Ultra-oxidized rocks in subduction mélanges? Decoupling between oxygen fugacity and oxygen availability in a Mn-rich metasomatic environment

Tumiati, Simone; Godard, Gaston; Martin, Silvana; Malaspina, Nadia; Poli, Stefano

doi:10.1016/j.lithos.2014.12.008

Cited by 54 publications

(57 citation statements)

References 67 publications

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“…However, Reaction is a reducing reaction. The driving force of this reduction might have been the strong gradient in the oxygen quantity ( n O 2 ; Evans, ; Tumiati, Godard, Martin, Malaspina, & Poli, ) between Ep‐metarodingite and host Chl‐harzburgites, as revealed by the sharp difference in their Fe 3+ /Fe Total ratios: ~0.8 and 0.25–0.5 respectively (Figure b). These low values in Chl‐harzburgite can be explained by the strong drop in Fe 3+ /Fe Total ratio produced during the transformation of Atg‐serpentinite (0.63–0.74) into Chl‐harzburgite owing to the very significant reduction of Fe 3+ hosted in both magnetite and antigorite during dehydration (Debret et al., ).…”

Section: Discussionmentioning

confidence: 99%

“…Nevertheless, the significance of metarodingites for the petrological and geochemical processes that take place in subduction zones has been usually disregarded. Increasing attention has been recently devoted to the presence of relatively oxidized materials in subduction zones and their role on deep element cycling (e.g., Evans & Powell, ; Malaspina et al., ; Tumiati et al., ). Oxidizing agents may be transported into the subarc mantle by metamorphic fluids produced by devolatilization of the subducting slab (Evans, ).…”

Section: Discussionmentioning

confidence: 99%

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High‐P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones

Laborda-López

Sánchez‐Vizcaíno

Marchesi

et al. 2018

Journal Metamorphic Geology

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The transition between antigorite‐serpentinite and chlorite‐harzburgite at Cerro del Almirez (Betic Cordillera, Southern Spain) exceptionally marks in the field the front of antigorite breakdown at high pressure (~16–19 kbar) and temperature (~650°C) in a paleosubducted serpentinite. These ultramafic lithologies enclose three types of metarodingite boudins of variable size surrounded by metasomatic reaction rims. Type 1 Grandite‐metarodingite (garnet+chlorite+diopside+titanite±magnetite±ilmenite) mainly crops out in the antigorite‐serpentinite domain and has three generations of garnet. Grossular‐rich Grt‐1 formed during rodingitization at the seafloor (<2 kbar, ~150–325°C, ~FMQ buffer). During subduction, the alternating growth of Grt‐2b (richer in andradite and pyralspite components than Grt‐1) and Grt‐3 (very rich in andradite component) reflects the change from internally buffered metamorphic conditions (>10 kbar, ~350–650°C, ~FMQ buffer) to influx events of oxidizing fluids (fO2 ~HM buffer) released by brucite breakdown in the host antigorite‐serpentinite. Type 2 Epidote‐metarodingite (epidote+diopside+titanite±garnet) derives from Type 1 and is the most abundant metarodingite type enclosed in dehydrated chlorite‐harzburgite. Type 2 formed by increasing μSiO2 (from −884 to −860 kJ/mol) and decreasing μCaO (from −708 to −725 kJ/mol) triggered by the flux of high amounts of oxidizing fluids during the high‐P antigorite breakdown in serpentinite. The growth of Grt‐4, with low‐grandite and high‐pyralspite components, in Type 2 metarodingite accounts for progressive reequilibration of garnet with changing intensive variables. Type 3 Pyralspite‐metarodingite (garnet+epidote+amphibole+chlorite±diopside+rutile) crops out in the chlorite‐harzburgite domain and formed at peak metamorphic conditions (16–19 kbar, 660–684°C) from Type 2 metarodingite. This transformation caused the growth of a last generation of pyralspite‐rich garnet (Grt‐5) and the recrystallization of diopside into tremolitic amphibole at decreasing fO2 and μCaO (from −726 to −735 kJ/mol) and increasing μMgO (from −630 to −626 kJ/mol) due to chemical mixing between the metarodingite and the reaction rims. The different bulk Fe3+/FeTotal ratios of antigorite‐serpentinite and chlorite‐harzburgite, and of the three metarodingite types, reflect the highly heterogeneous oxidation state of the subducting slab and likely point to the transfer of localized oxidized reservoirs, such as metarodingites, into the deep mantle.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

High‐P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones

Laborda-López

Sánchez‐Vizcaíno

Marchesi

et al. 2018

Journal Metamorphic Geology

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“…11; see also Scambelluri & Tonarini, 2012), which commonly display Fe 3+ /Fe tot higher than MORB and OIB basalts because of addition to their mantle sources of fluids carrying oxidised species, like H 2 O, CO 2 , Fe 2 O 3 and sulfate (Arculus, 1994;Kelley & Cottrell, 2009;Malaspina et al, 2009Malaspina et al, , 2010Evans & Tomkins, 2011;Evans & Powell, 2015;Evans et al, 2017). In turn, the speciation of subduction fluids is controlled by the variable oxidation state of the source rocks (Tumiati et al, 2015;Debret & Sverjensky, 2017;Evans et al, 2017;Cannaò & Malaspina, 2018;Tumiati & Malaspina, 2019). Because serpentinite is the rock that primarily controls the release of slab fluids, efforts have been recently done to determine the redox state of serpentinized rocks and fluids by means of (i) direct measurements of the Fe 3+ content of bulk rocks and serpentine (Andreani 420 M. Scambelluri et al et al, 2013;Debret et al, 2014bDebret et al, , 2015Evans et al, 2017) and (ii) theoretical calculations (Debret & Sverjensky, 2017).…”

Section: Redox Statementioning

confidence: 99%

The water and fluid-mobile element cycles during serpentinite subduction. A review

Scambelluri

Cannaò

Gilio

2019

ejm

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The key role of serpentinites in the global cycles of volatiles, halogens and fluid-mobile elements in oceans and in subduction zones is now ascertained by many studies quantifying their element budgets and the composition of fluids they release during subduction. Geochemical tracers (e.g. B, As, Sb; stable B and radiogenic Sr and Pb isotopes) have also been employed to trace the provenance of serpentinites (slab or forearc mantle?) accreted to the plate interface of fossil subduction zones. In turn, this helps defining the tectonic processes, seismicity and mass transfer attending rock burial and exhumation within subduction zones. The results suggest that the sole use of geochemical data is insufficient to track the origin of subduction-zone serpentinites and the timing of serpentinization, whether oceanic or subduction-related. Integrated multidisciplinary studies of ophiolitic serpentinites show that pristine, oceanic, geochemical imprints (e.g. high 11 B, marine Sr isotopes, low As + Sb) become reset towards more radiogenic Sr, lower 11 B, and higher As + Sb via metasomatic exchange with crust-derived fluids during subduction accretion to the plate interface.The dehydration fluids released by serpentinite dehydration at various subduction stages and still preserved in these rocks as inclusions, carry significant amounts of halogens and fluid-mobile elements. The key compositional similarities of antigorite-breakdown fluids from different localities (Betic Cordillera, Spain; Central Alps, Switzerland) indicate that rocks record comparable subduction processes. We individuate the fluid-mediated exchange with sedimentary and/or crustal reservoirs during subduction as the key mechanism for geochemical hybridization of serpentinite. The antigorite dehydration fluids produced by hybrid serpentinites have high Cs, Rb, Ba, B, Pb, As, Sb and Li overlapping those of the arc lavas and representing the mixed serpentinite-sediment (crustal) component released to arcs. This helps discriminating the mass transfer processes responsible for supra-subduction mantle metasomatism and arc magmatism. The studied plate-interface hybrid serpentinites are also proxies of forearc mantle metasomatized by slab fluids. Based on the above observations, we propose that the mass transfer from slabs to plate interface and/or forearc mantle and the subsequent down-drag of this altered mantle to subarc depths potentially is a major process operating in subduction zones.The nominally anhydrous olivine, orhopyroxene, clinopyroxene and garnet produced by serpentinite dehydration host appreciable amounts of halogens and fluid-mobile elements that can be recycled in the deep mantle beyond arcs. Involvement of de-serpentinized residues in lower mantle metasomatism begins to be increasingly recognized by studies of ocean island basalts (OIB) and of B-bearing blue diamonds and by the isotopic serpentinite compositions presented here.

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“…Many other manganese minerals have been observed: braunite, garnets (spessartine, blythite, calderite, etc. ; Martin & Kienast, 1987;Martin-Vernizzi, 1982;Tumiati et al, 2010Tumiati et al, , 2015; Mn-bearing augite, jadeite and chloromelanite; rhodonite; K-F-Mnrichterite; thulite hollandite, and rhodochrosite.…”

Section: The Sulphides and Manganese Mines Of The Saint-marcel Valleymentioning

confidence: 99%

“…In the Saint-Marcel valley, the metaophiolites mainly consist of metabasalts hosting Fe-Cu sulphide-bearing mineralisations and a Mn-ore (Praz-Bornaz) related to oceanic hydrothermal processes (Brown, Essene, & Peacor, 1978;Martin, Rebay, Kienast, & Mével, 2008;Rebay & Powell, 2012;Selverstone & Sharp, 2013;Tumiati, Martin, & Godard, 2010;Tumiati, Godard, Martin, Malaspina, & Poli, 2015). Metabasalts are covered by a thick sequence of metasediments interpreted to be the relict sedimentary cover of the oceanic basement (Tartarotti, Martin, & Polino, 1986).…”

Section: Introductionmentioning

confidence: 99%

Geology of the Saint-Marcel valley metaophiolites (Northwestern Alps, Italy)

Tartarotti

Martin

Monopoli³

et al. 2017

Journal of Maps

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The geological map of the Saint-Marcel valley at the scale of 1:20,000 illustrates the tectonic setting of metaophiolites from the southern Aosta Valley, in the Italian side of the Western Alpine belt. The map highlights the sharp contact between the metaophiolitic basement and its metasedimentary cover, which mainly consists of quartzites, marbles, and calcschists. In spite of the Alpine tectonics, this contact is regarded as deriving from the original oceanic crust/sediments interface. Metaophiolites mostly consist of metabasalts hosting Fe-Cu sulphide mineralisations, characterised by high-pressure metamorphic imprint. These rocks likely represent the shallowest portion of the Tethyan oceanic lithosphere created near the axis of the slow-spreading ridge where hydrothermal fluid circulation was active. Selected key-sections through metasediments reveal a consistent internal lithostratigraphy, in spite of the pervasive metamorphic and tectonic reworking acting during the Alpine evolution. Metasediments reflect various sedimentation episodes starting from pelagic and proximal settings to the onset of the orogenic stage. The Saint-Marcel valley metasediments thus reflect a changing in the sedimentation environments through time and space during the overall geologic evolution. ARTICLE HISTORY

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Ultra-oxidized rocks in subduction mélanges? Decoupling between oxygen fugacity and oxygen availability in a Mn-rich metasomatic environment

Cited by 54 publications

References 67 publications

High‐P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones

High‐P metamorphism of rodingites during serpentinite dehydration (Cerro del Almirez, Southern Spain): Implications for the redox state in subduction zones

The water and fluid-mobile element cycles during serpentinite subduction. A review

Geology of the Saint-Marcel valley metaophiolites (Northwestern Alps, Italy)

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