K and Ti metasomatism of the mantle wedge by fluids under sub-arc conditions

2020 ◽  
Author(s):  
Dimitri Sverjensky ◽  
Simon Matthews
Keyword(s):  
Mantle Wedge ◽  
Chemical Elements ◽  
Pure Water ◽  
Water Model ◽  
Island Arcs ◽  
Silicate Anion ◽  
Deep Earth ◽  
High Silica ◽  
Subducting Slab ◽  
Metasomatized Mantle

<p>It is well documented that subducting slabs influence arc volcanics. Slab components are transferred to the mantle wedge by fluids and/or melts. Aqueous fluids released from the slab are thought to trigger partial melting in the mantle wedge and potentially influence the chemistry of the lavas that erupt in island arcs. Both fluids and melts from the slab have been proposed to transfer chemical elements to the mantle wedge. However, exactly how this occurs chemically and physically remains unclear. Recent progress in developing a Deep Earth Water model calibrated with experimental mineral and rock solubility data under sub-arc conditions now enables the chemical mass transfer from slab to mantle wedge to be predicted for comparison with natural samples.</p><p>            We report a new aqueous speciation model for Ti-species calibrated with experimental data Kessel and co-workers and Antignano and Manning that includes a neutral Ti-OH species, a Na-Ti-silicate anion, and a Ti-silicate-bicarbonate anion. The Ti-OH species is only important in almost pure water. However, the Na-Ti-silicate anion is important in high-silica fluids (e.g. in equilibrium with quartz or coesite-bearing mafic eclogites) but is overtaken in importance by the Ti-silicate-bicarbonate complex in CO<sub>2</sub>-bearing fluids.</p><p>            In the present study, we modeled the metasomatic reactions when a fluid in equilibrium with a mafic eclogite leaves a subducting slab and encounters lherzolite in the overlying mantle wedge. Initially, the mafic eclogitic fluid was in equilibrium with clinopyroxene, garnet, coesite, diamond, magnesite solid-solution, and rutile at 700°C and 4.0 GPa. Whilst the presence of CO<sub>2</sub> enables the modelled fluid to carry 600 mg/kg H<sub>2</sub>O of nominally immobile Ti from the slab into the wedge, the fluid transports a factor of 30 more K. The fluid was then heated to 950°C and simultaneously reacted irreversibly with lherzolite containing 0.86 wt% K<sub>2</sub>O and 0.084 wt% TiO<sub>2</sub>. The resultant metasomatized peridotite consisted of olivine, orthopyroxene, clinopyroxene, and garnet to which phlogopite-rich biotite had been added, and from which the TiO<sub>2</sub> component was subtracted. Overall, the metasomatism resulted in K-enrichment and Ti-depletion in the metasomatized part of the mantle wedge. The final fluid was enriched in Ti (2,830 mg/kg H<sub>2</sub>O) with lowered K (11,600 mg/kg H<sub>2</sub>O). Both the remaining fluid and metasomatized mantle may serve as sources of the elevated K/Ti ratios in arc volcanics relative to MORB. </p>

scholarly journals Continental versus oceanic subduction zones

2016 ◽  
Vol 3 (4) ◽  
pp. 495-519 ◽  
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.

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

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

<p>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  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 H<sub>2</sub>O at 1.0-3.3 GPa and 600-900 ℃, 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 ℃ and 1.5 GPa，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.</p>

Solubility of magnetite-hematite assemblages in slab-derived saline fluids

2020 ◽  
Author(s):  
Carla Tiraboschi ◽  
Carmen Sanchez-Valle
Keyword(s):  
Subduction Zones ◽  
Microprobe Analysis ◽  
Mantle Wedge ◽  
Sedimentary Cover ◽  
Low Pressure ◽  
Oceanic Lithosphere ◽  
Major Elements ◽  
Piston Cylinder ◽  
Water Saturated ◽  
Subducting Slab

<p>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.</p><p>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 °C employing a piston cylinder apparatus. Single gold capsules were loaded with natural hematite, magnetite and synthetic haplogranite (Na<sub>0.56</sub>K<sub>0.38</sub>Al<sub>0.95</sub>Si<sub>5.19</sub>O<sub>12.2</sub>). Two sets of experiments were conducted: one with H<sub>2</sub>O-only fluids and the second one adding a 1.5 m H<sub>2</sub>O–NaCl solution. The capsule was kept frozen during welding to ensure no water loss. After quench, the presence of H<sub>2</sub>O in the quenched haplogranite glass was checked by Raman spectroscopy, while major elements were determined by microprobe analysis.</p><p>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 FeO<sub>tot</sub> quenched in the haplogranite glass ranges from 0.60 wt% at 700 °C, to 1.87 wt% at 900 °C. In the presence of NaCl, we observed an increase in the amount of iron quenched in the glass (e.g., at 800 °C from 1.04 wt% to 1.56 wt% of FeO<sub>tot</sub>). 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.</p>

scholarly journals Experimental evidence for decompression melting of metasomatized mantle beneath Colima Graben, Mexico

2020 ◽  
Vol 175 (11) ◽  
Author(s):  
Eduardo Becerra-Torres ◽  
Elena Melekhova ◽  
Jon D. Blundy ◽  
Richard A. Brooker
Keyword(s):  
Experimental Approach ◽  
Mantle Wedge ◽  
Thermal Structure ◽  
Liquidus Surface ◽  
Chemical Diversity ◽  
Phase Assemblage ◽  
Cinder Cones ◽  
Piston Cylinder ◽  
High K ◽  
Metasomatized Mantle

Abstract Primitive subduction zone magmas provide information about the composition and thermal structure of the underlying mantle wedge. In the Colima Graben, Mexico, primitive lavas erupted from cinder cones range from high magnesium calc-alkaline basalts to high-K trachybasalts. This chemical diversity suggests that the sub-arc mantle wedge from which they derive is heterogeneous. To explore the conditions of magma generation in the wedge beneath Colima we used an inverse experimental approach to constrain multiple saturation points on the liquidus surface of a primitive high-K basanite (COM-1). Equilibrium piston-cylinder experiments were carried out between 1.0 and 2.4 GPa under hydrous (1.8–3.8 wt% H2O) and oxidizing (ƒO2 = − 0.5 to 4.3 log units relative to NNO) conditions. COM-1 + 3.8 wt% H2O is shown to be multiply-saturated with a phlogopite-bearing spinel pyroxenite assemblage (cpx + opx + phl + sp) close to its liquidus at 1.9–2.4 GPa and 1300 ºC. Experimental mapping of the liquidus surface reveals a multiple saturation point (MSP) where a lherzolitic phase assemblage of ol + cpx + opx + sp + phl coexist. The topology of the MSP indicates a peritectic of the form cpx + opx + phl + sp = liquid + ol. Four bracketing experiments define the MSP of COM-1 as 1300 ± 10 °C, 1.7 ± 0.1 GPa, ∆NNO = 3.4 ± 0.5 log units, for melt containing 3.6 ± 0.4 wt% H2O. The MSP olivine is too forsterite-rich (Fo92-94) to be in equilibrium with mantle lherzolite, but matches phenocryst core compositions in the natural basanite. Thus, experimental results indicate that COM-1 was produced by incongruent melting of an olivine-free, phlogopite-pyroxenite source that itself is the result of metasomatism of mantle wedge by slab-derived fluids. These conditions provide a valuable constraint on the thermal structure and chemical composition of the mantle wedge beneath Colima.

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

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.

Bind3P: A Water Model to Improve the Accuracy of Binding Calculations

2018 ◽  
Author(s):  
Jian Yin ◽  
Niel M. Henriksen ◽  
Hari S. Muddana ◽  
Michael K. Gilson
Keyword(s):  
Pure Water ◽  
Bulk Water ◽  
Water Model ◽  
Pure Liquid ◽  
Free Energies ◽  
Water Properties ◽  
Binding Data ◽  
Guest Binding ◽  
The Mean ◽  
Binding Free Energies

We report a water model, Bind3P (Version 0.1), which was obtained by using sensitivity analysis to readjust the Lennard-Jones parameters of the TIP3P model against experimental binding free energies for six host-guest systems, along with pure liquid properties. Tests of Bind3P against >100 experimental binding free energies and enthalpies for host-guest systems distinct from the training set show a consistent drop in the mean signed error, relative to matched calculations with TIP3P. Importantly, Bind3P preserves the accuracy of bulk water properties, such as density and heat of vaporization. The same approach can be applied to more sophisticated water models that can better represent pure water properties. These results lend further support to concept of integrating host-guest binding data into force field parameterization.

scholarly journals XI. Second letter on the electrolysis of secondary compounds. Addressed to Michael Faraday, Esq. D. C. L. F. R. S., Fullerian Prof. Chem. Royal Institution, &c. &c. &c. By J . Frederic Daniell, Esq. F. R. S. For. Sec. R. S., Prof. Chem. in King's College, London

1840 ◽  
Vol 130 ◽  
pp. 209-224
Keyword(s):  
Royal Society ◽  
Chemical Elements ◽  
Pure Water ◽  
Secondary Compounds ◽  
King's College ◽  
Usual Manner ◽  
Royal Institution ◽  
The Subject ◽  
Michael Faraday ◽  
Epsom Salt

My dear Faraday, You will not, I think, be surprised or displeased at my addressing you again upon the Electrolysis of Secondary Compounds . The whole of my very limited leisure, since my last Letter which the Royal Society did me the honour to publish in the Philosophical Transactions for 1839, has been occupied with experiments upon the subject; and I have obtained some results which I trust will not be found unworthy of the continued attention of yourself and the Society. The mode of investigation which I have adopted seems to me calculated not only to throw light upon the nature of electrolytes, but upon the mode in which the chemical elements group themselves together to constitute Radicles or Proximate Principles , the question which now seems universally to occupy the attention of chemists. I feel more than ever satisfied that the laws of electrolysis will be found to lead to the solution of this great problem. Upon reflecting upon the constitution of the oxyacid salts, as developed in my last Letter, I conceived that it might be possible to obtain further evidence that the simple cathion travelled as a metal to the platinode, while the compound anion was passing in the opposite direction; and that means might be devised of stopping it, as it were, in transitu . Your beautiful experiment, which I have often repeated with success, of precipitating the magnesia from a solution of Epsom salt against a surface of pure water, in the course of a voltaic current, suggested the mode of proceeding. According to my view of that experiment, the first electrolyte was resolved into the compound anion, sulphuric acid + oxygen, which passed to the zincode; and the simple cathion, magnesium, which on its passage to the platinode was stopped at the surface of water, from not finding any ion , by temporarily combining with which it could be further transferred according to the laws of electrolysis. At this point, therefore, it gave up its charge to the hydrogen of the water, which passed in the usual manner to the platinode; and the circuit was completed by the decomposition of this second electrolyte. The corresponding oxygen, of course, met the magnesium at the point where it was arrested in its progress, and, combining with it, magnesia was precipitated.

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