SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland
In the northern and north-eastern part of the Perädpohja Schist Belt, northern Finland, an extensive supracrustal rock unit has been identified which is composed of alternating amphibolitic and arkositic components. The amphibolites form layers whose thickness varies from one millimeter to some tens...
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Geological Society of Finland
2005
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ftdoajarticles:oai:doaj.org/article:98d7179f47dc4182b99f4899ed5ff770 2023-05-15T16:13:10+02:00 SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland E. Hanski H. Huhma V. Perttunen 2005-06-01T00:00:00Z https://doi.org/10.17741/bgsf/77.1.001 https://doaj.org/article/98d7179f47dc4182b99f4899ed5ff770 EN eng Geological Society of Finland http://www.geologinenseura.fi/bulletin/Volume77/Hanskietal.pdf https://doaj.org/toc/0367-5211 https://doaj.org/toc/1799-4632 doi:10.17741/bgsf/77.1.001 0367-5211 1799-4632 https://doaj.org/article/98d7179f47dc4182b99f4899ed5ff770 Bulletin of the Geological Society of Finland, Vol 77, Iss 1, Pp 5-29 (2005) metasedimentary rocks arkosite Peräpohja Belt geochemistry absolute age U/Pb Sm/Nd zircon Paleoproterozoic northern Finland Geology QE1-996.5 article 2005 ftdoajarticles https://doi.org/10.17741/bgsf/77.1.001 2022-12-31T12:58:20Z In the northern and north-eastern part of the Perädpohja Schist Belt, northern Finland, an extensive supracrustal rock unit has been identified which is composed of alternating amphibolitic and arkositic components. The amphibolites form layers whose thickness varies from one millimeter to some tens of meters, being most often a few tens of centimeters. They represent mafic tuff beds deposited concurrently with more abundant arkositic rocks. Most of the arkosites have a modal and major and trace element composition similar to that of A2-type granites. For example, they exhibit high LREE/HREE, negative Eu anomalies, and flat HREE and are moderately enriched in Nb, Zr, and Y. The genesis of the arkosites is enigmatic as they show features supporting either a volcaniclastic or an epiclastic origin. In the latter case, they were derived via erosion of a source dominated by A2-type granitic rocks. Previous conventional ID-TIMS and new SIMS U-Pb dating of zircons from two arkosite samples and one mica schist sample, all three picked from the northern part of the schist belt, indicate that these rocks contain a single population of zircons with an age of ca. 1975 Ma suggesting that they are among the youngest supracrustal rocks in the schist belt. In contrast, one mica schist sample from the western part of the belt revealed only the presence of Archean zircons. The samples do not differ markedly in terms of their Nd isotope composition as they all have a moderately negative εNd(1900 Ma). Regardless of the genesis of the arkosites, their isotopic and geochemical data suggest a previously unknown occurrence of extensive A-type felsic magmatism at ca. 1.98 Ga, contemporaneously with some continental flood basalts. However, concrete evidence for this felsic A-type magmatism in the form of ca. 1.98 Ga felsic plutonic rocks is virtually absent in the presently exposed Fennoscandian Shield. Article in Journal/Newspaper Fennoscandian Northern Finland Directory of Open Access Journals: DOAJ Articles Bulletin of the Geological Society of Finland 77 1 5 29 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
metasedimentary rocks arkosite Peräpohja Belt geochemistry absolute age U/Pb Sm/Nd zircon Paleoproterozoic northern Finland Geology QE1-996.5 |
spellingShingle |
metasedimentary rocks arkosite Peräpohja Belt geochemistry absolute age U/Pb Sm/Nd zircon Paleoproterozoic northern Finland Geology QE1-996.5 E. Hanski H. Huhma V. Perttunen SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland |
topic_facet |
metasedimentary rocks arkosite Peräpohja Belt geochemistry absolute age U/Pb Sm/Nd zircon Paleoproterozoic northern Finland Geology QE1-996.5 |
description |
In the northern and north-eastern part of the Perädpohja Schist Belt, northern Finland, an extensive supracrustal rock unit has been identified which is composed of alternating amphibolitic and arkositic components. The amphibolites form layers whose thickness varies from one millimeter to some tens of meters, being most often a few tens of centimeters. They represent mafic tuff beds deposited concurrently with more abundant arkositic rocks. Most of the arkosites have a modal and major and trace element composition similar to that of A2-type granites. For example, they exhibit high LREE/HREE, negative Eu anomalies, and flat HREE and are moderately enriched in Nb, Zr, and Y. The genesis of the arkosites is enigmatic as they show features supporting either a volcaniclastic or an epiclastic origin. In the latter case, they were derived via erosion of a source dominated by A2-type granitic rocks. Previous conventional ID-TIMS and new SIMS U-Pb dating of zircons from two arkosite samples and one mica schist sample, all three picked from the northern part of the schist belt, indicate that these rocks contain a single population of zircons with an age of ca. 1975 Ma suggesting that they are among the youngest supracrustal rocks in the schist belt. In contrast, one mica schist sample from the western part of the belt revealed only the presence of Archean zircons. The samples do not differ markedly in terms of their Nd isotope composition as they all have a moderately negative εNd(1900 Ma). Regardless of the genesis of the arkosites, their isotopic and geochemical data suggest a previously unknown occurrence of extensive A-type felsic magmatism at ca. 1.98 Ga, contemporaneously with some continental flood basalts. However, concrete evidence for this felsic A-type magmatism in the form of ca. 1.98 Ga felsic plutonic rocks is virtually absent in the presently exposed Fennoscandian Shield. |
format |
Article in Journal/Newspaper |
author |
E. Hanski H. Huhma V. Perttunen |
author_facet |
E. Hanski H. Huhma V. Perttunen |
author_sort |
E. Hanski |
title |
SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland |
title_short |
SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland |
title_full |
SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland |
title_fullStr |
SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland |
title_full_unstemmed |
SIMS U-Pb, Sm-Nd isotope and geochemical study of an arkosite-amphibolite suite, Peräpohja Schist Belt: Evidence for ca. 1.98 Ga A-type felsic magmatism in northern Finland |
title_sort |
sims u-pb, sm-nd isotope and geochemical study of an arkosite-amphibolite suite, peräpohja schist belt: evidence for ca. 1.98 ga a-type felsic magmatism in northern finland |
publisher |
Geological Society of Finland |
publishDate |
2005 |
url |
https://doi.org/10.17741/bgsf/77.1.001 https://doaj.org/article/98d7179f47dc4182b99f4899ed5ff770 |
genre |
Fennoscandian Northern Finland |
genre_facet |
Fennoscandian Northern Finland |
op_source |
Bulletin of the Geological Society of Finland, Vol 77, Iss 1, Pp 5-29 (2005) |
op_relation |
http://www.geologinenseura.fi/bulletin/Volume77/Hanskietal.pdf https://doaj.org/toc/0367-5211 https://doaj.org/toc/1799-4632 doi:10.17741/bgsf/77.1.001 0367-5211 1799-4632 https://doaj.org/article/98d7179f47dc4182b99f4899ed5ff770 |
op_doi |
https://doi.org/10.17741/bgsf/77.1.001 |
container_title |
Bulletin of the Geological Society of Finland |
container_volume |
77 |
container_issue |
1 |
container_start_page |
5 |
op_container_end_page |
29 |
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1765998774950297600 |