1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland
The Svecofennian orogeny in southern Finland has traditionally been divided into two broadly defined compressional stages, the 1.89–1.87 Ga “synorogenic” stage and the ca 1.84–1.81 Ga “lateorogenic” stage. The term “intraorogenic” is used to describe a less studied stage that occurred between these...
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Geological Society of Finland
2025-03-01
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| Series: | Bulletin of the Geological Society of Finland |
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| Online Access: | https://www.geologinenseura.fi/sites/geologinenseura.fi/files/bulletin_2025_vol97_1_01_johnson-etal.pdf.pdf |
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| author | Olav Eklund Jussi S. Heinonen |
| author_facet | Olav Eklund Jussi S. Heinonen |
| author_sort | Olav Eklund |
| collection | DOAJ |
| description | The Svecofennian orogeny in southern Finland has traditionally been divided into two broadly defined compressional stages, the 1.89–1.87 Ga “synorogenic” stage and the ca 1.84–1.81 Ga “lateorogenic” stage. The term “intraorogenic” is used to describe a less studied stage that occurred between these two, with some overlap with both. Mafic and intermediate intrusions collectively named as the Kaiplot gabbros are situated on a number of islands and islets in Nagu (Nauvo) in the southwestern archipelago of Finland. The outcrops occur as dykes as well as plutonic bodies and have been emplaced in at least two separate pulses. Net-veining and other structures suggesting incomplete mixing between mafic and felsic magmas are found. The main plutonic body is a hornblende gabbronorite. U-Pb dating (TIMS, zircon) gives it an age of 1865 ± 2 Ma. Geochemically, the most primitive Kaiplot gabbros are tholeiitic and show affinity to back-arc basin basalts, indicating generation in an extensional tectonic environment. Their parental magmas appear to have originated from relatively high-degree partial melting of a shallow spinel-bearing and slightly subduction-modified depleted mantle. During transport and emplacement, both differentiation and assimilation of crustal material have taken place. The Kaiplot gabbros endorse an extensional tectonic episode of the Svecofennian orogeny at around 1865 Ma, possibly as a result of tectonic switching propagating southwestwards. |
| format | Article |
| id | doaj-art-36b9e42a7ea54aabb3f7ca0f9a0ca823 |
| institution | Kabale University |
| issn | 0367-5211 1799-4632 |
| language | English |
| publishDate | 2025-03-01 |
| publisher | Geological Society of Finland |
| record_format | Article |
| series | Bulletin of the Geological Society of Finland |
| spelling | doaj-art-36b9e42a7ea54aabb3f7ca0f9a0ca8232025-08-20T03:27:07ZengGeological Society of FinlandBulletin of the Geological Society of Finland0367-52111799-46322025-03-0197153010.17741/bgsf/97.1.0011865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern FinlandOlav Eklund0 Jussi S. Heinonen1Geology and Mineralogy, Åbo Akademi University, Turku, Finland Geology and Mineralogy, Åbo Akademi University, Turku, Finland, and Department of Geosciences and Geography, University of Helsinki, FinlandThe Svecofennian orogeny in southern Finland has traditionally been divided into two broadly defined compressional stages, the 1.89–1.87 Ga “synorogenic” stage and the ca 1.84–1.81 Ga “lateorogenic” stage. The term “intraorogenic” is used to describe a less studied stage that occurred between these two, with some overlap with both. Mafic and intermediate intrusions collectively named as the Kaiplot gabbros are situated on a number of islands and islets in Nagu (Nauvo) in the southwestern archipelago of Finland. The outcrops occur as dykes as well as plutonic bodies and have been emplaced in at least two separate pulses. Net-veining and other structures suggesting incomplete mixing between mafic and felsic magmas are found. The main plutonic body is a hornblende gabbronorite. U-Pb dating (TIMS, zircon) gives it an age of 1865 ± 2 Ma. Geochemically, the most primitive Kaiplot gabbros are tholeiitic and show affinity to back-arc basin basalts, indicating generation in an extensional tectonic environment. Their parental magmas appear to have originated from relatively high-degree partial melting of a shallow spinel-bearing and slightly subduction-modified depleted mantle. During transport and emplacement, both differentiation and assimilation of crustal material have taken place. The Kaiplot gabbros endorse an extensional tectonic episode of the Svecofennian orogeny at around 1865 Ma, possibly as a result of tectonic switching propagating southwestwards.https://www.geologinenseura.fi/sites/geologinenseura.fi/files/bulletin_2025_vol97_1_01_johnson-etal.pdf.pdfmafic magmatismsvecofennian orogenytholeiiticgeochemistryzircon u-pb agenagunauvosw finlandextensional tectonics |
| spellingShingle | Olav Eklund Jussi S. Heinonen 1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland Bulletin of the Geological Society of Finland mafic magmatism svecofennian orogeny tholeiitic geochemistry zircon u-pb age nagu nauvo sw finland extensional tectonics |
| title | 1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland |
| title_full | 1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland |
| title_fullStr | 1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland |
| title_full_unstemmed | 1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland |
| title_short | 1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland |
| title_sort | 1865 ma tholeiitic magmatism during an extensional episode of the svecofennian orogeny the kaiplot gabbros in nagu nauvo southwestern finland |
| topic | mafic magmatism svecofennian orogeny tholeiitic geochemistry zircon u-pb age nagu nauvo sw finland extensional tectonics |
| url | https://www.geologinenseura.fi/sites/geologinenseura.fi/files/bulletin_2025_vol97_1_01_johnson-etal.pdf.pdf |
| work_keys_str_mv | AT olaveklund 1865matholeiiticmagmatismduringanextensionalepisodeofthesvecofennianorogenythekaiplotgabbrosinnagunauvosouthwesternfinland AT jussisheinonen 1865matholeiiticmagmatismduringanextensionalepisodeofthesvecofennianorogenythekaiplotgabbrosinnagunauvosouthwesternfinland |