Alvaro, Matteo

Balic Zunic, Tonci

Nestola, Fabrizio

Ohashi, Haruo

Pasqual, Daria

Periotto, Benedetta

English

Copenhagen University Research Information System

u n i ve r s i t y  o f  co pe n h ag e n  Københavns UniversitetHigh-pressure systematic of NaMe3+Si2O6 pyroxenesPeriotto, Benedetta; Nestola, Fabrizio; Balic Zunic, Tonci; Pasqual, Daria; Alvaro, Matteo;Ohashi, HaruoPublished in:Geophysical Research AbstractsPublication date:2010Document versionPublisher's PDF, also known as Version of recordDocument license:CC BYCitation for published version (APA):Periotto, B., Nestola, F., Balic Zunic, T., Pasqual, D., Alvaro, M., & Ohashi, H. (2010). High-pressure systematicof NaMe3+Si2O6 pyroxenes: volume compression vs Me3+ cation radius. Geophysical Research Abstracts, 12.Download date: 02. Feb. 2020Geophysical Research AbstractsVol. 12, EGU2010-8576, 2010EGU General Assembly 2010© Author(s) 2010High-pressure systematic of NaMe3+Si2O6 pyroxenes: volumecompression vs Me3+ cation radiusBenedetta Periotto (1), Fabrizio Nestola (2), Tonci Balic-Zunic (1), Daria Pasqual (2), Matteo Alvaro (3), andHaruo Ohashi (4)(1) Department of Geography and Geology, University of Copenhagen, Copenhagen, Denmark (bp@geo.ku.dk) , (2)Università di Padova, Dipartimento di Geoscienze, Padova, Italy (fabrizio.nestola@unipd.it), (3) Dipartimento di Scienze dellaTerra, Università di Pavia, Pavia, Italy (matteo_alvaro@dst.unipv.it), (4) Hashi Institute for Silicate Sciences, Tokyo, Japan(haruohashi@hotmail.com)Recent investigations have been experimentally demonstrated that Na-clinopyroxenes (Na-cpx) can be stablethroughout a wide range of temperatures and pressures in the upper mantle and several works have been carriedout in order to better constrain their physical properties. In this work the equation of state of a synthetic NaInSi2O6clinopyroxene characterized by a trivalent non 3d-transition metal at the Me3+ crystallographic site (space groupC2/c) was determined up to about 8 GPa by in situ single-crystal X-ray diffraction. Since previous investigationson CaMe2+Si2O6 showed a different effect when 3d- and non 3d-transition elements located at Me site, the aimof this study is to provide a definitive model capable to predict the high-pressure behaviour of (Ca,Na)(Me2+,Me3+)Si2O6 clinopyroxenes.A single crystal of NaInSi2O6 with size 150*80*50 microns3 was selected for the high-pressure single-crystalX-ray diffraction study. The sample was loaded in an ETH-type diamond anvil cell assembled with a diamondculet of 600 microns in diameter and a gasket preindented to 90 microns with a spark eroded hole of 200 micronsin diameter. The cpx was loaded together with a single-crystal of quartz used as an internal pressure standardand some ruby chips used for more approximate determination of the internal pressure. The measurements wereperformed using a four-circles STOE STADI IV diffractometer on which the software SINGLE08 has beenrecently installed allowing to perform the eight-position diffracted-beam centering and to fit the diffraction peakprofiles. Such centering procedure allows to obtain precise and accurate unit-cell parameters in order to providevalues of room pressure bulk modulus affected by a significantly small error.The NaInSi2O6 cpx was investigated at 12 different pressures up to 7.83 GPa. No evidences of phase transfor-mation were found throughout the pressure range investigated. The sample compresses anisotropically with the bdirection being strongly the softest one (as expected for cpx) and a and c axes compressing by similar rates. Usinga third-order Birch-Murnaghan equation of state (BM3) to fit the pressure – unit-cell volume data we could refinesimultaneously the unit-cell volume V0, the room pressure bulk modulus KT0 and its first pressure derivative K’.Using EoSFIT5.2 software we obtained the following coefficients: V0 = 463.42(3) Å3, KT0 = 109.0(6) GPa, K’ =3.3(2).In order to obtain a reliable comparison among NaMe3+Si2O6 pyroxenes, we have plotted the relative compres-sion V/V0 calculated to 10 GPa versus the cation radius of Me3+ site for NaVSi2O6, NaAlSi2O6, NaCrSi2O6,NaFe3+Si2O6 end-members (all C2/c space group). For the NaTiSi2O6 end-member we have performed suchcalculation using the published P-V data up to 4.34 GPa as at greater pressures this cpx transforms to a triclinicsymmetry and cannot be considered for a comparison. According to this comparison, a perfect linear relationis showed for those cpx having a 3d-transition element at Me3+ site, while those cpx with Al and In at Me3+site totally lie out of trend. In good agreement with a previous work on CaMe2+Si2O6 C2/c compounds(Me2+ = Mg, Fe, Ni), the results of this work confirm that the empirical KT0 * V0 = constant relationship isfollowed in C2/c cpx only if the same valence electron character is shared and provide a definitive model for(Ca,Na)(Me2+,Me3+)Si2O6 clinopyroxene compounds.

High-pressure systematic of NaMe<sup>3+</sup>Si<sub>2</sub>O<sub>6</sub> pyroxenes:volume compression vs Me<sup>3+</sup> cation radius

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