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![Experimental hydrous mineral-water D/H fractionation factors (1000lna (mineral-water) ) versus temperature (T and 1/T 2 ), for hydrous minerals common to basaltic systems affected by hydrothermal alteration at ridge or dehydration during subduction. The fractionation factors are a complex function of temperature, composition, and pressure. Vertical gray regions show expected temperature ranges for region of alteration in the lower crust near spreading centers [Kawahata et al., 1987; Stakes, 1991; Zheng et al., 1998; Putlitz et al., 2000] and for the expected temperature range experienced by subducting slabs (see inset) [Staudigel and King, 1992]. Arrows with pressure labels show effect of pressure on 1000lna (mineral-water) for reactions shown [Driesner, 1997]. Data compiled from Wenner and Taylor [1973], Suzuoki and Epstein [1976], Sakai and Tsutsumi [1978], Graham et al. [1980] Graham et al. [1984], Satake and Matsuo [1984] Mineev and Grinenko [1996], Vennemann and O'Neil [1996], Driesner [1997], Chacko et al. [1999], and Xu and Zheng [1999]. Right-hand axis scale shows corresponding range of dD observed. Observed dD values in metabasalts and metagabbros can be directly compared to 1000lna (mineral-water) % D (mineral-water) , by assuming to first order that the dD value of the hydrothermal water is equal to SMOW = 0%. The range of altered oceanic crust observed from dredged or drilled rocks agree well with fractionation expected under equilibrium conditions. Data for the measured range of dD in dredged and drilled altered crust are from Sheppard and Epstein [1970], Wenner and Taylor [1973], Satake and Matsuda [1979], Stakes and O'Neil [1982], and Stakes [1991]. Note that the dD values measured for the Salas y Gomez mantle plume can be reasonably explained by fractionation during hydrothermal alteration by seawater.](profile/Jean-Guy-Schilling/publication/229014584/figure/fig6/AS:393889463717938@1470921974939/Experimental-hydrous-mineral-water-D-H-fractionation-factors-1000lna-mineral-water.png)
Experimental hydrous mineral-water D/H fractionation factors (1000lna (mineral-water) ) versus temperature (T and 1/T 2 ), for hydrous minerals common to basaltic systems affected by hydrothermal alteration at ridge or dehydration during subduction. The fractionation factors are a complex function of temperature, composition, and pressure. Vertical gray regions show expected temperature ranges for region of alteration in the lower crust near spreading centers [Kawahata et al., 1987; Stakes, 1991; Zheng et al., 1998; Putlitz et al., 2000] and for the expected temperature range experienced by subducting slabs (see inset) [Staudigel and King, 1992]. Arrows with pressure labels show effect of pressure on 1000lna (mineral-water) for reactions shown [Driesner, 1997]. Data compiled from Wenner and Taylor [1973], Suzuoki and Epstein [1976], Sakai and Tsutsumi [1978], Graham et al. [1980] Graham et al. [1984], Satake and Matsuo [1984] Mineev and Grinenko [1996], Vennemann and O'Neil [1996], Driesner [1997], Chacko et al. [1999], and Xu and Zheng [1999]. Right-hand axis scale shows corresponding range of dD observed. Observed dD values in metabasalts and metagabbros can be directly compared to 1000lna (mineral-water) % D (mineral-water) , by assuming to first order that the dD value of the hydrothermal water is equal to SMOW = 0%. The range of altered oceanic crust observed from dredged or drilled rocks agree well with fractionation expected under equilibrium conditions. Data for the measured range of dD in dredged and drilled altered crust are from Sheppard and Epstein [1970], Wenner and Taylor [1973], Satake and Matsuda [1979], Stakes and O'Neil [1982], and Stakes [1991]. Note that the dD values measured for the Salas y Gomez mantle plume can be reasonably explained by fractionation during hydrothermal alteration by seawater.
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1] Deuterium/Hydrogen isotope ratios were measured in 22 fresh basalt glasses dredged from young seamounts along the Easter-Salas y Gomez seamount chain (ESC) and from the spreading centers of the Easter Microplate (EMP). The dD values decrease regularly from À36% near Salas y Gomez to À63%, 800 km west on the East Pacific Rise (EPR) and the west r...
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... δ 2 H-H 2 values closer to -400‰ (as in MOR samples, Fig. 9) and to -100‰ (as in the Mid-Icelandic volcanic belt, Sigvaldson and Elisson, 1968;Arnason and Sigurgeirsson, 1968) may indicate H 2 from processes in the mantle, and perhaps some H 2 of primordial origin. Such interpretation is consistent with δ 2 H-H 2 values mostly between -95‰ and -35‰ in minerals and fluid inclusions in mantle-derived rocks (Kyser and O'Neil, 1984;Deloule et al., 1991;Kingsley et al., 2002;Loewen et al., 2019), the suggestion that primordial H 2 has δ 2 H-H 2 of about -75‰ (Craig and Fig. 5 for symbol legend. Samples that contain one gas (for example, H 2 ), but not the other (respectively, He), as, for example, some gases emanating from serpentinites in Oman (Zgonnik et al., 2019) are not displayed on this log-log plot. ...
Geologic molecular hydrogen (H2) occurs in the subsurface and vents and seeps at the surface. However, this valuable natural resource is under-utilized in the economy because the distribution, abundance and origins of H2 are poorly understood. I studied a global dataset of 6246 natural gases with reported H2 concentrations from 16 different geological habitats. The average H2 concentration in all gas samples is 3.5%, but the median concentration is only 0.01%. Gases sampled in Mid-Ocean Ridges and in serpentinites have the highest average concentrations of H2 (~24% and ~21%, respectively). More than 30 different processes may produce H2 observed in natural gases. Hydrogen isotopic composition (expressed as δ²H-H2 values) may indicate crustal (<-650‰) or mantle and primordial (from -650‰ to -100‰) sources of H2, or may result from temperature-dependent equilibration of H2 with water. Much of crustal H2 may be sourced by the reactions of serpentinization, while the quantitative significance of other H2-generating processes such as radiolytic decomposition of water and hydrocarbons, fracture-induced reduction of water, petroleum cracking and coal metamorphism remain speculative. Primordial H2 perhaps vents in some volcanic settings. Provided better understanding of H2 abundance and origins in different geological settings should enable the purposeful exploration for geologic H2 and the assessment of its economic resources.
... The hydrogen isotope compositions of terrestrial rocks have been used to trace geological processes such as water cycling in subduction zones, 2,3 volatile degassing in lavas, 4-6 fluidrock interactions, 7,8 and were furthermore used to study chemical heterogeneity of the mantle. [9][10][11] The hydrogen isotope compositions of extraterrestrial rocks have been used to study the abundance and origin of water on planetary and asteroidal bodies. [12][13][14][15][16] Different fluid sources or processes have distinct D/H ratios, which are expressed as δD ([(D/Hsample)/(D/HVSMOW)-1)] × 1000), where VSMOW (Vienna Standard Mean Ocean Water) has D/H = 0.00015576. ...
... The hydrogen isotope compositions of terrestrial rocks have been used to trace geological processes such as water cycling in subduction zones, 2,3 volatile degassing in lavas, 4-6 fluidrock interactions, 7,8 and were furthermore used to study chemical heterogeneity of the mantle. [9][10][11] The hydrogen isotope compositions of extraterrestrial rocks have been used to study the abundance and origin of water on planetary and asteroidal bodies. [12][13][14][15][16] Different fluid sources or processes have distinct D/H ratios, which are expressed as δD ([(D/Hsample)/(D/HVSMOW)-1)] × 1000), where VSMOW (Vienna Standard Mean Ocean Water) has D/H = 0.00015576. ...
Water is perhaps the most important molecule in the solar system, and determining its origin and distribution in planetary interiors has significant implications for understanding the formation and evolution of planetary bodies. Zircon (present in both extraterrestrial and terrestrial samples) is a resistant and versatile accessory mineral, and its water content has the potential to characterize the hydrous status of zircon-crystallizing magma. However, the hydrous status can be altered by magma fractionation, mixing, or degassing. Although hydrogen isotopes of zircon can help to trace these processes, the lack of relevant microanalytical technology and reference materials has hindered significant breakthroughs in this area. In this study, we employed an analytical technique of secondary ion mass spectrometry (SIMS) to simultaneously measure the hydrogen isotopes of zircon and their H2O content. The homogeneity test of hydrogen isotope and the H2O content of the potential reference materials (D15395, D15814, and Temora 2) were conducted by measuring the 16 OD and 16 O 1 H signals (using SIMS) in a conventional peak-hopping mono-collector mode with electron-multiplier (EM) detectors. SIMS results show that the apparent external precision (1SD) of hydrogen isotope of large grains D15395 and D15814 are 16‰ and 22‰, which is comparable with their internal error and theoretical precision according to counting statistics, indicating that they are sufficiently homogenous at the micrometer sampling level in terms of hydrogen isotopes. However, zircon Temora 2 shows a much worse external precision (83‰, 1SD) and an obvious negative correlation between hydrogen isotope and H2O content, hence it is not suitable to be used as reference material for hydrogen isotope. Both hydrogen isotope and H2O content of three samples were also measured using a continuous-flow thermal conversion elemental analyzer operating online with a mass spectrometer (TC/EA-MS). The homogeneous samples zircon D15395 and D15814 yielded recommended δD values of-87 ± 9‰ and-68 ± 2‰ (1SD) and H2O content of ~478 ppm and ~332 ppm, respectively. Additionally, H2O contents acquired by TC/EA-MS and SIMS (calibrated by FTIR determined standards) were consistent within a 10% error range, demonstrating the reliability of the SIMS H2O content calibration curve for zircon and the FTIR absorption coefficient used before.
... Ultimately, Poreda et al. (1986) could not determine whether the high δD values in high 3 He/ 4 He basalts indicated a stronger component of primordial water vs. water derived from recycled lithosphere/crust. A stronger relationship of high δD and high 3 He/ 4 He is present for basalts from the Easter Island hotspot region of the East Pacific Rise (data from Poreda et al., 1993;Kingsley et al., 2002). However, those results also do not resolve if the δD values were primarily influenced by recycled or primordial water, or both. ...
... δD varies along the SEIR between −90h and −51h, covering much of the range of δD reported globally for oceanic basalts (Kyser and O'Neil, 1984;Poreda et al., 1986;Kingsley et al., 2002;Dixon et al., 2017). Higher δD values are generally associated with geochemically enriched samples in the ASP Plateau region (Fig. 2). ...
... (For interpretation of the colors in the figure(s), the reader is referred to the web version of this article.) as might be expected from seawater assimilation (Figs. 4 and S1; Kingsley et al., 2002;Clog et al., 2013). This observation suggests that the process responsible for the elevated Cl in most ocean ridge basalts may be assimilation of halite that has minimal water content and high Cl (e.g., Michael and Cornell, 1998;Kent et al., 1999;, and thus has little effect on δD values. ...
The hydrogen isotope value (δD) of water indigenous to the mantle is masked by the early degassing and recycling of surface water through Earth's history. High ³He/⁴He ratios in some ocean island basalts, however, provide a clear geochemical signature of deep, primordial mantle that has been isolated within the Earth's interior from melting, degassing, and convective mixing with the upper mantle. Hydrogen isotopes were measured in high ³He/⁴He submarine basalt glasses from the Southeast Indian Ridge (SEIR) at the Amsterdam–St. Paul (ASP) Plateau (δD = −51 to −90‰, ³He/⁴He = 7.6 to 14.1 RA) and in submarine glasses from Loihi seamount south of the island of Hawaii (δD = −70 to −90‰, ³He/⁴He = 22.5 to 27.8 RA). These results highlight two contrasting patterns of δD for high ³He/⁴He lavas: one trend toward high δD of approximately −50‰, and another converging at δD = −75‰. These same patterns are evident in a global compilation of previously reported δD and ³He/⁴He results. We suggest that the high δD values result from water recycled during subduction that is carried into the source region of mantle plumes at the core–mantle boundary where it is mixed with primordial mantle, resulting in high δD and moderately high ³He/⁴He. Conversely, lower δD values of −75‰, in basalts from Loihi seamount and also trace element depleted mid-ocean ridge basalts, imply a primordial Earth hydrogen isotopic value of −75‰ or lower. δD values down to −100‰ also occur in the most trace element-depleted mid-ocean ridge basalts, typically in association with ⁸⁷Sr/⁸⁶Sr ratios near 0.703. These lower δD values may be a result of multi-stage melting history of the upper mantle where minor D/H fractionation could be associated with hydrogen retention in nominally anhydrous residual minerals. Collectively, the predominance of δD around −75‰ in the majority of mid-ocean ridge basalts and in high ³He/⁴He Loihi basalts is consistent with an origin of water on Earth that was dominated by accretion of chondritic material.
... The stable isotope behavior is critical to monitor budgets and recycling of volatiles (Van Soest et al. 1998;Dixon et al. 2002;Kingsley et al. 2002;Javoy 2004). Volatile components in the COH system, when dissolved in magmatic liquids, can affect stable isotope fractionation between the melt and coexisting fluids and crystalline materials (Dobson et al. 1989;Mattey et al. 1990;Deines 2002). ...
Abstract The behavior of COH fluids, their isotopes (hydrogen and carbon), and their interaction with magmatic liquids are at the core of understanding formation and evolution of the Earth. Experimental data are needed to aid our understanding of how COH volatiles affect rock-forming processes in the Earth’s interior. Here, I present a review of experimental data on structure of fluids and melts and an assessment of how structural factors govern hydrogen and carbon isotope partitioning within and between melts and fluids as a function of redox conditions, temperature, and pressure. The solubility of individual COH components in silicate melts can differ by several orders of magnitude and ranges from several hundred ppm to several wt%. Silicate solubility in fluid can reach several molecular at mantle temperatures and pressures. Different solubility of oxidized and reduced C-bearing species in melts reflects different solution equilibria. These equilibria are 2CH4 + Q n = 2CH3 − + H2O + Q n + 1 and 2CO3 2− + H2O + 2Q n + 1 = HCO3 − + 2Q n , under reducing and oxidizing conditions, respectively. In the Q n -notations, the superscript, n, denotes the number of bridging oxygen in the silicate species (Q-species). The structural changes of carbon and silicate in magmatic systems (melts and fluids) with variable redox conditions result in hydrogen and carbon isotope fractionation factors between melt, fluid, and crystalline materials that depend on redox conditions and can differ significantly from 1 even at magmatic temperatures. The ∆H of D/H fractionation between aqueous fluid and magma in silicate–COH systems is between − 5 and 25 kJ/mol depending on redox conditions. The ∆H values for 13C/12C fractionation factors are near − 3.2 and 1 kJ/mol under oxidizing and reducing conditions, respectively. These differences are because energetics of O–D, O–H, O–13C, and O–12C bonding environments are governed by different solution mechanisms in melts and fluids. From the above data, it is suggested that (COH)-saturated partial melts in the upper mantle can have δD values 100%, or more, lighter than coexisting silicate-saturated fluid. This effect is greater under oxidizing than under reducing conditions. Analogous relationships exist for 13C/12C. At magmatic temperatures in the Earth’s upper mantle, 13C/12C of melt in equilibrium with COH-bearing mantle in the − 7 to − 30‰ range increases with temperature from about 40 to > 100‰ and 80–120‰ under oxidizing and reducing conditions, respectively.
... Rhyolites are original samples from Newman et al. (1988) and Zierenberg et al. (2013); sample names and values in bold characters. Basalt sample (GL07-D48-4) is from Kingsley et al. (2002). Samples analyzed in Reston USGS lab by H. Qi. ...
... A range from −40 to −80‰ is commonly cited as encompassing variations obtained earlier by conventional methods (e.g. Kingsley et al., 2002;Kyser, 1986;Pineau et al., 2004;Poreda et al., 1986). A recent study recalibrated the conventional analytical methods and re-estimated the NMORB mantle δD value at −60‰ ±5‰ for the convecting mantle (Clog et al., 2013). ...
... Comparison between total water content measured via our method (TC/EA) and FTIR or manometric methods between 0 and 2 wt% for magmatic compositions (basalt to rhyolite). Rhyolite/dacite FTIR(Loewen and Bindeman, 2015;Newman et al., 1988;Zierenberg et al., 2013); rhyolite/dacite manometry:(Villemant and Boudon, 1999); basalt FTIR:(Bindeman et al., 2012); basalt manometry:(Kingsley et al., 2002). ...
The use of volcanic glass as recorder of paleoenvironmental conditions has existed for 30years. In this paper we investigate the methodological aspects of the determination of water content, isotopic composition, and water speciation in volcanic glass using the High Temperature Conversion/Elemental Analyzer (TCEA) mass spectrometer system on milligram quantities of glass concentrates. It is shown here that the precision and the reproducibility of this method is comparable to off-line conventional methods that require 100 times greater amount of material (δD±3‰; [H2O]tot ±10relative% if <1wt% and ±5 relative% if >1wt%) but is quicker and permits easy replication. This method extracts 100% of the water as verified by FTIR measurements. Finally, this study confirms the interest of DRIFT spectroscopy in the NIR range for the study of porous samples such as volcanic pumices and tephra, to determine the water speciation (H2O/OH). It may complement conventional FTIR transmission measurements in the MIR or NIR range that usually require homogeneous transparent sections or high degree of sample dilution in a non-absorbing matrix.Using these methods, we attempt to discriminate residual magmatic from secondary meteoric water in volcanic glass. Using mafic to differentiated samples from different geological settings and different climatic conditions, we show that the H-isotope composition and water content of volcanic glass alone are not always sufficient to provide clear distinction between magmatic and meteoric origin. However if the magma is known to have a δD between -90‰ and -40‰ (-60‰ for MORB mantle source), it is quite easy to resolve the δD evolution during magmatic degassing from post-depositional rehydration by meteoric water with δD<-50‰ or δD>-20‰. Water speciation measurements may provide additional information. In most cases, isotopic and total water measurements should be complemented by characterization of water speciation. During magmatic degassing (from 6wt% to ~0.1wt% water) the H2O/OH is expected to decrease from 2 to close to 0. However, our dataset suggests that during secondary glass hydration (from 0.1wt% to 6wt% water) the H2O/OH ratio decreases from ~5 to 2, which is the complete opposite.Overall our results support the use of H-isotopes of volcanic glass to discuss the composition of meteoric waters and paleo-climate within a specific region. To this purpose, the volcanic glass has to be almost fully rehydrated in order to fingerprint the isotopic composition of the ambient environmental water. As rehydration is exponentially faster with increasing temperature, efficient rehydration taking months to years, may occur in a cooling volcanic deposits that are meters-thick and thus can remain at a few hundred °C for a years to hundreds of years after the eruption. Such deposits could then provide a snap-shot view of climatic conditions at the time of the studied eruption.
... (e.g. Chaussidon and Marty, 1995;Harmon and Hoefs, 1995;Gurenko and Chaussidon, 1997;Eiler et al., 2000;Kingsley et al., 2002;Elliott et al., 2006;Holland and Ballentine, 2006;Nielsen et al., 2006;Sharp et al., 2007;Bonifacie et al., 2008;Shaw et al., 2012;Cabral et al., 2013;Labidi et al., 2013;Williams and Bizimis, 2014;Andersen et al., 2015;Pringle et al., 2016). Unlike radiogenic isotope variations, the information contained in these systems is independent of the residence time of the recycled components in the mantle but should be highly sensitive to their prior presence at the surface, where redox-dependent isotope fractionation should be greatest. ...
The application of Mo isotopes to study geodynamic processes is a rather new development that has gained considerable momentum over the past few years. Its redox-sensitivity causes significant mass-dependent isotope variability in low-temperature environments – mainly during weathering, sediment deposition and seafloor alteration. Potentially, these fractionated Mo isotope characteristics of surface materials could be used to identify recycled crustal components in mantle sources. Here we provide an overview of the first studies on mass-dependent isotope variations of Mo in igneous rocks and the Mo isotopic characteristics of major geochemical reservoirs before assessing the potential of Mo isotope variations as a new tracer in mantle geochemistry.
Mass-dependent Mo isotope variations induced by magmatic differentiation are in general muted owing to the incompatibility of Mo in common igneous minerals. However, fractionation of Mo isotopes by hydrous silicate mineral phases has been suggested. Sulphide fractionation can potentially have a marked influence on the Mo isotope composition of evolving magmatic systems but does not appear to be a major influence due to the limited modal abundance of sulphide phases precipitated during differentiation. The largest Mo isotope variations in igneous systems reported so far are found in arc-related rocks. Currently available data suggest that the δ98/95Mo values (i.e. the ⁹⁸Mo/⁹⁵Mo ratio relative to the reference material NIST SRM 3134) measured in arc basalts are higher than those of the upper mantle. This offset appears to be linked to the addition of isotopically heavy slab-derived fluid to the arc melts, whereby heavier Mo isotopes become enriched in the fluid as a result of the slab-dehydration. In contrast, lighter δ98/95Mo compositions found in some arc-related lavas could be linked to geochemical tracers commonly associated with sediment melt contribution. Overall, mass balance considerations suggest that the recycled crustal material has a Mo isotope composition equal to or most likely lighter than that of fresh oceanic crust.
Chondritic meteorites display a remarkably homogeneous δ98/95Mo of − 0.16 ± 0.02‰ suggesting a similar bulk composition for the inner solar system and thus the Earth. Residual Mo in the mantle after core formation is expected to be isotopically heavy but for temperatures in excess of 2500 K, typically proposed for core-mantle equilibration, the difference in δ98/95Mo of the mantle relative to chondrite is < 0.1‰. Analyses of Mo isotopes in mid-ocean ridge basalts suggest a slightly sub-chondritic composition of the depleted mantle (δ98/95Mo = − 0.21 ± 0.02‰). Similarly, late Archean komatiites yield slightly sub-chondritic δ98/95Mo of ca. − 0.21 ± 0.06‰ suggesting that the mantle may have maintained a similar Mo isotope composition throughout the post-Archean. The Mo isotope composition of the continental crust is currently the least well-constrained value of major geochemical reservoirs. A preliminary estimate available for maximum value for the upper continental crust yields a super-chondritic δ98/95Mo of ca. + 0.15‰. The value of the bulk continental crust remains unknown but is likely to be lower. Assuming a chondritic bulk silicate Earth differentiates solely into continental crust and depleted mantle reservoirs, the δ98/95Mo of the average continental crust would range between + 0.1 and + 0.35‰. This is broadly compatible with the initial observations, making Mo the first non-radiogenic isotopic system to show such an apparent complementarity between the continents and mantle reservoirs. Given that deep recycled crust is characterised by δ98/95Mo lower than that of depleted mantle, subduction provides a mechanism by which to affect this change.
... One of the first estimates was from mid-ocean ridge basalts (MORB) that have dD of À80& (Kyser and O'Neil 1984). Subsequent studies show that MORBs have a range of dD values from À100 to À20& (Poreda et al. 1986;Chaussidon et al. 1991;Honma et al. 1991;Kingsley et al. 2002;Pineau et al. 2004). Most recently, Clog et al. (2013) reinvestigated a suite of MORB samples and estimated that the dD value of the terrestrial depleted upper mantle is À60 AE 5&. ...
The hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets. The sources of water and the hydrological evolution of Mars may be inferred from the hydrogen isotopic compositions of mineral phases in Martian meteorites, which are currently the only samples of Mars available for Earth-based laboratory investigations. Previous studies have shown that δD values in minerals in the Martian meteorites span a large range of −250 to +6000‰. The highest hydrogen isotope ratios likely represent a Martian atmospheric component: either interaction with a reservoir in equilibrium with the Martian atmosphere (such as crustal water), or direct incorporation of the Martian atmosphere due to shock processes. The lowest δD values may represent those of the Martian mantle, but it has also been suggested that these values may represent terrestrial contamination in Martian meteorites. Here we report the hydrogen isotopic compositions and water contents of a variety of phases (merrillites, maskelynites, olivines, and an olivine-hosted melt inclusion) in Tissint, the latest Martian meteorite fall that was minimally exposed to the terrestrial environment. We compared traditional sample preparation techniques with anhydrous sample preparation methods, to evaluate their effects on hydrogen isotopes, and find that for severely shocked meteorites like Tissint, the traditional sample preparation techniques increase water content and alter the D/H ratios toward more terrestrial-like values. In the anhydrously prepared Tissint sample, we see a large range of δD values, most likely resulting from a combination of processes including magmatic degassing, secondary alteration by crustal fluids, shock-related fractionation, and implantation of Martian atmosphere. Based on these data, our best estimate of the δD value for the Martian depleted mantle is −116 ± 94‰, which is the lowest value measured in a phase in the anhydrously prepared section of Tissint. This value is similar to that of the terrestrial upper mantle, suggesting that water on Mars and Earth was derived from similar sources. The water contents of phases in Tissint are highly variable, and have been affected by secondary processes. Considering the H2O abundances reported here in the driest phases (most likely representing primary igneous compositions) and appropriate partition coefficients, we estimate the H2O content of the Tissint parent magma to be ≤0.2 wt%.
... As a consequence , the mantle source is usually enriched in deuterium with the alteration by aqueous fluid derived from the dehydration of subducting oceanic crust, but is depleted in deuterium with the metasomatism by hydrous melt derived from partial melting of the crustal rocks. Such a contrast in the hydrogen isotope composition of mantle sources may be inherited by their derivatives, oceanic and continental basalts (Poreda, 1985; Hochstaedter et al., 1990; Hauri, 2002; Kingsley et al., 2002; Shaw et al., 2008 Shaw et al., , 2012). While there have been many studies on the water content and hydrogen isotope composition of NAMs from xenolith peridotites enclosed by continental basalts, much less attention has been paid to phenocryst NAMs in continental basalts themselves. ...
... The negative trend can be explained by water species transformation during fractional crystallization, by which molecular water depleted in D becomes increasingly concentrated in evolving basaltic melts. This mechanism is different from magma degassing that results in simultaneous decreases of water contents and dD values in melt (e.g., Kyser and O'Neil, 1984; Taylor and Sheppard, 1986; Hauri, 2002; Kingsley et al., 2002). Because molecular water is depleted in D relative to structural hydroxyl (Chen et al., 2007; Gong et al., 2007b), decreasing molecular water in melt may result in an increase of melt dD values but a decrease of water content in the melt of the late stage of fractional crystallization. ...
The water contents of minerals and whole-rock in mantle-derived xenoliths from eastern China exhibit large variations and are generally lower than those from other on- and off-craton lithotectonic units. Nevertheless, the water contents of mineral and whole-rock in Junan peridotite xenoliths, which sourced from the juvenile lithospheric mantle, are generally higher than those elsewhere in eastern China. This suggests that the initial water content of juvenile lithospheric mantle is not low. There is no obvious correlation between the water contents and Mg# values of minerals in the mantle xenoliths and no occurrence of diffusion profile in pyroxene, suggesting no relationship between the low water content of mantle xenolith and the diffusion loss of water during xenolith ascent with host basaltic magmas. If the subcontinental lithospheric mantle (SCLM) base is heated by the asthenospheric mantle, the diffusion loss of water is expected to occur. On the other hand, extraction of basaltic melts from the SCLM is a more efficient mechanism to reduce the water content of xenoliths. The primary melts of Mesozoic and Cenozoic basalts in eastern China have water contents, as calculated from the water contents of phenocrysts, higher than those of normal mid-ocean ridge basalts (MORB). The Mesozoic basalts exhibit similar water contents to those of island arc basalts, whereas the Cenozoic basalts exhibit comparable water contents to oceanic island basalts and backarc basin basalts with some of them resembling island arc basalts. These observations suggest the water enrichment in the mantle source of continental basalts due to metasomatism by aqueous fluids and hydrous melts derived from dehydration and melting of deeply subducted crust. Mantle-derived megacrysts, minerals in xenoliths and phenocrysts in basalts from eastern China also exhibit largely variable hydrogen isotope compositions, indicating a large isotopic heterogeneity for the Cenozoic SCLM in eastern China. The water content that is higher than that of depleted MORB mantle and the hydrogen isotope composition that is deviated from that of depleted MORB mantle suggest that the Cenozoic continental lithospheric mantle suffered the metasomatism by hydrous melts derived from partial melting of the subducted Pacific slab below eastern China continent. The metasomatism would lead to the increase of water content in the SCLM base and then to the decrease of its viscosity. As a consequence, the SCLM base would be weakened and thus susceptible to tectonic erosion and delamination. As such, the crust-mantle interaction in oceanic subduction channel is the major cause for thinning of the craton lithosphere in North China.
... For the single hornblende analysed from the YIC the calculated water value in equilibrium with this sample lies within the mantle field for oxygen but is elevated to − 45.2‰ for deuterium, which is above the convecting mantle field but within the middle of the range of magmatically degassed values (e.g. Kingsley et al., 2002). Values of waters calculated for the three NIC hornblendes define a narrow range of δD (−38.8 to −46.0‰) and δ 18 O (6.5 to 7.3‰) values (Fig. 6). ...
... For deuterium, they are elevated to the upper end of the range of magmatically degassed values (e.g. Kingsley et al., 2002). ...
Archean mafic-ultramafic melts, crystallized as layered intrusions in the upper crust and extruded as komatiitic flows, are primary probes of upper mantle chemistry. However, the message from their primary chemical composition can be compromised by different modes of contamination. Contaminants are typically cryptic in terms of their geochemical and isotopic signals but may be related to metasomatised mantle sources, ambient crustal assimilation or subduction-related inputs. In this work we present critical evidence for both dry and wet Archean mantle sources for two juxtaposed layered intrusions in the Australian Yilgarn Craton. The ca. 2813Ma Windimurra and ca. 2800Ma Narndee Igneous Complexes in Western Australia are two adjacent layered intrusions and would be expected to derive via similar mantle sections. A key difference in their chemistry is the presence of crystal-bound water in the Narndee Igneous Complex, represented primarily by abundant hornblende. Such a primary hydrous phase is notably absent in the Windimurra Igneous Complex. New 40Ar/39Ar plateau ages for fresh Narndee hornblende (weighted mean: 2805±14Ma, MSWD=1.8, probability=0.18) agrees with the published U-Pb age of 2800±6Ma for the complex and is consistent with a magmatic origin for this phase. Zircon Hf and whole-rock Hf and Nd isotopes for the Narndee Igneous Complex indicate only minor crustal contamination, in agreement with H and O isotope values in amphibole and O isotope values in rare zircon crystals, plagioclase and pyroxene within both complexes. These findings illustrate a fast temporal transition, in proximal bodies, from anhydrous to hydrous mantle sources with very minor crustal contamination. These large layered mafic-ultramafic intrusions are igneous bodies with a primitive chemical bulk composition that requires large degrees of mantle melting. This has been attributed by many workers to mantle plume activity, yet not without dispute, as subduction-related flux melting may also generate large melt fractions. We conclude that the source of the magmatic water at Narndee is the mantle, which, in conjunction with its absence in the adjacent Windimurra Igneous Complex, argues for a heterogeneous hydration of mantle source regions under the Yilgarn Craton in the Mesoarchean.
