Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U–Pb geochronology of its Ordovician protolith

Korh, Afifé El; Schmidt, Susanne Theodora; Ballèvre, Michel; Ulianov, Alexey; Bruguier, Olivier

doi:10.1007/s00531-011-0732-5

Cited by 26 publications

(15 citation statements)

References 70 publications

(118 reference statements)

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“…The Ile de Groix essentially consists of blueschist-facies metasediments and metabasalts (Barrois, 1883;Triboulet, 1974;Audren et al, 1993;Bosse et al, 2002 and A C C E P T E D M A N U S C R I P T Ballèvre et al, 2003), with a few occurences of albite gneisses derived from felsic dykes or tuffites of Early Ordovician age (El Korh et al, 2012). However, rare occurrences of ultrabasic rocks are found in its easternmost (and structurally deepest) part, the first one in the Tréhor area, the second one at Beg Melen.…”

Section: The Ile De Groix Unitmentioning

confidence: 99%

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

Paquette

Ballèvre

Peucat

et al. 2017

Lithos

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International audienceIn the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples.Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism

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Section: The Ile De Groix Unitmentioning

confidence: 99%

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

Paquette

Ballèvre

Peucat

et al. 2017

Lithos

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“…The Cambro-Ordovician magmatism in the southern Armorican Massif is thought to result from the intra-continental back-arc basin rifting following the closure of the ProtoRheic ocean, as recognised in the allochthonous domain of the Variscan belt (von Raumer et al 2015). The metabasalts and metasediments were sheared off and imbricated in an accretionary prism during the Variscan subduction (El Korh et al 2012). The rocks recorded two main metamorphic events: (1) a prograde blueschist to eclogite facies metamorphism M1 related to subduction, and (2) a greenschist facies overprint M2 related to exhumation (e.g.…”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

“…The metabasites correspond to former hydrothermally altered enriched mid-ocean ridge basalts (E-MORB), interlayered with pelitic micaschists (Bernard-Griffiths et al 1986;Bosse et al 2002;El Korh et al 2009. Because of the lack of ultrabasic and gabbroic rocks, the high-pressure rocks were interpreted as remnants of the uppermost part of an oceanic lithosphere or of basaltic lavas, emplaced during the Cambro-Ordovican rifting widely recognised along the northern Gondwana margin (El Korh et al 2012;von Raumer et al 2015). The Cambro-Ordovician magmatism in the southern Armorican Massif is thought to result from the intra-continental back-arc basin rifting following the closure of the ProtoRheic ocean, as recognised in the allochthonous domain of the Variscan belt (von Raumer et al 2015).…”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Korh

Luais

Deloule

et al. 2017

Contrib Mineral Petrol

Self Cite

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1during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have δ 56 Fe values (+0.17 ± 0.01 to +0.27 ± 0.02‰) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities.Keywords Fe isotopes · Metabasites · Subduction · HP-LT metamorphism · Blueschists · Eclogites · Greenschists · Basaltic protoliths IntroductionHigh-pressure/low-temperature (HP-LT) rocks are remnants of ancient subduction zones. They provide information on geochemical processes and deep fluid-rock interactions occurring at present-day active convergent margins. Fluid infiltration during high-and lowtemperature hydrothermal alteration of the oceanic crust at mid-ocean ridges and on the seafloor is responsible for the hydration of basic rocks and serpentinisation of the lithospheric mantle. During subduction, the hydrothermally altered oceanic crust dehydrates continuously and releases large amounts of H 2 O at a relatively shallow level in the subduction zone (50-80 km) (Schmidt and Poli 1998;Rüpke et al. 2004). Deserpentinisation of the lithospheric mantle occurs at deeper levels (100-200 km), where fluids are expected to be the source of arc melting (Ulmer and Abstract Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes were measured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have δ 56 Fe values of +0.16 to +0.33‰, which are heavier than typical values of MORB and OIB, indicating that their basaltic protolith derives from a heavy-Fe mantle source. The δ 56 Fe correlates well with Y/Nb and (La/Sm) PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of δ 56 Fe by +0.06 to 0.10‰ compared to basalts may reflect hydrothermal alteration prior to subduction. The δ 56 Fe decrease from blueschists (+0.19 ± 0.03 to +0.33 ± 0.01‰) to eclogites (+0.16 ± 0.02 to +0.18 ± 0.03‰) reflects small variations in the protolith composition, rather than Fe fractionation

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“…Ma), which reveal a significant maxima at 477 Ma, equivalent in age to the identified ash-fall layer. Data used from this work and other present in the literature (Alexandre, 2007;Andonaegui et al, 2012;Antunes et al, 2009;Ballevre et al, 2012;Bea et al, 2006;Casas et al, 2010;Castiñeiras et al,2008;Cocherie et al, 2007;Cruciani et al, 2013;Dallmeyer and Tucker, 1993;Deloule et al, 2002;Denéle et al, 2009;Días da Silva et al, in press;Díez Montes et al, 2010;Díez-Fernández et al, 2012;El Khor et al, 2012;Farias et al, 2014;Garbarino et al, 2005;Giacomini et al, 2006;Gutiérrez-Alonso et al, 2007;Helbing and Tiepolo, 2005;Liesa et al, 2011;López-Sánchez et al, 2014;López-Guijarro et al, 2007;Ludwig and Turi, 1989;Martínez et al, 2011;Melleton et al, 2010;Mezger and Gerdes. in press;Montero et al, 2007;Navidad et al, 2010;Navidad and Castiñeiras, 2011;Neiva et al, 2009;Oggiano et al, 2010;Padovano et al, 2014;Pavanetto et al, 2012;Pitra et al, 2012;Roger et al, 2004;Rossi et al, 2009;Rubio-Ordoñez et al, 2012;…”

Section: Discussionmentioning

confidence: 96%

Was there a super-eruption on the Gondwanan coast 477 Ma ago?

et al. 2016

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Precise zircon and monazite ID-TIMS U-Pb dating of three Lower Ordovician altered ash-fall tuff beds (K-Bentonites) in the Cantabrian Zone of NW Iberia yielded coeval ages together with an equivalent previously studied sample (477.5±1 (Gutierrez-Alonso et al., 2007)), of 477±1.3 Ma, 477.2±1.1 Ma and 477.3±1 Ma, with a pooled concordia age (all analyses in the four samples) of 477.2±0.74 Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using exclusively the CZ data) yields a volume for the preserved deposits of ca. 37.5 km 3 (Volcanic Explosivity Index-VEI = 6, Colossal). When considering other putative equivalent beds in Iberia and neighboring realms (i.e. Armorica, Sardinia) the volume of ejecta associated to this *Revised manuscript with no changes marked Click here to view linked References event would make it reach the Supervolcanic-Apocalyptic status (VEI=8, >1000 km3). At variance with most known cases of this kind of gigantic eruption events, geological observations indicate that the studied magmatic event was related to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically equivalent large caldera event recognized in the geological record of NW Iberia could be ground zero of this super-eruption. INTRODUCTION Volcanic supereruptions (Rampino and Self, 1992) are considered to be those that eject magma in excess of 10 15 kg, equivalent to a volume of more than 450 km 3 (Self, 2006;

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Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U–Pb geochronology of its Ordovician protolith

Cited by 26 publications

References 70 publications

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Was there a super-eruption on the Gondwanan coast 477 Ma ago?

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