2022
|
Couzinié, S., Bouilhol, P., Laurent, O., Grocolas, T., Montel, J. M. Cambro--Ordovician ferrosilicic magmatism along the northern Gondwana margin: constraints from the Cézarenque--Joyeuse gneiss complex (French Massif Central) (Article de journal) Dans: BSGF- Earth Sciences Bulletin, vol. 193, no. 15, 2022. @article{Couzini_etal2022,
title = {Cambro--Ordovician ferrosilicic magmatism along the northern Gondwana margin: constraints from the C\'{e}zarenque--Joyeuse gneiss complex (French Massif Central)},
author = {S. Couzini\'{e} and P. Bouilhol and O. Laurent and T. Grocolas and J. M. Montel},
doi = {10.1051/bsgf/2022010},
year = {2022},
date = {2022-01-01},
journal = {BSGF- Earth Sciences Bulletin},
volume = {193},
number = {15},
abstract = {It is well-acknowledged that the northern margin of the Gondwana supercontinent was affected by a major magmatic event at late Cambrian (Furongian) to early Ordovician (Tremadocian--Floian) times. However, an accurate assessment of its extent, origin, and significance is partly hampered by the incomplete characterization of the numerous gneiss massifs exposed in the inner part of the Variscan belt, as some of them possibly represent dismembered and deformed Furongian--Lower Ordovician igneous bodies. In this study, we document the case of the ‘‘C\'{e}zarenque--Joyeuse’’ gneiss complex in the C\'{e}vennes parautochthon domain of the French Massif Central. The gneisses form decametre- to kilometre-thick concordant massifs interlayered within a pluri-kilometric sequence of mica- and quartz schists. They encompass two main petrological types: augen gneisses and albite gneisses, both typified by their blue and engulfed quartz grains with the augen facies differing by the presence of centimetre-sized pseudomorphs after K-feldspar and the local preservation of igneous textures. Whole-rock geochemistry highlights that many gneisses have magmatic ferrosilicic (acidic with anomalously high FeOt and low CaO) compositions while others are akin to greywackes. Collectively, it is inferred that the bulk of the C\'{e}zarenque--Joyeuse gneisses represents former rhyodacite lava flows or ignimbrites and associated epiclastic tuffs. Volumetrically subordinate, finer grained, and strongly silicic leucogneisses are interpreted as microgranite dykes originally intrusive within the volcanic edifices. LA--ICP--MS U--Pb dating of magmatic zircon grains extracted from an augen gneiss and a leucogneiss brackets the crystallization age of the silicic magmas between 486.1thinspacetextpmthinspace5.5thinspaceMa and 483.0thinspacetextpmthinspace5.5thinspaceMa which unambiguously ties the C\'{e}zarenque--Joyeuse gneisses to the Furongian--Lower Ordovician volcanic belt of SW Europe. Inherited zircon date distributions, Ti-in-zircon and zircon saturation thermometry demonstrate that they formed by melting at 750--820thinspacetextdegreeC of Ediacaran sediments. Zircon Eu/Eu* and Ce/Ce* systematics indicate that the melts were strongly reduced (fO2 probably close to the values expected for the iron--w\"{u}stite buffer), possibly because they interacted during ascent with Lower Cambrian black shales. This would have enhanced Fe solubility in the melt phase and may explain the peculiar ferrosilicic signature displayed by many Furongian--Lower Ordovician igneous rocks in the northern Gondwana realm. We infer that crustal melting resulted from a combination of mantle-derived magma underplating in an intracontinental rift setting and anomalously elevated radiogenic heat production within the Ediacaran sedimentary sequences.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
It is well-acknowledged that the northern margin of the Gondwana supercontinent was affected by a major magmatic event at late Cambrian (Furongian) to early Ordovician (Tremadocian--Floian) times. However, an accurate assessment of its extent, origin, and significance is partly hampered by the incomplete characterization of the numerous gneiss massifs exposed in the inner part of the Variscan belt, as some of them possibly represent dismembered and deformed Furongian--Lower Ordovician igneous bodies. In this study, we document the case of the ‘‘Cézarenque--Joyeuse’’ gneiss complex in the Cévennes parautochthon domain of the French Massif Central. The gneisses form decametre- to kilometre-thick concordant massifs interlayered within a pluri-kilometric sequence of mica- and quartz schists. They encompass two main petrological types: augen gneisses and albite gneisses, both typified by their blue and engulfed quartz grains with the augen facies differing by the presence of centimetre-sized pseudomorphs after K-feldspar and the local preservation of igneous textures. Whole-rock geochemistry highlights that many gneisses have magmatic ferrosilicic (acidic with anomalously high FeOt and low CaO) compositions while others are akin to greywackes. Collectively, it is inferred that the bulk of the Cézarenque--Joyeuse gneisses represents former rhyodacite lava flows or ignimbrites and associated epiclastic tuffs. Volumetrically subordinate, finer grained, and strongly silicic leucogneisses are interpreted as microgranite dykes originally intrusive within the volcanic edifices. LA--ICP--MS U--Pb dating of magmatic zircon grains extracted from an augen gneiss and a leucogneiss brackets the crystallization age of the silicic magmas between 486.1thinspacetextpmthinspace5.5thinspaceMa and 483.0thinspacetextpmthinspace5.5thinspaceMa which unambiguously ties the Cézarenque--Joyeuse gneisses to the Furongian--Lower Ordovician volcanic belt of SW Europe. Inherited zircon date distributions, Ti-in-zircon and zircon saturation thermometry demonstrate that they formed by melting at 750--820thinspacetextdegreeC of Ediacaran sediments. Zircon Eu/Eu* and Ce/Ce* systematics indicate that the melts were strongly reduced (fO2 probably close to the values expected for the iron--wüstite buffer), possibly because they interacted during ascent with Lower Cambrian black shales. This would have enhanced Fe solubility in the melt phase and may explain the peculiar ferrosilicic signature displayed by many Furongian--Lower Ordovician igneous rocks in the northern Gondwana realm. We infer that crustal melting resulted from a combination of mantle-derived magma underplating in an intracontinental rift setting and anomalously elevated radiogenic heat production within the Ediacaran sedimentary sequences. |
2018
|
Montel, J. M., Razafimahatratra, D., Perseval, P., Poitrasson, F., Moine, B., Seydoux-Guillaume, A. M., Pik, R., Arnaud, N., Gibert, F. The giant monazite crystals from Manangotry (Madagascar) (Article de journal) Dans: Chemical Geology, vol. 484, p. 36–50, 2018. @article{Montel_etal2018,
title = {The giant monazite crystals from Manangotry (Madagascar)},
author = {J. M. Montel and D. Razafimahatratra and P. Perseval and F. Poitrasson and B. Moine and A. M. Seydoux-Guillaume and R. Pik and N. Arnaud and F. Gibert},
doi = {10.1016/j.chemgeo.2017.10.034},
year = {2018},
date = {2018-01-01},
journal = {Chemical Geology},
volume = {484},
pages = {36--50},
abstract = {The Manangotry area in the South-East of Madagascar is famous for its giant monazite crystals. The studied occurrence is an outcrop near the Manangotry pass, were giant, cm-sized crystals have been found. The crystals are embedded in biotitite levels, also containing cm-sized xenomorphic ilmenite, and are associated with a 1 m thick layer of apatite. Besides giant crystals, monazite is also present as abundant small (mm-sized) grains. The surrounding rocks are leucogranites and charnockites. The monazite giant crystals are chemically homogeneous and thorium-rich, whereas small crystals tend to be heterogeneous. Both biotite and apatite are F-rich. Temperature estimates from biotite and apatite yielded 750 to 800 textdegreeC. Despite their high radioactivity, the giant crystals preserve a high degree of crystallinity. Electron microprobe U-Th-Pb dating produced ages of 537 textpm 14, 534 textpm 10 and 530 textpm 10 Ma, considered to be the age of the main monazite crystallization episode but some minor domains in small grains yielded 482 textpm 12 Ma. The enclosing biotites yielded 453 textpm 6 Ma Ar-Ar ages. More than 98 % of radiogenic helium have been retained in the studied monazite samples, and kinetic experiments indicates the intrinsic diffusion parameters for high-temperature to be Ea= 53 kcal/mol and D0= 3085 cm 2/s. The paragenesis (monazite-apatite-ilmenite-biotite) is different from any other occurrences of larges monazite elsewhere. Based on the current data and literature, the preferred genetic model for these giant monazites is crystallization from a high-temperature fluorine-rich fluid, possibly originating from surrounding charnockites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Manangotry area in the South-East of Madagascar is famous for its giant monazite crystals. The studied occurrence is an outcrop near the Manangotry pass, were giant, cm-sized crystals have been found. The crystals are embedded in biotitite levels, also containing cm-sized xenomorphic ilmenite, and are associated with a 1 m thick layer of apatite. Besides giant crystals, monazite is also present as abundant small (mm-sized) grains. The surrounding rocks are leucogranites and charnockites. The monazite giant crystals are chemically homogeneous and thorium-rich, whereas small crystals tend to be heterogeneous. Both biotite and apatite are F-rich. Temperature estimates from biotite and apatite yielded 750 to 800 textdegreeC. Despite their high radioactivity, the giant crystals preserve a high degree of crystallinity. Electron microprobe U-Th-Pb dating produced ages of 537 textpm 14, 534 textpm 10 and 530 textpm 10 Ma, considered to be the age of the main monazite crystallization episode but some minor domains in small grains yielded 482 textpm 12 Ma. The enclosing biotites yielded 453 textpm 6 Ma Ar-Ar ages. More than 98 % of radiogenic helium have been retained in the studied monazite samples, and kinetic experiments indicates the intrinsic diffusion parameters for high-temperature to be Ea= 53 kcal/mol and D0= 3085 cm 2/s. The paragenesis (monazite-apatite-ilmenite-biotite) is different from any other occurrences of larges monazite elsewhere. Based on the current data and literature, the preferred genetic model for these giant monazites is crystallization from a high-temperature fluorine-rich fluid, possibly originating from surrounding charnockites. |
2010
|
Yonta-Ngoune, C., Nkoumbou, C., Barbey, P., Breton, N. Le, Montel, J. M., Villieras, F. Geological context of the Boumnyebel talcschists (Cameroun): Inferences on the Pan-African Belt of Central Africa (Article de journal) Dans: Comptes Rendus. Géoscience, vol. 342, no. 2, p. 108–115, 2010. @article{Yonta-Ngoune_etal2010,
title = {Geological context of the Boumnyebel talcschists (Cameroun): Inferences on the Pan-African Belt of Central Africa},
author = {C. Yonta-Ngoune and C. Nkoumbou and P. Barbey and N. Le Breton and J. M. Montel and F. Villieras},
doi = {10.1016/j.crte.2009.12.007},
year = {2010},
date = {2010-01-01},
journal = {Comptes Rendus. G\'{e}oscience},
volume = {342},
number = {2},
pages = {108--115},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
1999
|
Barbey, P., Marignac, C., Montel, J. M., Macaudi`ere, J., Gasquet, D., Jabbori, J. Cordierite growth textures and the conditions of genesis and emplacement of crustal granitic magmas : the Valey Granite complex ( Massif Central, France) (Article de journal) Dans: Journal of Petrology, vol. 40, no. 9, p. 1425–1441, 1999. @article{Barbey_etal1999,
title = {Cordierite growth textures and the conditions of genesis and emplacement of crustal granitic magmas : the Valey Granite complex ( Massif Central, France)},
author = {P. Barbey and C. Marignac and J. M. Montel and J. Macaudi`ere and D. Gasquet and J. Jabbori},
doi = {10.1093/petrology/40.9.1425},
year = {1999},
date = {1999-01-01},
journal = {Journal of Petrology},
volume = {40},
number = {9},
pages = {1425--1441},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
1992
|
Montel, J. M., Marignac, C., Barbey, P., Pichavant, M. Thermobarometry and granite genesis : the Hercynian low-P high-T Velay anatectic dome (French Massif Central) (Article de journal) Dans: Journal of Metamorphic Geology, vol. 10, p. 1–15, 1992. @article{Montel_etal1992,
title = {Thermobarometry and granite genesis : the Hercynian low-P high-T Velay anatectic dome (French Massif Central)},
author = {J. M. Montel and C. Marignac and P. Barbey and M. Pichavant},
year = {1992},
date = {1992-01-01},
journal = {Journal of Metamorphic Geology},
volume = {10},
pages = {1--15},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
1989
|
Montel, J. M., Lhote, F., Claude, J. M. Monazite end members and solid solutions : synthesis, unit-cell characteristics, and utilization as microprobe standards (Article de journal) Dans: Mineralogical Magazine, vol. 53, p. 120–123, 1989. @article{Montel_etal1989,
title = {Monazite end members and solid solutions : synthesis, unit-cell characteristics, and utilization as microprobe standards},
author = {J. M. Montel and F. Lhote and J. M. Claude},
year = {1989},
date = {1989-01-01},
journal = {Mineralogical Magazine},
volume = {53},
pages = {120--123},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
1988
|
Montel, J. M. Premi`ere découverte dtextquoterightune vaugnérite `a orthopyrox`ene : pétrographie, géochimie et conséquences pour la gen`ese des vaugnérites (Article de journal) Dans: Comptes-Rendus de ltextquoterightAcadémie des Sciences, série II, vol. 306, p. 985–990, 1988. @article{Montel1988,
title = {Premi`ere d\'{e}couverte dtextquoterightune vaugn\'{e}rite `a orthopyrox`ene : p\'{e}trographie, g\'{e}ochimie et cons\'{e}quences pour la gen`ese des vaugn\'{e}rites},
author = {J. M. Montel},
year = {1988},
date = {1988-01-01},
journal = {Comptes-Rendus de ltextquoterightAcad\'{e}mie des Sciences, s\'{e}rie II},
volume = {306},
pages = {985--990},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Pichavant, M., Montel, J. M. Petrogenesis of a two-mica ignimbrite suite: the Macusani volcanics, SE Peru (Article de journal) Dans: Transactions of the Royal Society of Edinburgh-Earth Sciences, vol. 79, 1988. @article{Pichavant+Montel1988,
title = {Petrogenesis of a two-mica ignimbrite suite: the Macusani volcanics, SE Peru},
author = {M. Pichavant and J. M. Montel},
year = {1988},
date = {1988-01-01},
journal = {Transactions of the Royal Society of Edinburgh-Earth Sciences},
volume = {79},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
1986
|
Montel, J. M. Experimental determination of the solubility of Ce-monazite in SiO2-Al2O3-K2O-Na2O melts at 800textdegreeC, 2 kbar, under H2O-saturated conditions (Article de journal) Dans: Geology, vol. 14, p. 659–662, 1986. @article{Montel1986,
title = {Experimental determination of the solubility of Ce-monazite in SiO2-Al2O3-K2O-Na2O melts at 800textdegreeC, 2 kbar, under H2O-saturated conditions},
author = {J. M. Montel},
year = {1986},
date = {1986-01-01},
journal = {Geology},
volume = {14},
pages = {659--662},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Montel, J. M., Weber, C., Barbey, P., Pichavant, M. Thermo-barométrie du domaine anatectique du Velay (Massif Central, France) et conditions de gen`ese des granites tardi-migmatitiques (Article de journal) Dans: Comptes Rendus de ltextquoterightAcadémie des Sciences, série II, vol. 302, p. 647–652, 1986. @article{Montel_etal1986,
title = {Thermo-barom\'{e}trie du domaine anatectique du Velay (Massif Central, France) et conditions de gen`ese des granites tardi-migmatitiques},
author = {J. M. Montel and C. Weber and P. Barbey and M. Pichavant},
year = {1986},
date = {1986-01-01},
journal = {Comptes Rendus de ltextquoterightAcad\'{e}mie des Sciences, s\'{e}rie II},
volume = {302},
pages = {647--652},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Montel, J. M., Weber, C., Pichavant, M. Biotite-sillimanite-spinel assemblages in high-grade metamorphic rocks : occurrences, chemographic analysis and the thermobarometric interest (Article de journal) Dans: Bulletin de Minéralogie, vol. 109, p. 555–573, 1986. @article{Montel_etal1986_2,
title = {Biotite-sillimanite-spinel assemblages in high-grade metamorphic rocks : occurrences, chemographic analysis and the thermobarometric interest},
author = {J. M. Montel and C. Weber and M. Pichavant},
year = {1986},
date = {1986-01-01},
journal = {Bulletin de Min\'{e}ralogie},
volume = {109},
pages = {555--573},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Montel, J. M., Weisbrod, A. Characteristics and evolution of textquotelefttextquoteleftvaugneritic magmastextquoterighttextquoteright : an analytical and experimental approach, on the example of the Cévennes médianes (French Massif Central) (Article de journal) Dans: Bulletin de Minéralogie, vol. 109, p. 575–587, 1986. @article{Montel+Weisbrod1986,
title = {Characteristics and evolution of textquotelefttextquoteleftvaugneritic magmastextquoterighttextquoteright : an analytical and experimental approach, on the example of the C\'{e}vennes m\'{e}dianes (French Massif Central)},
author = {J. M. Montel and A. Weisbrod},
year = {1986},
date = {1986-01-01},
journal = {Bulletin de Min\'{e}ralogie},
volume = {109},
pages = {575--587},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
1985
|
Montel, J. M. Xénolithes peralumineux dans les dolérites du Peyron, en Velay (Massif Central, France). Indications sur ltextquoterightévolution de la cro^ute profonde tardi-hercynienne (Article de journal) Dans: Comptes Rendus de ltextquoterightAcadémie des Sciences, série II, vol. 301, p. 615–620, 1985. @article{Montel1985,
title = {X\'{e}nolithes peralumineux dans les dol\'{e}rites du Peyron, en Velay (Massif Central, France). Indications sur ltextquoteright\'{e}volution de la cro^ute profonde tardi-hercynienne},
author = {J. M. Montel},
year = {1985},
date = {1985-01-01},
journal = {Comptes Rendus de ltextquoterightAcad\'{e}mie des Sciences, s\'{e}rie II},
volume = {301},
pages = {615--620},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
