nb, Ba/Th and U/Th; Carr et al., 1990; Kessel et al., 2005; Pearce et al., 2005; Wehrmann et al., 2014) shows only very limited subduction additions and low degree of fluid flux from the subducting slab to the mantle wedge. Based on the ratio of more incompatible to less incompatible elements (e.g. Sm/Lu, La/Yb, La/Sm, Nb/Y; Carr et al., 1990; Yang et al., 2007, Wehrmann et al., 2014), the Enklinge rocks tend to show a higher degree of partial melting (Fig. 13A). Thus, different degrees of partial melting may explain some compositional differences between Orijärvi and Enklinge.

Crustal contamination is estimated through Nb/Th ratio combined with Nb/La ratio (Fig. 13B) which suggests that some of the Orijärvi rocks are more affected by such a process. Part of this is the result of magma mixing between mafic and felsic magmas, something which is also supported by field observations (Fig. 3) and visible in the rather high SiO₂ content of a few contaminated mafic rocks. We suggest that the small differences in the mafic rocks in the study areas are due to higher degree of partial melting in Enklinge and slightly more intense magma mixing between mafic and felsic magma in Orijärvi. However, scattered and partly overlapping data between the study areas hinders further interpretations.

The felsic rocks of both study areas are similar which indicate similar petrogenesis. The ASI mostly below 1.1, Na₂O over 3.2wt.% with a few exceptions, low K₂O/Na₂O ratios and abundant mafic magmatic enclaves suggest that the felsic rocks are I-type (Fig. 5; Table I; e.g. Chappell and White, 1974) with an amphibolitic source in the granite source diagram (Patiño Douce, 1999; Fig. 14). This suggests that the felsic rocks have formed by partial melting of mafic lithosphere and that no large scale sedimentary components have been involved in the magma generation.

The cumulate rocks from Enklinge and Orijärvi share the same ACM signature as the major group of the mafic rocks (Fig. 12A). However, they show very different geochemical features. The likely cause for the primitive signature of the Enklinge cumulates is accumulation of MgO-rich minerals like hornblende and pyroxene (±olivine). This is supported by low Na₂O and Al₂O₃, and moderate CaO contents. The characteristic geochemical signature of the Orijärvi layered intrusion rocks can be explained by mineral accumulation processes in a magma chamber. Different types of cumulates can be found within the layered intrusion (Sarapää et al., 2005) ranging from hornblendites to garnet-bearing gabbro and anorthosite, the latter being absent in Enklinge. In addition, the Orijärvi samples show much higher Eu/Eu* ratios compared to the Enklinge cumulates suggesting overall plagioclase accumulation within the layered intrusion. The Orijärvi sample 45-MAV-02 is extremely rich in P₂O₅ which can be explained by accumulation of apatite, whereas the sample 22-MJV-06 is high in TiO₂ due to titanite enrichment. Johansson et al. (2012) have studied arc cumulates of similar age from the Roslagen area of East- central Sweden, which show some similar features. For example, the Enklinge primitive cumulates are comparable to the olivine and pyroxene cumulates whereas the Orijärvi layered intrusion resembles the plagioclase cumulates of the Roslagen area. Moreover, the Enklinge cumulates might represent a low intersection of a magma chamber (i.e. early fractionates and/or bottom cumulates of a magma chamber) whereas the Orijärvi cumulates suggest later fractionation processes and a higher intersection.

In summary, the co-genetic relation between intrusive and extrusive rocks is supported by their similar whole rock compositions. In addition, the coeval relation between mafic and felsic magmatism is supported by field observations.

Age data

The crystallization age of 1892±4Ma for the Orijärvi granodiorite is supported by the previously obtained TIMS and SIMS ages of 1891±13Ma (Huhma, 1986) and

1898±9Ma (Väisänen et al., 2002), as well as the previous TIMS age for the adjacent Orijärvi rhyolite (1895±3Ma; Väisänen and Mänttäri, 2002). In contrast, several zircon populations were identified in the Enklinge granodiorite. The age 1882±6Ma for the crystallization is the same as the previous TIMS age 1882±15Ma (Suominen, 1987) and the SIMS age 1885±6Ma for the adjacent Enklinge rhyolite (Ehlers et al., 2004). The inherited zircons have several different ages between 2.25 and 1.95Ga. The oldest grains, with ages between 2.25 and 2.05Ga, probably do not belong to same population but are derived from different sources. The younger inherited zircons might represent two different magmatic source rocks with ages of 1988±13Ma and 1952±16Ma.

The origin of the inherited zircons in the Enklinge granodiorite is unclear but the age range is similar to that of the inherited zircon populations discovered from central Fennoscandian meta-sedimentary rocks (Huhma et al., 1991; Claesson et al., 1993; Lahtinen et al., 2002). Ehlers et al., (2004) found similar zircon ages, ca. 2040Ma, for the Kökar granodiorite (Fig. 1B), including the oldest xenocrystic core of 3136Ma. The Sarmatian segment, the southernmost crustal segment of the East European craton, has been proposed to be the provenance for the 2.10-1.95Ga zircon populations (Lahtinen et al., 2002). Recently, Samsonov et al. (2016) reported ca. 2.0Ga ages on juvenile volcanic rocks and granitoids from the southern part of the Central Russian Fold Belt, in the central part of the East European craton, now covered by platform sediments, which could also be a source. Another explanation is the possible presence of juvenile, ca. 2.20-1.93Ga “proto-Svecofennian” crust at depth, predating the early Svecofennian (1.90-1.86Ga) magmatism (e.g. Lahtinen and Huhma, 1997; Andersson et al., 2006b, 2011). This proto-crust is not exposed at the present erosion level but it could have been a source for the granodioritic melts.

The interpretation of the youngest zircon ages is somewhat ambiguous due to the heterogeneous zircon morphologies. The youngest zircons, with ²⁰⁷Pb/²⁰⁶Pb ages between 1859 and 1802Ma, are considered to represent a metamorphic event. The concordia age of 1849±9Ma is similar to the ²⁰⁷Pb/²⁰⁶Pb age of 1848±6Ma and the upper intercept age of 1850±6Ma which suggest a metamorphic phase at ca. 1850Ma in the Enklinge area. The three youngest analyses were omitted from the age calculations but they show ²⁰⁷Pb/²⁰⁶Pb ages around 1810Ma, and may indicate a second metamorphic event. Alternatively, since the ²⁰⁷Pb/²⁰⁶Pb ages for all the metamorphic zircons form a continuous trend between 1859 and 1802Ma they could indicate incomplete resetting of the “U-Pb clock” during a single metamorphic event at around 1800Ma, or even later. A third alternative, which does not exclude the two previous options, would be a continuous Pb loss after 1.86Ga due to late geological event(s) or long- term diffusive radiogenic Pb loss (cf. Whitehouse et al., 1999; Kusiak et al., 2013).

Metamorphic ages around 1.85Ga from southern Svecofennia are scarce as the metamorphic peak is usually dated at between 1.83 and 1.81Ga (Korsman et al., 1999; Väisänen et al., 2002; Mouri et al., 2005; Andersson et al., 2006b; Högdahl et al., 2008). However, Torvela et al. (2008) obtained a SIMS zircon age of 1850±12Ma for the metamorphic rims from a granodioritic gneiss, and a TIMS titanite age of 1842±8Ma for a wide mylonite zone at Kökar in the SW Finnish archipelago (Fig. 1B). This gives a strong evidence for a ca. 1.85Ga metamorphic phase in the study area. In addition, ca. 1.86-1.84Ga, intraorogenic mafic magmatism has been described from southern Finland Pajunen et al., 2008; Väisänen et al., 2012a; Nevalainen et al., 2014), which suggests that high heat flux had already started at ca. 1.85Ga (Skyttä and Mänttäri, 2008; Kurhila et al., 2010; Väisänen et al., 2012a, 2012b). Magmatic activity and a metamorphic phase at 1.87-1.85Ga have also been recognized in Bergslagen, Sweden (e.g. Stephens and Andersson, 2015; Johansson and Stephens, 2017). The nearest described ca. 1.85Ga coeval mafic and felsic magmatism is from Korppoo, 50km East of Enklinge (Väisänen et al., 2012a). The possible late metamorphic age of ca. 1.81-1.80Ga is based on only three analyses from two zircons. However, Torvela et al. (2008) found evidence for a ca. 1.80-1.79Ga metamorphic phase in the same area, and Stephens and Andersson (2015) have described such a late metamorphic pulse in Sweden. These observations could justify a late metamorphic event at ca. 1.81-1.80Ga in the Enklinge area. Based on present and previous studies, we thus suggest that two metamorphic events, at ca. 1.85Ga and ca. 1.80Ga, occurred in the Enklinge region.

The lack of inherited zircons and xenocrystic cores is the most obvious feature in the Orijärvi granodiorite (cf. Väisänen et al., 2002), although 2.12-1.93Ga zircons have been found in the Orijärvi meta-greywacke lying stratigraphically above the Orijärvi granodiorite (Claesson et al., 1993). The BSE-images reveal a few cores or core-like structures in zircons but they were too small to be analysed with a 25µm spot size. In any case, the inherited zircon material in the Orijärvi granodiorite is scarce. The new and the previously published age data support a co-genetic relationship between the volcanic and plutonic rocks in both localities.

Sm-Nd and Lu-Hf data

A rather homogeneous and geographically extensive “mildly depleted” mantle reservoir has been proposed as a source for the juvenile (2.10-) 1.90-1.86Ga Svecofennian crust based on both the whole rock Nd- (e.g. Lahtinen and Huhma, 1997; Andersson et al., 2007; Rutanen and Andersson, 2009; Rutanen et al., 2011) and the single grain zircon Hf-isotope data (e.g. Andersen et al., 2009; Andersson et al., 2011; Rutanen et al., 2011; Johansson et al., 2015). The characteristic mild depletion might be a result of prolonged depletion followed by subduction- related enrichment but the extent of this mantle source, both spatial and temporal, is poorly known.

The initial ε_Nd values between +1.1 to +2.9 suggest that the mafic rocks from both localities are rather juvenile and have been derived from the mildly depleted mantle source (Fig. 9). The sample 36-MJV-06 (basalt) from Orijärvi shows initial ε_Nd value of +1.1, which is slightly lower compared to that of the other mafic rocks. This small discrepancy could be attributed to small scale variations in the mantle source (cf. Rutanen et al., 2011; Dahlin et al., 2014) or magma mixing/crustal contamination. The sample 22-MJV-06 is from the Orijärvi layered intrusion and, although it has a different geochemical composition compared to the other mafic rocks, its Nd isotopic composition proves that it has been derived from a similar magma source. The Orijärvi mafic rocks show slightly older T_DM ages compared to the Enklinge rocks.

Somewhat more enriched (near-chondritic) initial ε_Nd values for the felsic rocks from both localities suggest involvement of crustal material in their magma genesis. This is best explained by the formation of the felsic rocks by partial melting of the juvenile Svecofennian proto- crust whereas the mafic rocks are derived from the mildly depleted upper mantle. It is unlikely that the near-chondritic ε_Nd values for the felsic rocks are due to subducted hydrous sediments because lowering the ε_Nd from depleted values to values around zero would require a huge sediment input via subduction (cf. Hawkesworth et al., 1991), which is not supported by the whole rock geochemical data. In addition, Lahtinen and Huhma (1997) considered only a minor part of the Nd in central Svecofennia to be derived from subducted sediments with the major contribution coming from subducted altered MORB. The small but systematic difference in initial ε_Nd between felsic and mafic rocks does not support the evolution of felsic rocks via differentiation from the mafic magmas.

The Enklinge mafic rocks show slightly higher initial ε_Nd values than the Orijärvi mafic rocks which suggests a slightly more primitive signature of the former. This is supported also by the initial ε_Nd values: around +1 in the felsic rocks from Enklinge and around zero from Orijärvi.

The Hf isotopic data from the two granodiorites are in accordance with the Nd isotopic data. However, the Hf isotopes yield a more detailed view of the magma generation. The average initial ε_Hf values for the magmatic zircons are -1.1 and 0 in the Orijärvi and Enklinge granodiorites, respectively, which suggests that both granodiorites are derived mainly from crustal sources (Fig. 10). The zircons have captured some variation in the initial ε_Hf values; the Orijärvi granodiorite shows a range of 7.3 ε-units (at 1892Ma) and the Enklinge shows a range of 7.4 ε-units (at 1882Ma). The variation exceeds the external precision of our Hf isotope analyses. This suggests a minor mixing in the magma genesis between mildly depleted parental magma (slightly positive ε_Hf values) and a partial melt from crustal sources (slightly negative ε_Hf values), which is considered the major source for the felsic rocks. The mafic parental magmas have probably mostly provided the heat and only small fractions of material to the formation of the felsic rocks.

Andersen et al. (2009) defined the Hf evolution trend for the Svecofennian crustal rocks (ε_Hf(1.90)=+2±3 and ¹⁷⁶Lu/¹⁷⁷Hf≈0.015) and for the mildly depleted mantle source (ε_Hf(1.90)=+3±3 and ¹⁷⁶Lu/¹⁷⁷Hf≈0.033). These trends were slightly modified by Andersson et al. (2011). The inherited zircons from Enklinge define a trend towards a more depleted source with increasing age between 1.95 and 2.25Ga which suggests their juvenile origin and support the presence of Svecofennian juvenile proto-crust. Linear regression of the data suggest an evolutionary trend of ε_Hf(2.25)=+8±3 and ¹⁷⁶Lu/¹⁷⁷Hf≈0.012 similar to that obtained by Andersen et al. (2009) for Svecofennian crust, and by Taylor and McLennan (1995) and Wedepohl (1995) for average continental crust (¹⁷⁶Lu/¹⁷⁷Hf≈0.0113). No clear Archean “contamination” can be identified in the inherited zircons based on the Hf isotope composition. However, it remains uncertain why the proto-crust trend intercepts the magmatic zircons at the upper end of their compositional range. It may suggest that the inherited zircons (and the upper end of the magmatic zircons) represent relatively juvenile lower proto-crust or oceanic crust while a more evolved continental proto-crust would have contributed to the lower end of the magmatic zircon spectrum. The linear trend of the inherited zircons is continued by metamorphic zircons, which have captured a continuum of the Hf-isotope evolution.

Implications for the early Svecofennian crustal growth

During the opening of the proposed pre-Svecofennian sea at ca. 2.2-2.0Ga (cf. Nironen 1997, Lahtinen et al., 2005; Hermansson et al., 2008; Guitreau et al., 2014) the rift-related mafic magmatism (Vuollo and Huhma, 2005) and/or ocean floor generation (Guitreau et al., 2014) resulted in depletion of the subcontinental lithospheric mantle beneath the Svecofennian domain (Andersson et al., 2006a, 2007, 2011). The depletion was followed by a subduction-related enrichment and an early arc (proto- crust) formation at ca. 2.1-1.91Ga, which resulted in characteristic mildly depleted values in the SCLM (e.g. initial ε_Nd values chondritic to mildly positive, LILE and LREE enrichment, HFSE depletion; Lahtinen and Huhma, 1997; Andersson et al., 2006a, 2011; Andersen et al., 2009; Rutanen et al., 2011; Johansson et al., 2012; Johansson and Hålenius, 2013).

The initial ε_Nd values and average initial ε_Hf values from both studied granodiorites match previously published data on Svecofennian rocks, and support the model with an extensive mildly depleted mantle source beneath central Fennoscandia at 1.89-1.88Ga. In addition, the Enklinge inherited zircons U-Pb and Hf isotope data suggest the presence of unexposed Svecofennian juvenile proto-crust. The proto-crust hypothesis is also supported by the whole rock geochemical data, which show clear continental arc affinities for all the samples as well as by the bimodal nature of the magmatism.

CONCLUSIONS

i) The Enklinge and Orijärvi volcanic rocks have formed in a continental volcanic arc environment. The intrusive and extrusive rocks are co-genetic, and the felsic and mafic rocks are coeval but not co-magmatic based on field observations, geochemical, age and isotopic data in both study areas. The differences between the Orijärvi and Enklinge mafic rocks are most likely due to a more extensive partial melting in the Enklinge area or a larger crustal contamination in the Orijärvi area.

ii)The age of the Orijärvi granodiorite was determined to be 1892±4Ma, and the age of the Enklinge granodiorite to be 1882±6Ma. Several inherited zircons were found from the Enklinge granodiorite ranging from 2.25 to 1.95Ga. Especially, the 1.99 and 1.95Ga populations are assumed to represent ages within the proposed Svecofennian proto- crust. A metamorphic phase occurred at ca. 1.85Ga in the Enklinge area, while the last metamorphic activity in the same area probably occurred at ca. 1.80Ga.

iii) The mafic rocks from both localities show mildly depleted mantle signatures with initial εNd values between +1.1 and +2.9, and exhibit T_DM ages between 2.35 and 2.0Ga. The felsic rocks exhibit initial ε_Nd values of -0.4 and +0.2 for Orijärvi, and +1.1 and +1.2 for Enklinge with T_DM ages between 2.2–2.1Ga for both localities, which suggests larger crustal contribution in their petrogenesis.

iv) The Lu-Hf data from the Orijärvi granodiorite (average initial ε_Hf -1.1 at 1892Ma) and the Enklinge granodiorite (average initial ε_Hf 0 at 1882Ma) are in accordance with the Nd data from the same rocks. The variation in the ε_Hf (ca. 7ε units for both samples) is assumed to result from mixing between depleted parental mantle magmas and partial melts from crustal sources.

v) The evolutionary trend for the Enklinge inherited zircons, ε_Hf(2.25)=+8±3 and ¹⁷⁶Lu/¹⁷⁷Hf≈0.012, adds more evidence to the presence of Svecofennian proto-crust. The data suggest that the proto-crust originated from a juvenile mantle source.

Acknowledgments

J. Kara was funded by the Turku University Foundation and the Finnish Cultural Foundation. The Laboratory for Isotope Geology at the Swedish Museum of Natural History provided funding, facilities and guidance for Sm-Nd analyses via SYNTHESYS (project SE TAF 2050), organized by the European Community–Research Infrastructure Action (FP6 programme: Structuring the European Research Area) to M.Väisänen. Maria Fischerström, Kjell Billström and Hans Schöberg helped in numerous ways with analyses. Pietari Skyttä and Karin Högdahl are thanked for their ideas in improving the manuscript and Arto Peltola is thanked for making the zircon mounts. W.L. Griffin and an anonymous reviewer are thanked for their constructive comments. This is a Finnish Geosciences Research Laboratory contribution.

REFERENCES

Albarède, F., 2005. The survival of mantle geochemical heterogeneities. In: van der Hilst, R.D., Bass, J.D., Matas, J., Trampert, J., (eds.). Earth’s Deep Mantle: Structure, Composition, and Evolution. American Geophysical Union, 27-46.

Andersen, T., Griffin, W.L., Jackson, S.E., Knudsen, T.-L., Pearson, N.J., 2004. Mid-Proterozoic magmatic arc evolution at the southwest margin of the Baltic Shield. Lithos, 73, 289- 318.

Andersen, T., Andersson, U.B., Graham, S., Åberg, G., Simonsen, S.L., 2009. Granitic magmatism by melting of juvenile continental crust: new constraints on the source of Palaeoproterozoic granitoids in Fennoscandia from Hf isotopes in zircon. Journal of the Geological Society, 166, 233-247.

Andersson, U.B., 1997. Petrogenesis of Some Proterozoic Granitoid Suites and Associated Basic Rocks in Sweden: geochemistry and isotope geology. Sveriges Geologiska Undersökning, 91, 1-216.

Andersson, U.B., Neymark, L.A., Billström, K., 2001. Petrogenesis of Mesoproterozoic (Subjotnian) rapakivi complexes of central Sweden: implications from U-Pb zircon ages, Nd, Sr and Pb isotopes. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 92, 201-228.

Andersson, U.B., Claeson, D.T., Högdahl, K., Sjöström, H., 2004. Geological features of the Småland-Värmland Belt along the Svecofennian margin. Part II: the Nygården, Karlskoga, and Filipstad areas. In: Högdahl, K., Andersson, U.B., Eklund, O., (eds). The Transscandinavian Igneous Belt (TIB) in Sweden: A Review of Its Character. Geological Survey of Finland, Special Paper, 37, 39-47.

Andersson, U.B., Eklund, O., Fröjdö, S., Konopelko, D., 2006a. 1.8Ga magmatism in the Fennoscandian Shield; lateral variations in subcontinental mantle enrichment. Lithos, 86, 110-136.

Andersson, U.B., Högdahl, K., Sjöström, H., Bergman, S., 2006b. Multistage growth and reworking of the Palaeoproterozoic crust in the Bergslagen area, southern Sweden; evidence from U-Pb geochronology. Geological Magazine, 143, 679-697.

Andersson, U.B., Rutanen, H., Johansson, Å., Mansfeld, J., Rimša, A., 2007. Characterization of the Paleoproterozoic mantle beneath the Fennoscandian Shield: Geochemistry and isotope geology (Nd, Sr) of ~1.8Ga mafic plutonic rocks from the Transscandinavian Igneous Belt in Southeast Sweden. International Geology Review, 49, 587-625.

Andersson, U.B., Begg, G.C., Griffin, W.L., Högdahl, K., 2011. Ancient and juvenile components in the continental crust and mantle: Hf isotopes in zircon from Svecofennian magmatic rocks and rapakivi granites in Sweden. Lithosphere, 3, 409- 419.

Appelquist, K., Brander, L., Johansson, Å., Andersson, U.B., Cornell, D., 2011. Character and origin of variably deformed granitoids in central southern Sweden: Implications from geochemistry and Nd isotopes. Geological Journal, 46, 597- 618.

Belousova, E.A., Griffin, W.L., O’Reilly, S.Y., 2006. Zircon crystal morphology, trace element signatures and Hf isotope composition as a tool for petrogenetic modelling: examples from Eastern Australian granitoids. Journal of Petrology, 47, 329-353.

Bergman, S., Högdahl, K., Nironen, M., Ogenhall, E., Sjöström, H., Lundqvist, L., Lahtinen R., 2008. Timing of Palaeoproterozoic intra-orogenic sedimentation in the central Fennoscandian Shield; evidence from detrital zircon in metasandstone. Precambrian Research, 161, 231-249.

Bogdanova, S., Gorbatschev, R., Skridlaite, G., Soesoo, A., Taran, L., Kurlovich, D., 2015. Trans-Baltic Palaeoproterozoic correlations towards the reconstruction of supercontinent Columbia/Nuna. Precambrian Research, 259, 5-33.

Bouvier, A., Vervoort, J.D., Patchett, P.J., 2008. The Lu-Hf and Sm-Nd isotopic composition of CHUR: constraints from unequilibrated chondrites and implications for the bulk composition of terrestrial planets. Earth and Planetary Science Letters, 273, 48-57.

Boynton, W.V., 1984. Cosmochemistry of the rare earth elements: meteorite studies. In: Henderson, R., (ed.). Rare Earth Element Geochemistry-Developments in Geochemistry 2. Elsevier Science, 63-114.

Carr, M.J., Feigenson, M.D., Bennett, E.A., 1990. Incompatible element and isotopic evidence for tectonic control of source mixing and melt extraction along the Central American arc. Contributions to Mineralogy and Petrology, 105, 369-380.

Chappell, B., White, A., 1974. Two contrasting granite types. Pacific Geology, 8, 173-174.

Chu, N.C., Taylor, R.N., Chavagnac, V., Nesbitt, R.W., Boella, R.M., Milton, J.A., German, C.R., Germain, B., Burton, K., 2002. Hf isotope ratio analysis using multi-collector inductively coupled plasma mass spectrometry: an evaluation of isobaric interference corrections. Journal of Analytical Atomic Spectrometry, 17, 1567-1574.

Claeson, D.T., Andersson, U.B., 2000. The 1.85Ga Nygård pluton, central southern Sweden: An example of early Transscandinavian Igneous Belt (TIB) noritic magmatism. Abstract, The 24^th Nordic Geological Winter Meeting in Trondheim, Norway, 6-9.1.2000. Geonytt 1, p.50.

Claesson, S., Huhma, H., Kinny, P.D., Williams, I.S., 1993. Svecofennian detrital zircon ages implications for the Precambrian evolution of the Baltic Shield. Precambrian Research, 64, 109-130.

Colley, H., Westra, L., 1987. The volcano-tectonic setting and mineralization of the early Proterozoic Kemiö- Orijärvi-Lohja belt, SW Finland. Geological Society, London, Special Publication, 33, 95-107.

Condie, K.C., 2013. Preservation and recycling of crust during accretionary and collisional phases of Proterozoic orogens: A bumpy road from Nuna to Rodinia. Geosciences, 3, 240-261.

Dahlin, P., Johansson, Å., Andersson, U.B., 2014. Source character, mixing, fractionation and alkali metasomatism in Palaeoproterozoic greenstone dykes, Dannemora area, NE Bergslagen region, Sweden. Geological Magazine, 151, 573-590.

DePaolo, D.J., 1981. Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Proterozoic. Nature, 291, 193-196.

Eerola, T.T., 2002. Mafic-silicic magma interaction in the layered 1.87Ga Soukkio Complex in Mäntsälä, southern Finland. Bulletin of the Geological Society of Finland, 74, 159-183.

Ehlers, C., 1976. Homogenous deformation in Precambrian supracrustal rocks of Kumlinge area, southwest Finland. Precambrian Research, 3, 481-504.

Ehlers, C., Lindroos, A., 1990. Early Proterozoic Svecofennian volcanism and associated plutonism in Enklinge, SW Finland. Precambrian Research, 47, 307- 318.

Ehlers, C., Skiöld, T., Vaasjoki, M., 2004. Timing of Svecofennian crustal growth and collisional tectonics in Åland, SW Finland. Bulletin of the Geological Society of Finland, 76, 63-91.

Eklund, O., Korsman, K., Scheinin, B., 2010. Jakob Johannes Sederholm. Lithos, 116, 203-208.

Eliasson, T., Greiling, R., Sträng, T., Triumf, C., 2001. Bedrock map 23H Stensele NV, scale 1:50,000. Geological Survey of Sweden, Uppsala, Ai126.

Eskola, P., 1914. On the petrology of the Orijärvi region in southwestern Finland. Bulletin de la Commission Géologique de Finlande, 40, 277pp.

Gerdes, A., Zeh, A., 2006. Combined U-Pb and Hf isotope LA- (MC-) ICPMS analyses of detrital zircons: Comparison with SHRIMP and new constraints for the provenance and age of an Armorican metasediment in Central Germany. Earth and Planetary Science Letters, 249, 47-61.

Gorbatschev, R., Bogdanova, S., 1993. Frontiers in the Baltic shield. Precambrian Research, 64, 3-21.

Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., Van Achterbergh, E., O’Reilly, S.Y., Shee, S.R., 2000. The Hf isotope composition of cratonic mantle: LAM- MC-ICPMS analysis of zircon megacrysts in kimberlites. Geochimica et Cosmochimica Acta, 64, 133-147.

Guitreau, M., Blichert-Toft, J., Billström, K., 2014. Hafnium isotope evidence for early-Proterozoic volcanic arc reworking in the Skellefte district (northern Sweden) and implications for the Svecofennian orogen. Precambrian Research, 252, 39- 52.

Hawkesworth, C.J., Hergt, J.M., Ellam, R.M., McDermott, F., 1991. Element fluxes associated with subduction related magmatism. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 335, 393-405.

Heinonen, A.P., Andersen, T., Rämö, O.T., 2010. Re-evaluation of rapakivi petrogenesis: Source constraints from the Hf isotope composition of zircon in the rapakivi granites and associated mafic rocks of southern Finland. Journal of Petrology, 51, 1687-1709.

Heim, M., Skiöld, T., Wolff, F.C., 1996. Geology, geochemistry and age of the ‘Tricolor’ granite and some other Proterozoic (TIB) granitoids at Trysil, southeast Norway. Norsk Geologisk Tidsskrift, 76, 45-54.

Hermansson, T., Stephens, M.B., Corfu, F., Page, L.M., Andersson, J., 2008. Migratory tectonic switching, western Svecofennian orogen, central Sweden: Constraints from U/ Pb zircon and titanite geochronology. Precambrian Research, 161, 250-278.

Hooper, P.R., Hawkesworth, C.J., 1993. Isotopic and geochemical constraints on the origin and evolution of the Columbia River Basalt. Journal of Petrology, 34, 1203-1246.

Huhma, H., 1986. Sm-Nd, U-Pb and Pb-Pb isotopic evidence for the origin of the Early Proterozoic Svecokarelian crust in Finland. Geological Survey of Finland, Bulletin 337, 48pp.

Huhma, H., 1987. Provenance of Early Proterozoic and Archaean metasediments in Finland: a Sm-Nd isotopic study. Precambrian Research, 35, 127-143.

Huhma, H., Claesson, S., Kinny, P.D., Williams, I.S., 1991. The growth of Early Proterozoic crust: new evidence from Svecofennian detrital zircons. Terra Nova, 3, 175-178.

Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho, T., Hanski, E., Hokkanen, T., Hölttä, P., Juopperi, H., Konnunaho, J., Layahe, Y., Luukkonen. E., Pietikäinen. K., Pulkkinen, A., Sorjonen-Ward, P., Vaasjoki, M., Whitehouse, M., 2012. The age of the Archaean greenstone belts in Finland. Geological Survey of Finland, Special Paper, 54, 74-175.

Högdahl, K., Sjöström, H., Andersson, U.B., Ahl, M., 2008. Continental margin magmatism and migmatisation in the west-central Fennoscandian Shield. Lithos, 102, 435-459.

Impola, J., 2004. Samanaikainen hapan–emäksinen magmatismi Enklingen tonaliitti-intruusiossa Ahvenanmaalla. Master Thesis, Department of Geology, University of Turku, 63pp. [In Finnish]

Jackson, S.E., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004. The application of laser ablation-inductively coupled plasma- mass spectrometry to in-situ U-Pb zircon geochronology. Chemical Geology, 211, 47-69.

Jacobsen, S.B., Wasserburg, G.J., 1984. Sm-Nd isotopic evolution of chondrites and achondrites, II. Earth and Planetary Science Letters, 67, 137-150.

Janousek, V., Farrow, C.M., Erban, V., 2006. Interpretation of whole- rock geochemical data in igneous geochemistry: introducing Geochemical Data Toolkit (GCDkit). Journal of Petrology, 47, 1255-1259.

Johansson, Å., Hålenius, U., 2013: Palaeoproterozoic mafic intrusions along the Avesta-Östhammar belt, east-central Sweden: mineralogy, geochemistry and magmatic evolution. International Geology Review, 55, 131-157.

Johansson, Å., Stephens, M.B., 2017. Timing of magmatism and migmatization in the 2.0-1.8Ga accretionary Svecokarelian orogen, south-central Sweden. International Journal of Earth Sciences, 106, 783-810.

Johansson, Å., Bogdanova, S., Čečys, A., 2006. A revised geochronology for the Blekinge Province, southern Sweden. GFF, 128, 287-302.

Johansson, Å., Andersson, U.B., Hålenius, U., 2012. Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area, east-central Sweden. Geological Journal, 47, 557-593.

Johansson, Å., Andersen, T., Simonsen, S.L., 2015. Hafnium isotope characteristics of late Palaeoproterozoic magmatic rocks from Blekinge, southeast Sweden: possible correlation of small-scale Hf and Nd isotope variations in zircon and whole rocks. GFF, 137, 74-82.

Kallioperä - Bedrock of Finland 1:200 000 [Electronic resource, first published 17.8.2016]. Geological Survey of Finland, Espoo, Finland. Version 1.0 [Referred 20.9.2016]

Kessel, R., Schmidt, M.W., Ulmer, P., Pettke, T., 2005. Trace element signature of subduction-zone fluids, melts and supercritical liquids at 120–180km depth. Nature, 437, 724-727.

Koistinen, T., Stephens, M.B., Bogatchev, V., Nordgulen, Ø., Wennerström, M., Korhonen, J.(compilation), 2001. Geological map of the Fennoscandian Shield. Scale 1:2,000,000. Geological Survey of Norway, Trondheim, Geological Survey of Sweden, Uppsala, Ministry of Natural Resources of Russia, Moscow, Geological Survey of Finland, Espoo.

Korja, A., Lahtinen, R., Nironen, M., 2006. The Svecofennian orogen: a collage of microcontinents and island arcs. Geological Society of London, Memoirs, 32, 561-578.

Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M., Ekdahl, E., Honkamo, M., Idman, H., Pekkala, Y., (eds.), 1997. Bedrock map of Finland. Scale 1:1,000,000. Geological Survey of Finland, Espoo.

Korsman, K., Korja, T., Pajunen, M., Virransalo, P. GGT/SVEKA Working group, 1999. The GGT/SVEKA transect: structure and evolution of the continental crust in the Paleoproterozoic Svecofennian orogen in Finland. International Geology Review, 41, 287-333.

Kumpulainen, R.A., Mansfeld, J., Sundblad, K., Neymark, L., Bergman, T., 1996. Stratigraphy, age, and Sm-Nd isotope systematics of the country rocks to Zn-Pb sulfide deposits, Ammeberg District, Sweden. Economic Geology, 91, 1009- 1021.

Kurhila, M., Vaasjoki, M., Mänttäri, I., Rämö, T., Nironen, M., 2005. U-Pb ages and Nd isotope characteristics of the lateorogenic, migmatizing microcline granites in southwestern Finland. Bulletin of the Geological Society of Finland, 77, 105-128.

Kurhila, M., Andersen, T., Rämö, O.T., 2010. Diverse sources of crustal granitic magma: Lu-Hf isotope data on zircon in three Paleoproterozoic leucogranites of southern Finland. Lithos, 115, 263-271.

Kusiak, M.A., Whitehouse, M.J., Wilde, S.A., Nemchin, A.A., Clark, C., 2013. Mobilization of radiogenic Pb in zircon revealed by ion imaging: Implications for early Earth geochronology. Geology, 41, 291-294.

Kähkönen, Y., 2005. Svecofennian supracrustal rocks. In: Lehtinen, M., Nurmi, P.A., Rämö, O.T., (eds.). Precambrian Geology of Finland– Key to the Evolution of the Fennoscandian Shield. Elsevier, Amsterdam, Developments in Precambrian Geology, 14, 343-405.

Lahtinen, R., 1994. Crustal evolution of the Svecofennian and Karelian domains during 2.1–1.79Ga, with special emphasis on the geochemistry and origin of 1.93–1.91Ga gneissic tonalites and associated supracrustal rocks in the Rautalampi area, Central Finland. Geological Survey of Finland, Bulletin 378, 128pp.

Lahtinen, R., 1996. Geochemistry of Palaeoproterozoic supracrustal and plutonic rocks in the Tampere–Hämeenlinna area, southern Finland. Geological Survey of Finland, Bulletin 389, 113pp.

Lahtinen, R., Huhma, H., 1997. Isotopic and geochemical constraints on the evolution of the 1.93-1.79Ga Svecofennian crust and mantle in Finland. Precambrian Research, 82, 13-34.

Lahtinen, R., Nironen, M., 2010. Paleoproterozoic lateritic paleosol– ultra-mature/mature quartzite–meta-arkose successions in southern Fennoscandia–intra-orogenic stage during the Svecofennian orogeny. Precambrian Research, 183, 770-790.

Lahtinen, R., Huhma, H., Kousa, J., 2002. Contrasting source components of the Paleoproterozoic Svecofennian metasediments: detrital zircon U-Pb, Sm-Nd and geochemical data. Precambrian Research, 116, 81-109.

Lahtinen, R., Korja, A., Nironen, M., 2005. Paleoproterozoic tectonic evolution. In: Lehtinen, M., Nurmi, P.A., Rämö, O.T., (eds.). Precambrian Geology of Finland-Key to the Evolution of the Fennoscandian Shield. Elsevier, Amsterdam, Developments in Precambrian Geology, 14, 481-532.

Latvalahti, U., 1979. Cu-Zn-Pb ores in the Aijala-Orijärvi area, Southwest Finland. Economic Geology, 74, 1035-1068.

Lauri, L.S., Andersen, T., Hölttä, P., Huhma, H., Graham, S., 2011. Evolution of the Archaean Karelian Province in the Fennoscandian Shield in the light of U-Pb zircon ages and Sm-Nd and Lu-Hf isotope systematics. Journal of the Geological Society, 168, 201-218.

Ludwig, K.R., 2003. User’s manual for Isoplot/Ex, Version 3.00. A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication No.4, 75pp.

Lundström, I., Allen, R.L., Persson, P.-O., Ripa, M., 1998. Stratigraphies and depositional ages of Svecofennian, Palaeoproterozoic metavolcanic rocks in E. Svealand and Bergslagen, South central Sweden. GFF, 120, 315-320.

Makkonen, H.V., Huhma, H., 2007. Sm-Nd data for mafic-ultramafic intrusions in the Svecofennian (1.88Ga) Kotalahti Nickel Belt, Finland–implications for crustal contamination at the Archaean/ Proterozoic boundary. Bulletin of the Geological Society of Finland, 79, 175-201.

Mansfeld, J., Beunk, F.F., Barling, J., 2005. 1.83-1.82Ga formation of a juvenile volcanic arc–implications from U-Pb and Sm- Nd analyses of the Oskarshamn-Jönköping Belt, southeastern Sweden. GFF, 127, 149-157.

Middlemost, E.A.K., 1985. Magmas and Magmatic Rocks. London, Longman, 266pp.

Morel, M.L.A., Nebel O., Nebel-Jacobsen Y.J., Miller J.S., Vroon P.Z., 2008. Hafnium isotope characterization of the GJ-1 zircon reference material by solution and laser-ablation MC-ICPMS. Chemical Geology, 255, 231-235.

Mouri, H., Väisänen, M., Huhma, H., Korsman, K., 2005. Sm-Nd garnet and U-Pb monazite dating of high-grade metamorphism and crustal melting in the West Uusimaa area, southern Finland. GFF, 127, 123-128.

Müller, W., Shelley, M., Miller, P., Broude, S., 2009. Initial performance metrics of a new custom-designed ArF excimer LA-ICPMS system coupled to a two-volume laser-ablation cell. Journal of Analytical Atomic Spectrometry, 24, 209-214.

Nevalainen, J., Väisänen, M., Lahaye, Y., Heilimo, E., Fröjdö, S., 2014. Svecofennian intra-orogenic gabbroic magmatism: a case study from Turku, southwestern Finland. Bulletin of the Geological Society of Finland, 86, 93-112.

Nironen, M., 1997. The Svecofennian Orogen: a tectonic model. Precambrian Research, 86, 21-44.

Nironen, M., Mänttäri, I., Väisänen, M., 2016. The Salittu Formation in southwestern Finland, part I: Structure, age and stratigraphy. Bulletin of the Geological Society of Finland, 88, 85-10.

Nyström, J.O., 1999. Origin and tectonic setting of the Dala volcanites. Sveriges Geologiska Undersökning, project 03- 889/96, Final report, 41pp.

Pajunen, M., Airo, M.L., Elminen, T., Mänttäri, I., Niemelä, R., Vaarma, M., Wennerström, M., 2008. Tectonic evolution of the Svecofennian crust in southern Finland. Geological Survey of Finland, Special Paper, 47, 15-160.

Patchett, J., Kouvo, O., 1986. Origin of continental crust of 1.9-1.7Ga age: Nd isotopes and U-Pb zircon ages in the Svecokarelian terrain of South Finland. Contributions to Mineralogy and Petrology, 92, 1-12.

Patchett, P.J., Kouvo, O., Hedge, C.E., Tatsumoto, M., 1981. Evolution of continental crust and mantle heterogeneity: evidence from Hf isotopes. Contributions to Mineralogy and Petrology, 78, 279-297.

Patchett, P.J., Todt, W., Gorbatschev, R., 1987. Origin of continental crust of 1.9-1.7Ga age: Nd isotopes in the Svecofennian orogenic terrains of Sweden. Precambrian Research, 35, 145- 160.

Patiño Douce, A.E., 1999. What do experiments tell us about the relative contributions of crust and mantle to the origin of granitic magmas? Geological Society, London, Special Publications, 168, 55-75.

Pearce, J.A., 1996. A user’s guide to basalt discrimination diagrams. In: Wyman, D.A., (ed.). Trace Element Geochemistry of Volcanic Rocks: Applications for Massive Sulphide Exploration. Geological Association of Canada, Short Course Notes, 12, 79-113.

Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos, 100, 14-48.

Pearce, J.A., Peate, D.W., 1995. Tectonic implications of the composition of volcanic arc magmas. Annual Review of Earth and Planetary Sciences, 23, 251-286.

Pearce, J.A., Stern, R.J., Bloomer, S.H., Fryer, P., 2005. Geochemical mapping of the Mariana arc-basin system: Implications for the nature and distribution of subduction components. Geochemistry, Geophysics, Geosystems, 6, 27pp. Peccerillo, A., Taylor, S.R., 1976. Geochemistry of Eocene calc- alkaline volcanic rocks from the Kastamonu area, northern Turkey. Contributions to Mineralogy and Petrology, 58, 63-81.

Peltonen, P., 2005. Svecofennian mafic-ultramafic intrusions. In: Lehtinen, M., Nurmi, P.A., Rämö, O.T., (eds.). Precambrian Geology of Finland–Key to the Evolution of the Fennoscandian Shield. Elsevier, Amsterdam, Developments in Precambrian Geology, 14, 407-441.

Pin, C., Zalduegui, J.S., 1997. Sequential separation of light rare-earth elements, thorium and uranium by miniaturized extraction chromatography: application to isotopic analyses of silicate rocks. Analytica Chimica Acta, 339, 79-89.

Ploegsma, M., Westra, L., 1990. The Early Proterozoic Orijärvi triangle (southwest Finland): a key area on the tectonic evolution of the Svecofennides. Precambrian Research, 47, 51-69.

Rancken, R., 1953. Uber eine Archäishce Superkrustale Formation im Schärenhof von Kumlinge, Ålandsgebiet, SW-Finnland. Åbo Akademi Meddelande, Geologi Och Mineralogi Institut, 35, 1-38.

Rogers, J.J., Santosh, M., 2002. Configuration of Columbia, a Mesoproterozoic supercontinent. Gondwana Research, 5, 5-22.

Rosa, D.R.N., Finch, A.A., Andersen, T., Inverno, C.M.C., 2009. U-Pb geochronology and Hf isotope ratios of magmatic zircons from the Iberian pyrite belt. Mineralogy and Petrology, 95, 47-69.

Rutanen, H., Andersson, U.B., 2009. Mafic plutonic rocks in a continental-arc setting: Geochemistry of 1.87–1.78Ga rocks from south-central Sweden and models of their palaeotectonic setting. Geological Journal, 44, 241-279.

Rutanen, H., Andersson, U.B., Väisänen, M., Johansson, Å., Fröjdö, S., Lahaye, Y., Eklund, O., 2011. 1.8Ga magmatism in southern Finland: strongly enriched mantle and juvenile crustal sources in a post-collisional setting. International Geology Review, 53, 1622-1683.

Rämö, O.T., Vaasjoki, M., Mänttäri, I., Elliott, B.A., Nironen, M., 2001. Petrogenesis of the post-kinematic magmatism of the Central Finland Granitoid Complex I; radiogenic isotope constraints and implications for crustal evolution. Journal of Petrology, 42, 1971- 1993.

Saalmann, K., Mänttäri, I., Ruffet, G., Whitehouse, M.J., 2009.Age and tectonic framework of structurally controlled Palaeoproterozoic gold mineralization in the Häme belt of southern Finland. Precambrian Research, 174, 53-77.

Samsonov, A.V., Spiridonov, V.A., Larionova, Y.O., Larionov, A.N., 2016. The Central Russian fold belt: Paleoproterozoic boundary of Fennoscandia and Volgo-Sarmatia, the East European Craton. The 32^nd Nordic Geological Winter Meeting in Helsinki, 2016. Bulletin of the geological Society of Finland, Special Volume, Abstracts, p. 162.

Sarapää, O., Ahtola, T., Lohva, J., Hagelberg, K., Karimerto, P., 2005. Tutkimustyöselostus Kiskon kunnassa valtausalueella Iso-Kisko (kaivosrekisterinumero 7495/1) tehdyistä ilmeniittitutkimuksista vuosina 2001-2003. Geologian Tutkimuskeskus, AGrkistoraportti, M 06/2014/2005/1/10, 17pp. [In Finnish]

Schandl, E.S., Gorton, M.P., 2002. Application of high field strength elements to discriminate tectonic settings in VMS environments. Economic Geology, 97, 629-642.

Scherer, E.E., Münker, C., Mezger, K., 2001. Calibration of the lutetium hafnium clock. Science, 293, 683-687.

Scherer, E.E., Münker, C., Mezger, K., 2007. The Lu-Hf systematics of meteorites: Consistent or not. Goldschmidt Conference Abstracts 2007. Geochimica et Cosmochimica Acta, 71:A888

Sederholm, J.J., 1934. On migmatites and associated Pre-Cambrian rocks of southwestern Finland, Part III. The Åland Islands. Bulletin de la Commission Géologique de Finlande, 107, 68pp.

Skyttä, P., Mänttäri, I., 2008. Structural setting of late Svecofennian granites and pegmatites in Uusimaa Belt, SW Finland: Age constraints and implications for crustal evolution. Precambrian Research, 164, 86-109.

Skyttä, P., Käpyaho, A., Mänttäri, I., 2005. Supracrustal rocks in the Kuovila area, southern Finland: structural evolution, geochemical characteristics and the age of volcanism. Bulletin of the Geological Society of Finland, 77, 129-150.

Skyttä, P., Väisänen, M., Mänttäri, I., 2006. Preservation of Palaeoproterozoic early Svecofennian structures in the Orijärvi area, SW Finland–Evidence for polyphase strain partitioning. Precambrian Research, 150, 153-172.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters, 26, 207-221.

Stephens, M.B., Andersson, J., 2015. Migmatization related to mafic underplating and intra-or back-arc spreading above a subduction boundary in a 2.0–1.8Ga accretionary orogen, Sweden. Precambrian Research, 264, 235-257.

Stephens, M.B., Ripa, M., Lundström, I., Persson, L., Bergman, T., Ahl, M., Wahlgren, C.H., Persson, P.O., Wickström, L., 2009. Synthesis of the bedrock geology in the Bergslagen region, Fennoscandian Shield, south-central Sweden. Sveriges Geologiska Undersökning (SGU), 58, 260pp.

Suominen, V., 1987. Lounais-Suomen mafiset juonikivet. In: Aro, K., Laitakari I., (eds.). Suomen Diabaasit ja muut mafiset juonikivilajit. Geological Survey of Finland, Report of Investigation, 76, 151-172.

Suominen, V., 1988. Radiometric ages on zircons from a cogenetic gabbro and plagioclase porphyrite suite in Hyvinkää, southern Finland. Bulletin of the Geological Society of Finland, 60, 135- 140.

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J., (eds.). Magmatism in the Ocean Basins. Geological Society, London, Special Publications, 42, 313-345.

Söderlund, U., Patchett, P.J., Vervoort, J., Isachsen, C.E., 2004. The 176Lu decay constant determined by Lu-Hf and U-Pb isotope systematics of Precambrian mafic intrusions. Earth and Planetary Science Letters, 219, 311-324.

Söderlund, U., Isachsen, C.E., Bylund, G., Heaman, L.M., Patchett, P.J., Vervoort, J.D., Andersson, U.B., 2005. U-Pb baddeleyite ages and Hf, Nd isotope chemistry constraining repeated mafic magmatism in the Fennoscandian Shield from 1.6 to 0.9Ga. Contributions to Mineralogy and Petrology, 150, 174-194.

Söderlund, U., Elming, S.Å., Ernst, R.E., Schissel, D., 2006. The central Scandinavian dolerite Group-Protracted hotspot activity or back-arc magmatism? Constraints from U-Pb baddeleyite geochronology and Hf isotopic data. Precambrian Research, 150, 136-152.

Talikka, M., Mänttäri, I., 2005. Pukala intrusion, its age and connection to hydrothermal alteration in Orivesi, southwestern Finland. Bulletin of the Geological Society of Finland, 77, 165- 180.

Tatsumi, Y., Takahashi, T., 2006. Operation of subduction factory and production of andesite. Journal of Mineralogical and Petrological Sciences, 101, 145-153.

Taylor, S.R., McLennan, S.M., 1995. The geochemical evolution of the continental crust. Reviews of Geophysics, 33, 241-265.

Torvela, T., Ehlers, C., 2010. From ductile to brittle deformation: structural development and strain distribution along a crustal- scale shear zone in SW Finland. International Journal of Earth Sciences, 99, 1133-1152.

Torvela, T., Mänttäri, I., Hermansson, T., 2008. Timing of deformation phases within the South Finland shear zone, SW Finland. Precambrian Research, 160, 277-298.

Vaasjoki, M., Huhma, H., 1999. Lead and neodymium isotopic results from metabasalts of the Haveri Formation, southern Finland: Evidence for Palaeoproterozoic enriched mantle. Bulletin of the Geological Society of Finland, 71, 143-153.

Vaasjoki, M., Huhma, H., Lahtinen, R., Vestin, J., 2003. Sources of Svecofennian granitoids in the light of ion probe U-Pb measurements on their zircons. Precambrian Research, 121, 251-262.

Valbracht, P.J., Oen, I.S., Beunk, F.F., 1994. Sm-Nd isotope systematics of 1.9-1.8Ga granites from western Bergslagen, Sweden: inferences on a 2.1-2.0Ga crustal precursor. Chemical Geology, 112, 21-37.

Van Achterbergh, E., Ryan C., Jackson, S., Griffin W., 2001. Data reduction software for LA-ICP-MS, In: Sylverster, P., (ed.). Laser-Ablation ICPMS in the Earth Sciences–Principles and applications. Mineralogical Association of Canada short course series, 29, St John, Newfoundland, 239-243.

Vervoort, J.D., Patchett, P.J., 1996. Behavior of hafnium and neodymium isotopes in the crust: constraints from Precambrian crustally derived granites. Geochimica et Cosmochimica Acta, 60, 3717-3733.

Vervoort, J.D., Patchett, P.J., Soderlund, U., Baker, M., 2004. Isotopic composition of Yb and the determination of Lu concentrations and Lu/Hf ratios by isotope dilution using MC- ICPMS. Geochemistry Geophysics Geosystems, 5, 15pp.

Vuollo, J., Huhma, H., 2005. Paleoproterozoic mafic dikes in NE Finland. In: Lehtinen, M., Nurmi, P.A., Rämö, O.T. (eds.). Precambrian Geology of Finland–Key to the Evolution of the Fennoscandian Shield. Developments in Precambrian Geology, 14, 195-236.

Väisänen, M., Mänttäri, I., 2002. 1.90-1.88Ga arc and back-arc basin in the Orijärvi area, SW Finland. Bulletin of the Geological Society of Finland, 74, 185-214.

Väisänen, M., Kirkland, C.L., 2008. U-Th-Pb geochronology of igneous rocks in the Toija and Salittu Formations, Orijärvi area, southwestern Finland: Constraints on the age of volcanism and metamorphism. Bulletin of the Geological Society of Finland, 80, 73-87.

Väisänen, M., Mänttäri, I., Hölttä, P., 2002. Svecofennian magmatic and metamorphic evolution in southwestern Finland as revealed by U-Pb zircon SIMS geochronology. Precambrian Research, 116, 111-127.

Väisänen, M., Eklund, O., Lahaye, Y., O’Brien, H., Fröjdö, S., Högdahl, K., Lammi, M., 2012a. Intra-orogenic Svecofennian magmatism in SW Finland constrained by LA-MC-ICP-MS zircon dating and geochemistry. GFF, 134, 99-114.

Väisänen, M., Johansson, Å., Andersson, U.B., Eklund, O., Hölttä, P., 2012b. Palaeoproterozoic adakite- and TTG-like magmatism in the Svecofennian orogen, SW Finland. Geologica Acta, 10, 351-371.

Wasström, A., 1993. The Knaften granitoids of Västerbotten county, northern Sweden. In: Lundqvist, T., (ed.). Radiometric dating results. Sveriges geologiska undersökning. Serie C, 823, 60-64.

Wasström, A., 2005. Petrology of a 1.95Ga granite-granodiorite- tonalite-trondhjemite complex and associated extrusive rocks in the Knaften area, northern Sweden. GFF, 127, 67-82.

Wedepohl, K.H., 1995. The composition of the continental crust. Geochimica et Cosmochimica Acta, 59, 1217-1232.

Weihed, P., Arndt, N., Billström, K., Duchesne, J.-C., Eilu, P., Martinsson, O., Papunen, H., Lahtinen, R., 2005. Precambrian geodynamics and ore formation: the Fennoscandian Shield. Ore Geology Reviews, 27, 273-322.

Wehrmann, H., Hoernle, K., Garbe-Schönberg, D., Jacques, G., Mahlke, J., Schumann, K., 2014. Insights from trace element geochemistry as to the roles of subduction zone geometry and subduction input on the chemistry of arc magmas. International Journal of Earth Sciences, 103, 1929-1944.

Whitehouse, M.J., Kamber, B.S., Moorbath, S., 1999. Age significance of U-Th-Pb zircon data from early Archaean rocks of west Greenland–a reassessment based on combined ion-microprobe and imaging studies. Chemical Geology, 160, 201-224.

Wikström, A., Andersson, U.B., 2004. Geological features of the Småland-Värmland Belt along the Svecofennian margin, part I: from the Loftahammar to the Tiveden-Askersund areas. In: Högdahl, K., Andersson, U.B., Eklund, O., (eds.). The Transscandinavian Igneous Belt (TIB) in Sweden: A Review of Its Character. Geological Survey of Finland, Special Paper, 37, 22-39.

Wilson, M., Hamilton, P.J., Fallick, A.E., Aftalion, M., Michard, A., 1985. Granites and early Proterozoic crustal evolution in Sweden: evidence from Sm-Nd, U-Pb and O isotope systematics. Earth and Planetary Science Letters, 72, 376- 388.

Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, 20, 325-343.

Yang, J.H., Sun, J.F., Chen, F., Wilde, S.A., Wu, F.Y., 2007. Sources and petrogenesis of Late Triassic dolerite dikes in the Liaodong Peninsula: Implications for post-collisional lithosphere thinning of the eastern North China Craton. Journal of Petrology, 48, 1973-1997.

Notas de autor

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