Oceanic slab-top melting during subduction: Implications for trace-element recycling and adakite petrogenesis

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 216-220 ◽  
Author(s):  
David Hernández-Uribe ◽  
Juan David Hernández-Montenegro ◽  
Kim A. Cone ◽  
Richard M. Palin
Keyword(s):  
Trace Element ◽  
Oceanic Crust ◽  
Subduction Zones ◽  
Large Scale ◽  
Thermal Structure ◽  
Experimental Petrology ◽  
Chemical Recycling ◽  
Almost All ◽  
Water Saturated ◽  
Altered Basalt

Abstract Arc volcanism and trace-element recycling are controlled by the devolatilization of oceanic crust during subduction. The type of fluid—either aqueous fluids or hydrous melts—released during subduction is controlled by the thermal structure of the subduction zone. Recent thermomechanical models and results from experimental petrology argue that slab melting occurs in almost all subduction zones, although this is not completely supported by the rock record. Here we show via phase equilibrium modeling that melting of either fresh or hydrothermally altered basalt rarely occurs during subduction, even at water-saturated conditions. Melting occurs only along the hottest slab-top geotherms, with aqueous fluids being released in the forearc region and anatexis restricted to subarc depths, leading to high-SiO2 adakitic magmatism. We posit that aqueous fluids and hydrous melts preferentially enhance chemical recycling in “hot” subduction zones. Our models show that subducted hydrothermally altered basalt is more fertile than pristine basaltic crust, enhancing fluid and melt production during subduction and leading to a greater degree of chemical recycling. In this contribution, we put forward a petrological model to explain (the lack of) melting during the subduction of oceanic crust and suggest that many large-scale models of mass transfer between Earth’s surface and interior may require revision.

Constraints imposed by experimental petrology on possible and impossible magma sources and products

1984 ◽  
Vol 310 (1514) ◽  
pp. 439-456 ◽  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Basaltic Andesite ◽  
Subduction Zones ◽  
Mantle Peridotite ◽  
Experimental Petrology ◽  
Source Rocks ◽  
Calc Alkaline ◽  
Physical Constraints ◽  
Inverse Results

Experimental petrology can be used in forward and inverse approaches. The forward approach defines the compositions of liquids generated by partial melting of possible source rocks at various depths. The inverse approach determines conditions for multiple-mineral saturation at the liquidus of primitive magmas, correlates them with residual minerals of possible source rocks, and thus provides estimates of depths and temperatures required for their derivation. Review of a selection of forward and inverse results is followed by evaluation of petrological and geophysical processes in layered mantle and in subduction zones. Physical constraints imposed by solidus curves and geotherms present problems for models that derive basalts from deep mantle reservoirs, separated from overlying convecting layers. Magmas from mantle are limited to compositions less siliceous than basaltic andesite, with rare exceptions. Granite liquids cannot be generated from normal peridotite, nor from oceanic crust at mantle pressures in subduction zones. In continental crust, hydrous granite liquid is generated at depths of less than 30 km. Basaltic andesite and picritic basalt are parental magmas for the calc-alkaline series. Andesite is not primary from subcontinental depths, and can be generated as liquid in continental crust only if temperatures exceed about 1100°C. Calc-alkaline magmas may contain components from mantle peridotite, subducted oceanic crust, and continental crust.

The Aksug Porphyry Cu–Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma

2021 ◽  
Vol 62 (4) ◽  
pp. 445-459
Author(s):  
A.N. Berzina ◽  
A.P. Berzina ◽  
V.O. Gimon
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Large Scale ◽  
Basaltic Magma ◽  
Igneous Rocks ◽  
Magmatic System ◽  
Copper Mineralization ◽  
Geochemical Parameters ◽  
Depleted Mantle ◽  
Two Stages

Abstract ––Two stages are recognized in the evolution of the Aksug ore-magmatic system (OMS): (1) formation of the Aksug granitoid pluton and (2) emplacement of small ore-bearing intrusions. Intrusive bodies of the two stages are composed of rocks of the same type and bear copper mineralization: poor dispersed and large-scale veinlet-disseminated, respectively. The pluton and small intrusions are formed by gabbroid and granitoid rocks, with similar petrogeochemical characteristics of igneous rocks of the same type. The plutonic gabbroic association includes gabbro, gabbrodiorites, and pyroxene–amphibole diorites/quartz diorites. The small subvolcanic gabbroic intrusions are gabbrodiorite and diorite porphyrites. The trace element patterns of the gabbroids are similar to those of igneous rocks in subduction zones. The gabbroids are characterized by isotope parameters εNd(500) = +6.1 to +7.2 and (87Sr/86Sr)500 = 0.7022–0.7030 and model age TNd(DM) = 0.85–0.74 Ga. As follows from the geochemical parameters, the depleted mantle metasomatized by subduction fluids was the source of basaltic magma. The plutonic granitoid association includes tonalites, plagiogranites, and amphibole diorites/quartz diorites; the small subvolcanic granitoid intrusions are tonalite porphyry and quartz diorite porphyrites. The trace element patterns and Nd and Sr isotope compositions of the granitoids are much similar to those of the gabbroids. According to the geochemical parameters, tonalitic and plagiogranitic magmas formed through the melting of juvenile mafic crust, and dioritic magma resulted from the mixing of basaltic and tonalitic/plagiogranitic magmas. In the course of the OMS formation, metals and volatiles were introduced by basaltic and granitoid magmas from the metasomatized mantle and juvenile mafic crust. The compression setting during the pluton formation hampered the separation of ore-bearing fluids, which led to poor dispersed mineralization. The extension setting during the emplacement of small intrusions favored the intense separation of ore-bearing fluids. The interaction of magma and fluids of the small intrusions with rocks of the pluton was accompanied by the removal of metals from the latter and their involvement in the ore-forming process. This increased the ore potential of the magmatic system and favored the formation of rich mineralization at the final stage of its evolution.

Os isotopic composition of western Aleutian adakites: Implications for the Re/Os of oceanic crust processed through hot subduction zones

2021 ◽  
Vol 292 ◽  
pp. 452-467
Author(s):  
Rachel Bezard ◽  
Simon Turner ◽  
Bruce Schaefer ◽  
Gene Yogodzinski ◽  
Kaj Hoernle
Keyword(s):  
Isotopic Composition ◽  
Oceanic Crust ◽  
Subduction Zones

scholarly journals The role of sulphur on the melting of Ca-poor sediment and on trace element transfer in subduction zones: an experimental investigation

2021 ◽  
Author(s):  
Anne-Aziliz Pelleter ◽  
Gaëlle Prouteau ◽  
Bruno Scaillet
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Arc Magmas ◽  
Trace Element Contents ◽  
The Stability ◽  
Element Transfer ◽  
High Sediment

Abstract We performed phase equilibrium experiments on a natural Ca-poor pelite at 3 GPa, 750-1000 °C, under moderately oxidizing conditions, simulating the partial melting of such lithologies in subduction zones. Experiments investigated the effect of sulphur addition on phase equilibria and compositions, with S contents of up to ∼ 2.2 wt. %. Run products were characterized for their major and trace element contents, in order to shed light on the role of sulphur on the trace element patterns of melts produced by partial melting of oceanic Ca-poor sediments. Results show that sulphur addition leads to the replacement of phengite by biotite along with the progressive consumption of garnet, which is replaced by an orthopyroxene-kyanite assemblage at the highest sulphur content investigated. All Fe-Mg silicate phases produced with sulphur, including melt, have higher MgO/(MgO+FeO) ratios (relative to S-free/poor conditions), owing to Fe being primarily locked up by sulphide in the investigated redox range. Secular infiltration of the mantle wedge by such MgO and K2O-rich melts may have contributed to the Mg and K-rich character of the modern continental crust. Addition of sulphur does not affect significantly the stability of the main accessory phases controlling the behaviour of trace elements (monazite, rutile and zircon), although our results suggest that monazite solubility is sensitive to S content at the conditions investigated. The low temperature (∼ 800 °C) S-bearing and Ca-poor sediment sourced slab melts show Th and La abundances, Th/La systematics and HFSE signatures in agreement with the characteristics of sediment-rich arc magmas. Because high S contents diminish phengite and garnet stabilities, S-rich and Ca-poor sediment sourced slab melts have higher contents of Rb, B, Li (to a lesser extent), and HREE. The highest ratios of La/Yb are observed in sulphur-poor runs (with a high proportion of garnet, which retains HREE) and beyond the monazite out curve (which retains LREE). Sulphides appear to be relatively Pb-poor and impart high Pb/Ce ratio to coexisting melts, even at high S content. Overall, our results show that Phanerozoic arc magmas from high sediment flux margins owe their geochemical signature to the subduction of terrigenous, sometimes S-rich, sediments. In contrast, subduction of such lithologies during Archean appears unlikely or unrecorded.

Wet-mechanical processing of a plastic-rich two-dimensional-fraction from mixed wastes for chemical recycling

2021 ◽  
pp. 0734242X2199643
Author(s):  
Möllnitz Selina ◽  
Bauer Markus ◽  
Schwabl Daniel ◽  
Sarc Renato
Keyword(s):  
Large Scale ◽  
Sewage Treatment Plant ◽  
Treatment Plant ◽  
Process Water ◽  
Chemical Recycling ◽  
Mechanical Processing ◽  
Municipal Solid Wastes ◽  
Core Element ◽  
Metal Levels ◽  
Mixed Wastes

The recycling of source separated polyolefins (POs) (e.g., light weight packaging waste) is already state of the art. Therefore, further plastic materials contained in mixed wastes have become more important due to increasing legal pressure. Mixed commercial and municipal solid wastes contain large quantities of POs. These mixed wastes would usually be treated in waste incinerators or processed to refuse-derived fuel for cement plants. Large-scale experiments were conducted to assess the potential of such POs from these waste streams for recycling processes. The potential and applicability of a dry-mechanical and subsequently wet-mechanical (Wet-mechanical) processing with the aim of generating a PO concentrate for chemical recycling purposes was assessed. These investigations’ focus was put on the centrifugal force separator technology as the core element of Wet-mechanical processing. In addition to the input material, all output materials and process water streams were chemically and physically characterized to estimate potential treatment or recycling paths. Results demonstrate that a two-stage purification is necessary to produce POs with sufficient purity out of both wastes. Chlorine and heavy metal levels are simultaneously reduced. The increased quantity of impurities only slightly changes the density of the process waters. Process water analyses show that wastewater treatment is necessary before discharge into a receiving water or sewage treatment plant. The sediment does not fulfil any hazard-relevant properties, and different thermal treatment options are possible.

Boninites as windows into trace element mobility in subduction zones

2010 ◽  
Vol 74 (2) ◽  
pp. 684-704 ◽  
Author(s):  
Stephan König ◽  
Carsten Münker ◽  
Stephan Schuth ◽  
Ambre Luguet ◽  
J. Elis Hoffmann ◽  
...  
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Element Mobility ◽  
Trace Element Mobility

scholarly journals The Fluid Mobilities of K and Zr in Subduction Zones: Thermodynamic Constraints

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 394
Author(s):  
Richen Zhong ◽  
Min Zhang ◽  
Chang Yu ◽  
Hao Cui
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Critical Role ◽  
High Field Strength ◽  
Trace Element Pattern ◽  
Arc Magmas ◽  
Thermodynamic Simulations ◽  
Element Pattern ◽  
Element Transfer ◽  
Complex Ion

A subduction zone plays a critical role in forging continental crust via formation of arc magmas, which are characteristically enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). This trace element pattern results from the different mobilities of LILEs and HFSEs during slab-to-wedge mass transfer, but the mechanisms of trace element transfer from subducting crusts are not fully understood. In this study, thermodynamic simulations are carried out to evaluate the mobilities of K and Zr, as representative cases of LILE and HFSE, respectively, in slab fluids. The fluids buffered by basaltic eclogite can dissolve > 0.1 molal of K at sub-arc depths (~3 to 5.5 GPa). However, only minor amounts of K can be liberated by direct devolatilization of altered oceanic basalt, because sub-arc dehydration mainly takes place at temperatures < 600 °C (talc-out), wherein the fluid solubility of K is very limited (<0.01 molal). Therefore, serpentinite-derived fluids are required to flush K from the eclogite. The solubility of K can be enhanced by the addition of NaCl to the fluid, because fluid Na+ can unlock phengite-bonded K via a complex ion exchange. Finally, it is further confirmed that Zr and other HFSEs are immobile in slab fluids.

RESEARCH OF EXTERNAL MASS TRANSFER PROCESSES FOR ADSORPTION FROM SOLUTIONS IN A APPARATUS WITH STIRRING

2021 ◽  
pp. 11-20
Author(s):  
V. Solovej ◽  
K. Gorbunov ◽  
V. Vereshchak ◽  
O. Gorbunova
Keyword(s):  
Mass Transfer ◽  
Energy Spectrum ◽  
Energy Dissipation ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Wave Number ◽  
Wave Form ◽  
Local Isotropy ◽  
Stirred Vessel ◽  
Almost All

A study has been mode of transport-controlled mass transfer-controlled to particles suspended in a stirred vessel. The motion of particle in a fluid was examined and a method of predicting relative velocities in terms of Kolmogoroff’s theory of local isotropic turbulence for mass transfer was outlined. To provide a more concrete visualization of complex wave form of turbulence, the concepts of eddies, of eddy velocity, scale (or wave number) and energy spectrum, have proved convenient. Large scale motions of scale contain almost all of the energy and they are directly responsible for energy diffusion throughout the stirring vessel by kinetic and pressure energies. However, almost no energy is dissipated by the large-scale energy-containing eddies. A scale of motion less than is responsible for convective energy transfer to even smaller eddy sires. At still smaller eddy scales, close to a characteristic microscale, both viscous energy dissipation and convection are the rule. The last range of eddies has been termed the universal equilibrium range. It has been further divided into a low eddy size region, the viscous dissipation subrange, and a larger eddy size region, the inertial convection subrange. Measurements of energy spectrum in mixing vessel are shown that there is a range, where the so called -(5/3) power law is effective. Accordingly, the theory of local isotropy of Kolmogoroff can be applied because existence of the internal subrange. As the integrated value of local energy dissipation rate agrees with the power per unit mass of liquid from the impeller, almost all energy from the impeller is viscous dissipated in eddies of microscale. The correlation for mass transfer to particles suspended in a stirred vessel is recommended. The results of experimental study are approximately 12 % above the predicted values.

Why Do People Stay Poor?

2021 ◽  
Author(s):  
Clare Balboni ◽  
Oriana Bandiera ◽  
Robin Burgess ◽  
Maitreesh Ghatak ◽  
Anton Heil
Keyword(s):  
Occupational Choice ◽  
Large Scale ◽  
Choice Model ◽  
Effective Means ◽  
Threshold Level ◽  
Poverty Traps ◽  
Asset Transfer ◽  
Small Livestock ◽  
Program Costs ◽  
Almost All

Abstract There are two broad views as to why people stay poor. One emphasizes differences in fundamentals, such as ability, talent, or motivation. The other, the poverty traps view, emphasizes differences in opportunities which stem from access to wealth. To test between these two views, we exploit a large-scale, randomized asset transfer and an 11-year panel of 6,000 households who begin in extreme poverty. The setting is rural Bangladesh and the assets are cows. The data supports the poverty traps view—we identify a threshold level of initial assets above which households accumulate assets, take on better occupations (from casual labor in agriculture or domestic services to running small livestock businesses), and grow out of poverty. The reverse happens for those below the threshold. Structural estimation of an occupational choice model reveals that almost all beneficiaries are misallocated in the work they do at baseline and that the gains arising from eliminating misallocation would far exceed the program costs. Our findings imply that large transfers which create better jobs for the poor are an effective means of getting people out of poverty traps and reducing global poverty.

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