The stability of hydrous phases beyond antigorite breakdown for a magnetite-bearing natural serpentinite between 6.5 and 11 GPa

Maurice, Juliette; Bolfan-Casanova, Nathalie; Padrón‐Navarta, José Alberto; Manthilake, Geeth; Hammouda, Tahar; Hénot, Jean-Marc; Andrault, Denis

doi:10.1007/s00410-018-1507-9

Cited by 14 publications

(19 citation statements)

References 81 publications

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“…Mg2.62Fe 2+ 0.08Fe 3+ 0.02Al0.09Cr0.01Si1.97O6.82(OH)3.65 was obtained by means of an electron probe micro-analyzer and a Fe 3+ /∑Fe ratio of 0.23. The calculated water content (12.05 wt.% H2O) by stoichiometry) was obtained for an anticipated polysome (m = 17, Capitani and Mellini, 2004) in agreement with the totals of electron probe analysis ranging around 86.5 +/-0.5 %, see (Table 1, see also Maurice et al, 2018). Bulk analyses were performed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) on 5 distinct batches of about 100 mg of serpentinite powder, separately grinded, in order to test the homogeneous distribution of magnetite grains within the bulk rock.…”

Section: The Composition Of Antigoritesupporting

confidence: 78%

“…The pressure in the 25 mm assembly was calibrated using three systems: (i) Bi I-II phase transition occurring at 2.5 GPa and room temperature (Bean et al, 1986), (ii) the coesite/stishovite phase transition of SiO2 at 8.01 GPa at 800 °C (Zhang et al, 1996) and (iii) the garnet to perovskite phase transition of CaGeO3 at 6.2 GPa and 1000 °C (Susaki et al, 1985). For experiments using the 18/11 assemblies see (Maurice et al, 2018). All the ceramic parts (except graphite) of the highpressure cell were fired at 1000 °C for 30 minutes prior to loading the capsule and cementing.…”

Section: High-pressure Experimentsmentioning

confidence: 99%

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The intrinsic nature of antigorite breakdown at 3 GPa: Experimental constraints on redox conditions of serpentinite dehydration in subduction zones

Maurice

Bolfan-Casanova

Demouchy

et al. 2020

Contrib Mineral Petrol

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Antigorite is considered as the most important source of water in subduction zones, playing a key role during arc magma genesis. Although, these magmas seem more oxidized than midoceanic ridge basalts (MORB), the possible inherent link between the oxidation state of arc magmas and serpentinite-derived hydrous fluids is still not well established. Here, we have performed dehydration experiments of natural antigorite serpentinite containing 5 weight percent (wt%) magnetite at 3 GPa and in a temperature range from 600 to 900 °C using a multianvil apparatus. These experiments aim to reproduce the different stages of H2O release, forming chlorite, olivine and orthopyroxene and water. Our experimental set up permits to preserve the intrinsic oxygen fugacity (fO2) of serpentinites during their dehydration. The new olivine and orthopyroxene which formed in equilibrium with antigorite, chlorite and magnetite have high XMg numbers setting up the oxygen fugacity to high values, between 3.0 and 4.1 log units above QFM (Quartz-Fayalite-Magnetite buffer). Hematite is observed concomitantly with high XMg in olivine, of 0.94-0.97, generally at low temperatures, below 800 °C, in coexistence with chlorite. Once the magnetite is destabilized, upon chlorite breakdown, above 800°C, the oxygen fugacity decreases to 3.7 due to the decrease of the XMg of silicates. This study demonstrates the highly oxidizing nature of the fluids released from antigorite dehydration. Thus, at high pressure and high temperature conditions, fO2-sensitive elements such as carbon and sulfur are expected to be mobilized under their oxidized form, providing an oxidizing context for arc magmas genesis and assuming that they are not completely reduced by their percolation through meta-gabbro, meta-basalts and meta-sediments.

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Section: The Composition Of Antigoritesupporting

confidence: 78%

Section: High-pressure Experimentsmentioning

confidence: 99%

The intrinsic nature of antigorite breakdown at 3 GPa: Experimental constraints on redox conditions of serpentinite dehydration in subduction zones

Maurice

Bolfan-Casanova

Demouchy

et al. 2020

Contrib Mineral Petrol

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“…Balangeroite and aluminous phase E form instead [20] but within a narrower temperature range compared to that of brucite in the simplified system. These differences in phase assemblages lead to significantly different water lines.…”

Section: Thermopetrological Modeling Of Present-day Subduction Zonesmentioning

confidence: 86%

“…the last phase transition beyond which hydrous minerals are unstable, between depths of 250 km and 310 km. For T lower than 600°C, antigorite and phase A form at pressures lower and higher than 6 GPa, respectively, in both peridotite models [17,20]. Chlorite is stable at T and P higher than 600°C and lower than 6 GPa, respectively.…”

Section: Thermopetrological Modeling Of Present-day Subduction Zonesmentioning

confidence: 97%

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Sea-level stability over geologic time owing to limited deep subduction of hydrated mantle

Cerpa¹,

Arcay²,

Padrón‐Navarta³

2022

Preprint

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The presence of liquid water makes our planet unique. Its budget over geological timescales, i.e., the long-term global sea level, depends on the balance of water exchanges between the Earth's mantle and the surface through both volcanism (mantle degassing) and subduction of hydrous minerals (mantle regassing). Current estimates of subduction water fluxes predict that regassing exceeds degassing by 50%, thereby suggesting a sea-level drop of several hundred meters in the last 540 Ma. The models further suggest that the subducting crust is the main supplier of water to the deep mantle. In contrast, various observations advocate for a near-steady state long term sea level and report voluminous water subduction via the hydrated lithospheric mantle. We have revised the subduction water flux calculations using constraints from recent experimental data on natural peridotites under high-pressure and high-temperature conditions. Our novel thermopetrological models show that the present-day global water retention in subducting plates beyond mid-upper mantle depths barely exceeds the estimations of mantle degassing, and thus quantitatively support the steady-state sea level scenario over geological times. Furthermore, the limited mantle regassing is solely driven by the lithospheric mantle of the coldest subduction zones.

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Cycling of CO2 and H2O constrained by experimental investigation of a model ophicarbonate at deep subduction zone conditions

Eguchi

Dasgupta

2022

Earth and Planetary Science Letters

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The stability of hydrous phases beyond antigorite breakdown for a magnetite-bearing natural serpentinite between 6.5 and 11 GPa

Cited by 14 publications

References 81 publications

The intrinsic nature of antigorite breakdown at 3 GPa: Experimental constraints on redox conditions of serpentinite dehydration in subduction zones

The intrinsic nature of antigorite breakdown at 3 GPa: Experimental constraints on redox conditions of serpentinite dehydration in subduction zones

Sea-level stability over geologic time owing to limited deep subduction of hydrated mantle

Cycling of CO2 and H2O constrained by experimental investigation of a model ophicarbonate at deep subduction zone conditions

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