Petrogenesis of syenites at a rifted continental margin: origin, contamination and interaction of alkaline mafic and felsic magmas in the Astrophyllite Bay Complex, East Greenland
“… Figure 7. Summary of precise (≤2.5% 2 σ error) U–Pb, 40 Ar/ 39 Ar, Rb–Sr and Re–Os ages for alkaline (filled symbols) and tholeiitic (unfilled symbols) intrusions of the Kangerlussuaq Fjord compiled from the literature. Data from Nevle et al (1994), Hirschman et al (1997), Tegner et al (1998, 2008), Riishuus et al (2005), Holm, Heaman & Pedersen (2006), Holwell et al (2012), Wotzlaw et al (2012) and this study (concordia age for East Granite). Error bars indicate 2 σ errors.…”
Section: Discussionmentioning
confidence: 52%
“…2). These intrusions are concentrated around the Amdrup Fjord at the southeast margin of the KAC, and geochronology data indicate that most were emplaced between 46 and 48 Ma (Riishuus et al 2005; Tegner et al 2008). Exceptions are the Cirque 1320 and Flammefjeld complexes, for which Re–Os molybdenite ages of 52.7±0.3 and 39.7±0.2 Ma have been obtained (Brooks et al 2004; Holwell et al 2012).…”
Section: Geological Background and Previous Geochronologymentioning
confidence: 99%
“…Tholeiitic dykes include the THOL-1 and THOL-2 swarms. Data compiled from Nielsen (1978, 1987), McBirney (1989), Larsen & Brooks (1994), Hansen et al (2002), Peate & Stecher (2003), Peate et al (2003), Andreasen, Peate & Brooks (2004), Riishuus et al (2005, 2006, 2008) and Holm, Heaman & Pedersen (2006). …”
Several major tholeiitic (e.g. the Skaergaard intrusion) and alkaline (e.g. the Kangerlussuaq Syenite) intrusive complexes of the North Atlantic Large Igneous Province are exposed along the Kangerlussuaq Fjord in East Greenland. The Kærven Complex forms a satellite intrusion to the Kangerlussuaq Syenite and includes early tholeiitic gabbros and a series of cross-cutting alkaline intrusions ranging from monzonite to alkali granite. The alkaline intrusions cut the gabbros, and are cut by the outer nordmarkite zone of the Kangerlussuaq Syenite. This study presents the first U–Pb zircon ages from the alkaline units of the Kærven Complex. Fourteen multi-grain zircon fractions have been analysed by thermal ionization mass spectrometry (TIMS). Absolute age differences could not be resolved between the different units, suggesting a relatively rapid succession of intrusions between c. 53.5 and 53.3 Ma. Our compilation of precise radiometric age data shows that most of the alkaline magmatism in the Kangerlussuaq Fjord occurred prior to 50 Ma. Moreover, pre-50 Ma alkaline intrusions and lavas show a SSE-younging trend, which is interpreted as the track of the Iceland hotspot during the rift-to-drift transition of the North Atlantic.
“… Figure 7. Summary of precise (≤2.5% 2 σ error) U–Pb, 40 Ar/ 39 Ar, Rb–Sr and Re–Os ages for alkaline (filled symbols) and tholeiitic (unfilled symbols) intrusions of the Kangerlussuaq Fjord compiled from the literature. Data from Nevle et al (1994), Hirschman et al (1997), Tegner et al (1998, 2008), Riishuus et al (2005), Holm, Heaman & Pedersen (2006), Holwell et al (2012), Wotzlaw et al (2012) and this study (concordia age for East Granite). Error bars indicate 2 σ errors.…”
Section: Discussionmentioning
confidence: 52%
“…2). These intrusions are concentrated around the Amdrup Fjord at the southeast margin of the KAC, and geochronology data indicate that most were emplaced between 46 and 48 Ma (Riishuus et al 2005; Tegner et al 2008). Exceptions are the Cirque 1320 and Flammefjeld complexes, for which Re–Os molybdenite ages of 52.7±0.3 and 39.7±0.2 Ma have been obtained (Brooks et al 2004; Holwell et al 2012).…”
Section: Geological Background and Previous Geochronologymentioning
confidence: 99%
“…Tholeiitic dykes include the THOL-1 and THOL-2 swarms. Data compiled from Nielsen (1978, 1987), McBirney (1989), Larsen & Brooks (1994), Hansen et al (2002), Peate & Stecher (2003), Peate et al (2003), Andreasen, Peate & Brooks (2004), Riishuus et al (2005, 2006, 2008) and Holm, Heaman & Pedersen (2006). …”
Several major tholeiitic (e.g. the Skaergaard intrusion) and alkaline (e.g. the Kangerlussuaq Syenite) intrusive complexes of the North Atlantic Large Igneous Province are exposed along the Kangerlussuaq Fjord in East Greenland. The Kærven Complex forms a satellite intrusion to the Kangerlussuaq Syenite and includes early tholeiitic gabbros and a series of cross-cutting alkaline intrusions ranging from monzonite to alkali granite. The alkaline intrusions cut the gabbros, and are cut by the outer nordmarkite zone of the Kangerlussuaq Syenite. This study presents the first U–Pb zircon ages from the alkaline units of the Kærven Complex. Fourteen multi-grain zircon fractions have been analysed by thermal ionization mass spectrometry (TIMS). Absolute age differences could not be resolved between the different units, suggesting a relatively rapid succession of intrusions between c. 53.5 and 53.3 Ma. Our compilation of precise radiometric age data shows that most of the alkaline magmatism in the Kangerlussuaq Fjord occurred prior to 50 Ma. Moreover, pre-50 Ma alkaline intrusions and lavas show a SSE-younging trend, which is interpreted as the track of the Iceland hotspot during the rift-to-drift transition of the North Atlantic.
“…Essas rochas podem ser formadas pela fusão parcial de rochas crustais mediante o influxo de materiais voláteis ou em altas pressões na base da crosta espessada, pela cristalização fracionada de magmas derivados do manto, com ou sem assimilação crustal, ou por processos de mistura de magmas básicos e mantélicos com magmas graníticos (Barker et al, 1975;Huang e Wyllie, 1975;Brown e Becker, 1986;Dorais, 1990;Lubala et al, 1994;Sheppard, 1995;Zhao et al, 1995;Litvinovsky et al, 2002;Riishuus et al, 2005; Boynton, 1984). (B) Diagrama multielementar normalizado para manto primitivo (segundo McDonough e Sun, 1995).…”
Disponível on-line no endereço www.igc.usp.br/geologiausp -185 -Resumo Diversos corpos plutônicos alcalinos de alto potássio paleoproterozoicos ocorrem no embasamento do cráton São Francisco, bem como no embasamento dos orógenos que o bordejam. Localizado no bordo oeste do cráton São Francisco, o bloco Itacambira-Monte Azul integra o embasamento do orógeno Araçuaí, em partes retrabalhado pelo evento tectonometamórfico Brasiliano. Nesse bloco, os plutonitos Paciência, Morro do Quilombo e Serra Branca, constituídos de rochas alcalinas, são englobados na Suíte Paciência. Os resultados petrográficos para a Suíte Paciência mostram o predomínio de monzonitos e sienitos, equigranulares a porfiríticos, com ocorrência de enclaves máficos. As análises químicas indicam altas concentrações de álcalis, bem como o enriquecimento de óxidos ferromagnesianos e alto Mg# (número de magnésio). Essas rochas são dominantemente metaluminosas, alcalinas a alcalino-cálcicas e magnesianas, enriquecidas em Ba, Sr e Rb e depletadas em Nb, P, Ti e em elementos incompatíveis. Mostram altos conteúdos em elementos terras raras (ETR) com fracionamento dos ETR leves sobre os pesados e anomalias de Eu que variam de negativas a fracamente positivas. As características geoquímicas dessas rochas são similares às de granitoides potássicos originados tardiamente em eventos orogênicos associados à subducção, com fonte mantélica metassomatizada e enriquecida em elementos incompatíveis e participação de crosta arqueana na geração desse magma. A idade de cristalização em 2053 ± 6.3 Ma indica que as rochas da Suíte Paciência se relacionam aos estágios tardios da orogênese Transamazônica, possivelmente associados com a evolução de um extenso arco magmático desenvolvido ao final do Riaciano. Dessa forma, a Suíte Paciência e também as demais suítes alcalinas paleoproterozoicas presentes no embasamento do orógeno Araçuaí registram um período de estabilização do paleocontinente São Francisco-Congo na transição Riaciano-Orosiriano.Palavras-chave: Magmatismo alcalino; Suíte Paciência; Riaciano; Paleoproterozoico; Paleocontinente São Francisco-Congo.
AbstractSeveral high potassium-rich alkaline plutons from the Paleoproterozoic occur at the basement of the São Francisco craton, as well as at the basement of its surrounding orogens. Located in the western edge of the São Francisco craton, the Itacambira-Monte Azul block integrates the Araçuaí orogen basement rocks, which were partially reworked during the Brasiliano tectono-metamorphic event. In this block, alkaline rocks from the Paciência, Morro do Quilombo and Serra Branca plutonites are included in the Paciência Suite. Petrographic studies within the Paciência Suite show predominance of monzonites and syenites with equigranular to porphyritic textures and mafic enclaves. Chemical data indicate high concentrations of alkalis and enrichment in ferromagnesian oxides, which result in a high Mg#. These rocks are predominantly metaluminous, alkaline to alkaline-calcic and magnesian, enriched in Ba, Sr, Rb and deplete...
“…Burmakina & Tsygankov, 2013; Mingram, Trumbull, Littman, & Gerstenberger, 2000; Vernikovsky et al, 2003); and (vii) fractional crystallization (with or without crustal assimilation) of mantle‐derived magmas (e.g. Litvinovsky et al, 2002; Mingram et al, 2000; Riishuus et al, 2005; Zhu et al, 2017). The petrogenesis of syenite remains a subject of considerable controversy, and some models are in direct conflict with the results of experimental studies.…”
SHRIMP U-Pb dating of zircon from two representative samples of the Bardkish syenitic pluton, Urumieh plutonic complex, northwestern Iran, yielded a Late Cretaceous weighted mean 206 Pb/ 238 U age of 91.1 ±0.8 Ma (Turonian). The pluton is characterized by high K 2 O content, Ti-Nb-Ta depletion, enrichment in light rare earth elements and large ion lithophile elements compared to high field strength element, Mg-rich biotite and calcic amphibole, suggesting a shoshonitic affinity. Geochemical features of the Bardkish syenite are consistent with derivation by fractional crystallization of initial mafic parent magmas. It is most likely that primary magma of the syenite originated from a metasomatized subcontinental lithospheric mantle source with minor crustal component, and underwent a fractional crystallization process during its emplacement. The estimates of trapping pressures and temperatures suggest that crystallization began at the middle crustal level (less than 11 km) near 700-730 C. The generation of the Bardkish syenite could be related to the subduction of Neo-Tethyan oceanic crust beneath the Central Iranian microcontinent and it possibly marks a major magmatic episode prior to the final closure of the Neo-Tethyan ocean in northwest Iran.
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