Evidence of two metamorphic cycles preserved in garnet from felsic granulite in the southern Variscan belt of Corsica, France

Cruciani, Gabriele; Franceschelli, Marcello; Massonne, Hans‐Joachim; Musumeci, Giovanni

doi:10.1016/j.lithos.2020.105919

Cited by 8 publications

(5 citation statements)

References 79 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Compared with other ECMs, the peak pressure conditions of HP metamorphism in the ARM are similar to the ~1.8 GPa recorded in the Gothard massif (Abrecht et al, 1991; Biino, 1994), but slightly higher than the ~1.5 GPa estimated in the Argentera massif (Ferrando et al, 2008; Jouffray et al, 2020) or the 1.4 GPa estimated in the NE Belledonne massif (Jacob et al, 2021) (Figure 15b). Our P – T path of the ARM is similar to those calculated for the eclogites from the Montagne Noire gneiss dome (Pitra et al, 2021; Whitney et al, 2015, 2020) and the Sardinia‐Corsica massifs (Cortesogno et al, 2004; Cruciani et al, 2011, 2012, 2015, 2021; Giacomini et al, 2005; Libourel & Vielzeuf, 1988) (Figure 15b) and also for pre‐alpine eclogites occurrences in the internal Alps in the Adula, Tambo and Suretta nappes (see Biino et al, 1997).…”

Section: Discussionsupporting

confidence: 81%

“…Given the P-T conditions, the shape of the P-T path and the geochronological record, the eclogites of the ARM can be compared with those of the Belledonne, Argentera and Sardinia-Corsica massifs that share a similar timing and P-T evolution (Figure 15) with peak pressure conditions between 1.5-2 GPa at 600-750 C (Figure 14; Table 1) (Cruciani et al, 2011(Cruciani et al, , 2012(Cruciani et al, , 2015(Cruciani et al, , 2021Ferrando et al, 2008;Franceschelli et al, 2007;Giacomini et al, 2005;Jacob et al, 2021;Jouffray et al, 2020). The P-T-t similarities between eclogites of the ARM and others massifs of the south-western branch of the Variscan belt suggest that all these mafic rocks might be the HP relics of the root of an orogenic plateau that could correspond to the French Central Massif (Vanderhaeghe et al, 2020).…”

Section: Comparison With Other Eclogites From the South-western Branc...mentioning

confidence: 99%

See 1 more Smart Citation

Exhumation of deep continental crust in a transpressive regime: The example of Variscan eclogites from the Aiguilles‐Rouges massif (Western Alps)

Vanardois

Roger

Trap

et al. 2022

Journal Metamorphic Geology

View full text Add to dashboard Cite

Mafic eclogites are found in many orogens as lenses embedded in quartzofeldspathic migmatites. These high‐pressure relics are interpreted either as remnants of ancient sutures and thus formed during oceanic subduction or as fragments of lower crust exhumed from the root of orogenic thickened crust. It is critical to distinguish between these two endmember scenarios as the resulting palaeogeographic and geodynamic reconstructions may significantly differ. In this contribution, we investigated eclogite relics from Lac Cornu in the Aiguilles‐Rouges massif, one of the External Crystalline Massifs of the Western Alps. Phase equilibrium modelling suggests that these mafic rocks were buried along a prograde path (M1) from ~600°C/1.2 to 1.6 GPa to peak conditions of ~630–775°C and >1.6 GPa. Zircon rims, with a rare earth element signature typical of eclogite facies zircon (no Eu anomalies, flat HREE spectrum), and rutile were dated by U–Th–Pb laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) at c. 335–330 Ma. Prograde deformation has not been identified in the field and is only recognized thanks to the crystallographic preferred orientation (CPO) of inclusions of omphacite and rutile in garnet. Peak pressure conditions were followed by a decompression stage (M2) from ~760°C/1.4 GPa to ~600–650°C/0.9 GPa supported by the breakdown of omphacite into plagioclase–clinopyroxene symplectite and the crystallization of plagioclase–amphibole corona around garnet. The M2 retrogression stage is associated with the development of a main sub‐horizontal planar fabric and the CPO of minerals composing symplectite. This deformation stage is interpreted as the result of horizontal lower crustal flow. The final stage of exhumation (M3) is characterized by the replacement of symplectite and garnet by plagioclase and large euhedral amphibole and by the breakdown of rutile and ilmenite into titanite dated at c. 300 Ma. The CPO of titanite and amphibole are consistent with the development of vertical dextral shear zone in a transpressive regime. The combination of field observations and petrological, microtextural and geochemical analyses suggests that the mafic eclogites preserved in migmatitic rocks of the Aiguilles‐Rouges massif are remnants of a continental lower crust exhumed and juxtaposed with lower‐grade migmatites in crustal‐scale vertical transpressive shear zones.

show abstract

Section: Discussionsupporting

confidence: 81%

Section: Comparison With Other Eclogites From the South-western Branc...mentioning

confidence: 99%

Exhumation of deep continental crust in a transpressive regime: The example of Variscan eclogites from the Aiguilles‐Rouges massif (Western Alps)

Vanardois

Roger

Trap

et al. 2022

Journal Metamorphic Geology

View full text Add to dashboard Cite

show abstract

“…A break in chemical composition at the interface between garnet outer cores and garnet rims (see chemical profiles of Fig. 9) is observed and this resembles those found in multistage garnet associated with two orogenic cycles (e.g., Karabinos 1984;Ganne et al 2003;Gaidies et al 2006;Le Bayon et al 2006;Feenstra et al 2007;Sandmann et al 2014;Giuntoli et al 2018;Cruciani et al 2021;Klug and Froitzheim 2021;Nosenzo et al 2022) or in metamorphic garnet overgrowths on detrital grains (Yardley et al 1996;Manzotti and Ballèvre 2013). The chemistry of garnet core may be marginally compatible with its growth at low P in a biotite-talc-amphibole-ilmenite with plagioclase or paragonite assemblage.…”

Section: The Garnet Recordmentioning

confidence: 68%

A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps)

Manzotti¹,

Schiavi

Nosenzo³

et al. 2022

Preprint

View full text Add to dashboard Cite

The distribution of ultrahigh-pressure metamorphism (UHP) at the scale of a mountain belt is of prime importance for deciphering its past subduction history. In the Western Alps, coesite has been recognized in the southern Dora-Maira massif, in the lens-shaped Brossasco-Isasca Unit, but has not been found up to now in the other parts of the massif. We report the discovery of a new UHP unit in the northern Dora-Maira Massif (Western Alps), named Chasteiran Unit (Manzotti et al. 2022). It is only a few tens of metres thick and consists of garnet-chloritoid micaschists. Garnet inclusions (chloritoid, rutile) and its growth zoning allow to precisely model the P&#8211;T evolution. Coesite crystals, which are pristine or partially transformed to palisade quartz occur as inclusions in the garnet outer cores. According to thermodynamic modelling, garnet displays a continuous record of growth during the prograde increase in P and T (25&#8211;27 kbar 470&#8211;500 &#176;C) (stage 1), up to the coesite stability field (27&#8211;28 kbar 520&#8211;530 &#176;C) (stage 2), as well as sub-isothermal decompression of about 10 kbar (down to 15 kbar 500&#8211;515 &#176;C) (stage 3). The main regional, composite, foliation, marked by chloritoid and rutile, began to develop during this stage, and was then overprinted by chlorite-ilmenite (stage 4). The Chasteiran Unit is discontinuously exposed in the immediate hangingwall of the Pinerolo Unit, and it is located far away from, and without physical links to the classic UHP Brossasco-Isasca Unit. Moreover, it records a different, much colder, P&#8211;T evolution, showing that different slices were detached from the downgoing subduction slab. The Chasteiran Unit is the fourth and the coldest Alpine UHP unit known so far in the entire Alpine belt. Its P&#8211;T conditions are comparable to the ones of the Tian Shan coesite-chloritoid-bearing rocks. &#160; Manzotti, P., Schiavi, F., Nosenzo, F., Pitra, P., Ball&#232;vre, M. (2022). A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps). Contributions to Mineralogy and Petrology, in press. &#160;

show abstract

“…Metamorphic evolution under lower pressure conditions is dated between ca. 360 and 330 Ma and described in the Corsican basement (Li et al, 2014;Massonne et al, 2018;Cruciani et al, 2020). In Sardinia, eclogitefacies metamorphism developed prior to the regional-scale Barrovian-type metamorphism that has been dated to ca.350 Ma (del Moro et al, 1991;Franceschelli et al, 2007;Carosi et al, 2012).…”

Section: C-p-t Peak Conditionsmentioning

confidence: 99%

Deciphering the nature and age of the protoliths and peakP−Tconditions in retrogressed mafic eclogites from the Maures-Tannneron Massif (SE France) and implications for the southern European Variscides

JOUFFRAY¹,

Lardeaux²,

Tabaud³

et al. 2023

BSGF - Earth Sci. Bull.

View full text Add to dashboard Cite

We present new constraints on age, nature and tectonic setting of mafic eclogites protoliths from the Maures-Tanneron Massif, southern Variscan belt. Whole-rock major and trace elements geochemistry was combined with 206Pb/238U zircon dating to improve the understanding of this key-target of the European Southern Variscides. Geochemical data show that protoliths of the mafic eclogites are typical MORBs, while REE and HFSE patterns suggest an E-MORB affinity. However, the geochemical study shows several signs of crustal contamination, increasing with degree of retrogression. A comparison with Sardinian eclogites, which belong to the same Variscan micro-plate “MECS” (Maures-Estérel-Corsica-Sardinia), demonstrate that the eclogites included in migmatites, which is the case of the studied samples, are the most contaminated. Anyway, the Maures-Tanneron mafic eclogites represent the witness of oceanic basaltic crust. Zircon cores display homogeneous Th/U ratios (0.3-0.4), consistent with a magmatic origin, and define an age peak at ca. 500 Ma interpreted as the most plausible emplacement age of the basaltic protolith. This age suggests that this protolith was part of an oceanic floor older than the Rheic Ocean and located north of the Gondwana active continental margin as predicted by recent unified full plates reconstruction models. Although the eclogites studied are retrogressed the study of frozen mineral inclusions trapped in garnets combined with thermodynamic modelling yields a P-T range of 16.8-18.5 kbar for 630-660°C, coherent with standard subduction paleo-geotherm. These new data suggest that mafic eclogites recognized in the “MECS” Variscan micro-plate represent the closure of oceanic domains of different ages.

show abstract

Evidence of two metamorphic cycles preserved in garnet from felsic granulite in the southern Variscan belt of Corsica, France

Cited by 8 publications

References 79 publications

Exhumation of deep continental crust in a transpressive regime: The example of Variscan eclogites from the Aiguilles‐Rouges massif (Western Alps)

Exhumation of deep continental crust in a transpressive regime: The example of Variscan eclogites from the Aiguilles‐Rouges massif (Western Alps)

A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps)

Deciphering the nature and age of the protoliths and peakP−Tconditions in retrogressed mafic eclogites from the Maures-Tannneron Massif (SE France) and implications for the southern European Variscides

Contact Info

Product

Resources

About