Ediacaran to Carboniferous magmatism in the NE Armorican Massif: a LA-ICP-MS study
Abstract
In the Central and Northern Armorican Domains (Brittany and part of Normandy and Maine), the Precambrian basement displays evidence for a late Proterozoic orogeny, called the Cadomian orogeny. In its eastern part (Fougères and Maine Units), the late Neoproterozoic sediments are intruded by a large number of peraluminous granitoids, collectively grouped under the heading of Mancellian Batholith. The emplacement age of these granites is classically considered to be around 540 Ma. Given that the Precambrian-Cambrian boundary is currently set at 538.8 ± 0.2 Ma, this age warrants further investigation. Within the framework of the Normandy-Maine Geopark project (which is funding this study), we undertook a revision of the ages of granites from the northeastern part of the Armorican Massif. We selected first two cordierite granodiorite samples, one from the la Ferté-Macé granite (MAG-1) from an old quarry near La Raitière in Joué-du-Bois, and the other from the Athis granite (MAG-2), just below the unconformity with the Cambrian cover at La Roche d’Oëtre. In both samples, some zircons exhibit inherited cores and magmatic margins, with inherited ages ranging from 2430 to 600 Ma. Sample MAG-1 yielded a concordant age of 552 ± 2 Ma (MSWD=1.1, n=11) and sample MAG-2 an age of 552 ± 4 Ma (MSWD=0.6, n=8). Therefore, two major conclusions are (i) the age of emplacement of the granites of Athis and of La Ferté-Macé at 552 Ma and (ii) a metasedimentary source for these granites having a maximum depositional age of 600 Ma and a weak inheritance from Icartian protoliths (around 2.43 Ga). Another sample from the Saint-Pierre-des-Nids granodiorite (sample MAG-4), classically considered as belonging to the Mancellian Batholith, has provided a concordant age of 496.2 ± 2.5 Ma (MSWD=0.53, n=17). This late Cambrian emplacement age is consistent with field data and previous monazite ages obtained on a nearby intrusion (Alexain-Deux Evailles). Few Carboniferous intrusions are known in this part of the Armorican Massif. We report an age of 301.5 ± 6.6 Ma (MSWD=1.9, n=12) for the Alençon leucogranite, consistent with the field observations indicating that it developed a contact aureole in the Palaeozoic sediments. The Grosville rhyolite, up to now considered as part of the late Proterozoic Saint-Germain-le-Gaillard Complex, has provided a lower intercept date of 309.5 ± 5.6 Ma (MSWD=0.21, n=12), confirmed by a concordia date of 311.6 ± 6.1 Ma (MSWD=1.1, n=4). Overall, the new data indicate that most of the Mancellian granitoids are 10 to 15 Ma older than the Precambrian-Cambrian boundary, and that they were quickly unroofed, providing zircon detrital grains found in most of the Brioverian sediments from the Central Armorican Domain. Some peraluminous granites (Saint-Pierre-des-Nids, Alexain-Deux Evailles) may represent the magma chambers that have been hypothesized below the caldera-bearing rift of the Maine Unit, an unexpected result of this study.
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BibTeX
@article{ballevre2026ediacaran,
title = {{Ediacaran to Carboniferous magmatism in the NE Armorican Massif: a LA-ICP-MS study}},
author = {Michel Ballèvre and Marc Poujol and Hugo Champie and Bastien Lesage and Isabelle Aubron},
journal = {Bulletin de la Société Géologique de France},
year = {2026},
month = oct,
doi = {10.1051/bsgf/2026013},
url = {https://hal.science/hal-05820698v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Ediacaran to Carboniferous magmatism in the NE Armorican Massif: a LA-ICP-MS study
AU - Michel Ballèvre
AU - Marc Poujol
AU - Hugo Champie
AU - Bastien Lesage
AU - Isabelle Aubron
PY - 2026
DA - 2026/10/20
JO - Bulletin de la Société Géologique de France
DO - 10.1051/bsgf/2026013
UR - https://hal.science/hal-05820698v1
AB - In the Central and Northern Armorican Domains (Brittany and part of Normandy and Maine), the Precambrian basement displays evidence for a late Proterozoic orogeny, called the Cadomian orogeny. In its eastern part (Fougères and Maine Units), the late Neoproterozoic sediments are intruded by a large number of peraluminous granitoids, collectively grouped under the heading of Mancellian Batholith. The emplacement age of these granites is classically considered to be around 540 Ma. Given that the Precambrian-Cambrian boundary is currently set at 538.8 ± 0.2 Ma, this age warrants further investigation. Within the framework of the Normandy-Maine Geopark project (which is funding this study), we undertook a revision of the ages of granites from the northeastern part of the Armorican Massif. We selected first two cordierite granodiorite samples, one from the la Ferté-Macé granite (MAG-1) from an old quarry near La Raitière in Joué-du-Bois, and the other from the Athis granite (MAG-2), just below the unconformity with the Cambrian cover at La Roche d’Oëtre. In both samples, some zircons exhibit inherited cores and magmatic margins, with inherited ages ranging from 2430 to 600 Ma. Sample MAG-1 yielded a concordant age of 552 ± 2 Ma (MSWD=1.1, n=11) and sample MAG-2 an age of 552 ± 4 Ma (MSWD=0.6, n=8). Therefore, two major conclusions are (i) the age of emplacement of the granites of Athis and of La Ferté-Macé at 552 Ma and (ii) a metasedimentary source for these granites having a maximum depositional age of 600 Ma and a weak inheritance from Icartian protoliths (around 2.43 Ga). Another sample from the Saint-Pierre-des-Nids granodiorite (sample MAG-4), classically considered as belonging to the Mancellian Batholith, has provided a concordant age of 496.2 ± 2.5 Ma (MSWD=0.53, n=17). This late Cambrian emplacement age is consistent with field data and previous monazite ages obtained on a nearby intrusion (Alexain-Deux Evailles). Few Carboniferous intrusions are known in this part of the Armorican Massif. We report an age of 301.5 ± 6.6 Ma (MSWD=1.9, n=12) for the Alençon leucogranite, consistent with the field observations indicating that it developed a contact aureole in the Palaeozoic sediments. The Grosville rhyolite, up to now considered as part of the late Proterozoic Saint-Germain-le-Gaillard Complex, has provided a lower intercept date of 309.5 ± 5.6 Ma (MSWD=0.21, n=12), confirmed by a concordia date of 311.6 ± 6.1 Ma (MSWD=1.1, n=4). Overall, the new data indicate that most of the Mancellian granitoids are 10 to 15 Ma older than the Precambrian-Cambrian boundary, and that they were quickly unroofed, providing zircon detrital grains found in most of the Brioverian sediments from the Central Armorican Domain. Some peraluminous granites (Saint-Pierre-des-Nids, Alexain-Deux Evailles) may represent the magma chambers that have been hypothesized below the caldera-bearing rift of the Maine Unit, an unexpected result of this study.
SN - 0037-9409
SN - 1777-5817
ER -