P. Skyttä, M. Määttä, Simo Piippo, Jaakko Kara, A. Käpyaho, E. Heilimo, H. O’Brien, Palsatech Oy
The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of tonalites within the magmatic core of the complex occurred at 2711±8 Ma, somewhat earlier than previously considered. A new pulse of magmatism occurred at 2675±10 Ma as demonstrated by hornblende-tonalites cutting the 2.71 Ga rocks. The results further indicate that the first deformation event responsible for development of penetrative foliations occurred after the first magmatic event at 2.71 Ga and prior to the subsequent tectonothermal event at 2.68 Ga. These findings are in concert with the known major periods of magmatism (2.8–2.7 Ga) and deformation (2.7 Ga) within better-known Archean domains in northern Fennoscandia, and hence support their correlation with KGC. Three complementary age determinations on the Haparanda-suite granites and tonalites were conducted: the results indicate crystallization ages of 1.90–1.89 Ga, overlapping with the known age range of the suite and supporting its predominance over the 1.8 Ga Lina suite granites in the TornioHaparanda area.
芬诺斯坎迪亚北部的太古宙地壳保留了零碎的地质记录，使得太古宙区域之间的直接关联具有挑战性。本研究从横跨芬兰和瑞典边界的太古宙Kukkola片麻岩杂岩（KGC）中提出了两个新的锆石U-Pb年龄测定。结果表明，杂岩岩浆核内英云闪长岩的结晶发生在2711±8Ma，比以前认为的要早一些。一个新的岩浆作用脉冲发生在2675±10Ma，角闪石英云闪长岩切割2.71 Ga岩石证明了这一点。结果进一步表明，导致穿透叶理发育的第一次变形事件发生在2.71 Ga的第一次岩浆事件之后，在2.68 Ga的随后构造热事件之前。这些发现与芬诺斯坎迪亚北部已知的太古宙域内已知的主要岩浆作用期（2.8–2.7 Ga）和变形期（2.7 Ga。对Haparanda套花岗岩和英云闪长岩进行了三次补充年龄测定：结果表明结晶年龄为1.90–1.89 Ga，与已知的该套年龄范围重叠，并支持其在Tornio-Hparanda地区优于1.8 Ga Lina套花岗岩。
{"title":"Constraints over the age of magmatism and subsequent deformation for the Neoarchean Kukkola Gneiss Complex, northern Fennoscandia","authors":"P. Skyttä, M. Määttä, Simo Piippo, Jaakko Kara, A. Käpyaho, E. Heilimo, H. O’Brien, Palsatech Oy","doi":"10.17741/bgsf/92.1.002","DOIUrl":"https://doi.org/10.17741/bgsf/92.1.002","url":null,"abstract":"The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of tonalites within the magmatic core of the complex occurred at 2711±8 Ma, somewhat earlier than previously considered. A new pulse of magmatism occurred at 2675±10 Ma as demonstrated by hornblende-tonalites cutting the 2.71 Ga rocks. The results further indicate that the first deformation event responsible for development of penetrative foliations occurred after the first magmatic event at 2.71 Ga and prior to the subsequent tectonothermal event at 2.68 Ga. These findings are in concert with the known major periods of magmatism (2.8–2.7 Ga) and deformation (2.7 Ga) within better-known Archean domains in northern Fennoscandia, and hence support their correlation with KGC. Three complementary age determinations on the Haparanda-suite granites and tonalites were conducted: the results indicate crystallization ages of 1.90–1.89 Ga, overlapping with the known age range of the suite and supporting its predominance over the 1.8 Ga Lina suite granites in the TornioHaparanda area.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"92 1","pages":"19-38"},"PeriodicalIF":0.7,"publicationDate":"2020-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47679860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Kärenlampi, A. Kontinen, E. Hanski, H. Huhma, Y. Lahaye, J. Krause, T. Heinig
The Otanmäki area in central Finland hosts two occurrences of Nb-Zr-REE mineralization, Katajakangas and Kontioaho, within a suite of ca. 2.04–2.06 Ga (A1-type) gneissic granites, syenite and monzonite-monzodiorite. They exhibit trace element characteristics and whole-rock εNd(2050 Ma) values (from +2.6 to -1.3) consistent with derivation by differentiation of mantle-derived mafic magmas with variable interaction with crustal material. The mineralization is localized in 0.1to 1.4-m-thick dikes (Katajakangas) and a 30to 50-m-thick sheet-like body (Kontioaho), containing allanite-(Ce), zircon, titanite, and Nb-REE-Th-U oxides. Their wall rocks are composed of ca. 2.06 Ga peraluminous monzogranite, which is genetically unrelated to the mineralized rock units, as evidenced by whole-rock chemical and Sm-Nd isotope data and zircon U-Pb geochronology. Instead, the mineralization is linked to the nearby peralkaline to metaluminous alkali feldspar granite magmatism dated at ca. 2.04–2.05 Ga. The development of REE-HFSE enrichment in the mineralized rock units required extensive crystallization of a peralkaline granite magma, producing residual metaluminous, highsilica melts enriched in REE-HFSE, Ca, and Fe relative to Na, K, and Al. The REE-HFSE and Ca enrichment was further promoted by volatile complexing with dissolved F-, CO3 2and SO4 2-. These highly evolved melts were parental to the mineralized dikes and the sheet-like intrusive body, which were emplaced into the monzogranite capping the intrusions of peralkaline granite.
{"title":"Age and origin of the Nb-Zr-REE mineralization in the Paleoproterozoic A1-type granitoids at Otanmäki, central Finland","authors":"K. Kärenlampi, A. Kontinen, E. Hanski, H. Huhma, Y. Lahaye, J. Krause, T. Heinig","doi":"10.17741/bgsf/92.1.003","DOIUrl":"https://doi.org/10.17741/bgsf/92.1.003","url":null,"abstract":"The Otanmäki area in central Finland hosts two occurrences of Nb-Zr-REE mineralization, Katajakangas and Kontioaho, within a suite of ca. 2.04–2.06 Ga (A1-type) gneissic granites, syenite and monzonite-monzodiorite. They exhibit trace element characteristics and whole-rock εNd(2050 Ma) values (from +2.6 to -1.3) consistent with derivation by differentiation of mantle-derived mafic magmas with variable interaction with crustal material. The mineralization is localized in 0.1to 1.4-m-thick dikes (Katajakangas) and a 30to 50-m-thick sheet-like body (Kontioaho), containing allanite-(Ce), zircon, titanite, and Nb-REE-Th-U oxides. Their wall rocks are composed of ca. 2.06 Ga peraluminous monzogranite, which is genetically unrelated to the mineralized rock units, as evidenced by whole-rock chemical and Sm-Nd isotope data and zircon U-Pb geochronology. Instead, the mineralization is linked to the nearby peralkaline to metaluminous alkali feldspar granite magmatism dated at ca. 2.04–2.05 Ga. The development of REE-HFSE enrichment in the mineralized rock units required extensive crystallization of a peralkaline granite magma, producing residual metaluminous, highsilica melts enriched in REE-HFSE, Ca, and Fe relative to Na, K, and Al. The REE-HFSE and Ca enrichment was further promoted by volatile complexing with dissolved F-, CO3 2and SO4 2-. These highly evolved melts were parental to the mineralized dikes and the sheet-like intrusive body, which were emplaced into the monzogranite capping the intrusions of peralkaline granite.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"92 1","pages":"39-71"},"PeriodicalIF":0.7,"publicationDate":"2020-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47088802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Johanna Tepsell, T. Rämö, A. Heinonen, Y. Lahaye, Pieti Haapala, T. Halkoaho, J. Heinonen, Henri Höytiä, J. Konnunaho, V. Järvinen
Archean terranes are generally poorly exposed and structurally complicated, making models of geological evolution difficult to establish. Because of pervasive metamorphism, strong deformation, and poorly exposed bedrock, the stratigraphy, geochronology, and geological evolution of the northeastern part of the Archean Western Karelia Subprovince, Finnish Lapland, is still deficient. Three new U-Pb age determinations were made using the LA-ICP-MS method on zircon in search of more profound understanding of the geochronology of the area. Data from the Pultoselkä granite yield an age of 2795±5 Ma, providing a minimum age of 2.8 Ga for the Tulppio suite. The age is coeval with widespread 2.74–2.70 Ga granitoids of the Karelia Province, likely representing the same magmatic event. The data from the Kontioselkä pegmatite define a maximum age for the pegmatite and a minimum age for mafic volcanic rocks in Kontioselkä at 1781±27 Ma. The age coincides with major deformation and metamorphism in the Karelia Province around 1.76 Ga. Zircon from the Jänesselkä mafic-ultramafic complex yields a minimum age of 2425±17 Ma, complying rather well with the 2.5–2.4 Ga mafic layered intrusions of the northern Fennoscandian Shield. Our new data show that the Archean of the northeastern part of the Western Karelia Subprovince was affected by Proterozoic thermal events more extensively than thus far perceived.
{"title":"Some new insights into the geochronology of the Western Karelia Subprovince, Finnish Lapland","authors":"Johanna Tepsell, T. Rämö, A. Heinonen, Y. Lahaye, Pieti Haapala, T. Halkoaho, J. Heinonen, Henri Höytiä, J. Konnunaho, V. Järvinen","doi":"10.17741/bgsf/92.1.001","DOIUrl":"https://doi.org/10.17741/bgsf/92.1.001","url":null,"abstract":"Archean terranes are generally poorly exposed and structurally complicated, making models of geological evolution difficult to establish. Because of pervasive metamorphism, strong deformation, and poorly exposed bedrock, the stratigraphy, geochronology, and geological evolution of the northeastern part of the Archean Western Karelia Subprovince, Finnish Lapland, is still deficient. Three new U-Pb age determinations were made using the LA-ICP-MS method on zircon in search of more profound understanding of the geochronology of the area. Data from the Pultoselkä granite yield an age of 2795±5 Ma, providing a minimum age of 2.8 Ga for the Tulppio suite. The age is coeval with widespread 2.74–2.70 Ga granitoids of the Karelia Province, likely representing the same magmatic event. The data from the Kontioselkä pegmatite define a maximum age for the pegmatite and a minimum age for mafic volcanic rocks in Kontioselkä at 1781±27 Ma. The age coincides with major deformation and metamorphism in the Karelia Province around 1.76 Ga. Zircon from the Jänesselkä mafic-ultramafic complex yields a minimum age of 2425±17 Ma, complying rather well with the 2.5–2.4 Ga mafic layered intrusions of the northern Fennoscandian Shield. Our new data show that the Archean of the northeastern part of the Western Karelia Subprovince was affected by Proterozoic thermal events more extensively than thus far perceived.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"92 1","pages":"5-17"},"PeriodicalIF":0.7,"publicationDate":"2020-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48150474","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Mäkitie, H. O’Brien, O. Selonen, M. Kurhila, Turku Finland Mineralogy
{"title":"The 1.79 Ga Särkilahti leucogranite – a horizontal magma layer below granulite-grade migmatites in SE Finland","authors":"H. Mäkitie, H. O’Brien, O. Selonen, M. Kurhila, Turku Finland Mineralogy","doi":"10.17741/bgsf/91.2.003","DOIUrl":"https://doi.org/10.17741/bgsf/91.2.003","url":null,"abstract":"","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2019-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45865340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Hanski, H. Huhma, Y. Lahaye, J. Lunkka, E. Nilsson, T. Mäki, H. O’Brien, K. Strand, Mountain View Usa Atle Arctica
{"title":"Zn-Pb-Cu sulfide-bearing glacial sandstone erratics near Raahe on the western coast of Finland: Indicators of Paleozoic base metal mineralization at the bottom of the Bothnian Bay","authors":"E. Hanski, H. Huhma, Y. Lahaye, J. Lunkka, E. Nilsson, T. Mäki, H. O’Brien, K. Strand, Mountain View Usa Atle Arctica","doi":"10.17741/bgsf/91.2.001","DOIUrl":"https://doi.org/10.17741/bgsf/91.2.001","url":null,"abstract":"","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"91 1","pages":"143-178"},"PeriodicalIF":0.7,"publicationDate":"2019-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46519425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Ojala, M. Saarnisto, H. Jungner, I. Snowball, R. Muscheler
We present here radiocarbon dating results from two boreal lakes in Finland, which are permanently (meromictic) or seasonally stratified and contain continuous sequences of annually laminated sedim ...
{"title":"Biases in radiocarbon dating of organic fractions in sediments from meromictic and seasonally hypoxic lakes","authors":"A. Ojala, M. Saarnisto, H. Jungner, I. Snowball, R. Muscheler","doi":"10.17741/bgsf/91.2.004","DOIUrl":"https://doi.org/10.17741/bgsf/91.2.004","url":null,"abstract":"We present here radiocarbon dating results from two boreal lakes in Finland, which are permanently (meromictic) or seasonally stratified and contain continuous sequences of annually laminated sedim ...","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"91 1","pages":"221-235"},"PeriodicalIF":0.7,"publicationDate":"2019-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42056360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Glaciofluvial ice-contact deltas were mapped and altitudes of the highest shorelines defined in the eastern arc of the Salpausselkä zone, southern Finland, using Light Detection and Ranging (LiDAR)-based digital elevation models and GIS tools. Mapping of deltas and the highest shorelines in the Salpausselkä zone were undertaken in order to calculate and define the glacio-isostatic uplift palaeo-isobases, uplift gradients and equidistant diagrams (distance diagrams) for the Salpausselkä zone. The results indicate that the glacio-isostatic uplift palaeo-isobases were orientated NE-SW (50°–230°) and the uplift gradients for both the First and the Second Salpausselkä in the eastern arc, are virtually the same, namely 0.6 mkm-1. This suggests that both Salpausselkä ridge complexes, which were originally laid down in front of the Finnish Lake District Ice Lobe (FLDIL) in relatively shallow water, were deposited within a short time period during the Late Weichselian Younger Dryas Stadial. The results also suggest that the Baltic Ice Lake water level regressed 7.5 metres from Baltic Ice Lake level B I to level B III as the ice retreated in its eastern arc from the First to the Second Salpausselkä.
{"title":"Baltic Ice Lake levels and a LiDAR/DEM-based estimate of the glacio-isostatic uplift gradient of the Salpausselkä zone, SE Finland","authors":"J. Lunkka, T. Nikarmaa, N. Putkinen","doi":"10.17741/BGSF/91.1.005","DOIUrl":"https://doi.org/10.17741/BGSF/91.1.005","url":null,"abstract":"Glaciofluvial ice-contact deltas were mapped and altitudes of the highest shorelines defined in the eastern arc of the Salpausselkä zone, southern Finland, using Light Detection and Ranging (LiDAR)-based digital elevation models and GIS tools. Mapping of deltas and the highest shorelines in the Salpausselkä zone were undertaken in order to calculate and define the glacio-isostatic uplift palaeo-isobases, uplift gradients and equidistant diagrams (distance diagrams) for the Salpausselkä zone. The results indicate that the glacio-isostatic uplift palaeo-isobases were orientated NE-SW (50°–230°) and the uplift gradients for both the First and the Second Salpausselkä in the eastern arc, are virtually the same, namely 0.6 mkm-1. This suggests that both Salpausselkä ridge complexes, which were originally laid down in front of the Finnish Lake District Ice Lobe (FLDIL) in relatively shallow water, were deposited within a short time period during the Late Weichselian Younger Dryas Stadial. The results also suggest that the Baltic Ice Lake water level regressed 7.5 metres from Baltic Ice Lake level B I to level B III as the ice retreated in its eastern arc from the First to the Second Salpausselkä.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2019-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45474246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Huhta, P. Tuisku, T. Balić-Žunić, A. Kärki, Kivitieto Oy
The Finnish soapstone industry has found through practical experience that the surface of the magnesite soapstone used in fire chambers and funnels hardens over time. We have studied a magnesite soapstone used in a fireplace continuously for 60 years. The mineralogical changes, that took place during heating and subsequent cooling of the fireplace have been investigated with electron probe microanalyzer and X-ray diffractometer to find an explanation, what kind of reactions caused the hardening. We found that ferromagnesite has been altered to pseudomorphic aggregates composed of ferropericlase and magnesioferrite in the nearest ~30 mm from the surface exposed to fire. Iron has been mobilized in the uppermost 3 mm, enriched in the rims, and depleted from the cores of the ferropericlase aggregates. Magnesioferrite occurs preferably in the fire chamber side of the aggregates in the uppermost 0.20 mm. Talc rims are altered to forsterite and/or enstatite in the reaction with ferromagnesite or its alteration products in the uppermost ~1 mm. In addition, wood combustion gases caused considerable enrichment of zinc and potassium in the chamber surface rock to the depth on 0.20 mm and 3 mm, respectively. The enrichment occurred by crystallization of Zn bearing ferropericlase and magnesioferrite and by crystallization of K bearing sheet silicates.
{"title":"Magnesite soapstone in use of fire chamber constructions: composition and structure adaptation","authors":"A. Huhta, P. Tuisku, T. Balić-Žunić, A. Kärki, Kivitieto Oy","doi":"10.17741/BGSF/91.1.004","DOIUrl":"https://doi.org/10.17741/BGSF/91.1.004","url":null,"abstract":"The Finnish soapstone industry has found through practical experience that the surface of the magnesite soapstone used in fire chambers and funnels hardens over time. We have studied a magnesite soapstone used in a fireplace continuously for 60 years. The mineralogical changes, that took place during heating and subsequent cooling of the fireplace have been investigated with electron probe microanalyzer and X-ray diffractometer to find an explanation, what kind of reactions caused the hardening. We found that ferromagnesite has been altered to pseudomorphic aggregates composed of ferropericlase and magnesioferrite in the nearest ~30 mm from the surface exposed to fire. Iron has been mobilized in the uppermost 3 mm, enriched in the rims, and depleted from the cores of the ferropericlase aggregates. Magnesioferrite occurs preferably in the fire chamber side of the aggregates in the uppermost 0.20 mm. Talc rims are altered to forsterite and/or enstatite in the reaction with ferromagnesite or its alteration products in the uppermost ~1 mm. In addition, wood combustion gases caused considerable enrichment of zinc and potassium in the chamber surface rock to the depth on 0.20 mm and 3 mm, respectively. The enrichment occurred by crystallization of Zn bearing ferropericlase and magnesioferrite and by crystallization of K bearing sheet silicates.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":"1 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2019-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41364504","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The 2.05 Ga Otanmäki suite represents a globally rare occurrence of Paleoproterozoic non-orogenic A1-type magmatism. It consists of a broad variety of A-type felsic and intermediate igneous rocks including monzodiorites, monzonites, syenites and peralkaline to peraluminous granites, containing both plutonic and subvolcanic members. The suite has chemical characteristics similar to those of A1-type suites formed in intraplate hotspots or continental rifts by differentiation of variably crustally contaminated, mafic mantle-derived magmas. However, compared to the Otanmäki rocks, most A1-type suites are considerably younger. original geologic because the suite deformed metamorphosed under amphibolite facies C, kbar) orogeny i.e., initial emplacement. result, Otanmäki pervasively foliated rocks within two nappe units sandwiched between Archean granitoid gneiss of 1950 Ma ocean-continent-transition ophiolitic rocks in the same thrust belt and the proximity of the Otanmäki suite to the Karelia-Svecofennia margin suggest that the suite records an early stage of a slow, ca. 100-Ma-long extension-rifting process which, at ca. 1950 Ma, eventually led to the final break-up of the Karelia craton and formation of the nascent ocean basin witnessed by the Jormua ophiolite complex.
2.05 Ga Otanmäki套代表了全球罕见的古元古代非造山a1型岩浆活动。它由种类繁多的a型长英质和中间火成岩组成，包括二长岩、二长岩、正长岩和过碱性至过铝质花岗岩，包括深成岩和次火山岩。该套具有类似于a1型套的化学特征，这些a1型套形成于板块内热点或大陆裂谷，是由受不同地壳污染的基性幔源岩浆分异形成的。然而，与Otanmäki岩石相比，大多数a1型套相当年轻。原始地质由于套体变形变质，在角闪岩相C、kbar造山作用下形成，即初始侵位。结果，夹在同一冲断带上的1950 Ma洋陆过渡蛇绿岩之间的两个推覆体单元内的Otanmäki普遍片理岩石，以及Otanmäki套件与Karelia-Svecofennia边缘的接近表明，该套件记录了一个大约100 Ma长的缓慢伸展-裂陷过程的早期阶段，该过程大约在1950 Ma左右。最终导致了卡累利阿克拉通的最终分裂，形成了由Jormua蛇绿岩复合体见证的新生海洋盆地。
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The 1.64 Ga Ahvenisto complex, southeastern Finland, is an anorthosite-mangeritecharnokite-granite (AMCG) suite in which diverse interaction styles of coeval mafic and felsic magmas are observed. Commingling, resulting in mafic pillows and net-veined granite dykes, and chemical mixing producing hybrid rocks, are the most common interaction types. Detailed description of the factors that controlled the interaction styles and relationships between involved rock types are provided using targeted mapping, petrography, and geochemical analyses complemented by chemical mixing and melt viscosity modeling. Interaction occurred at intermediate stages in the magmatic evolution of the complex: when the last fractions of mafic (monzodioritic) melts and the earliest fractions of felsic (hornblende granitic) melts existed simultaneously. Differentiation of mafic magma has produced three monzodioritic rock types: 1) olivine monzodiorite (most mafic, Mg# 49–40), 2) ferrodiorite (Mg# 42–33), and 3) massive monzodiorite (most evolved, Mg# 28–27). The types form an evolutionary trend, and each exhibits different style of interaction with coeval hbl-granite resulting from contrasting conditions and properties (temperature, viscosity, composition). The variation in these properties due to magma evolution and relative proportions of interacting magmas dictated the interaction style: interaction between olivine monzodiorites and granite was almost negligible; ferrodiorites intermingled forming pillows with granitic veins intruding them; and chemical mixing of massive monzodiorite and hbl-granite produced hybrid rocks.
芬兰东南部的1.64 Ga Ahvenisto杂岩是一个斜长岩-镁铁质-长英质花岗岩（AMCG）岩套，其中观察到同时代镁铁质和长英质岩浆的不同相互作用样式。混合作用是最常见的相互作用类型，产生镁铁质枕和网状脉花岗岩脉，以及化学混合产生混合岩石。通过有针对性的绘图、岩石学和地球化学分析以及化学混合和熔体粘度建模，对控制相互作用风格和相关岩石类型之间关系的因素进行了详细描述。相互作用发生在杂岩岩浆演化的中间阶段：镁铁质（二闪长质）熔体的最后部分和长英质（角闪花岗岩）熔体的最早部分同时存在。镁铁质岩浆的分化产生了三种二长闪长岩类型：1）橄榄石二长闪岩（大部分镁铁质，Mg#49-40），2）铁闪长岩（Mg#42-33），3）块状二长闪岩体（大部分演化，Mg#28-27）。这些类型形成了一种进化趋势，由于不同的条件和性质（温度、粘度、成分），每种类型都表现出与同时代hbl花岗岩不同的相互作用风格。由于岩浆演化和相互作用岩浆的相对比例，这些性质的变化决定了相互作用的风格：橄榄石二长闪长岩和花岗岩之间的相互作用几乎可以忽略不计；铁闪长岩混杂在一起形成枕状物，花岗岩脉侵入其中；块状二长闪长岩和hbl花岗岩的化学混合产生了混合岩。
{"title":"Tracing the styles of mafic-felsic magma interaction: A case study from the Ahvenisto igneous complex, Finland","authors":"Riikka Fred, A. Heinonen, Pasi Heikkilä","doi":"10.17741/BGSF/91.1.001","DOIUrl":"https://doi.org/10.17741/BGSF/91.1.001","url":null,"abstract":"The 1.64 Ga Ahvenisto complex, southeastern Finland, is an anorthosite-mangeritecharnokite-granite (AMCG) suite in which diverse interaction styles of coeval mafic and felsic magmas are observed. Commingling, resulting in mafic pillows and net-veined granite dykes, and chemical mixing producing hybrid rocks, are the most common interaction types. Detailed description of the factors that controlled the interaction styles and relationships between involved rock types are provided using targeted mapping, petrography, and geochemical analyses complemented by chemical mixing and melt viscosity modeling. Interaction occurred at intermediate stages in the magmatic evolution of the complex: when the last fractions of mafic (monzodioritic) melts and the earliest fractions of felsic (hornblende granitic) melts existed simultaneously. Differentiation of mafic magma has produced three monzodioritic rock types: 1) olivine monzodiorite (most mafic, Mg# 49–40), 2) ferrodiorite (Mg# 42–33), and 3) massive monzodiorite (most evolved, Mg# 28–27). The types form an evolutionary trend, and each exhibits different style of interaction with coeval hbl-granite resulting from contrasting conditions and properties (temperature, viscosity, composition). The variation in these properties due to magma evolution and relative proportions of interacting magmas dictated the interaction style: interaction between olivine monzodiorites and granite was almost negligible; ferrodiorites intermingled forming pillows with granitic veins intruding them; and chemical mixing of massive monzodiorite and hbl-granite produced hybrid rocks.","PeriodicalId":55302,"journal":{"name":"Bulletin of the Geological Society of Finland","volume":" ","pages":""},"PeriodicalIF":0.7,"publicationDate":"2019-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41925578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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