Formation of secondary olivine after orthopyroxene during hydration of mantle wedge: evidence from the Khantaishir Ophiolite, western Mongolia

Dandar, Otgonbayar; Okamoto, Atsushi; Uno, Masaoki; Oyanagi, Ryosuke; Nagaya, Teruo; Ulziiburen, Burenjargal; Miyamoto, Takaya; Tsuchiya, Noriyoshi

doi:10.1007/s00410-019-1623-1

Cited by 15 publications

(8 citation statements)

References 75 publications

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“…This sample did not form brucite in the Atg-Lz and Atg stages. The lack of brucite is consistent with the lower Mg/Si ratios of serpentinites in the Taishir Massif (Dandar et al, 2019) and suggests serpentinization was associated with input of silica. One key characteristic is the presence of hourglass Atg-Lz with magnetite.…”

Section: Discussionsupporting

confidence: 61%

“…4a). The spinel Cr# values (Cr/[Cr + Al]) of 0.76-0.78 and Mg# values [Mg/(Mg + Fe total )] of 0.28-0.52 (Table 1) are largely consistent with those in forearc peridotites (Ishii et al, 1992) and meta-dunite and -harzburgite in the Naran Massif (Cr# = 0.67-0.89; Mg# = 0.40-0.57; Dandar et al, 2019).…”

Section: Mineralogy and Microstrutcturesupporting

confidence: 61%

“…1b). The Naran Massif comprises a thick ultramafic body that consists of meta-harzburgite and -dunite and a thin section of crustal rocks (Gianola et al, 2017;Dandar et al, 2019). In contrast, the Taishir Massif contains a thin body (2 km) of ultramafic rocks and thick section of crustal rocks (gabbros = 1.8 km; volcanic rocks = 2.5 km).…”

Section: Geological Background and Samplementioning

confidence: 99%

“…In contrast, the Taishir Massif contains a thin body (2 km) of ultramafic rocks and thick section of crustal rocks (gabbros = 1.8 km; volcanic rocks = 2.5 km). The meta-harzburgite in the Naran Massif contains both primary and secondary olivine, and the latter formed after orthopyroxene during antigorite formation (Dandar et al, 2019). In contrast to the Naran Massif, the ultramafic rocks in the Taishir Massif are completely serpentinized and experienced intense shear deformation.…”

Section: Geological Background and Samplementioning

confidence: 99%

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Redistribution of magnetite during multi–stage serpentinization: Evidence from the Taishir Massif, Khantaishir ophiolite, western Mongolia

Dandar

Okamoto

Uno

et al. 2021

Journal of Mineralogical and Petrological Sciences

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Magnetite veins are commonly observed in serpentinized peridotite, but the mobility of iron during serpentinization is poorly understood. The completely serpentinized ultramafic rocks (originally dunite) in the Taishir Massif in the Khantaishir ophiolite, western Mongolia, contain abundant antigorite + magnetite (Atg + Mag) veins, which show an unusual distribution of Mag. The serpentinite records multi-stage serpentinization in the order: (1) Atg + lizardite (Lz) with a hourglass texture (Atg-Lz); (2) thin vein networks and thick veins of Atg; (3) chrysotile (Ctl) that cuts all earlier textures. Mg# values of the Atg-Lz (0.94-0.96) are lower than those of the Atg (~0.99) and chrysotile (~0.98). In the Atg-Lz regions, magnetite occurs as arrays of fine grains (<50 µm) around the hourglass texture, and magnetite is absent in the thin Atg vein networks replacing Atg-Lz. Magnetite occurs as coarse grains (100-250 µm) in the center of some thick Atg veins. As the volume ratio of thin Atg veins to Atg-Lz increases, both the modal abundance of Mag and the bulk iron content decrease. These features indicate that hydrogen generation occurred mainly during Atg-Lz formation, and that the Mag distribution was largely modified by dissolution and precipitation in response to the infiltration of the higher temperature fluids associated with the Atg veins. The transport of iron during redistribution of Mag in the late-stage of serpentinization is potentially important for ore deposit formation and modifying the magnetic properties of ultramafic bodies.

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Section: Discussionsupporting

confidence: 61%

Section: Mineralogy and Microstrutcturesupporting

confidence: 61%

Section: Geological Background and Samplementioning

confidence: 99%

Section: Geological Background and Samplementioning

confidence: 99%

See 2 more Smart Citations

Redistribution of magnetite during multi–stage serpentinization: Evidence from the Taishir Massif, Khantaishir ophiolite, western Mongolia

Dandar

Okamoto

Uno

et al. 2021

Journal of Mineralogical and Petrological Sciences

Self Cite

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“…Although large uncertainties still exist regarding the definition of serpentinization patterns in the mantle wedge above subducting slabs, several examples of inferred high-pressure, mantlewedge serpentinized peridotites exhibit mineral assemblages comparable to the samples presented in this study 60,61 . Therefore, our petrological data and thermodynamic modelling can be extrapolated to portions of the hydrated mantle wedge above subducting slabs 24,30 , where variable degrees of high-pressure serpentinization occur along more than 55,000 km of forearc mantle domains 24 .…”

Section: Resultsmentioning

confidence: 55%

Subduction hides high-pressure sources of energy that may feed the deep subsurface biosphere

et al. 2020

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Geological sources of H 2 and abiotic CH 4 have had a critical role in the evolution of our planet and the development of life and sustainability of the deep subsurface biosphere. Yet the origins of these sources are largely unconstrained. Hydration of mantle rocks, or serpentinization, is widely recognized to produce H 2 and favour the abiotic genesis of CH 4 in shallow settings. However, deeper sources of H 2 and abiotic CH 4 are missing from current models, which mainly invoke more oxidized fluids at convergent margins. Here we combine data from exhumed subduction zone high-pressure rocks and thermodynamic modelling to show that deep serpentinization (40-80 km) generates significant amounts of H 2 and abiotic CH 4 , as well as H 2 S and NH 3. Our results suggest that subduction, worldwide, hosts large sources of deep H 2 and abiotic CH 4 , potentially providing energy to the overlying subsurface biosphere in the forearc regions of convergent margins.

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Dehydration of brucite + antigorite under mantle wedge conditions: insights from the direct comparison of microstructures before and after experiments

Nagaya

Okamoto

Kido

et al. 2022

Contrib Mineral Petrol

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Formation of secondary olivine after orthopyroxene during hydration of mantle wedge: evidence from the Khantaishir Ophiolite, western Mongolia

Cited by 15 publications

References 75 publications

Redistribution of magnetite during multi–stage serpentinization: Evidence from the Taishir Massif, Khantaishir ophiolite, western Mongolia

Redistribution of magnetite during multi–stage serpentinization: Evidence from the Taishir Massif, Khantaishir ophiolite, western Mongolia

Subduction hides high-pressure sources of energy that may feed the deep subsurface biosphere

Dehydration of brucite + antigorite under mantle wedge conditions: insights from the direct comparison of microstructures before and after experiments

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