Fluid-present melting of sulfide-bearing ocean-crust: Experimental constraints on the transport of sulfur from subducting slab to mantle wedge

In subduction zones, aqueous fluids derived from devolatilization processes of the oceanic lithosphere and its sedimentary cover, are major vectors of mass transfer from the slab to the mantle wedge and contribute to the recycling of elements and to their geochemical cycles. In this setting, assessing the mobility of redox sensitive elements, such as iron, can provide useful insights on the oxygen fugacity conditions of slab-derived fluid. However, the amount of iron mobilized by deep aqueous fluids and melts, is still poorly constrained.We experimentally investigate the solubility of magnetite-hematite assemblages in water-saturated haplogranitic liquids, which represent the felsic melt produced by subducted eclogites. Experiments were conducted at 1 GPa and temperature ranging from 700 to 900 &#176;C employing a piston cylinder apparatus. Single gold capsules were loaded with natural hematite, magnetite and synthetic haplogranite (Na0.56K0.38Al0.95Si5.19O12.2). Two sets of experiments were conducted: one with H2O-only fluids and the second one adding a 1.5 m H2O&#8211;NaCl solution. The capsule was kept frozen during welding to ensure no water loss.&#160;After quench, the presence of H2O in the quenched haplogranite glass was checked by Raman spectroscopy, while major elements were determined by microprobe analysis.Preliminary results indicate that a significant amount of Fe is released from magnetite and hematite in hydrous melts, even at relatively low-pressure conditions. At 1 GPa the FeOtot quenched in the haplogranite glass ranges from 0.60 wt% at 700 &#176;C, to 1.87 wt% at 900 &#176;C. In the presence of NaCl, we observed an increase in the amount of iron quenched in the glass (e.g., at 800 &#176;C from 1.04 wt% to 1.56 wt% of FeOtot).&#160;Our results suggest that hydrous melts can effectively mobilize iron even at low-pressure conditions and represent a valid agent for the cycling of iron from the subducting slab to the mantle wedge.

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Experimental constraints on the partial melting of sediment-metasomatized lithospheric mantle in subduction zones

American Mineralogist ◽

10.2138/am-2020-7403 ◽

2020 ◽

Vol 105 (8) ◽

pp. 1191-1203

Author(s):

Yanfei Zhang ◽

Xuran Liang ◽

Chao Wang ◽

Zhenmin Jin ◽

Lüyun Zhu ◽

...

Keyword(s):

Upper Mantle ◽

Lithospheric Mantle ◽

Subduction Zones ◽

Mantle Wedge ◽

The Other ◽

Central American ◽

Bulk Sediment ◽

Series Of Experiments ◽

The Stability ◽

Subducting Slab

Abstract Sedimentary diapirs can be relaminated to the base of the lithosphere during slab subduction, where they can interact with the ambient lithospheric mantle to form variably metasomatized zones. Here, high-pressure experiments in sediment-harzburgite systems were conducted at 1.5–2.5 GPa and 800–1300 °C to investigate the interaction between relaminated sediment diapirs and lithospheric mantle. Two end-member processes of mixed experiments and layered (reaction) experiments were explored. In the first end-member, sediment and harzburgite powders were mixed to a homogeneous proportion (1:3), whereas in the second, the two powders were juxtaposed as separate layers. In the first series of experiments, the run products were mainly composed of olivine + orthopyroxene + clinopyroxene + phlogopite in subsolidus experiments, while the phase assemblages were then replaced by olivine + orthopyroxene + melt (or trace phlogopite) in supersolidus experiments. Basaltic and foiditic melts were observed in all supersolidus mixed experiments (~44–52 wt% SiO2 at 1.5 GPa, ~35–43 wt% SiO2 at 2.5 GPa). In the phlogopite-rich experiment (PC431, 1.5 GPa and 1100 °C), the formed melts had low alkali contents (~<2 wt%) and K2O/Na2O ratios (~0.4–1.1). In contrast, the quenched melt in phlogopite-free/poor experiments showed relatively higher alkali contents (~4–8 wt%) and K2O/Na2O ratios (~2–5). Therefore, the stability of phlogopite could control the bulk K2O and K2O/Na2O ratios of magmas derived from the sediment-metasomatized lithospheric mantle. In layered experiments, a reaction zone dominated by clinopyroxene + amphibole (or orthopyroxene) was formed because of the reaction between harzburgite and bottom sediment-derived melts (~62.5–67 wt% SiO2). The total alkali contents and K2O/Na2O ratios of the formed melts were about 6–8 wt% and 1.5–3, respectively. Experimentally formed melts from both mixed and reaction experiments were rich in large ion lithosphile elements and displayed similar patterns with natural potassium-rich arc lavas from oceanic subduction zones (i.e., Mexican, Sunda, Central American, and Aleutian). The experimental results demonstrated that bulk sediment diapirs, in addition to sediment melt, may be another possible mechanism to transfer material from a subducting slab to an upper mantle wedge or lithospheric mantle. On the other hand, the breakdown of phlogopite may play an important role in the mantle source that produces potassium-rich arc lavas in subduction zones.

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Geochemistry of the Neoarchaean Volcanic Rocks of the Kilimafedha Greenstone Belt, Northeastern Tanzania

Journal of Geological Research ◽

10.1155/2012/603971 ◽

2012 ◽

Vol 2012 ◽

pp. 1-18 ◽

Cited By ~ 4

Author(s):

Charles W. Messo ◽

Shukrani Manya ◽

Makenya A. H. Maboko

Keyword(s):

Partial Melting ◽

Greenstone Belt ◽

Mantle Wedge ◽

Spatial Association ◽

Volcanic Rocks ◽

Low Concentrations ◽

Peridotite Mantle ◽

Ree Patterns ◽

Subducting Slab ◽

Oceanic Slab

The Neoarchaean volcanic rocks of the Kilimafedha greenstone belt consist of three petrological types that are closely associated in space and time: the predominant intermediate volcanic rocks with intermediate calc-alkaline to tholeiitic affinities, the volumetrically minor tholeiitic basalts, and rhyolites. The tholeiitic basalts are characterized by slightly depleted LREE to nearly flat REE patterns with no Eu anomalies but have negative anomalies of Nb. The intermediate volcanic rocks exhibit very coherent, fractionated REE patterns, slightly negative to absent Eu anomalies, depletion in Nb, Ta, and Ti in multielement spidergrams, and enrichment of HFSE relative to MORB. Compared to the other two suites, the rhyolites are characterized by low concentrations of TiO2 and overall low abundances of total REE, as well as large negative Ti, Sr, and Eu anomalies. The three suites have a εNd (2.7 Ga) values in the range of −0.51 to +5.17. The geochemical features of the tholeiitic basalts are interpreted in terms of derivation from higher degrees of partial melting of a peridotite mantle wedge that has been variably metasomatized by aqueous fluids derived from dehydration of the subducting slab. The rocks showing intermediate affinities are interpreted to have been formed as differentiates of a primary magma formed later by lower degrees of partial melting of a garnet free mantle wedge that was strongly metasomatized by both fluid and melt derived from the subducting oceanic slab. The rhyolites are best interpreted as having been formed by shallow level fractional crystallization of the intermediate volcanic rocks involving plagioclase and Ti-rich phases like ilmenite and magnetite as well as REE-rich phases like apatite, zircon, monazite, and allanite. The close spatial association of the three petrological types in the Kilimafedha greenstone belt is interpreted as reflecting their formation in an evolving late Archaean island arc.

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A Strong Seismic Reflector within the Mantle Wedge above the Ryukyu Subduction of Northern Taiwan

Seismological Research Letters ◽

10.1785/0220190174 ◽

2019 ◽

Vol 91 (1) ◽

pp. 310-316

Author(s):

Cheng‐Horng Lin ◽

Min‐Hung Shih ◽

Ya‐Chuan Lai

Keyword(s):

Opposite Direction ◽

Mantle Wedge ◽

Seismic Velocity ◽

Low Velocity ◽

P Waves ◽

Deep Earthquake ◽

Subduction System ◽

Subducting Slab ◽

Seismic Reflector ◽

Northern Taiwan

Abstract Major structures within the mantle wedge are often revealed from seismic velocity anomalies, such as low‐velocity zones at magma reservoirs, partial melting regions, or the upwelling asthenosphere. However, no significant seismic boundaries have been reported in the shallow mantle wedge beneath volcanic arcs. Here, we present evidence for a strong seismic reflector dipping in the opposite direction of the subducting slab in the mantle wedge beneath northern Taiwan in the western end of the Ryukyu subduction system. We find that two unambiguous P waves generated by a deep earthquake (ML 5.1) at a depth of 132.5 km were clearly recorded by the dense seismic array (Formosa Array), composed of 140 broadband seismic stations with a station spacing of approximately 5 km in northern Taiwan. Forward modeling using both raytracing and travel times shows that a seismic reflector exists beneath the Tatun volcano group (TVG) around depths of 80–110 km. The reflector dips in the opposite direction of the subducting slab and is unlikely to be associated with mantle wedge corner flow. Instead, it probably belonged to parts of possible structures such as the asthenospheric flow, the mantle diapir, or other undiscovered structures above the subducting slab. No matter what the seismic boundary is exactly, it might be associated with the active volcanism in the TVG. The detailed geometry and mechanism of the seismic boundary in the mantle wedge will be obtained as the Formosa Array collects more seismic data in the near future.

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Mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1302040110 ◽

2013 ◽

Vol 110 (24) ◽

pp. 9663-9668 ◽

Cited By ~ 71

Author(s):

T. Kawamoto ◽

M. Yoshikawa ◽

Y. Kumagai ◽

M. H. T. Mirabueno ◽

M. Okuno ◽

...

Keyword(s):

Mantle Wedge ◽

Subducting Slab

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Continental versus oceanic subduction zones

National Science Review ◽

10.1093/nsr/nww049 ◽

2016 ◽

Vol 3 (4) ◽

pp. 495-519 ◽

Cited By ~ 88

Author(s):

Yong-Fei Zheng ◽

Yi-Xiang Chen

Keyword(s):

Subduction Zones ◽

Mantle Wedge ◽

Ultrahigh Pressure ◽

Metamorphic Rocks ◽

Crustal Rocks ◽

Incompatible Elements ◽

Ultrahigh Temperature ◽

Subducting Slab ◽

Oceanic Slab ◽

Metasomatized Mantle

Abstract Subduction zones are tectonic expressions of convergent plate margins, where crustal rocks descend into and interact with the overlying mantle wedge. They are the geodynamic system that produces mafic arc volcanics above oceanic subduction zones but high- to ultrahigh-pressure metamorphic rocks in continental subduction zones. While the metamorphic rocks provide petrological records of orogenic processes when descending crustal rocks undergo dehydration and anataxis at forearc to subarc depths beneath the mantle wedge, the arc volcanics provide geochemical records of the mass transfer from the subducting slab to the mantle wedge in this period though the mantle wedge becomes partially melted at a later time. Whereas the mantle wedge overlying the subducting oceanic slab is of asthenospheric origin, that overlying the descending continental slab is of lithospheric origin, being ancient beneath cratons but juvenile beneath marginal arcs. In either case, the mantle wedge base is cooled down during the slab–wedge coupled subduction. Metamorphic dehydration is prominent during subduction of crustal rocks, giving rise to aqueous solutions that are enriched in fluid-mobile incompatible elements. Once the subducting slab is decoupled from the mantle wedge, the slab–mantle interface is heated by lateral incursion of the asthenospheric mantle to allow dehydration melting of rocks in the descending slab surface and the metasomatized mantle wedge base, respectively. Therefore, the tectonic regime of subduction zones changes in both time and space with respect to their structures, inputs, processes and products. Ophiolites record the tectonic conversion from seafloor spreading to oceanic subduction beneath continental margin, whereas ultrahigh-temperature metamorphic events mark the tectonic conversion from compression to extension in orogens.

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Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges

Science Advances ◽

10.1126/sciadv.1501631 ◽

2016 ◽

Vol 2 (5) ◽

pp. e1501631 ◽

Cited By ~ 26

Author(s):

Geeth Manthilake ◽

Nathalie Bolfan-Casanova ◽

Davide Novella ◽

Mainak Mookherjee ◽

Denis Andrault

Keyword(s):

Electrical Conductivity ◽

Subduction Zone ◽

Mantle Wedge ◽

Aqueous Fluid ◽

Stability Field ◽

Initial Increase ◽

High Electrical Conductivity ◽

Additional Source ◽

Slab Dehydration ◽

Subducting Slab

Mantle wedge regions in subduction zone settings show anomalously high electrical conductivity (~1 S/m) that has often been attributed to the presence of aqueous fluids released by slab dehydration. Laboratory-based measurements of the electrical conductivity of hydrous phases and aqueous fluids are significantly lower and cannot readily explain the geophysically observed anomalously high electrical conductivity. The released aqueous fluid also rehydrates the mantle wedge and stabilizes a suite of hydrous phases, including serpentine and chlorite. In this present study, we have measured the electrical conductivity of a natural chlorite at pressures and temperatures relevant for the subduction zone setting. In our experiment, we observe two distinct conductivity enhancements when chlorite is heated to temperatures beyond its thermodynamic stability field. The initial increase in electrical conductivity to ~3 × 10−3S/m can be attributed to chlorite dehydration and the release of aqueous fluids. This is followed by a unique, subsequent enhancement of electrical conductivity of up to 7 × 10−1S/m. This is related to the growth of an interconnected network of a highly conductive and chemically impure magnetite mineral phase. Thus, the dehydration of chlorite and associated processes are likely to be crucial in explaining the anomalously high electrical conductivity observed in mantle wedges. Chlorite dehydration in the mantle wedge provides an additional source of aqueous fluid above the slab and could also be responsible for the fixed depth (120 ± 40 km) of melting at the top of the subducting slab beneath the subduction-related volcanic arc front.

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Granitic magmas: possible and impossible sources, water contents, and crystallization sequences

Canadian Journal of Earth Sciences ◽

10.1139/e76-104 ◽

1976 ◽

Vol 13 (8) ◽

pp. 1007-1019 ◽

Cited By ~ 110

Author(s):

Peter J. Wyllie ◽

Wuu-Liang Huang ◽

Charles R. Stern ◽

Sven Maaløe

Keyword(s):

Continental Crust ◽

Oceanic Crust ◽

Mantle Wedge ◽

Regional Metamorphism ◽

Mantle Peridotite ◽

Ocean Crust ◽

Crustal Rocks ◽

Subducted Oceanic Crust ◽

Water Contents ◽

Phase Relationships

The calc-alkalic rocks of batholiths or their precursors may be generated in deep continental crust, in subducted oceanic crust, in the mantle wedge above, or in processes involving material from all three sources. For the series gabbro–tonalite–granite, we have phase relationships with excess H2O to 35 kbar (3500 MPa), and the H2O-undersaturated liquidus surfaces mapped with contours for H2O contents and with fields for near-liquidus minerals. Isobaric diagrams with low H2O contents provide grids potentially useful in defining limits for the H2O content of magmas, based on the sequence of crystallization. Conclusions from the experimental framework include: (1) The H2O content of large granitic bodies is less than 1.5%. (2) Primary granite magmas can not be derived from the mantle or subducted ocean crust. (3) Primary granite magmas with low H2O content are generated in the crust, and erupted as rhyolites. (4) Primary tonalite and andesite are not generated from mantle peridotite; the H2O contents required are unrealistically high. (5) Primary tonalite and andesite are not generated in the crust unless temperatures are significantly higher than those of regional metamorphism. (6) Subducted ocean crust yields magmas with intermediate SiO2 content, but not primary tonalite and andesite. (7) Batholiths are produced from crustal rocks as a normal consequence of regional metamorphism, with the formation of H2O-undersaturated granite liquid and mobilized migmatites. Some batholiths receive in addition contributions of material and heat from mantle and subducted ocean crust.

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Experimental determination of magnesite solubility in water and silicate saturated saline solutions under high temperature and pressure

10.5194/egusphere-egu2020-6178 ◽

2020 ◽

Author(s):

Wan-Cai Li ◽

Qinxia Wang ◽

Huaiwei Ni

Keyword(s):

High Temperature ◽

Carbon Cycle ◽

Mantle Wedge ◽

Pure Water ◽

Aqueous Fluid ◽

In Situ Observation ◽

Metasedimentary Rocks ◽

High Temperature And Pressure ◽

Temperature And Pressure ◽

Subducting Slab

Aqueous fluid derived from the dehydration of subducting slab can dissolve and transfer carbon to mantle wedge, and thus plays an important role in the globe deep carbon cycle. Carbonates are major phases of carbon in the subducting slab, however their solubilities in the subduction zone fluid are poorly constrained. This heavily hinder our understanding of the&#160; deep carbon cycle. Magnesite is one of the carbonates in the subducting slab, and can be stabilized to sub-arc depth. We determined the solubility of magnesite in pure water and saline fluids buffered by silicate by in situ observation of quantitative magnesite totally dissolved in quantitative fluid under high temperature and pressure in Hydrothermal Diamond Anvil Cell (HDAC). The results demonstrated that the solubility of magnesite in pure water is 0.010-0.026 mol/kg H2O at 1.0-3.3 GPa and 600-900 &#8451;, and that it increases as increasing temperature, but has no obvious pressure effect. This data is close to the experimental measurement of calcite solubility in literature, but slightly higher than the theoretical results calculated using DEW model. The solubility of magnesite in 5 wt % NaCl solution equilibrium with quartz is 0.22 mol/ kg, at 700 &#8451; and 1.5 GPa&#65292;an order of magnitudes higher than that in the pure water. Since the formation of new silicate minerals, such as olivine or talc, depends on silicon activity in the fluid, the dissolution of silicate would boost the solubility of magnesite. This mechanism has been previously reported in the Alps metasedimentary rocks. Therefore, the aqueous fluid, rich in saline and silicon in fore-arc and sub-arc depths, has the ability to dissolve and transfer almost all the carbonates in the subducting slab to the overlying mantle wedge.

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Numerical simulation of subduction zone pressure-temperature-time paths: constraints on fluid production and arc magmatism

Philosophical Transactions of the Royal Society of London Series A Physical and Engineering Sciences ◽

10.1098/rsta.1991.0050 ◽

1991 ◽

Vol 335 (1638) ◽

pp. 341-353 ◽

Cited By ~ 88

Keyword(s):

Heat Transfer ◽

Partial Melting ◽

Subduction Zone ◽

Subduction Zones ◽

Mantle Wedge ◽

Thermal Structure ◽

Oceanic Lithosphere ◽

Transfer Model ◽

Temperature Time ◽

Subducting Slab

The location and sequence of metamorphic devolatilization and partial melting reactions in subduction zones may be constrained by integrating fluid and rock pressure-temperature-time ( P-T-t ) paths predicted by numerical heat-transfer models with phase diagrams constructed for metasedimentary, metabasaltic, and ultramafic bulk compositions. Numerical experiments conducted using a two-dimensional heat transfer model demonstrate that the primary controls on subduction zone P-T-t paths are: (1) the initial thermal structure; (2) the amount of previously subducted lithosphere; (3) the location of the rock in the subduction zone; and (4) the vigour of mantle wedge convection induced by the subducting slab. Typical vertical fluid fluxes out of the subducting slab range from less than 0.1 to 1 (kg fluid) m -2 a -1 for a convergence rate of 3 cm a -1 . Partial melting of the subducting, amphibole-bearing oceanic crust is predicted to only occur during the early stages of subduction initiated in young (less than 50 Ma) oceanic lithosphere. In contrast, partial melting of the overlying mantle wedge occurs in many subduction zone experiments as a result of the infiltration of fluids derived from slab devolatilization reactions. Partial melting in the mantle wedge may occur by a twostage process in which amphibole is first formed by H 2 O infiltration and subsequently destroyed as the rock is dragged downward across the fluid-absent ‘hornblende-out’ partial melting reaction.

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