About age of the Central Puolanka Group of Kainuu Schist Belt, Finland

[Hannu Poropudas]

About age of the Central Puolanka Group of Kainuu Schist Belt, Finland

Age of the Akanvaara Formation is smaller than 2539 Ma and greater than 2360 Ma.
Age of the Puolankajärvi Formation is smaller than 2539 Ma and greater than 2360 Ma.
Age of the Pärekangas Formation is smaller than 2721 Ma and greater than 2699+-7 Ma.

In order to have no contradiction for these ages of all three parts of the Centarl Puolanka Group then perhaps the Pärekangas Formation could be some kind of ancient overthrust formation ?

Best Regards,

Hannu Poropudas


References:
1. Hannu Huhma, Eero Hanski, Asko Kontinen, Jouni Vuollo, Irmeli Mänttäri and Yann Lahaye, 2018.
Sm–Nd and U–Pb isotope geochemistry of the Palaeoproterozoic mafic magmatism in eastern and northern Finland.
Geological Survey of Finland, Bulletin 405, 150 pages, 128 figures, 1 table and 11 appendixes.
( 7.3 The Kapustakangas intrusive suite (A1373), A1373 Paha Kapustasuo metagabro, 2358+-24Ma, grain A1373-12a, Fig. 92, pp. 96-97. Age of the whole Central Puolanka Group (Pärekangas Fm. + Akanvaara Fm. + Puolankajärvi Fm.) greater than > about 2360 Ma. )

2. Kauko Laajoki,1991.

Stratigraphy of the northern end of the early Proterozoic (Karelian)
Kainuu Schist Belt and associated gneiss complexes, Finland.

Geological Survey of Finland, Bulletin 358, 105 pages, 55 figures, 4 tables, 5 appendices.

( A0760 ( = A760) Kettukallio Amphibolite, Banded calcareous amphibolite interlayer in the Kettukallio Quartsite, 2539 Ma U-Pb/zircon. The zircon may be partly inherited. In any case it proves that sedimentation of the Kettukallio Quartsite is about 2540 Ma. Page 97, Table 4.
Page 96, Fig. 55. Summary of the chronostratigraphy of the area.

Ages of the Akanvaara Fm. and the Puolankajärvi Fm. is smaller than < 2539 Ma and there is contact to Kalpio Complex. Age of the Pärekangas Fm. = ? and there is no contact to Kalpio Complex. )

3. Asko Kontinen, Hannu Huhma and Kauko Laajoki, 1996.
Sm/Nd isotope data on the Central Puolanka Group, Kainuu Schist Belt, Finland; constraints for Provenance and age of deposition, Abstract: The 22nd Nordic Geological Winter Meeting.
In:
Kauko Laajoki and Ansgar Wanke (Editors), 2002.
Stratigraphy and Sedimentology of the Palaeoproterozoic Kainuu, Kuusamo and Peräpohja Belts, Northern Finland. Guidebook of a Nordic-baltic-NW Russian Research Course 8th-15th June, 2002.
ResTerrae, Ser.A, No.22, 102 pages and 19 plates, Oulu University Press, Oulu 2002.

Page 26, Age of the Pärekangas Fm. is between 2699+-7 Ma (A conventional U-Pb age from a felsic dyke in the Pärekangas Formation is 2699+-7 Ma) and 2721 Ma (Zircons from a tuff-like rock of the Pärekangas Formation give SIMS ages of 2721 Ma.)

[Hannu Poropudas]

On Friday, March 23, 2018 at 11:59:26 AM UTC+2, Hannu Poropudas wrote:
> About age of the Central Puolanka Group of Kainuu Schist Belt, Finland
>
> Age of the Akanvaara Formation is smaller than 2539 Ma and greater than 2360 Ma.
> Age of the Puolankajärvi Formation is smaller than 2539 Ma and greater than 2360 Ma.
> Age of the Pärekangas Formation is smaller than 2721 Ma and greater than 2699+-7 Ma.
>
> In order to have no contradiction for these ages of all three parts of the Centarl Puolanka Group then perhaps the Pärekangas Formation could be some kind of ancient overthrust formation ?
>
> Best Regards,
>
> Hannu Poropudas
>
>
> References:
> 1. Hannu Huhma, Eero Hanski, Asko Kontinen, Jouni Vuollo, Irmeli Mänttäri and Yann Lahaye, 2018.
> Sm–Nd and U–Pb isotope geochemistry of the Palaeoproterozoic mafic magmatism in eastern and northern Finland.
> Geological Survey of Finland, Bulletin 405, 150 pages, 128 figures, 1 table and 11 appendixes.
> ( 7.3 The Kapustakangas intrusive suite (A1373), A1373 Paha Kapustasuo metagabro, 2358+-24Ma, grain A1373-12a, Fig. 92, pp. 96-97. Age of the whole Central Puolanka Group (Pärekangas Fm. + Akanvaara Fm. + Puolankajärvi Fm.) greater than > about 2360 Ma. )
>
> 2. Kauko Laajoki,1991.
>
> Stratigraphy of the northern end of the early Proterozoic (Karelian)
> Kainuu Schist Belt and associated gneiss complexes, Finland.
>
> Geological Survey of Finland, Bulletin 358, 105 pages, 55 figures, 4 tables, 5 appendices.
>
> ( A0760 ( = A760) Kettukallio Amphibolite, Banded calcareous amphibolite interlayer in the Kettukallio Quartsite, 2539 Ma U-Pb/zircon. The zircon may be partly inherited. In any case it proves that sedimentation of the Kettukallio Quartsite is about 2540 Ma. Page 97, Table 4.
> Page 96, Fig. 55. Summary of the chronostratigraphy of the area.
>
> Ages of the Akanvaara Fm. and the Puolankajärvi Fm. is smaller than < 2539 Ma and there is contact to Kalpio Complex. Age of the Pärekangas Fm. = ? and there is no contact to Kalpio Complex. )
>
> 3. Asko Kontinen, Hannu Huhma and Kauko Laajoki, 1996.
> Sm/Nd isotope data on the Central Puolanka Group, Kainuu Schist Belt, Finland; constraints for Provenance and age of deposition, Abstract: The 22nd Nordic Geological Winter Meeting.

And

Hannu Huhma, Asko Kontinen and Kauko Laajoki, 2000.
Age of metavolcanic-sedimentary units of the Central Puolanka Group, Kainuu Schist Belt, Finland: Nordiske Geologiske Vintermöte, pp. 87-88.

[Hannu Poropudas]

Sample names and age determinations are found on this reference:

A1292, 2721 Ma +- 12 Ma,

A1251, 2699 Ma +- 7 Ma.

More details is found from the 2012 reference:

The Archean of the Karelia Province in Finland.
Geological Survey of Finland. Special Paper 54. 254 pages,
on page 194 and on page 213.

A1292, Haapalanmäki dacitic tuff, 2700 Ma, map 343208,
YKJ-North, YKJ-East 7149860, 3525280 .

A1251, Petäjäniemi Paltamo, porphyry 2718 Ma, map 343208,
YKJ-North, YKJ-East 7147020, 3524020 .

And more dtail about Laajoki K (1991) sample:
A0760 (=A760), Kettukallio Amphibolite, 2539 Ma, U-Pb/zircon. Kettukallio Amphibolite. Banded calcareous interlayer in the Kettukallio Quartzite.
Small hill 2 km north of Lake Isojärvi.

Best Regards,

Hannu Poropudas

[Hannu Poropudas]

If zircon populations are partly inherited (heterogenous) in these cases
then one possibility could be that we could only conclude that

age of the Pärekangas Formation is smaller than ( < ) about 2700 Ma ?

Hannu

>
> And more dtail about Laajoki K (1991) sample:
> A0760 (=A760), Kettukallio Amphibolite, 2539 Ma, U-Pb/zircon. Kettukallio Amphibolite. Banded calcareous interlayer in the Kettukallio Quartzite.
> Small hill 2 km north of Lake Isojärvi.

A0760 (=A760), Kettukallio Amphibolite, 2539 Ma, U-Pb/zircon. Kettukallio Amphibolite. Banded calcareous interlayer in the Kettukallio Quartzite.
Small hill 2 km north of Lake Isojärvi.

YKJ-North YKJ-East 7185360, 3525230 .

Hannu

[Hannu Poropudas]

FINAL CONCLUSIONS:

About age of the Central Puolanka Group of Kainuu Schist Belt, Finland

Age of the Akanvaara Formation is smaller ( < ) than 2539 Ma and
greater ( > ) than 2360 Ma.

Age of the Puolankajärvi Formation is smaller ( < ) than 2539 Ma and
greater ( > ) than 2360 Ma.

Age of the Pärekangas Formation is smaller ( < ) than about 2700 Ma and
most probably smaller ( < ) than 2539 Ma
(if no detrical zircons are found of age about 2700 Ma and
if no new data from AvF reveal something new relevant geologic data)
and greater ( > ) than 2360 Ma.

So, the age of the Central Puolanka Group (PjF+AvF+PkF)
is smaller ( < ) than 2539 Ma and greater ( > ) than 2360 Ma.

PjF = Puolankajärvi Formation
AvF = Akanvaara Formation
PkF = Pärekangas Formation

Best Regards,

Hannu Poropudas

[Hannu Poropudas]

If detrital zircons are found in the Pärekangas Formationone possibility
could also be:

In order to have no contradiction for these ages of all three parts of the Centarl Puolanka Group then perhaps the Pärekangas Formation could be some kind of ancient overthrust formation ?

This possibility is also accepted as one possibility by Kauko Laajoki
when I asked him this.

Best Regards,

Hannu Poropudas

[Hannu Poropudas]

I found old 1986 paper of Kauko Laajoki (copy below):

“It is quite probable that this Pärekangas Formation (PkF) forms a continuous N-S trending metasedimentary unit at least 1000 m thick running from Askanjärvi in north via the lakes of Vilpusjärvi and Somerjärvi to Osmankanjärvi and Kivesvaara in the south. This area is, however, almost completely covered by glacial deposits. At Pärekangas, the PkF overlies the AvF (Akanvaara Formation) conformably. The change from the AvF to the PkF takes place abruptly. “

“The upper contact of the uppermost formation, the PkF, of the CPG (Central Puolanka Group) is not directly exposed anywhere. However, the Mäntykangas-type conglomerates which start the next Karelian sequence, the East Puolanka Group, at Puolanka have derived their phenoclasts predominantly from the PkF and the AvF (Fig. 14).”

Other important matter::

It seems that Fennoscandian Schield has been at least two times quite
close to the Supercarton Superia, namely first about 2.5 Ga ago and
secondly about 2.1 Ga ago.

If reference 2 (Salminen et al 2014) and reference 3 (Ernst at al 2010)
are right as I suppose now then Peräpohja Belt (Rantamaa Stromatolites)
and Pudasjärvi Complex (Fennoscandia/north Finland) could have been
near Lac Esprit (2070 Ma) and Minto (2000 Ma) of Supercraton Superia
(Fig 8, p. 717) at time about 2.1 Ga ?

Best Regards,

Hannu Poropudas

Kolamäentie 9E,
90900 Kiiminki / Oulu
Finland

References:

1. Laajoki K. 1986.
The Central Puolanka Group – A Precambrian regressive metasedimentary sequence in northern Finland.
Bull. Geol. Soc. Finland 58, Part 1, 179-193. pp. 190-191.
(Text parts is copied below from pages 190-191.)

“It is quite probable that this Pärekangas Formation (PkF) forms a continuous N-S trending metasedimentary unit at least 1000 m thick running from Askanjärvi in north via the lakes of Vilpusjärvi and Somerjärvi to Osmankanjärvi and Kivesvaara in the south. This area is, however, almost completely covered by glacial deposits. At Pärekangas, the PkF overlies the AvF (Akanvaara Formation) conformably. The change from the AvF to the PkF takes place abruptly. “

“The upper contact of the uppermost formation, the PkF, of the CPG (Central Puolanka Group) is not directly exposed anywhere. However, the Mäntykangas-type conglomerates which start the next Karelian sequence, the East Puolanka Group, at Puolanka have derived their phenoclasts predominantly from the PkF and the AvF (Fig. 14).”

2. Salminen J. Halls H.C. Mertanen S. Pesonen L.J. Vuollo J. Söderlund U. 2014.
Paleomagnetic and geochronological studies
on Paleoproterozoic diabase dykes of Karelia, East Finland
– Key for testing the Superia supercraton.
Precambrian Research 244 (2014) 87-99.
(Fig. 9. on page 96 and Fig 10 on page 97 and table 3 on page 94.)

3. Ernst R. E. Bleeker W. 2010.
Large igneous provinces (LIPs), giant dyke swarms, and mantle plumes,
significance for breakup events within Canada and adjacent regions
from 2.5 Ga to present.
Canadian Journal of Earth Sciences 47, 695-739.
(Supercraton Superia, Fig. 8 on page 717.)

[Jean-Paul Turcaud]

Hi,

http://blog.go-here.nl/7917

THE TRUE GEOLOGY

If something can help you, this would be to look at an initial paper on the True Geology.
Discontinued unfortunately due to all those mining criminals around on the hunt for a free lunch.
You will learn, may be, how the present Column of Ages is a fraudulent fiction and how most geologist (in fact Rock surveyors) enjoy waddling & paddling in the mire landscape of fiction & foggy understanding.
Oh, and by the way there never was any Glaciations ever (not questioning glaciers' existence of course) These were the invention of fiction writers such as Charpentier, Agassiz, Buckland, Murchison etc.
Indeed we come from the (very) warm and ineluctably are drifting on the ecliptic towards the cold and of course oblivion.
Cheers
Jean-Paul Turcaud
Exploration geologist
Australia Mining Pioneer

[Hannu Poropudas]

Some later notes of mine about age of the CPG :
(PjF = Puolankajärvi Formation, AvF = Akanvaara Formation, PkF = Pärekangas Formation, Ref. Laajoki K. 1991. mentioned earlier in my postings)

PkF boundary to AvF contains scaplolite bed near boundary to AvF. This scapolite is metamorphic limestone. What is meaning of this scabolite bed ?

About age of the Central Puolanka Group (CPG=PjF+AvF+PkF):

Age of all three formations is greater than 2359 Ma +- 12 Ma, (Pahakapustasuo metagabro grain A1373-12a).
(Ref. Appendix 11, Huhma H. et al. 2018, Geological Survey of Finland, Bulletin 405).
Kapustakangas metagabro (Pahakapustasuo metagabro is part of Kapustakangas metagabro) intrudes into all three formation PjF, AvF and PkF.

Age of PjF+AvF is smaller than (2495 Ma - 2515 Ma), (A760 C, A760 B, Kettukallio amphibolite (analyzed 1980)), A760A Titanite 1784 Ma (age of meamorphism,
no signs of hydrothermal alterations?). (Ref. Appendix 5, Huhma H. et al. 2018, Geological Survey of Finland, Bulletin 405) )

Age of PkF is little unclear, but Hannu Huhma said to me (email) that no magmatism age could be determined from PkF tuffite heterogenous zircons of many different ages,
from which smallest age was about 2700 Ma. This indicates no deposition age exist for PkF at the moment. It is also possible that PkF could be some kind of over thrust formation?

If I define Karelian SUMI ages roughly 2500 Ma - 2400 Ma, then I would like to consider age of whole Central Puolanka Group (CPG) is SUMI age?
I would also like to define Karelian SARIOLA ages roughly 2400 Ma - 2300 Ma ?

Best Regards,

Hannu Poropudas

Kolamäentie 9E

[Hannu Poropudas]

I would like to say that at least the lowest formation called Puolankajärvi Formation
(pjF) in Central Puolanka Group (CPG) is really SUMI age (roughly 2500 Ma - 2400 Ma) ?

(more accurately age of pjF is smaller than 2495 Ma - 2515 Ma and age of pjF is
greater than 2359 Ma +- 12 Ma).

If so then this would mean that correlations concerning this Puolankajärvi Formation
written in below reference 2005 by professor Kauko Laajoki are not known at the moment ?

In my opinion only this correlation of pjF error should be corrected of below
reference , nothing else ?

Reference:
Lehtinen, M. Nurmi, P.A. Rämö, O.T. (editors) 2005.
Precambrian Geology of Finland.
Key to the Evolution of the Fennoscandian Shield.
Elsevier B. V., 736 pages.
(Chapter 7. Karelian Supracrustal Rocks. pp. 279-341. Written by
Laajoki Kauko, 2005.)

Best Regards,

Hannu Poropudas
Kolamäentie 9E
90900 Kiiminki / Oulu

Finland.

"It is Not What You Know that Matters... It's Knowing What You Don't"

[Hannu Poropudas]

I took a quick look on to the bedrock map of Kainuu Schist bedrocks
(in Laajoki K. 1991 reference mentioned above postings of mine)
and

I did not find Kapustakangas intriusions inside Akanvaara Formation
which formation is between Puolankajärvi Formation and Pärekangas Formation
in the Central Puolanka Group?

Kapustakangas intrusions seems to be present in the Puolankajärvi Formation
and in the Pärekangas Formation.
The Pahakapustasuon metagabro which belogs in to the Kapustakangas intrusions are
older than 2359 Ma +- 12 Ma as was mentioned above.

It was mentioned in Laajoki K. 1991 reference that Akanvaara Formation is poorly
investigated, if so this formation and its boundaries below and above should be
reinvestigated more properly ?

Best Regards,
Hannu Poropudas
Kolamäentie 9E,
90900 Kiiminki / Oulu

Finland.

[Hannu Poropudas]

I read following Kontinen A. et al. 2014 article (1.):

References:

1. Kontinen, A. , Huhma, H., Lahaye, Y., O'Brien, H., 2014.
The Problem with the age of the Central Puolanka Group keeps fighting us.
In:
Lauri, L. S., Helimo,E.,Levaniemi, H., Tuusjärvi, M., Lehtinen,R., Hölttä, P. (eds), 2014.
Geologian tutkimuskeskus, Tutkimusraportti 207 - Geological Survey of Finland,
Report of Investigation 207, 2014. pp. 68-71.

2. Sturt, B. A. et al. 1994.
Terra Nova 6, 618-633.

3. Laajoki, K. 1991. Geological Survey of Finland. Bulletin 358, 105 pages, p. 57 and also p. 65,
" Kettukangas Paragneiss is regarded as the western lithodemic derivative of this formation." (lower part of the Puolankajärvi Formation).
(Kettukangas Paragneiss is part of the Kalpio Complex, p. 56-64)


My quick notices about the article (1.):

On page 68: Age period 2.35-2.20 Ga (Laajoki 2005) are Table 7 / p. 291,
Pärekangas Fm. and Akanvaara Fm. are marked at this point on the Table 7.

I remember that age 2.35 Ga comes from regoliths which are not directly dated
(2453 Ma - 2330 Ma was the range from Sturt et al. 1994 reference, 2453 Ma was age of the layered intrusion (Sm-Nd)
and Ahmalahti Volcanics, Kola Penissua, 2330 Ma +- 36 Ma age determined
somewhat unreliable method (Rb-Sr), both ages are from Russian side),

Laajoki K. (Laajoki 2005) used Sturt B. A. et al. 1994 calculated average age 2.35 Ga
about 31 regoliths if I remember right.

Older intrusion, the Mountain Generalskaya age 2505.1 Ma +- 1.6 Ma (U-Pb, Zr bd),
exist also in Kola Penissula (PreCambrian Research, 75, 31-46, year ?).

On end page 68 and start on page 69 is few lines on which I would like to
conclude only that age of the Varislahti basalts (= Varisniemi basalts, named
on GTK base rock map also, GTK net version 12.5.2022)
is less (<) than 2.4 Ga, if I assume that stratigraphy is correct on those text lines.

On start of page 69:
Varislahti basalts (=Varisnimemi basalts) have epsilon_Nd = -2.1 and
Greenstone I (= Kuntijärvi Fm.) has epsilon_Nd = -2.8, so explanations is needed
how these cold be properly correlated (Huhma, H. et al. 2018, mentioned in my earlier postings in this posting chain)?

On page 69: Junttilannimemi Gabro intersects Pitkälika volvanics, but I don't understand that how Pitkälika volcanics can be correlated to Pärekangas Fm.
and concluded that Pärekangas age and (age of CPG) is greater (>) than 2.44 Ga, due
Pitkälika volcanics and Pärekangas Fm. do not intersect on this paper map and also
do not intersect on GTK net map, mentioned above ?

On end page 69: Laajoki's (Laajoki 2005) view of the Kalpio gneisses as
lithodemic derivatives of schists in lower parts of the CPG, this would mean that
the latter rocks should be older than ca. 2.70 Ga.

First I do not find this mentioned in reference (Laajoki 2005), but I find that this mentioned
in reference (Laajoki, K. 1991).
I Understood that Laajoki K. claim that formations of CPG and Kettukallio Paragneiss are
trusted (?) (in evolution) from the East to West when they formed (Laajoki 2005),
but of course situation can be also such way as Kontinen A. et al. 2014 claim in their paper, so this matter should be reinvestigated further and more complete age determinations
is also needed due age period about 2.7 Ga to about 2.5 Ga seems not be properly
age-investigated in Pudasjärvi archean side (West side of the CPG)?

---
One other notice of my earlier postings:

One other notice of my earlier postings in this posting chain is that the Paha Kapustasuo metagabro which belongs in the Repokallio Serpentine Suite (p. 94 in Laajoki, K. 1991) intersects at least the Puolankajärvi Formation as shown in Laajoki K. 1991, appendix
geologic maps. How this intrusion is related to the Kapustakangas intrusion (The Kapustakangas Metagabro Suite, p. 92-93, Laajoki, K. 1991) is little open question that could they be about same age as I originally thought?

Best Regards,

Hannu Poropudas
(amateur geologist)

[Hannu Poropudas]

I found one important reference in which is one age determination
with help of practical explanation how to separate
DETRITAL zircons from sedimentary rocks:

Reference:

A. Fralick Philip, Davis Don W. and Kissin Stephen A, 2002.
The age of the Gunflint Formation, Ontario, Canada:
single zircon U-Pb age age determinations from reworked volcanic ash.
Can. J. Earth Sci. 39: 1085-1091 (2002). Page 1087.

"Detrital zircons, all of size ca. 0.2 mm (in long dimension).
Divide zircons into three groups:
1. Clear, colorless, well-rounded zircons.
2. transparent, brown, euhedral zircons with no evidence of abrasion.
3. dark, cracked, and altered zircons.
Only group 2. is accepted to sediment formation dating purpose.
Group 2. = light (flying) ashes from volcanic eruption."

References related to the age problem of the Central Puolanka Group:

B. Huhma Hannu, Kontinen Asko and Laajoki Kauko, 2000.
Age of the metavolcanic-sedimentary units of the Central Puolanka Group,
Kainuu schist belt, Finland.
24. Nordiske Geologiske Vintermöte,
Trondheim 6.-9. januar 2000. Geonytt 1, 87-88.

(copy below from pages 87-88, samples A1292, A1250, A1251 explained)

"In order to constrain the age of the formation and provenance of the CPG,
zircons from five samples have been analyzed using NORDSIM ion probe.

Four of these samples are from the Kivesvaara area, where
basaltic to dacitic metavolcanic rocks are exposed.

Zircons analyzed from two highly sodic, felsic metatuffite-tuff
samples from the Pärekangas Formation (PkF),
the uppermost unit of the CPG, all yield Archean ages.

The data are, however, slightly heterogeneous presumably
due inherited zircon in felsic magma, and metamorphic effects.

DETRITAL origin for some grains in metatuffite cannot be definitely excluded.

For the more pure tuff sample (A1292), twelve grains out of the
17 analyzed yield an age of 2721+-12 Ma (3 grains being ca. 2.8 Ga in age),
which probably is close to the age of the felsic magmatism.

This interpretation is supported by conventional U-Pb zircon analyzes from
another tuff sample in the same locality (A1250), and by conventional
U-Pb age of 2600+-7Ma from a coarse-grained, similarly highly sodic, felsic
dyke rock (A1251) in CPG below the PkF.

Zircons analyzed from the metasediments of the
Puolankajärvi and Akanvaara Formations from the middle part of the CPG also
are all Archean in age, the bulk of the grains being about 2.73 Ga, many about 2.78 Ga and some 2.8 Ga to > 3.0 Ga (207_Pb/206_Pb ages).

The oldest encountered grain is about 3.5 Ga, being the oldest zircon found in
Finnish recks, so far.

The Sm-Nd data on the LTEE enriched metasediments and metavolcanics of the CPG
give T-DM model ages from 3.23 to 2.83 Ga.

Thus all isotopic data available indicate a totally Archean provenance for the CPG,
supporting the emerging concept of the CPG as a part of the Archean basement
structure instead of the Paleoproterozoic Kainuu Schist Belt.

The corarse-grained and immature (arkosic) nature of many of the
arenites in the CPG may imply nonrecycled derivation from a relative close source terrain.

As no middle Archean component is apparent in the Archean terrains east of CPG, the
SOURCE likely was in the west, possibly in the adjacent, chronostratigraphically still poorly
known Archean Pudasjärvi Complex."

C. Kontinen, A., Huhma, H., Laajoki, K., 1996.
Sm/Nd Isotope Data on the Central Puolanka Group, Kainuu Schist Belt,
Finland, Constraints for Provenance and Age of the Deposiition.
The 22nd Nordic Geol. Winter Meeting,
Turku-Åbo, 8-11, January 1996. Abstracts, p.95.

D. Huhma, H. et al. 2012.
Nd Isotopic Evidence for Archean Crustal Growth in Finland.
Geological Survey of Finland, Special Paper 54, 176-213.
20 figures and 1 appendix. Page 213.

" Central Puolanka Group (p. 213, appendix):
Sample: A1292, Haapalanmäki, dactic tuff, age 2700 Ma, epsilon_Nd=-1.6.
Sample: ATK-14B, Haapalanmäki, andesite, age 2700 Ma, epsilon_Nd=-0.0.
Sample: A1235, Kivesvaara, felsic tuffite, age 2700 Ma, epsilon_Nd=-0.3.
Sample: Petäjäniemi Paltamo, porphyry, age 2718 Ma, epsilon_Nd=+1.3."

[Hannu Poropudas]

I suppose that no this group 2. type zircons were founded in Pärekangas Formation.

U-Pb age of 2699+-7Ma from a coarse-grained, similarly highly sodic, felsic

Sample: A1251, Petäjäniemi Paltamo, porphyry, age 2718 Ma, epsilon_Nd=+1.3."

> Best Regards,
>
> Hannu Poropudas
> (amateur geologist)

I can only conclude in case of age determination of the Pärekangas Formation that

"SOURCE likely was in the west, possibly in the adjacent, chronostratigraphically

still poorly known Archean Pudasjärvi Complex." AND " No depositional age exist
at the moment for the Pärekangas Formation."