scholarly journals Water contents of nominally anhydrous orthopyroxenes from oceanic peridotites determined by SIMS and FTIR

2021 ◽  
Author(s):  
Kirsten T. Wenzel ◽  
Michael Wiedenbeck ◽  
Jürgen Gose ◽  
Alexander Rocholl ◽  
Esther Schmädicke
Keyword(s):  
Upper Mantle ◽  
Secondary Ion Mass Spectrometry ◽  
Spinel Peridotite ◽  
Structural Water ◽  
Major Element Composition ◽  
Mantle Peridotites ◽  
History Of ◽  
Polarized Ftir ◽  
Water Contents ◽  
Forearc Region

AbstractThis study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic reference orthopyroxenes from spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al2O3 ranges between 4.02 and 5.56 wt%, and Cr2O3 ranges between 0.21 and 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the water contents of the eleven reference orthopyroxenes vary from dry to 249 ± 6 µg/g H2O. Using these reference grains, a set of orthopyroxene samples obtained from variably altered abyssal spinel peridotites from the Atlantic and Arctic Ridges as well as from the Izu-Bonin-Mariana forearc region was analyzed by SIMS and FTIR regarding their incorporation of water. The major element composition of the sample orthopyroxenes is typical of spinel peridotites from the upper mantle, characterized by Mg#s between 0.90 and 0.92, Al2O3 between 1.66 and 5.34 wt%, and Cr2O3 between 0.62 and 0.96 wt%. Water contents as measured by SIMS range from 68 ± 7 to 261 ± 11 µg/g H2O and correlate well with Al2O3 contents (r = 0.80) and Cr#s (r. = -0.89). We also describe in detail an optimized strategy, employing both SIMS and FTIR, for quantifying structural water in highly altered samples such as abyssal peridotite. This approach first analyzes individual oriented grains by polarized FTIR, which provides an overview of alteration. Subsequently, the same grain along with others of the same sample is measured using SIMS, thereby gaining information about homogeneity at the hand sample scale, which is key for understanding the geological history of these rocks.

Electrical conductivity of omphacite and garnet in eclogite: implications for water recycling in the mantle

2020 ◽  
Author(s):  
Hanyong Liu ◽  
Xiaozhi Yang
Keyword(s):  
Electrical Conductivity ◽  
Water Content ◽  
Deep Water ◽  
Upper Mantle ◽  
Critical Role ◽  
High Resistivity ◽  
Water Recycling ◽  
Structural Water ◽  
Crust And Upper Mantle ◽  
Water Contents

<p>Eclogite is an important constituent of subduction slabs and plays a critical role in transporting surface materials (e.g., water) into the deep Earth. Eclogite consists mainly of omphacite and garnet. Although nominally anhydrous, omphacite and garnet contain some amount of structural water (OH) in the lattice, which is up to >1500 ppm wt. H<sub>2</sub>O. This is virtually the highest content in nominally anhydrous minerals (NAMs) derived from the crust and upper mantle (Ingrin and Skogby, 2000). The electrical property of NAMs is very sensitive to water content and a small amount of water could dramatically enhance the conductivity. Thus, laboratory measured conductivity data of omphacite and garnet may help to understand the deep water recycling by eclogitized slab.</p><p>In this study, we have systemically determined the conductivity of omphacite and garnet with different water contents. The experiments were carried out at 350-800 °C, 1 GPa (note that the effect of pressure itself on conductivity is very small) and Ni-NiO buffered conditions. The data show that the conductivity of both omphacite and garnet increases with water content or temperature. The bulk conductivity is then modeled for different mineral compositions and water contents over a range of conditions (Liu et al., 2019). In combination with the geophysically documented high resistivity of the crustal part in deep subducted slabs, we suggest that the water content in omphacite and garnet in the deep-subducted eclogites should not be high at mantle depths. This provides new insights into the deep water recycling by subducted eclogites.</p><p> </p><p><strong>References:</strong></p><p>Ingrin, J., and Skogby, H., 2000, Hydrogen in nominally anhydrous upper-mantle minerals: Concentration levels and implications: European Journal of Mineralogy, 12, 543–570.</p><p>Liu, H., Zhu, Q., and Yang, X., 2019, Electrical conductivity of OH-bearing omphacite and garnet in eclogite: the quantitative dependence on water content: Contributions to Mineralogy and Petrology, 174, doi:10.1007/s00410-019-1593-3.</p><p></p><p></p><p></p><p></p>

Drifting Through a Planetary System

2018 ◽  
Author(s):  
Karel Schrijver
Keyword(s):  
Seventeenth Century ◽  
Solar System ◽  
Virtual Worlds ◽  
Planetary System ◽  
System P ◽  
History Of ◽  
Or Team ◽  
Water Contents

This chapter describes how the first found exoplanets presented puzzles: they orbited where they should not have formed or where they could not have survived the death of their stars. The Solar System had its own puzzles to add: Mars is smaller than expected, while Venus, Earth, and Mars had more water—at least at one time—than could be understood. This chapter shows how astronomers worked through the combination of these puzzles: now we appreciate that planets can change their orbits, scatter water-bearing asteroids about, steal material from growing planets, or team up with other planets to stabilize their future. The special history of Jupiter and Saturn as a pair bringing both destruction and water to Earth emerged from the study of seventeenth-century resonant clocks, from the water contents of asteroids, and from experiments with supercomputers imposing the laws of physics on virtual worlds.

scholarly journals Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Costanza Bonadiman ◽  
Valentina Brombin ◽  
Giovanni B. Andreozzi ◽  
Piera Benna ◽  
Massimo Coltorti ◽  
...  
Keyword(s):  
Oxygen Fugacity ◽  
Upper Mantle ◽  
Mantle Xenoliths ◽  
Spinel Peridotite ◽  
Simultaneous Formation ◽  
Empirical Potentials ◽  
Elastic Data ◽  
Mineralogical Study ◽  
Semi Empirical ◽  
T Locus

AbstractThe occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P–T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3–3.0 GPa/540–1500 K, yields a negative Clapeyron slope of -0.003 GPa K–1 (on average). The intersection of the P–T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190 K, that represents a plausible depth of ~ 70 km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [Δ(FMQ) = –1.97 ± 0.35; –1.83 ± 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity.

Experimental investigation of the composition of incipient melts in upper mantle peridotites in the presence of CO2 and H2O

Lithos ◽  
2021 ◽  
pp. 106224
Author(s):  
Zsanett Pintér ◽  
Stephen F. Foley ◽  
Gregory M. Yaxley ◽  
Anja Rosenthal ◽  
Robert P. Rapp ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Upper Mantle ◽  
Mantle Peridotites

On the Vp/Vs–Mg# correlation in mantle peridotites: Implications for the identification of thermal and compositional anomalies in the upper mantle

2010 ◽  
Vol 289 (3-4) ◽  
pp. 606-618 ◽  
Author(s):  
Juan Carlos Afonso ◽  
Giorgio Ranalli ◽  
Manel Fernàndez ◽  
William L. Griffin ◽  
Suzanne Y. O'Reilly ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Mantle Peridotites

scholarly journals An Overview of the Experimental Studies on the Electrical Conductivity of Major Minerals in the Upper Mantle and Transition Zone

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 408 ◽  
Author(s):  
Lidong Dai ◽  
Haiying Hu ◽  
Jianjun Jiang ◽  
Wenqing Sun ◽  
Heping Li ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Transition Zone ◽  
Oxygen Fugacity ◽  
Upper Mantle ◽  
Activation Enthalpy ◽  
Small Polaron ◽  
Experimental Studies ◽  
Transport Processes ◽  
Structural Water ◽  
Nominally Anhydrous Minerals

In this paper, we present the recent progress in the experimental studies of the electrical conductivity of dominant nominally anhydrous minerals in the upper mantle and mantle transition zone of Earth, namely, olivine, pyroxene, garnet, wadsleyite and ringwoodite. The main influence factors, such as temperature, pressure, water content, oxygen fugacity, and anisotropy are discussed in detail. The dominant conduction mechanisms of Fe-bearing silicate minerals involve the iron-related small polaron with a relatively large activation enthalpy and the hydrogen-related defect with lower activation enthalpy. Specifically, we mainly focus on the variation of oxygen fugacity on the electrical conductivity of anhydrous and hydrous mantle minerals, which exhibit clearly different charge transport processes. In representative temperature and pressure environments, the hydrogen of nominally anhydrous minerals can tremendously enhance the electrical conductivity of the upper mantle and transition zone, and the influence of trace structural water (or hydrogen) is substantial. In combination with the geophysical data of magnetotelluric surveys, the laboratory-based electrical conductivity measurements can provide significant constraints to the water distribution in Earth’s interior.

Sign in / Sign up

Export Citation Format

Share Document