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Michel Faure - One of the best experts on this subject based on the ideXlab platform.
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middle carboniferous crustal melting in the variscan belt new insights from u th pbtot monazite and u pb zircon ages of the montagne noire axial zone southern french massif central
Gondwana Research, 2010Co-Authors: Michel Faure, Alain Cocherie, Eugene Be Mezeme, Nicolas Charles, Philippe RossiAbstract:Abstract In France, the Devonian–Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean–Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of Migmatization was not clearly settled. Eleven U–Th–Pbtot. ages on monazite and three U–Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Angles, Vialais, Soulie) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333–326 Ma (Visean) and late granitoids emplaced around 325–318 Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560 Ma and 480 Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the “Tufs anthraciferes” volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale.
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Middle Carboniferous crustal melting in the Variscan Belt: New insights from U-Th-Pbtot. monazite and U-Pb zircon ages of the Montagne Noire Axial Zone (southern French Massif Central)
Gondwana Research, 2010Co-Authors: Michel Faure, E. Be Mezeme, Alain Cocherie, Nicolas Charles, Philippe RossiAbstract:In France, the Devonian-Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean-Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of Migmatization was not clearly settled. Eleven U-Th-Pbtot. ages on monazite and three U-Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Anglès, Vialais, Soulié) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333-326Ma (Visean) and late granitoids emplaced around 325-318Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560Ma and 480Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the "Tufs anthracifères" volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale.
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Electron microprobe monazite geochronology of magmatic events: Examples from Variscan migmatites and granitoids, Massif Central, France
Lithos, 2006Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, Olivier Legendre, Ph. RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cévennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cévennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events
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Electron microprobe monazite geochronology : a tool for evaluating magmatic ages with examples from Variscan Massif Central migmatites and granotoids, France.
Lithos, 2006Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, O. Lengendre, Philippe RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cévennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cévennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events.
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Electron microprobe monazite geochronology of magmatic events: Examples from Variscan migmatites and granitoids, Massif Central, France
Lithos, 2005Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, Olivier Legendre, Ph. RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cevennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cevennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events.
Philippe Rossi - One of the best experts on this subject based on the ideXlab platform.
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middle carboniferous crustal melting in the variscan belt new insights from u th pbtot monazite and u pb zircon ages of the montagne noire axial zone southern french massif central
Gondwana Research, 2010Co-Authors: Michel Faure, Alain Cocherie, Eugene Be Mezeme, Nicolas Charles, Philippe RossiAbstract:Abstract In France, the Devonian–Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean–Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of Migmatization was not clearly settled. Eleven U–Th–Pbtot. ages on monazite and three U–Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Angles, Vialais, Soulie) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333–326 Ma (Visean) and late granitoids emplaced around 325–318 Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560 Ma and 480 Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the “Tufs anthraciferes” volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale.
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Middle Carboniferous crustal melting in the Variscan Belt: New insights from U-Th-Pbtot. monazite and U-Pb zircon ages of the Montagne Noire Axial Zone (southern French Massif Central)
Gondwana Research, 2010Co-Authors: Michel Faure, E. Be Mezeme, Alain Cocherie, Nicolas Charles, Philippe RossiAbstract:In France, the Devonian-Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean-Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of Migmatization was not clearly settled. Eleven U-Th-Pbtot. ages on monazite and three U-Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Anglès, Vialais, Soulié) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333-326Ma (Visean) and late granitoids emplaced around 325-318Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560Ma and 480Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the "Tufs anthracifères" volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale.
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Electron microprobe monazite geochronology : a tool for evaluating magmatic ages with examples from Variscan Massif Central migmatites and granotoids, France.
Lithos, 2006Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, O. Lengendre, Philippe RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cévennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cévennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events.
Alain Cocherie - One of the best experts on this subject based on the ideXlab platform.
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middle carboniferous crustal melting in the variscan belt new insights from u th pbtot monazite and u pb zircon ages of the montagne noire axial zone southern french massif central
Gondwana Research, 2010Co-Authors: Michel Faure, Alain Cocherie, Eugene Be Mezeme, Nicolas Charles, Philippe RossiAbstract:Abstract In France, the Devonian–Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean–Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of Migmatization was not clearly settled. Eleven U–Th–Pbtot. ages on monazite and three U–Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Angles, Vialais, Soulie) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333–326 Ma (Visean) and late granitoids emplaced around 325–318 Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560 Ma and 480 Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the “Tufs anthraciferes” volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale.
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Middle Carboniferous crustal melting in the Variscan Belt: New insights from U-Th-Pbtot. monazite and U-Pb zircon ages of the Montagne Noire Axial Zone (southern French Massif Central)
Gondwana Research, 2010Co-Authors: Michel Faure, E. Be Mezeme, Alain Cocherie, Nicolas Charles, Philippe RossiAbstract:In France, the Devonian-Carboniferous Variscan orogeny developed at the expense of continental crust belonging to the northern margin of Gondwana. A Visean-Serpukhovian crustal melting has been recently documented in several massifs. However, in the Montagne Noire of the Variscan French Massif Central, which is the largest area involved in this partial melting episode, the age of Migmatization was not clearly settled. Eleven U-Th-Pbtot. ages on monazite and three U-Pb ages on associated zircon are reported from migmatites (La Salvetat, Ourtigas), anatectic granitoids (Laouzas, Montalet) and post-migmatitic granites (Anglès, Vialais, Soulié) from the Montagne Noire Axial Zone are presented here for the first time. Migmatization and emplacement of anatectic granitoids took place around 333-326Ma (Visean) and late granitoids emplaced around 325-318Ma (Serpukhovian). Inherited zircons and monazite date the orthogneiss source rock of the Late Visean melts between 560Ma and 480Ma. In migmatites and anatectic granites, inherited crystals dominate the zircon populations. The migmatitization is the middle crust expression of a pervasive Visean crustal melting event also represented by the "Tufs anthracifères" volcanism in the northern Massif Central. This crustal melting is widespread in the French Variscan belt, though it is restricted to the upper plate of the collision belt. A mantle input appears as a likely mechanism to release the heat necessary to trigger the melting of the Variscan middle crust at a continental scale.
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Electron microprobe monazite geochronology : a tool for evaluating magmatic ages with examples from Variscan Massif Central migmatites and granotoids, France.
Lithos, 2006Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, O. Lengendre, Philippe RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cévennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cévennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events.
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Electron microprobe monazite geochronology of magmatic events: Examples from Variscan migmatites and granitoids, Massif Central, France
Lithos, 2006Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, Olivier Legendre, Ph. RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cévennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cévennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events
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Electron microprobe monazite geochronology of magmatic events: Examples from Variscan migmatites and granitoids, Massif Central, France
Lithos, 2005Co-Authors: E. Be Mezeme, Alain Cocherie, Michel Faure, Olivier Legendre, Ph. RossiAbstract:U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method offering high spatial resolution. This method has been applied on monazite from the Cevennes migmatites and granitoids from the southeast of the French Massif Central. Measurements were performed on separated grains after systematic back-scattered electron (BSE) imaging. Monazites from migmatites record two main ages: (i) a protolith age of about 550–543 Ma obtained on inherited cores, and (ii) a Migmatization event between 329 ± 5 and 323 ± 3 Ma recorded by monazite rims and all other monogenetic grains. Monazite from the peraluminous Rocles pluton yields a 318 ± 3 Ma age. Finally, three granite dykes are dated at 333 ± 6, 318 ± 5 and 311 ± 5 Ma; the older dyke is the most deformed of them and is interpreted as linked to the Migmatization event; the two other dykes are geochronologically, petrologically and structurally coeval with the Rocles pluton. The data constrain the timing of crustal melting following Variscan thickening in the northern Cevennes area. Migmatization of Ordovician protoliths took place at 329–323 Ma and was shortly followed by intrusion of leucogranite at 318–311 Ma. The study shows that EPMA dating of monazite can be successfully used to resolve a close succession of regional melting events.
Jean-charles Poilvet - One of the best experts on this subject based on the ideXlab platform.
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two stage partial melting during the variscan extensional tectonics montagne noire france
International Journal of Earth Sciences, 2017Co-Authors: Marc Poujol, Gilles Ruffet, Romain Tartese, Jeanlouis Paquette, Jean Van Den Driessche, Pavel Pitra, Jean-charles PoilvetAbstract:One of the striking features that characterise the late stages of the Variscan orogeny is the development of gneiss and migmatite domes, as well as extensional Late Carboniferous and Permian sedimentary basins. It remains a matter of debate whether the formation of domes was related to the well-documented late orogenic extension or to the contractional tectonics that preceded. Migmatization and magmatism are expected to predate extension if the domes are compression-related regional anticlines, but they must both precede and be contemporaneous with extension if they are extensional core complexes. In the Montagne Noire area (southern French Massif Central), where Migmatization, magmatism and the deformation framework are well documented, the age of the extensional event was unequivocally constrained to 300–290 Ma. Therefore, dating Migmatization in this area is a key point for discriminating between the two hypotheses and understanding the Late Palaeozoic evolution of this part of the Variscan belt. For this purpose, a migmatite and an associated anatectic granite from the Montagne Noire dome were dated by LA-ICP-MS (U–Th–Pb on zircon and monazite) and laser probe 40Ar-39Ar (K–Ar on muscovite). Although zircon did not record any Variscan age unequivocally related to compression (380-330 Ma), two age groups were identified from the monazite crystals. A first event, at ca. 319 Ma (U–Th–Pb on monazite), is interpreted as a first stage of Migmatization and as the emplacement age of the granite, respectively. A second event at ca. 298–295 Ma, recorded by monazite (U–Th–Pb) and by the muscovite 40Ar-39Ar system in the migmatite and in the granite, could be interpreted as a fluid-induced event, probably related to a second melting event identified through the syn-extensional emplacement of the nearby Montalet leucogranite ca. 295 Ma ago. The ages of these two events post-date the Variscan compression and agree with an overall extensional context for the development of the Montagne Noire dome-shaped massif. Comparison of these results with published chemical (EPMA) dating of monazite from the same rocks demonstrates that the type of statistical treatment applied to EPMA data is crucial in order to resolve different monazite age populations.
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two stage partial melting during the variscan extensional tectonics montagne noire france
International Journal of Earth Sciences, 2017Co-Authors: Marc Poujol, Gilles Ruffet, Romain Tartese, Jeanlouis Paquette, Jean Van Den Driessche, Pavel Pitra, Jean-charles PoilvetAbstract:One of the striking features that characterise the late stages of the Variscan orogeny is the development of gneiss and migmatite domes, as well as extensional Late Carboniferous and Permian sedimentary basins. It remains a matter of debate whether the formation of domes was related to the well-documented late orogenic extension or to the contractional tectonics that preceded. Migmatization and magmatism are expected to predate extension if the domes are compression-related regional anticlines, but they must both precede and be contemporaneous with extension if they are extensional core complexes. In the Montagne Noire area (southern French Massif Central), where Migmatization, magmatism and the deformation framework are well documented, the age of the extensional event was unequivocally constrained to 300–290 Ma. Therefore, dating Migmatization in this area is a key point for discriminating between the two hypotheses and understanding the Late Palaeozoic evolution of this part of the Variscan belt. For this purpose, a migmatite and an associated anatectic granite from the Montagne Noire dome were dated by LA-ICP-MS (U–Th–Pb on zircon and monazite) and laser probe 40Ar-39Ar (K–Ar on muscovite). Although zircon did not record any Variscan age unequivocally related to compression (380-330 Ma), two age groups were identified from the monazite crystals. A first event, at ca. 319 Ma (U–Th–Pb on monazite), is interpreted as a first stage of Migmatization and as the emplacement age of the granite, respectively. A second event at ca. 298–295 Ma, recorded by monazite (U–Th–Pb) and by the muscovite 40Ar-39Ar system in the migmatite and in the granite, could be interpreted as a fluid-induced event, probably related to a second melting event identified through the syn-extensional emplacement of the nearby Montalet leucogranite ca. 295 Ma ago. The ages of these two events post-date the Variscan compression and agree with an overall extensional context for the development of the Montagne Noire dome-shaped massif. Comparison of these results with published chemical (EPMA) dating of monazite from the same rocks demonstrates that the type of statistical treatment applied to EPMA data is crucial in order to resolve different monazite age populations.
Romain Tartese - One of the best experts on this subject based on the ideXlab platform.
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two stage partial melting during the variscan extensional tectonics montagne noire france
International Journal of Earth Sciences, 2017Co-Authors: Marc Poujol, Gilles Ruffet, Romain Tartese, Jeanlouis Paquette, Jean Van Den Driessche, Pavel Pitra, Jean-charles PoilvetAbstract:One of the striking features that characterise the late stages of the Variscan orogeny is the development of gneiss and migmatite domes, as well as extensional Late Carboniferous and Permian sedimentary basins. It remains a matter of debate whether the formation of domes was related to the well-documented late orogenic extension or to the contractional tectonics that preceded. Migmatization and magmatism are expected to predate extension if the domes are compression-related regional anticlines, but they must both precede and be contemporaneous with extension if they are extensional core complexes. In the Montagne Noire area (southern French Massif Central), where Migmatization, magmatism and the deformation framework are well documented, the age of the extensional event was unequivocally constrained to 300–290 Ma. Therefore, dating Migmatization in this area is a key point for discriminating between the two hypotheses and understanding the Late Palaeozoic evolution of this part of the Variscan belt. For this purpose, a migmatite and an associated anatectic granite from the Montagne Noire dome were dated by LA-ICP-MS (U–Th–Pb on zircon and monazite) and laser probe 40Ar-39Ar (K–Ar on muscovite). Although zircon did not record any Variscan age unequivocally related to compression (380-330 Ma), two age groups were identified from the monazite crystals. A first event, at ca. 319 Ma (U–Th–Pb on monazite), is interpreted as a first stage of Migmatization and as the emplacement age of the granite, respectively. A second event at ca. 298–295 Ma, recorded by monazite (U–Th–Pb) and by the muscovite 40Ar-39Ar system in the migmatite and in the granite, could be interpreted as a fluid-induced event, probably related to a second melting event identified through the syn-extensional emplacement of the nearby Montalet leucogranite ca. 295 Ma ago. The ages of these two events post-date the Variscan compression and agree with an overall extensional context for the development of the Montagne Noire dome-shaped massif. Comparison of these results with published chemical (EPMA) dating of monazite from the same rocks demonstrates that the type of statistical treatment applied to EPMA data is crucial in order to resolve different monazite age populations.
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two stage partial melting during the variscan extensional tectonics montagne noire france
International Journal of Earth Sciences, 2017Co-Authors: Marc Poujol, Gilles Ruffet, Romain Tartese, Jeanlouis Paquette, Jean Van Den Driessche, Pavel Pitra, Jean-charles PoilvetAbstract:One of the striking features that characterise the late stages of the Variscan orogeny is the development of gneiss and migmatite domes, as well as extensional Late Carboniferous and Permian sedimentary basins. It remains a matter of debate whether the formation of domes was related to the well-documented late orogenic extension or to the contractional tectonics that preceded. Migmatization and magmatism are expected to predate extension if the domes are compression-related regional anticlines, but they must both precede and be contemporaneous with extension if they are extensional core complexes. In the Montagne Noire area (southern French Massif Central), where Migmatization, magmatism and the deformation framework are well documented, the age of the extensional event was unequivocally constrained to 300–290 Ma. Therefore, dating Migmatization in this area is a key point for discriminating between the two hypotheses and understanding the Late Palaeozoic evolution of this part of the Variscan belt. For this purpose, a migmatite and an associated anatectic granite from the Montagne Noire dome were dated by LA-ICP-MS (U–Th–Pb on zircon and monazite) and laser probe 40Ar-39Ar (K–Ar on muscovite). Although zircon did not record any Variscan age unequivocally related to compression (380-330 Ma), two age groups were identified from the monazite crystals. A first event, at ca. 319 Ma (U–Th–Pb on monazite), is interpreted as a first stage of Migmatization and as the emplacement age of the granite, respectively. A second event at ca. 298–295 Ma, recorded by monazite (U–Th–Pb) and by the muscovite 40Ar-39Ar system in the migmatite and in the granite, could be interpreted as a fluid-induced event, probably related to a second melting event identified through the syn-extensional emplacement of the nearby Montalet leucogranite ca. 295 Ma ago. The ages of these two events post-date the Variscan compression and agree with an overall extensional context for the development of the Montagne Noire dome-shaped massif. Comparison of these results with published chemical (EPMA) dating of monazite from the same rocks demonstrates that the type of statistical treatment applied to EPMA data is crucial in order to resolve different monazite age populations.