Trace element and isotopic fingerprints in HP–LT metamorphic rocks as a result of fluid–rock interactions (Ile de Groix, France)

Korh, Afifé El; Schmidt, Susanne Theodora; Vennemann, Torsten; Ballèvre, Michel

doi:10.1016/j.gr.2012.07.014

Cited by 13 publications

(33 citation statements)

References 79 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1) (see Bosse et al 2002;Ballèvre et al 2003;El Korh et al 2013; and references therein). 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.…”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

“…In micaschists, the maximum peak P-T conditions were estimated to be 1.6-1.8 GPa, 450-500 °C using the NFMASH system (Bosse et al 2002). Based on trace element and bulk rock δ 18 O analyses, El Korh et al (2013) have shown that pervasive fluidrock interactions occurred as an open system during seafloor hydrothermal alteration, as well as during the early subduction metasomatism (interaction with pelite-derived fluids). During HP metamorphism, fluid migration in the metabasites is relatively slow because of their low porosity and low permeability that result in low and slow fluid fluxes (El Korh et al 2013).…”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

“…Based on trace element and bulk rock δ 18 O analyses, El Korh et al (2013) have shown that pervasive fluidrock interactions occurred as an open system during seafloor hydrothermal alteration, as well as during the early subduction metasomatism (interaction with pelite-derived fluids). During HP metamorphism, fluid migration in the metabasites is relatively slow because of their low porosity and low permeability that result in low and slow fluid fluxes (El Korh et al 2013). Only vein channels show high fluid-rock ratios, high fluid fluxes and significant fluid-rock interactions along vein boundaries (El Korh et al 2011).…”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

“…The retrograde metamorphism (<1 GPa; <400-450 °C) was interpreted as an overprint of fluids that were already in equilibrium with the metabasites under HP-LT conditions, without infiltration of additional externally derived fluids. Metabasites that underwent pervasive alteration by pre-HP metasomatic processes, show greater effects of retrogression (El Korh et al 2013). …”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

“…Overall, thirteen metabasites were analysed during this study and include five blueschists (GR 02, 04, 11b, Fig. 1 Geological map of the Ile de Groix (after Audren et al 1993;Bosse et al 2002;El Korh et al 2013). *The beach "Plage des Grands Sables" periodically moves with the oceanic currents 12b and 25a), three eclogites (GR 21, 24a and 29) and five retrograde greenschists (GR 06a, 23 and 25b and albitic greenschists GROA 43 and 52) [for the detailed description of the samples see El Korh et al 2009Korh et al , 2011Korh et al , 2013 and Table 1].…”

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

See 4 more Smart Citations

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

Korh

Luais

Deloule

et al. 2017

Contrib Mineral Petrol

View full text Add to dashboard Cite

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

show abstract

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

Section: Geological Setting and Investigated Samplesmentioning

confidence: 99%

See 3 more Smart Citations

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

Korh

Luais

Deloule

et al. 2017

Contrib Mineral Petrol

View full text Add to dashboard Cite

show abstract

Investigation of Ge and Ga exchange behaviour and Ge isotopic fractionation during subduction zone metamorphism

et al. 2017

View full text Add to dashboard Cite

Germanium (Ge) and gallium (Ga) are slightly to moderately incompatible trace elements during magmatic processes and may be indicators of the nature of the mantle source. Because of their solubility in fluids, Ge and Ga are also geochemical tracers of various hydrothermal processes. Understanding high-pressure/low-temperature (HP-LT) recycling processes of Ge and Ga through fluid-mediated mass transfers in subduction zones can then allow discussing whether they can be source of geochemical heterogeneities in the mantle wedge. We have analysed Ge and Ga abundances and Ge isotope composition of a series of well-characterised HP-LT metabasites of mid-ocean ridge basalt (MORB) affinity and pelitic micaschists from the Ile de Groix (France), to determine Ge and Ga behaviour and Ge isotope fractionation during subduction zone metamorphism (SZM). Metabasites have Ge and Ga contents of 1.2-2.1 ppm and 17-22 ppm, respectively, typical of tholeiitic basalts. Garnet-bearing blueschists and eclogites have δ 74 Ge values (+0.42 to +0.65‰) similar within error to that of tholeiitic basalts (+0.55 to +0.57‰; Luais, 2012). Our study shows that during the prograde metamorphism, Ge and Ga abundances and δ 74 Ge values do not vary from blueschists to eclogites, owing to the large stability field of Geand Ga-hosting minerals (epidote, garnet, titanite, amphiboles and omphacite) under varying P-T conditions. During the retrograde metamorphism, the slight decrease of the Ga content of c. 8% in greenschists (19 ± 1 ppm; 2σ) compared to HP rocks (21 ± 1 ppm; 2σ) suggests Ga loss during retrogression, whereas Ge abundances remain within the same range as blueschists and eclogites. In the garnet-bearing greenschists (early stages of retrogression), the δ 74 Ge values (+0.38 to +0.49‰) remain similar within error to HP rocks. However, albiteand calcite-bearing greenschists have higher δ 74 Ge values (+0.84 to +0.98‰), showing evidence of Ge fractionation under intensive fluid-rock interactions (late stage of retrogression). Micaschists have Ge and Ga abundances within the same range as continental 3 crust and schists. Their variations in δ 74 Ge (+0.29 to +0.70‰) reflect variations in the sedimentary source and protolith composition. The relatively small variation of  74 Ge values in metabasites compared to mantle rocks implies that the subducted oceanic crust cannot trigger Ge isotopic heterogeneities in the mantle through fluid-induced metasomatism or recycling in the deep mantle. However, during the late stages of retrogression, migration of oxidising fluids along the crust-mantle wedge may be responsible for a resolvable increase of the  74 Ge value of the mantle wedge along the subduction channel. Besides, the larger range of Ge concentrations and  74 Ge values in the micaschists suggests that recycling of subducted sediments may generate mantle Ge elemental and isotopic heterogeneities.

show abstract

Trace element and oxygen isotope study of eclogites and associated rocks from the Münchberg Massif (Germany) with implications on the protolith origin and fluid-rock interactions

et al. 2021

View full text Add to dashboard Cite

Trace element and isotopic fingerprints in HP–LT metamorphic rocks as a result of fluid–rock interactions (Ile de Groix, France)

Cited by 13 publications

References 79 publications

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

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

Investigation of Ge and Ga exchange behaviour and Ge isotopic fractionation during subduction zone metamorphism

Trace element and oxygen isotope study of eclogites and associated rocks from the Münchberg Massif (Germany) with implications on the protolith origin and fluid-rock interactions

Contact Info

Product

Resources

About