Magnesium Isotope Composition of Subduction Zone Fluids as Constrained by Jadeitites From Myanmar

Chen, Yi; Huang, Fang; Shi, Gongle; Wu, Fu‐Yuan; Chen, Xi; Jin, Qi-Zhen; Su, Bin; Guo, S.; Sein, Kyaing; Nyunt, Thet Tin

doi:10.1029/2018jb015805

Cited by 21 publications

(8 citation statements)

References 140 publications

(290 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Other processes leading to the formation of nearly pure forsterite include serpentinization/deserpentinization of dunites and silicification of dolomite [18][19][20][21][22][23]. However, there has not been any mechanism to concentrate thus-formed forsterite grains to form a massive monomineralic rock like the jianite reported in this study.…”

mentioning

confidence: 71%

“…Their genesis has been attributed to some special processes such as subsurface oxidation, subsolidus re-equilibration, and interaction with carbonates [14]. Additionally, narrow pseudomorphic olivine rims with Mg# > 96 were occasionally found surrounding primary olivine grains (Mg# = ~89-92) in some serpentinites, with their genesis ascribed to the serpentinization or deserpentinization reaction [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Jianite: Massive Dunite Solely Made of Virtually Pure Forsterite from Ji’an County, Jilin Province, Northeast China

Wang

Yan

et al. 2020

Minerals

View full text Add to dashboard Cite

A rare massive yellowish-green serpentinized dunite, covering a minimum area up to ~50 m2, has been found in Ji’an County, Jilin Province, Northeast China. It contains primary olivine and secondary serpentine (antigorite) and brucite. Other primary minerals like orthopyroxene, clinopyroxene, and aluminum-rich phase (such as garnet, spinel, and plagioclase), frequently appearing in ultramafic rocks, have not been identified. The olivine is essentially pure forsterite, with an Mg# (100 × Mg/(Mg + Fe)) of ~99.6–99.7. Due to these distinct features, we especially name the protolith of this dunite as jianite (集安岩). The forsterite grains range up to ~2 mm, show clear equilibrium textures such as nearly straight grain boundaries and ~120° dihedral angles at their triple junctions, and display no intragranular or intergranular composition variations. They are extensively ruptured and hydrated (i.e., serpentinized), with the fractures (and the grain boundaries as well) filled by fine-grained antigorite (ideally Mg6(Si4O10)(OH)8) and brucite (ideally Mg(OH)2). These secondary phases are also extremely poor in Fe, indicating a good chemical equilibrium with the forsterite. The serpentinization reaction may have proceeded as forsterite + fluid = antigorite + brucite at temperatures of ~425(25) °C and at relatively low but undetermined pressures. The fluid was likely a B-rich, but Si-poor dilute aqueous fluid, as implied by the trace element characteristics and water-related infrared features of the forsterites in equilibrium. The petrogenesis of the jianite is presently unclear.

show abstract

mentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Jianite: Massive Dunite Solely Made of Virtually Pure Forsterite from Ji’an County, Jilin Province, Northeast China

Wang

Yan

et al. 2020

Minerals

View full text Add to dashboard Cite

show abstract

“…Fumagalli et al, 2014). This interpretation differs from Chen et al (2018) for the Hkamti Jade Mine in Myanmar, where similar dark granofels are considered as a blackwall alteration formed by reaction of the jadeitite with the host serpentinites (see Table S1).…”

Section: Replacement Processes and Incoming Fluid Composition Evolumentioning

confidence: 95%

Drainage of subduction interface fluids into the forearc mantle evidenced by a pristine jadeitite network (Polar Urals)

Glodny

Cambeses

Raimondo

et al. 2020

Journal Metamorphic Geology

View full text Add to dashboard Cite

The physical and mechanical processes rooted in the hydrated, serpentinized mantle above subduction zones remain insufficiently explored despite fundamental implications for our understanding of rheology and fluid recycling along subduction interfaces. Through a field-based investigation, serpentinized peridotites and jadeitite samples from a fossil forearc mantle in the Polar Urals (Russia) are studied here to document fluid-rock interaction processes in the high-P field, as well as the long-term evolution of the base of the mantle wedge. Petrographic, geochemical and microstructural observations reveal a complex, protracted evolution of the jadeitite-forming fluid pathway throughout the gradual cooling of the forearc mantle and increasing serpentinization of the host. It is shown that the jadeitite lenses in the studied locality (a) derive for a large part from a trondhjemitic dyke earlier emplaced in a warm subduction environment, and (b) record the cooling of the subduction hangingwall under high-P conditions associated with increasing host serpentinization. In the studied locality, the majority of the jadeitites formed at relatively high temperatures (>600°C) by the influx of Na-Al-rich, slab-derived metamorphic fluids that were drained along the base of the mantle wedge, parallel to the subduction interface. Changes in bulk-rock geochemical signatures and in paragenetic sequences also constrain the compositional evolution of the fluid channelized along this drainage, with an increasing sedimentary component. The phlogopite-bearing walls of the dyke exhibit Rb-Sr and Ar-Ar ages ranging between c. 405 and c. 390 Ma, a range partly overlapping within uncertainty with the previously dated zircons from the jadeitite core (410-400 Ma; U-Pb). This study opens a unique window on the pristine structures formed above the plate interface by melting and fluid-rock interaction in the early subduction stages, as well as their evolution during secular cooling of the base of the mantle wedge.

show abstract

“…Chen et al . [ 60 ] measured Mg isotopic compositions of the jadeitites from Myanmar. These white jadeitites were precipitated from Na-Al-Si fluids at the forearc slab-mantle interface (1–1.5 GPa, and 300–500°C).…”

Section: Magnesium Isotope Fractionation During Subductionmentioning

confidence: 99%

Magnesium isotope geochemistry of the carbonate-silicate system in subduction zones

Wang

2022

National Science Review

View full text Add to dashboard Cite

The lighter magnesium (Mg) isotopic signatures observed in intraplate basalts are commonly thought to result from deep carbonate recycling, provided that the sharp difference in Mg isotopic composition between surface carbonates and the normal mantle likely preserves during plate subduction. However, deep subduction of carbonates and silicates could potentially fractionate Mg isotopes and change their chemical compositions. Subducting silicate rocks that experienced metamorphic dehydration lose a small amount of Mg, and preserve the original Mg isotopic signature of their protoliths. When the dehydrated fluids dissolve carbonate minerals, they may evolve to lighter Mg isotopic compositions. The solubility of carbonate minerals in fluids decreases in the order of calcite, aragonite, dolomite, magnesite and siderite, leading to selective and partial dissolution of carbonate minerals along subduction path. At the island arc depth (70-120 km), the metamorphic fluid dissolves mainly Mg-poor calcites, and thus the fluid is difficult to modify the Mg isotopic system of the mantle wedge and associated arc basalts. At greater depth of the back arc system or continental margin (> 150 km), the supercritical fluid can dissolve Mg-rich carbonate minerals, and its interaction with the mantle wedge could significantly imprint the light Mg isotopic signature to the mantle rocks and the derivatives. Meanwhile, the carbonate and silicate remaining within the subducting slab could experience elemental and isotopic exchange, during which the silicate can obtain light Mg isotopic signature and high CaO/Al2O3, whereas the carbonates, particularly the Ca-rich limestone, shift Mg isotopes and MgO contents towards higher values. If this isotopic and elemental exchange event occurs widely during crustal subduction, subducted Ca-rich carbonates can partially transform to be Mg-rich, and a portion of recycled silicates (e.g., carbonated eclogites) can have light Mg isotopic composition alongside carbonates. Both serves as the low-δ26Mg endmember recycled back into the deep mantle, but the latter is not related to the deep carbonate recycling. Therefore, it is important to discriminate whether the light Mg isotopic signatures observed in intraplate basalts are linked to deep carbonate recycling, or alternatively, recycling of carbonated eclogites.

show abstract

Magnesium Isotope Composition of Subduction Zone Fluids as Constrained by Jadeitites From Myanmar

Cited by 21 publications

References 140 publications

Jianite: Massive Dunite Solely Made of Virtually Pure Forsterite from Ji’an County, Jilin Province, Northeast China

Jianite: Massive Dunite Solely Made of Virtually Pure Forsterite from Ji’an County, Jilin Province, Northeast China

Drainage of subduction interface fluids into the forearc mantle evidenced by a pristine jadeitite network (Polar Urals)

Magnesium isotope geochemistry of the carbonate-silicate system in subduction zones

Contact Info

Product

Resources

About