... DHZ) zone; 4-Sarajevo-Sigmoid (SS) zone; 5-East Bosnian-Durmitor zone; 6-Dinaric Ophiolite Be... more ... DHZ) zone; 4-Sarajevo-Sigmoid (SS) zone; 5-East Bosnian-Durmitor zone; 6-Dinaric Ophiolite Belt (DOB); 7-Drina-Ivanjica and Pelagonian zones (DIE); 8-Vardar zone (VZ); 9 ... ratios very similar to those of the high-K calc-alkaline lavas of Central Serbia, Fruka Gora ...
Zusammenfassung Das proterozoische Grundgebirge der Provinz Zambesi (Mosambique) befindet sich in... more Zusammenfassung Das proterozoische Grundgebirge der Provinz Zambesi (Mosambique) befindet sich in der Nähe des südlichen Endes des sogenannten Mozambique Belt. Rb/Sr Daten aus 66 Ganzgesteins-und einigen Mineralanalysen zeugen von einer ...
Abstract This paper presents the results of an investigation carried out on young volcanic rocks ... more Abstract This paper presents the results of an investigation carried out on young volcanic rocks from the Gedemsa and Fanta 'Ale complexes, located in the Main Ethiopian Rift, the site of an intense magmatism since Eocene–Oligocene. The earlier NW–SE direction of extension of the Rift, which generated NE–SW trending faults, rotated around E–W in Quaternary times, and produced the still active N to N–NE Wonji Fault System. The Gedemsa volcano is located in the central part of the Ethiopian Rift, about 100 km SE of Addis Ababa. It is characterized by a wide central caldera, about 8 km in diameter. The general stratigraphic sequence in the area includes, from base upwards, rift-floor ignimbrites, pantelleritic and subordinate trachytic pyroclastic deposits and lava flows and domes, and widespread basaltic deposits. The Fanta 'Ale volcanic complex is located in the northern part of the Main Ethiopian Rift, where the Afar depression begins. It is characterized by a summit caldera of which the diameter is about 4 km. This volcano erupted trachytic and rhyolitic lavas, whereas the most diffuse unit is an ignimbrite related to the caldera collapse. Explosive activity has occurred inside and outside the caldera, forming tuff cones and thick pumice-fallout deposits. The only mafic unit is represented by a basaltic eruption that occurred in 1870 AD. Historical eruptions and intense fumarolic activity are evidence for the persistence activity of the Fanta 'Ale in this part of the Main Ethiopian Rift. New geochemical and Sr–Nd–Pb isotope data on representative samples from Gedemsa and Fanta 'Ale volcanoes are presented and discussed in order to shed light on the genesis of mafic and felsic magmas, the genetic link between them, and their possible interaction with the local crust. Volcanic rocks show a typical mafic–felsic bi-modal distribution with few intermediate terms (Daly Gap), as observed at regional scale along the Main Ethiopian Rift as well as on the plateau. Geochemical data and modeling suggest that magmas evolved mainly through fractional crystallization processes, accounting for the entire mafic–felsic compositional variation. However, Sr–Nd–Pb isotope data reveal also open-system evolution processes. The most differentiated, Sr-poor rhyolites suffered important low temperature contamination by shallow fluids of hydrothermal and/or meteoric origin. This affected mostly the Sr isotopic composition of whole-rocks, and much less that of separated feldspars that provide more reliable 87Sr/86Sr values. Mafic rocks, as well as the least contaminated felsic rocks, provide evidence for two components involved in the genesis and evolution of mafic magmas: a mantle component, carrying the isotopic composition of the Afar plume, and a crustal component, likely Pan-African sialic lower crust, that might have been added in small amounts, about 2%, to mafic magmas. The origin of the primary magmas is inferred to have occurred by 7% partial melting of a mixed source region including both depleted and enriched mantle components.
ABSTRACT Early Cretaceous volcanic rocks (basanite to phonolite) from the Mecsek Mountains (South... more ABSTRACT Early Cretaceous volcanic rocks (basanite to phonolite) from the Mecsek Mountains (South Hungary) represent the products of Late Mesozoic extension-related alkaline magmatism at the southern margin of the European plate. Two mafic groups have been distinguished: ankaramite-alkali basalt and Na-basanite-phonotephrite. Phonolites could have been formed from the Na-basanitic magma by low-pressure fractionation. The major and trace element characteristics of the Mecsek basalts are similar to those of alkaline basalts of other intraplate areas and have a St. Helena-type OIB affinity. The mantle source of the Mecsek volcanics could be similar to that proposed by Wilson and Downes (1991) as one of the mantle endmembers for extension-related Tertiary-Quaternary alkaline basalts in Europe. Geochemical modelling indicates that the primary magmas of the Na-basanite series were formed by about 4% partial melting, whereas ankaramites and alkali basalts originated by about 6% partial melting of a garnet-peridotite source.
Journal of Volcanology and Geothermal Research, 1995
Two flank eruptions took place at Mt. Etna during 1989–1993. The former (September–October 1989) ... more Two flank eruptions took place at Mt. Etna during 1989–1993. The former (September–October 1989) produced lavas among the most primitive of this century while the latter (December 1991–March 1993) was unusually long lasting and the largest of the last three centuries. Alkali basalts of 1989 displayed initial enrichments of Rb and K accompanied by an higher value of radiogenic-Sr and
Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogeni... more Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogenic belt has led to the opening of the Tyrrhenian basin. Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Italian mainland during this time, building up the Tuscan Magmatic Province as the fold belt was progressively thinned, heated and intruded by mafic magmas. An intrusive complex was progressively built on western Elba Island by emplacement, within a stack of nappes, of multiple, shallow-level porphyritic laccoliths, a major pluton, and a final dyke swarm, all within the span from about 8 to 6.8 Ma. New geochemical and Sr–Nd isotopic investigations constrain the compositions of materials involved in the genesis of the magmas of Elba Island compared to the whole Tuscan Magmatic Province. Several distinct magma sources, in both the crust and mantle, have been identified as contributing to the Elba magmatism as it evolved from crust-, to hybrid-, to m...
... Samples were selected from relatively high-B lavas (Taddeucci, 1964) belonging to the Neogene... more ... Samples were selected from relatively high-B lavas (Taddeucci, 1964) belonging to the Neogene-Quaternary volcanism in central Italy. ... Moreover, in several studies of volcanic suites (eg, Ryan and Langmuir 1993; Ryan et al 1996; Benton et al 1999 and Tonarini et al 2001, in ...
... DHZ) zone; 4-Sarajevo-Sigmoid (SS) zone; 5-East Bosnian-Durmitor zone; 6-Dinaric Ophiolite Be... more ... DHZ) zone; 4-Sarajevo-Sigmoid (SS) zone; 5-East Bosnian-Durmitor zone; 6-Dinaric Ophiolite Belt (DOB); 7-Drina-Ivanjica and Pelagonian zones (DIE); 8-Vardar zone (VZ); 9 ... ratios very similar to those of the high-K calc-alkaline lavas of Central Serbia, Fruka Gora ...
Zusammenfassung Das proterozoische Grundgebirge der Provinz Zambesi (Mosambique) befindet sich in... more Zusammenfassung Das proterozoische Grundgebirge der Provinz Zambesi (Mosambique) befindet sich in der Nähe des südlichen Endes des sogenannten Mozambique Belt. Rb/Sr Daten aus 66 Ganzgesteins-und einigen Mineralanalysen zeugen von einer ...
Abstract This paper presents the results of an investigation carried out on young volcanic rocks ... more Abstract This paper presents the results of an investigation carried out on young volcanic rocks from the Gedemsa and Fanta 'Ale complexes, located in the Main Ethiopian Rift, the site of an intense magmatism since Eocene–Oligocene. The earlier NW–SE direction of extension of the Rift, which generated NE–SW trending faults, rotated around E–W in Quaternary times, and produced the still active N to N–NE Wonji Fault System. The Gedemsa volcano is located in the central part of the Ethiopian Rift, about 100 km SE of Addis Ababa. It is characterized by a wide central caldera, about 8 km in diameter. The general stratigraphic sequence in the area includes, from base upwards, rift-floor ignimbrites, pantelleritic and subordinate trachytic pyroclastic deposits and lava flows and domes, and widespread basaltic deposits. The Fanta 'Ale volcanic complex is located in the northern part of the Main Ethiopian Rift, where the Afar depression begins. It is characterized by a summit caldera of which the diameter is about 4 km. This volcano erupted trachytic and rhyolitic lavas, whereas the most diffuse unit is an ignimbrite related to the caldera collapse. Explosive activity has occurred inside and outside the caldera, forming tuff cones and thick pumice-fallout deposits. The only mafic unit is represented by a basaltic eruption that occurred in 1870 AD. Historical eruptions and intense fumarolic activity are evidence for the persistence activity of the Fanta 'Ale in this part of the Main Ethiopian Rift. New geochemical and Sr–Nd–Pb isotope data on representative samples from Gedemsa and Fanta 'Ale volcanoes are presented and discussed in order to shed light on the genesis of mafic and felsic magmas, the genetic link between them, and their possible interaction with the local crust. Volcanic rocks show a typical mafic–felsic bi-modal distribution with few intermediate terms (Daly Gap), as observed at regional scale along the Main Ethiopian Rift as well as on the plateau. Geochemical data and modeling suggest that magmas evolved mainly through fractional crystallization processes, accounting for the entire mafic–felsic compositional variation. However, Sr–Nd–Pb isotope data reveal also open-system evolution processes. The most differentiated, Sr-poor rhyolites suffered important low temperature contamination by shallow fluids of hydrothermal and/or meteoric origin. This affected mostly the Sr isotopic composition of whole-rocks, and much less that of separated feldspars that provide more reliable 87Sr/86Sr values. Mafic rocks, as well as the least contaminated felsic rocks, provide evidence for two components involved in the genesis and evolution of mafic magmas: a mantle component, carrying the isotopic composition of the Afar plume, and a crustal component, likely Pan-African sialic lower crust, that might have been added in small amounts, about 2%, to mafic magmas. The origin of the primary magmas is inferred to have occurred by 7% partial melting of a mixed source region including both depleted and enriched mantle components.
ABSTRACT Early Cretaceous volcanic rocks (basanite to phonolite) from the Mecsek Mountains (South... more ABSTRACT Early Cretaceous volcanic rocks (basanite to phonolite) from the Mecsek Mountains (South Hungary) represent the products of Late Mesozoic extension-related alkaline magmatism at the southern margin of the European plate. Two mafic groups have been distinguished: ankaramite-alkali basalt and Na-basanite-phonotephrite. Phonolites could have been formed from the Na-basanitic magma by low-pressure fractionation. The major and trace element characteristics of the Mecsek basalts are similar to those of alkaline basalts of other intraplate areas and have a St. Helena-type OIB affinity. The mantle source of the Mecsek volcanics could be similar to that proposed by Wilson and Downes (1991) as one of the mantle endmembers for extension-related Tertiary-Quaternary alkaline basalts in Europe. Geochemical modelling indicates that the primary magmas of the Na-basanite series were formed by about 4% partial melting, whereas ankaramites and alkali basalts originated by about 6% partial melting of a garnet-peridotite source.
Journal of Volcanology and Geothermal Research, 1995
Two flank eruptions took place at Mt. Etna during 1989–1993. The former (September–October 1989) ... more Two flank eruptions took place at Mt. Etna during 1989–1993. The former (September–October 1989) produced lavas among the most primitive of this century while the latter (December 1991–March 1993) was unusually long lasting and the largest of the last three centuries. Alkali basalts of 1989 displayed initial enrichments of Rb and K accompanied by an higher value of radiogenic-Sr and
Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogeni... more Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogenic belt has led to the opening of the Tyrrhenian basin. Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Italian mainland during this time, building up the Tuscan Magmatic Province as the fold belt was progressively thinned, heated and intruded by mafic magmas. An intrusive complex was progressively built on western Elba Island by emplacement, within a stack of nappes, of multiple, shallow-level porphyritic laccoliths, a major pluton, and a final dyke swarm, all within the span from about 8 to 6.8 Ma. New geochemical and Sr–Nd isotopic investigations constrain the compositions of materials involved in the genesis of the magmas of Elba Island compared to the whole Tuscan Magmatic Province. Several distinct magma sources, in both the crust and mantle, have been identified as contributing to the Elba magmatism as it evolved from crust-, to hybrid-, to m...
... Samples were selected from relatively high-B lavas (Taddeucci, 1964) belonging to the Neogene... more ... Samples were selected from relatively high-B lavas (Taddeucci, 1964) belonging to the Neogene-Quaternary volcanism in central Italy. ... Moreover, in several studies of volcanic suites (eg, Ryan and Langmuir 1993; Ryan et al 1996; Benton et al 1999 and Tonarini et al 2001, in ...
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Papers by Sonia Tonarini