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Michael B Stephens - One of the best experts on this subject based on the ideXlab platform.
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middle thrust sheets in the caledonide orogen sweden the outer margin of baltica the continent ocean transition zone and late cambrian ordovician subduction accretion
Geological Society London Memoirs, 2020Co-Authors: David G Gee, Iwona Klonowska, Pergunnar Andreasson, Michael B StephensAbstract:Nappes of continental outer and outermost margin affinities (Middle Allochthon) were transported from locations west of the present Norwegian coast and thrust eastwards onto the Baltoscandian foreland basin and platform. They are of higher metamorphic grade than underlying thrust sheets and most are more penetratively deformed. These allochthons are treated here in three groups. The lower thrust sheets comprise Paleoproterozoic crystalline basement (e.g. Tannas Augen Gneiss Nappe) and greenschist facies, Neoproterozoic, siliciclastic metasedimentary rocks (e.g. Offerdal Nappe). These are overthrust by a Cryogenian’Ediacaran succession intruded by c. 600 Ma dolerites (Baltoscandian Dyke Swarm) with an affinity to mid-ocean ridge basalt containing normal to enriched incompatible element contents (Sarv Nappes). The upper sheets are dominated by higher-grade allochthons (Seve Nappe Complex) with similar, mainly siliciclastic sedimentary protoliths, more mafic magmatism and some solitary ultramafic bodies. Within this early Ediacaran continent’ocean transition zone (COT) assemblage, generally metamorphosed in amphibolite facies, some nappes experienced migmatization, and eclogites are present. Evidence of ultrahigh-pressure metamorphism has been obtained from garnet peridotites and eclogites; recently, microdiamonds have been discovered in paraGneisses. Subduction of the COT started by the late Cambrian and accretion continued through the Ordovician, prior to the Baltica–Laurentia collision. Thrusting of all these Middle allochthons onto the foreland basin exceeds a distance of 400 km. (Less)
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chapter 21 middle thrust sheets in the caledonide orogen sweden the outer margin of baltica the continent ocean transition zone and late cambrian ordovician subduction accretion
Geological Society London Memoirs, 2020Co-Authors: Iwona Klonowska, Pergunnar Andreasson, Michael B StephensAbstract:Abstract Nappes of continental outer and outermost margin affinities (Middle Allochthon) were transported from locations west of the present Norwegian coast and thrust eastwards onto the Baltoscandian foreland basin and platform. They are of higher metamorphic grade than underlying thrust sheets and most are more penetratively deformed. These allochthons are treated here in three groups. The lower thrust sheets comprise Paleoproterozoic crystalline basement (e.g. Tannas Augen Gneiss Nappe) and greenschist facies, Neoproterozoic, siliciclastic metasedimentary rocks (e.g. Offerdal Nappe). These are overthrust by a Cryogenian−Ediacaran succession intruded by c. 600 Ma dolerites (Baltoscandian Dyke Swarm) with an affinity to mid-ocean ridge basalt containing normal to enriched incompatible element contents (Sarv Nappes). The upper sheets are dominated by higher-grade allochthons (Seve Nappe Complex) with similar, mainly siliciclastic sedimentary protoliths, more mafic magmatism and some solitary ultramafic bodies. Within this early Ediacaran continent−ocean transition zone (COT) assemblage, generally metamorphosed in amphibolite facies, some nappes experienced migmatization, and eclogites are present. Evidence of ultrahigh-pressure metamorphism has been obtained from garnet peridotites and eclogites; recently, microdiamonds have been discovered in paraGneisses. Subduction of the COT started by the late Cambrian and accretion continued through the Ordovician, prior to the Baltica–Laurentia collision. Thrusting of all these Middle allochthons onto the foreland basin exceeds a distance of 400 km.
Maia, Soraia Maria Carlos - One of the best experts on this subject based on the ideXlab platform.
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Estudo integrado geológico/tecnológico de rochas ornamentais: os granitos flores e jacarandá, RN
Universidade Federal do Rio Grande do Norte, 2015Co-Authors: Maia, Soraia Maria CarlosAbstract:Este trabalho tem como obejetivo um estudo integrado geológico e tecnológico de rochas ornamentais nas áreas de ocorrência dos granitos Flores e Jacarandá, localizados próximo ao Município de Afonso Bezerra, na porção centro norte do Estado do Rio Grande do Norte. Geologicamente, a área compreende quatro unidades litoestraligráficas: um complexo Gnáissico Migmático (embasamento), formado essencialmente por gnaisses bandados, usualmente milonitizados e com feições migmatíticas diversas; um Augen Gnaisse que ocorrecomo um corpo alongado e constitui o "Granito Jacarandá"; um pequeno estock granítico que apresenta-se de forma subcircular (Granito Flores) onde dominam rochas de textura fina a fina-média de coloração rosa; por fim, sedimentos aluvionares finos a grossos, formando extensas áreas de plançies aluviais. A caracterização tecnológica dos granitos ornamentais Flores e Jacarandá, realizada por meio de ensaios diversos, teve como objetivo a obtenção de parâmetros petrográficos, físicos e meânicos que permitiram a qualificação dessas rochas. Estes ensaios foram executados segundo procedimentos normatizados por entidades brasileiras (ABNT - Associação Brasileira de Normas Técnicas) e estrangeiras (ASTM - American Society for Testing andMaterials). A análise petrográfica mostrou que as rochas estudadas são granitos senso estrito, somando em média 85 - 90% modal. O Granito Flores é a rocha mais félsica, com teor de máficos em torno de 10%, e de composição monzogranítica. O Granito Jacarandá é um Augen gnaisse de composição sienogranítica com máficos em torno de 15% modal. Os vários ensaios tecnológicos realizados (alterabilidade, ídices físicos, velociodade de propagação de ondas ultra-sônicas, compressão uniaxial, resistência a reflexão, desgaste Amsler e resistência ao congelamento e degelo) mostram parâmetros e valores similares para ambos os granitos estudados e encontram-se dentro dos especificados em normas nacionais internacionais para rochas silicáticas de uso ornamental. Da mesma forma, quando comparados com os granitos ornamentais estudados no Brasil, os parâmetros e valores aqui encontrados mostram-se similares. A análise do conjunto de resultados dos ensaios realizados mostra que tanto o Granito Flores quanto o Jacarandá são rochas de boa qualidade tecnológica, er que se prestam muito bem para uso como material de revestimento interno e externo em edificaçõesThe main purpose of the present study is to integrate a geological and technological investigation of ornamental rocks of the Flores and Jacarandá granites, which are located near the Afonso Bezerra city, in the north central part of the Rio Grande do Norte State. The study area encompasses four litho-stratigrafic units: a Gneiss-Migmatitic Complex(cristalline basement), which is mainly composed of banded Gneisses, usually deformed as mylonitic rocks and with several migmatic features, an Augen Gneiss, which occurs as an elongated body that constitutes the Jacarandá granite, a small granite stock, which presents a semi-circular form, named Flores granite, composed of pink, fine to medium coarse rocks, and fine to coarse alluvial sediments, which form extensive areas of large fluvial deposits. The technological characterization of the Flores and Jacarandá granites, carried out through several tests, has as the main purpose the determination of petrographic, physical, and mechanic parameters that allowed the characterization of these rocks. The test followed procedures recommended by Brazilian (ABNT Associação Brasileira de Normas Técnicas) and foreigner institutions (ASTM American Society for Testing and Materials). The petrografhic analysis indicated that the rocks investigated are granite sensu estrictu, summing an average 85-90% modal. The Flores granite is the more felsic rock, which presents mafic content ∼ 10% and monzonitic composition. The Jacarandá granite is an Augen Gneiss rock that presents sienogranitic composition and mafic modal content ∼ 15%. Several technological tests carried out (alterability, physical indices, velocity of ultrasonic wave propagation, uniaxial compression, flection resistence, Amsler desgaste, and resistence to freezing and heating) indicated that parameters and values were identical for both granites investigated. These parameters and values are consistent with the Brazilian and international standards for siliciclastic rocks of ornamental use, as well as other Brazilian ornamental granites. The analysis of all results indicates that both the Flores and Jacarandá granites present good quality, and that they are indicated for ornamental use of revetment interior and exterior of building
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Estudo integrado geológico/tecnológico de rochas ornamentais: os granitos flores e jacarandá, RN
Geodinâmica; Geofísica, 2004Co-Authors: Maia, Soraia Maria CarlosAbstract:The main purpose of the present study is to integrate a geological and technological investigation of ornamental rocks of the Flores and Jacarandá granites, which are located near the Afonso Bezerra city, in the north central part of the Rio Grande do Norte State. The study area encompasses four litho-stratigrafic units: a Gneiss-Migmatitic Complex(cristalline basement), which is mainly composed of banded Gneisses, usually deformed as mylonitic rocks and with several migmatic features, an Augen Gneiss, which occurs as an elongated body that constitutes the Jacarandá granite, a small granite stock, which presents a semi-circular form, named Flores granite, composed of pink, fine to medium coarse rocks, and fine to coarse alluvial sediments, which form extensive areas of large fluvial deposits. The technological characterization of the Flores and Jacarandá granites, carried out through several tests, has as the main purpose the determination of petrographic, physical, and mechanic parameters that allowed the characterization of these rocks. The test followed procedures recommended by Brazilian (ABNT Associação Brasileira de Normas Técnicas) and foreigner institutions (ASTM American Society for Testing and Materials). The petrografhic analysis indicated that the rocks investigated are granite sensu estrictu, summing an average 85-90% modal. The Flores granite is the more felsic rock, which presents mafic content ∼ 10% and monzonitic composition. The Jacarandá granite is an Augen Gneiss rock that presents sienogranitic composition and mafic modal content ∼ 15%. Several technological tests carried out (alterability, physical indices, velocity of ultrasonic wave propagation, uniaxial compression, flection resistence, Amsler desgaste, and resistence to freezing and heating) indicated that parameters and values were identical for both granites investigated. These parameters and values are consistent with the Brazilian and international standards for siliciclastic rocks of ornamental use, as well as other Brazilian ornamental granites. The analysis of all results indicates that both the Flores and Jacarandá granites present good quality, and that they are indicated for ornamental use of revetment interior and exterior of buildingsConselho Nacional de Desenvolvimento Científico e TecnológicoEste trabalho tem como obejetivo um estudo integrado geológico e tecnológico de rochas ornamentais nas áreas de ocorrência dos granitos Flores e Jacarandá, localizados próximo ao Município de Afonso Bezerra, na porção centro norte do Estado do Rio Grande do Norte. Geologicamente, a área compreende quatro unidades litoestraligráficas: um complexo Gnáissico Migmático (embasamento), formado essencialmente por gnaisses bandados, usualmente milonitizados e com feições migmatíticas diversas; um Augen Gnaisse que ocorrecomo um corpo alongado e constitui o "Granito Jacarandá"; um pequeno estock granítico que apresenta-se de forma subcircular (Granito Flores) onde dominam rochas de textura fina a fina-média de coloração rosa; por fim, sedimentos aluvionares finos a grossos, formando extensas áreas de plançies aluviais. A caracterização tecnológica dos granitos ornamentais Flores e Jacarandá, realizada por meio de ensaios diversos, teve como objetivo a obtenção de parâmetros petrográficos, físicos e meânicos que permitiram a qualificação dessas rochas. Estes ensaios foram executados segundo procedimentos normatizados por entidades brasileiras (ABNT - Associação Brasileira de Normas Técnicas) e estrangeiras (ASTM - American Society for Testing andMaterials). A análise petrográfica mostrou que as rochas estudadas são granitos senso estrito, somando em média 85 - 90% modal. O Granito Flores é a rocha mais félsica, com teor de máficos em torno de 10%, e de composição monzogranítica. O Granito Jacarandá é um Augen gnaisse de composição sienogranítica com máficos em torno de 15% modal. Os vários ensaios tecnológicos realizados (alterabilidade, ídices físicos, velociodade de propagação de ondas ultra-sônicas, compressão uniaxial, resistência a reflexão, desgaste Amsler e resistência ao congelamento e degelo) mostram parâmetros e valores similares para ambos os granitos estudados e encontram-se dentro dos especificados em normas nacionais internacionais para rochas silicáticas de uso ornamental. Da mesma forma, quando comparados com os granitos ornamentais estudados no Brasil, os parâmetros e valores aqui encontrados mostram-se similares. A análise do conjunto de resultados dos ensaios realizados mostra que tanto o Granito Flores quanto o Jacarandá são rochas de boa qualidade tecnológica, er que se prestam muito bem para uso como material de revestimento interno e externo em edificaçõe
Bernard Bingen - One of the best experts on this subject based on the ideXlab platform.
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geochronology of paleoproterozoic Augen Gneisses in the western Gneiss region norway evidence for sveconorwegian zircon neocrystallization and caledonian zircon deformation
The Journal of Geology, 2013Co-Authors: Torkil S Rohr, Peter Robinson, Bernard Bingen, Steven M ReddyAbstract:AbstractThe Western Gneiss Region, western Norway, consists of Paleoproterozoic crust of Baltica ancestry (Baltican Basement), partly subducted to high- and ultrahigh-pressure (HP-UHP) conditions during the Scandian Orogeny between 415 and 395 Ma. The dominant felsic Gneisses carry little evidence for the HP-UHP history but were affected by amphibolite-facies reworking during exhumation. Laser ablation–ICP-MS and secondary ion mass spectrometry (SIMS) zircon U-Pb data collected in Augen Gneiss samples constrain the magmatic and metamorphic geochronology in this crust. Five samples from the eclogite-bearing HP-UHP basement near Molde yield intrusion ages ranging from to Ma. Two samples of the structurally underlying eclogite-free basement yield ages of and Ma, and a sample from the infolded Middle Allochthon Risberget Nappe yields an equivalent age of Ma. Two samples of the eclogite-bearing basement contain low Th/U neocrystallized zircon with an age of Ma. This zircon provides the northernmost direct evid...
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hornblende 40ar 39ar geochronology across terrane boundaries in the sveconorwegian province of s norway
Precambrian Research, 1998Co-Authors: Bernard Bingen, A Boven, L Punzalan, J R Wijbrans, Daniel DemaiffeAbstract:Abstract Hornblende incremental heating 40 Ar/ 39 Ar data were obtained from Augen Gneiss and amphibolite of the Sveconorwegian Province of S. Norway. In the Rogaland-Vest Agder and Telemark terranes, four pyroxene-rich samples, located close (≤ 10 km) to the anorthosite-charnockite Rogaland Igneous Complex, define an age group at 916 + 12/ − 14 Ma and six samples distributed in the two terranes yield another group at 871 + 8/ − 10 Ma. The first age group is close to the reported zircon UPb intrusion age of the igneous complex (931 ± 2 Ma) and the regional titanite UPb age (918 ± 2 Ma), whereas the second group overlaps reported regional mineral RbSr ages (895-853 Ma) as well as biotite KAr ages (878-853 Ma). In the first group, the comparatively dry parageneses of low- P thermal metamorphism (M2) associated with the intrusion of the igneous complex are well developed, and hornblende 40 Ar/ 39 Ar ages probably record a drop in temperature shortly after this phase. In other hornblende + biotite-rich samples, with presumably a higher fluid content, the hornblende ages are probably a response to hornblende-fluid interaction during a late Sveconorwegian metamorphic or hydrothermal event. A ca 220 m.y. diachronism in hornblende 40 Ar/ 39 Ar ages is documented between S. Telemark ( ca 870 Ma) and Bamble ( ca 1090 Ma). Differential uplift between these terranes was mostly accommodated by shearing along the Kristiansand-Porsgrunn shear zone. The final stage of extension along this zone occurred after intrusion of the Herefoss post-kinematic granite at 926 ± 8 Ma. On the contrary, the southern part of the Rogaland-Vest Agder and Telemark terranes share a common cooling evolution as mineral ages are similar on both sides of the Mandal-Ustaoset Line the tectonic zone between them. The succession within 20 m.y. of a voluminous pulse of post-tectonic magmatism at 0.93 Ga, a phase of high- T -low- P metamorphism at 0.93-0.92 Ga, and fast cooling at a regional scale ca 0.92 Ga, suggests that the southern parts of Rogaland-Vest Agder and Telemark were affected by an event of post-thickening extension collapse at that time. This event is not recorded in Bamble.
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tectonic regimes and terrane boundaries in the high grade sveconorwegian belt of sw norway inferred from u pb zircon geochronology and geochemical signature of Augen Gneiss suites
Journal of the Geological Society, 1998Co-Authors: Bernard Bingen, Otto Van BreemenAbstract:Six units from three suites of Gneissic megacrystic granitoids in the Sveconorwegian Province of SW Norway were dated by the U–Pb zircon method. The Gjerstad suite crystallized between 1.19 and 1.15 Ga in the Bamble, Telemark and Rogaland–Vest Agder terranes; it has an A-type geochemical signature suggesting intrusion in a tensional setting. The Vennesla unit of this suite yields an age of 1166+ 61 −21 Ma. The Feda suite intruded in Rogaland–Vest Agder during a short period at 1.05 Ga (four units between 1051 +2 −8 and 1049 +2 −8 Ma) and has a high-K calc-alkaline trend suggesting a subduction- related setting. The Fennefoss Augen Gneiss of Telemark (1035 +2 −3 Ma) possesses a geochemical signature transitional between high-K calc-alkaline and A-type. The spatial association of tensional plutonism with the Kristiansand–Porsgrunn shear zone between Bamble and Telemark suggests that crustal thinning occurred along this axis between 1.19 and 1.13 Ga, preceding Sveconorwegian compressive shearing. The boundary between Rogaland–Vest Agder and Telemark, the Mandal line, probably separated, at 1.05 Ga, a mobile belt (Rogaland–Vest Agder) and a colder, more rigid terrane (Telemark). Major strike-slip shearing along the southern section of the Mandal line was probably associated with intrusion of an elongate pluton of the Feda suite and ductile amphibolite-facies deformation along a banded Gneiss unit.
Ian S Williams - One of the best experts on this subject based on the ideXlab platform.
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archaean fluid assisted crustal cannibalism recorded by low δ 18 o and negative e hf t isotopic signatures of west greenland granite zircon
Contributions to Mineralogy and Petrology, 2011Co-Authors: Vickie C Bennett, Joe Hiess, Allen P Nutman, Ian S WilliamsAbstract:The role of fluids during Archaean intra-crustal magmatism has been investigated via integrated SHRIMP U–Pb, δ18O and LA-MC-ICPMS 176Hf isotopic zircon analysis. Six rock samples studied are all from the Nuuk region (southern West Greenland) including two ~3.69 Ga granitic and trondhjemitic Gneisses, a 3.64 Ga granitic Augen Gneiss, a 2.82 Ga granodioritic Ikkattoq Gneiss, a migmatite with late Neoarchaean neosome and a homogeneous granite of the 2.56 Ga Qorqut Granite Complex (QGC). All zircon grains were thoroughly imaged to facilitate analysis of magmatic growth domains. Within the zircon analysed, there is no evidence for metamictization. Initial eHf zircon values (n = 63) are largely sub-chondritic, indicating the granitic host magmas were generated by the remelting of older, un-radiogenic crustal components. Zircon from some granite samples displays more than one 207Pb/206Pb age, and correlated with 176Hf/177Hf compositions can trace multiple phases of remelting or recrystallization during the Archaean. Model ages calculated using Lu/Hf arrays for each sample indicate that the crustal parental rocks to the granites, granodiorites and trondhjemites segregated from a chondrite-like reservoir at an earlier time during the Archaean, corresponding to known formation periods of more primitive tonalite–trondhjemite–granodiorite (TTG) Gneisses. Zircon from the ~3.69 Ga granite, the migmatite and QGC granite contains Eoarchaean cores with chondritic 176Hf/177Hf and mantle-like δ18O compositions. The age and geochemical signatures from these inherited components are identical to those of surrounding tonalitic Gneisses, further suggesting genesis of these granites by remelting of broadly tonalitic protoliths. Zircon oxygen isotopic compositions (n = 62) over nine age populations (six igneous and three inherited) have weighted mean or mean δ18O values ranging from 5.8 ± 0.6 to 3.7 ± 0.5‰. The 3.64 Ga granitic Augen Gneiss sample displays the highest δ18O with a mildly supra-mantle composition of 5.8 ± 0.6‰. Inherited Eoarchaean TTG-derived zircon shows mantle-like values. Igneous zircon from all other samples, spanning more than a billion years of Archaean time, record low δ18O sub-mantle compositions. These are the first low δ18O signatures reported from Archaean zircon and represent low δ18O magmas formed by the remelting and metamorphism of older crustal rocks following high-temperature hydrothermal alteration by meteoric water. Meteoric fluid ingress coupled with crustal extension, associated high heat flow and intra-crustal melting are a viable mechanism for the production of the low δ18O granites, granodiorites and trondhjemites reported here. Both high and low δ18O magmas may have been generated in extensional environments and are distinct in composition from Phanerozoic I-type granitic plutonic systems, which are typified by increasing δ18O during intra-crustal reworking. This suggests that Archaean magmatic processes studied here were subtly different from those operating on the modern Earth and involved extensional tectonic regimes and the predominance of remelting of hydrothermally altered crystalline basement.
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evidence for prolonged mid paleozoic plutonism and ages of crustal sources in east central alaska from shrimp u pb dating of syn magmatic inherited and detrital zircon
Canadian Journal of Earth Sciences, 2009Co-Authors: Cynthia Duselbacon, Ian S WilliamsAbstract:Sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses of igneous zircons from the Lake George assemblage in the eastern Yukon–Tanana Upland (Tanacross quadrangle) indicate both Late Devonian (∼370 Ma) and Early Mississippian (∼350 Ma) magmatic pulses. The zircons occur in four textural variants of granitic orthoGneiss from a large area of muscovite–biotite Augen Gneiss. Granitic orthoGneiss from the nearby Fiftymile batholith, which straddles the Alaska–Yukon border, yielded a similar range in zircon U–Pb ages, suggesting that both the Fiftymile batholith and the Tanacross orthoGneiss body consist of multiple intrusions. We interpret the overall tectonic setting for the Late Devonian and Early Mississippian magmatism as an extending continental margin (broad back-arc region) inboard of a northeast-dipping (present coordinates) subduction zone. New SHRIMP U–Pb ages of inherited zircon cores in the Tanacross orthoGneisses and of detrital zircons from quartzite from the Jarvis belt in the Alaska Ra...
Daniel Demaiffe - One of the best experts on this subject based on the ideXlab platform.
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hornblende 40ar 39ar geochronology across terrane boundaries in the sveconorwegian province of s norway
Precambrian Research, 1998Co-Authors: Bernard Bingen, A Boven, L Punzalan, J R Wijbrans, Daniel DemaiffeAbstract:Abstract Hornblende incremental heating 40 Ar/ 39 Ar data were obtained from Augen Gneiss and amphibolite of the Sveconorwegian Province of S. Norway. In the Rogaland-Vest Agder and Telemark terranes, four pyroxene-rich samples, located close (≤ 10 km) to the anorthosite-charnockite Rogaland Igneous Complex, define an age group at 916 + 12/ − 14 Ma and six samples distributed in the two terranes yield another group at 871 + 8/ − 10 Ma. The first age group is close to the reported zircon UPb intrusion age of the igneous complex (931 ± 2 Ma) and the regional titanite UPb age (918 ± 2 Ma), whereas the second group overlaps reported regional mineral RbSr ages (895-853 Ma) as well as biotite KAr ages (878-853 Ma). In the first group, the comparatively dry parageneses of low- P thermal metamorphism (M2) associated with the intrusion of the igneous complex are well developed, and hornblende 40 Ar/ 39 Ar ages probably record a drop in temperature shortly after this phase. In other hornblende + biotite-rich samples, with presumably a higher fluid content, the hornblende ages are probably a response to hornblende-fluid interaction during a late Sveconorwegian metamorphic or hydrothermal event. A ca 220 m.y. diachronism in hornblende 40 Ar/ 39 Ar ages is documented between S. Telemark ( ca 870 Ma) and Bamble ( ca 1090 Ma). Differential uplift between these terranes was mostly accommodated by shearing along the Kristiansand-Porsgrunn shear zone. The final stage of extension along this zone occurred after intrusion of the Herefoss post-kinematic granite at 926 ± 8 Ma. On the contrary, the southern part of the Rogaland-Vest Agder and Telemark terranes share a common cooling evolution as mineral ages are similar on both sides of the Mandal-Ustaoset Line the tectonic zone between them. The succession within 20 m.y. of a voluminous pulse of post-tectonic magmatism at 0.93 Ga, a phase of high- T -low- P metamorphism at 0.93-0.92 Ga, and fast cooling at a regional scale ca 0.92 Ga, suggests that the southern parts of Rogaland-Vest Agder and Telemark were affected by an event of post-thickening extension collapse at that time. This event is not recorded in Bamble.