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![Comparison of 3.5 GPa hydrous garnet peridotite partial melt compositions (solid red squares) to komatiites. SiO 2 , Al 2 O 3 , FeO, MgO, and CaO concentrations of hydrous partial melts are from Table 6, while TiO 2 concentrations are from Table 4. Abitibi data are from Puchtel et al. [2004] and Kostomuksha data are from Puchtel and Humayun [2005]. Small gray symbols are komatiite data (excluding cumulates) from the GeoRoc database [Sarbas and Nohl, 2008].](profile/Travis-Tenner/publication/258645627/figure/fig5/AS:669032617357319@1536521214641/Comparison-of-35-GPa-hydrous-garnet-peridotite-partial-melt-compositions-solid-red.png)
Comparison of 3.5 GPa hydrous garnet peridotite partial melt compositions (solid red squares) to komatiites. SiO 2 , Al 2 O 3 , FeO, MgO, and CaO concentrations of hydrous partial melts are from Table 6, while TiO 2 concentrations are from Table 4. Abitibi data are from Puchtel et al. [2004] and Kostomuksha data are from Puchtel and Humayun [2005]. Small gray symbols are komatiite data (excluding cumulates) from the GeoRoc database [Sarbas and Nohl, 2008].
Source publication
We present experimental determinations of the influence of
H2O on partial melting of garnet peridotite (+1.5, 2.5, and 5
wt. % added H2O) at 3.5 GPa and 1200-1450°C. Experiments
produced complex polyphase regions of quenched melt and equilibrium
partial melt compositions were reconstructed by combined EMP and
LA-ICP-MS analyses. Mass balance-derive...
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The Huxiaoqin mafic rocks which distribute in the Central Kunlun Suture Zone, are mainly composed of hornblende diabases. LA-ICP-MS zircon U-Pb analyses gave 438 ±2Ma (MSWD = 1. 06, n = 15) of the crystallization age, suggesting Huxiaoqin mafic rocks are the products of the Early Silurian magmatism. All the rock samples are characterized by relativ...
Citations
... Elemental and isotopic constraints on the mantle source (for samples with 45 wt% < SiO 2 < 60 wt%). (a) K 2 O/MgO and (b) SiO 2 vs. CaO/Al 2 O 3 plots with fields of experimental melts derived from metasomatized phlogopite/amphibole-bearing peridotite (Conceição and Green, 2004;Condamine et al., 2016;Condamine and Médard, 2014), hornblendite and mixed hornblendite with DM (Pilet et al., 2008), hybridized peridotite and granitoid sources (Mallik et al., 2015;Rapp et al., 2010), and phlogopite/amphibole-free peridotite and pyroxenite (Gaetani and Grove, 1998;Herzberg and Zhang, 1996;Hirschmann et al., 2003;Tenner et al., 2012). Upper (UCC), lower (LCC), and bulk (BCC) continental crust data are from Rudnick and Gao (2003). ...
The early Ediacaran Capela pluton (ca. 630 Ma) is intruded into the metasedimentary succession of the Sergipano Orogenic System along the oriental segment of the Macururé Domain, southeastern Borborema Province, NE Brazil. This body is an uncommon example of mantle-derived shoshonitic mafic rocks associated with high-K calc-alkaline granitoids emplaced in a pre- to early-collisional context. Here, we aim to unravel the petrogenesis of this plutonic association to determine the role of crustal contribution to magmatism and its geodynamical significance during the early stages of the Brasiliano/Pan-African Orogeny. The Capela pluton comprises cumulate hornblendites, gabbronorites, gabbros, diorites, granodiorites, quartz monzonites, and granites. Shoshonitic mafic rocks and high-K calc-alkaline granitoids show significant enrichments in LILE and LREE compared to HREE and HFSE. Ultramafic and mafic rocks display a conspicuous crustal signature, yielding subchondritic εNd(t) and zircon εHf(t) values, along with variable radiogenic Sr–Pb isotopic compositions. The dominant factors controlling the geochemical features of the mafic magmas were the enriched signature of the lithospheric mantle source and the degree of partial melting. Mantle source metasomatism is thought to have occurred by incorporating subducted sediments into the mantle wedge before the onset of the Brasiliano Orogeny. Geochemical modeling demonstrated that low partial melting degrees (5–10%) of phlogopite-bearing lithospheric mantle in the spinel stability field metasomatized by 5–10% subducted sediments may account for the main characteristics of the mafic rocks. Introducing sedimentary material into the mantle caused a decrease in Sm/Nd and Lu/Hf ratios while increasing the Rb/Sr, U/Pb, and Th/Pb ratios, which led to the time-integrated evolved isotopic signature observed in the mafic rocks. The coeval granitoids are metaluminous to slightly peraluminous and display Nd–Pb isotopic compositions similar to those of mafic–ultramafic rocks. The petrological and isotopic features of the granitoids are consistent with derivation from an ancient mafic lower crustal source. We argue that the ascent and emplacement of hydrous mantle-derived magmas as successive sills into the lower crust produced a deep hot zone beneath the Sergipano Orogenic System during the onset of the Brasiliano/Pan-African Orogeny. Aqueous fluids released from such potassic mafic magmas favored the partial melting of surrounding rocks, producing contemporary felsic magmatism.
... SiO 2 and CaO concentrations of experimental partial melts generated at 1.0-3.5 GPa plotted on a volatile free basis using dry peridotite (Hirose & Kushiro, 1993;Laporte et al., 2004), peridotite + CO 2 peridotite + H 2 O (Tenner et al., 2012;Mallik et al., 2015Mallik et al., , 2016Pirard & Hermann, 2015;Grove & Till, 2019;Lara & Dasgupta, 2020) and peridotite + H 2 O + CO 2 compositions (Lara & Dasgupta, 2022) plotted against the extent of melting of each experiment. Each data point for volatile-bearing experiments is filled according to the colorbar, which represents the XCO 2 of the bulk compositions in each experiment. ...
... In this section, we compare melt compositions from this study and previous peridotite + H 2 O ± CO 2 studies run at 2-3.5 GPa and with 2.5 to 4.2 wt.% bulk H 2 O (Tenner et al., 2012;Grove & Till, 2019;Lara & Dasgupta, 2020, 2022 to the global dataset of primitive arc melts (PAM) from Schmidt & Jagoutz (2017) and to ultra-calcic, silica undersaturated melt inclusions (UCMI) sampled from Mt. Etna and the Luzon, Sunda and Vanuatu arcs (Kamenetsky & Clocchiatti, 1996;Schiano et al., 2000;Kamenestsky et al., 2007;Elburg et al., 2007;Sorbadere et al., 2011). Because primitive arc magmas tend to be more oxidized than mid-ocean ridge and ocean island basalts, and even for the latter two the f O 2 conditions favor oxidized form of carbon (e.g. ...
... The data are separated into partial melts derived from oxidized peridotite + H 2 O + CO 2 experiments and reduced peridotite + H 2 O + CH 4 experiments as indicated by the color bars, which represent the XCO 2 or XCH 4 of the starting compositions from which the partial melts are derived. The gray field represents the compositional space of partial melts from fertile peridotite + H 2 O experiments compiled from the studies by Grove & Till (2019), Tenner et al., (2012, Mitchell & Grove (2015), and Pirard & Hermann (2015). Vertical error bars on data are ±1σ uncertainties based on replicate microprobe analyses, as given in Table 5. ...
Many lines of evidence from high P–T experiments, thermodynamic models, and natural observations suggest that slab-derived aqueous fluids, which flux mantle wedges contain variable amounts of dissolved carbon. However, constraints on the effects of H2O–CO2 fluids on mantle melting, particularly at mantle wedge P–T conditions, are limited. Here, we present new piston cylinder experiments on fertile and depleted peridotite compositions with 3.5 wt.% H2O and XCO2 [= molar CO2 / (CO2 + H2O)] of 0.04–0.17. Experiments were performed at 2–3 GPa and 1350°C to assess how temperature, peridotite fertility, and XCO2 of slab-derived fluid affects partial melting in mantle wedges. All experiments produce olivine + orthopyroxene +7 to 41 wt.% partial melt. Our new data, along with previous lower temperature data, show that as mantle wedge temperature increases, primary melts become richer in SiO2, FeO*, and MgO and poorer CaO, Al2O3, and alkalis when influenced by H2O–CO2 fluids. At constant P–T and bulk H2O content, the extent of melting in the mantle wedge is largely controlled by peridotite fertility and XCO2 of slab-fluid. High XCO2 depleted compositions generate ~7 wt.% melt, whereas, at identical P–T, low XCO2 fertile compositions generate ~30 to 40 wt.% melt. Additionally, peridotite fertility and XCO2 have significant effects on peridotite partial melt compositions. At a constant P–T–XCO2, fertile peridotites generate melts richer in CaO and Al2O3 and poorer in SiO2, MgO + FeO, and alkalis. Similar to previous experimental studies, at a constant P–T fertility condition, as XCO2 increases, SiO2 and CaO of melts systematically decrease and increase, respectively. Such distinctive effects of oxidized form of dissolved carbon on peridotite partial melt compositions are not observed if the carbon-bearing fluid is reduced, such as CH4-bearing. Considering the large effect of XCO2 on melt SiO2 and CaO concentrations and the relatively oxidized nature of arc magmas, we compare the SiO2/CaO of our experimental melts and melts from previous peridotite + H2O ± CO2 studies to the SiO2/CaO systematics of primitive arc basalts and ultra-calcic, silica-undersaturated arc melt inclusions. From this comparison, we demonstrate that across most P–T–fertility conditions predicted for mantle wedges, partial melts from bulk compositions with XCO2 ≥ 0.11 have lower SiO2/CaO than all primitive arc melts found globally, even when correcting for olivine fractionation, whereas partial melts from bulk compositions with XCO2 = 0.04 overlap the lower end of the SiO2/CaO field defined by natural data. These results suggest that the upper XCO2 limit of slab-fluids influencing primary arc magma formation is 0.04 < XCO2 < 0.11, and this upper limit is likely to apply globally. Lastly, we show that the anomalous SiO2/CaO and CaO/Al2O3 signatures observed in ultra-calcic arc melt inclusions can be reproduced by partial melting of either CO2-bearing hydrous fertile and depleted peridotites with 0 < XCO2 < 0.11 at 2–3 GPa, or from nominally CO2-free hydrous fertile peridotites at P > 3 GPa.
... where T is the temperatures of partial melting, ΔS fusion peridotite (0.4 J/K/g) is the entropy of fusion per unit mass, M (59 g/mole) is the number of grams in one mole of silicate, R is the gas constant, X melt OH À is the mole fraction of hydroxyl in the melt at the solidus. X melt OH À can be calculated by the following equation 67 : ...
Water is the most common volatile component inside the Earth. A substantial amount of water can be carried down to the interior of the Earth by subducting plates. However, how the subducted water evolves after the subducting slab breaks off remains poorly understood. Here we use the data from a passive seismic experiment using ocean bottom seismometers (OBSs) together with the land stations to determine the high-resolution, three-dimensional seismic structure of the Southwest Sub-basin (SWSB) of the South China Sea (SCS). At depths below 40 km, the mantle shear velocity (Vsv) beneath the northern side of the SWSB is similar to that of the conventional oceanic pyrolite mantle, but roughly 3% shear-velocity reduction is found beneath the southern side of the SWSB. Results of thermal dynamic modeling reveal that the observed shear-velocity reduction could be explained by the presence of 150–300 ppm of water and 5–10% of lower continental crust. The inferred high-water content at the southern side of the SWSB is consistent with a model in which the Proto-SCS plate subducted southward prior to and during the formation of the SCS basin, releasing water into the upper mantle of the SWSB.
... The a 0 SiO2 at 3 GPa is calculated from Davis et al. (2011), Hirose & Kushiro (1993, Mallik et al. (2016) and Walter (1998). The 3.5 GPa curve is calculated from Pirard & Hermann (2015) and Tenner et al. (2012). The data at 1 and 0.9 GPa are taken from Hirose & Kawamoto (1995) and Kinzler & Grove (1992), respectively. ...
Siliceous slab-derived partial melts infiltrate the sub-arc mantle and cause rock-melt reactions, which govern the formation of diverse primary arc magmas and lithological heterogeneities. The effect of bulk water content, composition of reactants, and nature of melt infiltration (porous versus channelized) on the rock-melt reactions at sub-arc conditions have been investigated by previous studies. However, the effect of multiple episodes of rock-melt reactions in such scenarios has not been investigated before. Here, we explore mantle wedge modifications through serial additions of hydrous-silicic slab partial melts and whether such a process may ultimately explain the origin of high-Mg# andesites found in arcs worldwide. A series of piston-cylinder experiments simulate a serial addition of silicic slab melts in up to three stages (I through III) at 3 GPa and 800–1050°C, using rock-melt proportions of 75–25 and 50–50. A synthetic KLB-1 and a natural rhyolite (JR-1) represented the mantle and the slab components, respectively. Right from the first rock-melt interaction, the peridotite mantle transforms into olivine-free mica-rich pyroxenites ± amphibole ± quartz/coesite in equilibrium with rhyolitic-hydrous melts (72–80 wt% SiO2 and 40–90 Mg#). The formation of olivine-free pyroxenite seems to be controlled by complex functions of T, P, rock-melt ratio, wedge composition, and silica activity of the slab-melt. Remarkably, the pyroxenites approach a melt-buffered state with progressive stages of rock-melt reactions, where those rhyolitic melts inherit and preserve the major (alkalis, Fe, Mg, Ca) and trace element slab-signature. Our results demonstrate that lithological heterogeneities such as pyroxenites formed as products of rock-melt reactions in the sub-arc mantle may function as melt ‘enablers,’ implying that they may act as pathways that enable the infiltrating melt to retain their slab signature without undergoing modification. Moreover, the density contrast between the products of rock-melt reaction (melts and residues) and the average mantle wedge (~150 to 400 kg/m3) may help forming instabilities and diapiric rise of the slab components into the mantle wedge. However, the fate of the primitive slab-melts seems to be associated with the length of the pathway of mantle interaction which explains the evident wide magma spectrum as well as their degree of slab garnet-signature dilution. This work and the existence of high-Mg# Mexican-trondhjemites indicates that almost pristine slab-melts can make their way up to crustal levels and contribute to the arc magma diversity.
... Basalt from Dixon et al. (1995) also contained 0.19 and 0.15 wt% of P 2 O 5 and S, respectively. (Whittington et al., 2000), [4] (Dixon et al., 1995), [5] (Ohlhorst et al., 2001), [6] (Tenner et al., 2012). Suppsupplementary. ...
... In the peridotitic glasses, a doublet band with peaks at 4400 and 4270 cm −1 is observed, in contrast to more polymerized glasses, e.g., basaltic glasses, with a single OH combination band representative of the SiOH group. Comparison with literature data (Ohlhorst et al., 2001;Tenner et al., 2012) suggests that the higher-wavenumber peak is caused by the SiOH group (Fig. 6), or, more precisely, (Si,Al)OH group (Malfait, 2009). With increasing MgO content from 10 to 43 wt%, the (Si,Al)OH peak shifts from 4470 cm −1 in the basaltic to 4400 cm −1 in the peridotitic glasses. ...
... Here, we have identified peaks arising from MgOH and CaOH groups using FTIR spectroscopy for the first time to our knowledge. The peak that we attribute to the (Mg,Ca)OH group was previously observed in a number of studies (e.g., Aubaud et al., 2008;Behrens et al., 2009;Bondar et al., 2020;Fanara and Behrens, 2011;Tenner et al., 2012), and in each case its presence is consistent with our interpretation. The presence of free hydroxyl was previously identified by 1 H NMR for some of these glasses, e.g., diopside glass (Fanara and Behrens, 2011;Xue and Kanzaki, 2008). ...
The dissolution of water changes the chemical and physical properties of melts. The effect of water dissolution depends on the bulk H2O content and dissolution mechanisms. Previous research mainly focused on relatively polymerized glasses, whereas dissolution mechanisms of water in highly depolymerized glasses have not been well studied. We investigated three sets of hydrous (up to 5 wt.% H2O), highly depolymerized glasses using Fourier transform infrared spectroscopy. The three suites of glasses can be classified as tephritic (non-bridging oxygens to tetrahedral cations, NBO/T ≈ 0.9), basanitic (NBO/T ≈ 1.5), and peridotitic (NBO/T ≈ 2.5). The comparison of infrared spectra indicated four prominent features. First, the combination band related to molecular H2O at ∼5200 cm⁻¹ decreases in relative intensity with increasing depolymerization. At 2 wt.% bulk H2O, the proportion of H2O molecules decreases from the tephritic through basanitic to peridotitic glasses, where the proportion of H2O molecules is below 10%. At 5 wt.% bulk H2O, the proportion of H2O molecules in the peridotitic glass is around 20%, whereas it is around 50% in the basaltic glass with the same H2O content. Second, a second peak appears at 4270-4180 cm–1, next to the (Si,Al)OH combination peak (network hydroxyl), with increasing CaO and MgO contents in basanitic (∼25 wt.% CaO) and peridotitic (∼40 wt.% MgO) glasses, respectively. We assign this peak to the (Mg,Ca)OH group (free hydroxyl); this is the first identification of this group based on infrared spectroscopy. This assignment is also supported by IR data on Mg(OH)2 and Ca(OH)2 crystalline phases from the literature. Third, the ratio of (Si,Al)OH and (Mg,Ca)OH peak absorbances remains nearly constant with increasing water content in basanitic and peridotitic glasses, suggesting no effect of water on polymerization of extremely depolymerized melts. Fourth, the (Si,Al)OH peak shifts to lower wavenumbers with increasing depolymerization. As a result, the (Si,Al)OH peak position could potentially be used to evaluate the degree of melt polymerization in general, and the effect of water on melt polymerization in particular.
... This suggestion is supported by the elevated SiO 2 /(MgO + FeO total) (5.79-7.3) of all fractionation-corrected melts that resemble the melts produced by hydrous partial melting in peridotite experiment (SiO 2 /(MgO + FeO) >2.3; e.g., Grove, 1998, 2003). Melting experiments indicate, however, that hydrous partial melts of garnet peridotite, unlike spinel peridotite, are generally alkali-and MgOrich and poor in SiO 2 and Al 2 O 3 (e.g., Hirose and Kawamoto, 1995;Hirose, 1997;Kawamoto and Holloway, 1997;Gaetani and Grove, 1998;Irving and Green, 2008;Tenner et al., 2012). This implies that the La Conception lavas were probably initially silica-undersaturated and acquired most of their silica contents through re-equilibration with mantle peridotite during ascent, which involves incongruent melting of orthopyroxene to olivine within the mantle peridotite and decreasing MgO and increasing SiO 2of the ascending melt (Opx mantle + MgO melt ↑ → Olivine mantle + SiO 2 melt ↑ (e.g., Kubo, 2002;Abu El-Rus et al., 2006;Neumann et al., 2015). ...
New Caledonia is one of the world’s best-exposed subduction/obduction complexes and is central to understanding the geodynamic evolution of the southwest Pacific region. We present new geochemical and Ar/Ar age dates from the in situ eruptive sequences of the La Conception basaltic-andesite lavas (ca. 29.12 Ma) and correlate the generation of these lavas with the generation of the Saint Louis and Koum/Borindi Massifs (ca. 24 Ma) to provide information on the magmatic processes operating within the mantle wedge over time and to indicate the direction of the subducted slab during the Oligocene. The La Conception basaltic-andesite lavas were emplaced in an arc-to-trench direction to the southwest of New Caledonia due to the partial melting of metasomatized, amphibole-bearing garnet peridotites at the base of mantle wedge (∼112−118 km). However, both the Saint Louis and Koum/Borindi granodiorite massifs were derived from melting within the lower crust of an island arc overlying a mantle wedge. Such temporal and spatial variations of magmatism in New Caledonia are consistent with a northeast subduction zone during the Oligocene. The absence of voluminous arc magmatism related to the Oligocene subduction is a consequence of the low Tp temperatures of the mantle wedge, the old age and the high sinking velocity of the downgoing slab, and the absence of stress within the overriding plate. The Oligocene subduction beneath New Caledonia, therefore, is an ideal example of Ampferer-type subduction, which is an amagmatic closure area due to the inefficient subduction of hydrated lithologies into the convective upper mantle. Once the Paleocene to Miocene contraction in the southwest Pacific region ceased, the subduction west of New Caledonia shut down, the system relaxed, and no more melting occurred during the Oligocene.
... The model co-solves the thermometer and barometer, and enables estimation of both with no prior assumptions as to P or T. This is accomplished by incorporating a Si-term into the Mg-thermometer to account for the pressure effect, and then using that temperature as input to the Si-barometer. Although the model includes the effect of H 2 O on melting temperatures, it underpredicts the basalt liquidus depression according to more targeted experiments and compilations Tenner et al., 2012; see also the discussion in Plank & Forsyth, 2016). Thus, we calculate the temperatures dry with the Lee et al. (2009) Table S10). ...
... For the solidus, we use the expression in Hirschmann (2000) for fertile lherzolite, and we raise that solidus T by 39 • C for depleted lherzolite (after Wasylenki et al., 2003). For the cryoscopic effect due to H 2 O, we again use the function illustrated in Tenner et al. (2012) appropriate to 1 GPa (given in Table S10). For the melt productivity of fertile lherzolite, dT/dF = 550-40P (i.e. ...
... For example, Parman & Grove (2004) see no change in the melting mode of their harzburgite melting experiments, with and without H 2 O (0-6 wt %). Likewise, Tenner et al. (2012) find little change in melt productivity from 1.5 to 5% H 2 O. Thus, it remains difficult to achieve F > 25% without higher H 2 O or higher T than recorded in Tonga magmas. For example, the H 2 O content of Volcano A would have to be raised from 4 wt % to more than 8 wt % in order to melt fertile mantle >30%, again due to the dramatic drop in melt productivity once clinopyroxene is consumed at ∼22%. ...
Analyses of olivine-, pyroxene- and plagioclase-hosted melt (now preserved as glass) inclusions (MI) in submarine glasses and subaerial scoria from seven volcanoes along the volcanic front of the Tonga arc provide the first comprehensive dataset including volatile contents (H2O, CO2, S, Cl and F) for this arc. Maximum water contents at each volcano are typical (3-5 wt%) of other arc volcanoes worldwide, and within each volcano, water generally correlates with sulfur, consistent with degassing but not diffusive re-equilibration. The Tonga arc is notable for the eruption of magmas sourced from strongly depleted upper mantle, including boninites in the northern half of the active arc. A key question has been whether such boninites are derived from high degrees of melting actively occurring under the arc, driven by high mantle temperatures and water contents, or from high integrated degrees of melting including melting of depleted mantle in the backarc. This study supports the latter view, based on sub-arc mantle melt fractions of 17-23%, calculated from primary melt water contents and mantle-melt thermobarometry. Such fractions are not high enough to generate boninites from a typical, fertile mantle source in a single melting stage, and melt fractions do not increase north of 22°S, where the boninitic magmas appear. Instead, the northern Tonga arc boninites reflect high cumulative degrees of melting (> 30%, with respect to fertile mantle) and occur along the volcanic front where adjacent backarc spreading is fast, proximal and mature. Slab tracers such as the Ba/La ratio peak at around 20-21°S, in the central part of the Tonga arc. A Ba/La peak also appears at about the same latitude in the Lau backarc basin. This peak is consistent with the coolest slab temperatures beneath the arc and backarc at this latitude, as the slab warms to the north due to an increase in mantle potential temperature, and to the south due to less heat extraction from melting. A new concept developed here is cooling of the mantle wedge by melting, due to the supply of the heat of fusion and melt removal. Such a process can cool the mantle by more than 100 degrees, and thus affect slab heating as well. We find a critical distance of slab influence in the Lau spreading centers; back-arc magmas erupted > 70 km from the arc are > 210 km above the slab, beyond the point of slab dehydration, and show no enrichment in Ba/La. The coupled dynamics of the Tonga arc-Lau basin are rich in their connections, and demonstrate how melting processes beneath the back-arc and arc can affect slab processes, which in turn can affect the composition of fluids that feed the arc and backarc.
... The geochemical nature of the metasomatic agent is critical in evaluating how the bulk composition of the peridotite is modified, leading to the stabilization of volatilebearing phases and the formation of a fluid or melt phase. Previous experimental studies on the interaction of volatilebearing fluids and upper mantle peridotite focused on fertile peridotite with H 2 O, CO 2, or H 2 O + CO 2 [peridotite + CO 2: Falloon and Green (1990); Hirose (1997); Hirschmann (2006, 2007b); Brey et al. (2008); Mallik and Dasgupta (2013); Ghosh et al. (2014); Mallik and Dasgupta (2014); Mallik et al. (2015); Peridotite + H 2 O: Konzett and Ulmer (1999); Niida and Green (1999); Falloon and Danyushevsky (2000); Conceição and Green (2004); Grove et al. (2006); Fumagalli et al. (2009) ;Balta et al. (2011);Tenner et al. (2012); Till et al. (2012); Kawamoto et al. (2013); Kessel et al. (2015); Pirard and Hermann (2015); Peridotite + H 2 O + CO 2 : Olafsson and Eggler (1983); Wallace and Green (1988); Wallace and Green (1991); Thibault and Edgar (1992); Tumiati et al. (2012); Dvir and Kessel (2017)]. These studies, among others, simulate the interaction of fluids with the fertile mantle wedge in subduction zones but cannot be directly applied to the metasomatism of a depleted peridotite constituting the SCLM. ...
Understanding the interaction between fluids and the depleted peridotite is essential in deciphering the geochemical and mineralogical variability of the sub-continental lithospheric mantle (SCLM). High-density fluid (HDF) inclusions trapped in diamonds during their formation in the SCLM are potential metasomatic agents. In this study, experiments were performed on a harzburgite+silicic fluid system at an 80:20 rock:fluid ratio (bulk 5 wt% H2O and 3 wt% CO2), simulating the infiltration of a slab-derived silicic fluid into the SCLM. Experiments were performed at 3-6 GPa and 900-1200˚C on a rocking multi-anvil apparatus, conditions corresponding to the deep SCLM. The fluid and melt compositions were directly determined using the cryogenic LA-ICP-MS technique. The metasomatized peridotite consisted of olivine, clinopyroxene, phlogopite, orthopyroxene, amphibole, and magnesite. The H2O-CO2-saturated solidus in this system is located between 900-1000˚C at 3 GPa and between 1000-1100˚C at 4-6 GPa. The fluids at all pressures are alkali-rich. With increasing temperature and crossing the solidus, the melts evolve towards the initial silicic fluid composition.
Together with previous studies on various peridotite+H2O±CO2 systems, the results presented here suggest a positive correlation between the bulk alkali/volatile ratio and the solidus temperatures. An increase in this parameter and in the mantle fertility (i.e., Ca#) increases the near-solidus isobaric melt production rate. The experimental fluid compositions found in this study are similar to saline HDFs. We propose a scenario where the percolation of a slab-derived silicic fluid into the depleted cratonic peridotite leads to the formation of near-solidus saline fluids. Such sequence of metasomatic events was reported from fluid inclusions in diamonds from several localities in the Kaapvaal craton in South Africa (e.g., De Beers, Finsch, Voorspoed).
... We also re-analyzed an unspiked melting experiment of Condamine and Médard (2014;sta12) performed using a natural starting material at 1 GPa and 1050°C for trace elements. Because melts from experiments at 3 GPa did not quench to glassy pools, we analyzed them by LA-ICP-MS to obtain their representative major element compositions (Humayun et al., 2010;Davis et al., 2011;Tenner et al., 2012). We used a laser frequency of 3 Hz and a beam size ranging between 20 and 70 mm. ...
Potassium-rich magmatism represents subordinate magma volumes worldwide but has been observed in many geodynamic settings. Most potassic magmas are thought to derive from very-low degrees of melting of metasomatized mantle lithologies. We performed piston-cylinder experiments to determine trace element partition coefficients between incipient potassic silicate melts and phlogopite ± pargasite peridotite in the spinel (1 GPa) and garnet stability fields (3 GPa). Most of the rare Earth elements (REEs) are compatible in pargasite but incompatible in phlogopite. Although garnet remains the mineral phase most efficiently fractionating heavy from light REEs (DYbgrt/melt/DLagrt/melt > 750), orthopyroxene can also significantly fractionate REEs, e.g., achieving DYbopx/melt/DLaopx/melt > 100 at 3 GPa. Mineral-liquid partition coefficients vary by about one order of magnitude between incipient melts derived from the spinel and garnet stability fields. We thus show that trace element partitioning at the onset of melting is controlled more by pressure (through melt composition) than by the extent of melting. With increasing pressure, Rb and Ba exhibit different behaviors in phlogopite, with DBaphl/melt>DRbphl/melt at 1 GPa and the opposite at 3 GPa. At 1 GPa, a decrease of melt polymerization (lower NBO/T) with increasing melt fraction translates into a significant decrease of most phlogopite partition coefficients. Finally, we show that resolvable inter-element fractionations do occur when phlogopite- (and pargasite)-bearing peridotite are melted, indicating that trace element ratios are not always faithfully representative of that of their sources but bear the imprint of varied P–T conditions of melting and contrasted pre-metasomatic histories. This self-consistent partition coefficient dataset thus gives a new scope to understand the complex petrogenesis of K-rich magmas in orogenic settings.
... Although hydrous silicate glasses exhibit inferior mechanical properties [11] than their H 2 O-free counterparts, the study of these materials is essential for geoscientists. Since even relatively small amounts of H 2 O present in the Earth's mantle significantly affect physical and chemical properties of mantle minerals, rocks and melts [12][13][14][15][16][17], both fundamental understanding of mantle dynamics and modeling of magma rheology for the minimization of volcanic risk require knowledge of the effect of H 2 O. ...
... b H 2 O in run products is estimated by shortfall of oxide totals. c Hydrous_2 is an averaged composition between batch 1 and 2 from Tenner et al. [12]. d Hydrous_5 is the same as batch 3 from Tenner et al. [12]. ...
... c Hydrous_2 is an averaged composition between batch 1 and 2 from Tenner et al. [12]. d Hydrous_5 is the same as batch 3 from Tenner et al. [12]. ...
Experimental and spectroscopic investigation of glasses synthesized at high pressure provides fundamental information about the structure/physical properties relationships of these materials. However, glass synthesis in conventional large-volume high-pressure devices is limited by the achievable quenching rates. This study reports the first successful quenching, recovery, and characterization of high-pressure hydrous silicate glasses of peridotite composition, with H2O contents from 0 to 5 wt%, using a large-volume high-pressure apparatus equipped with a novel rapid-quench cell. The synthesized glasses are transparent, optically isotropic, and chemically homogeneous, but they contain nano- to micron-size metal droplets from the capsules. Except for the two glasses with the highest H2O contents, the glasses are crystal-free. Raman spectroscopy revealed the absence of long-range ordering in the atomic structure of peridotitic glasses. However, it was demonstrated that dissolution of H2O leads to an increase in melt polymerization. This study provides fertile ground for developing new studies of the structure/physical properties relationships of extremely depolymerized melts.
