The pressure behavior of clinozoisite and zoisite; an X-ray diffraction study

Abstract

Other| February 01, 1997 The pressure behavior of clinozoisite and zoisite: An X-ray diffraction study Paola Comodi; Paola Comodi Universita di Perugia, Dipartimento di Scienze della Terra, Perugia, Italy Search for other works by this author on: GSW Google Scholar Pier Francesco Zanazzi Pier Francesco Zanazzi Search for other works by this author on: GSW Google Scholar Author and Article Information Paola Comodi Universita di Perugia, Dipartimento di Scienze della Terra, Perugia, Italy Pier Francesco Zanazzi Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 1997 by the Mineralogical Society of America American Mineralogist (1997) 82 (1-2): 61–68. https://doi.org/10.2138/am-1997-1-208 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Paola Comodi, Pier Francesco Zanazzi; The pressure behavior of clinozoisite and zoisite: An X-ray diffraction study. American Mineralogist 1997;; 82 (1-2): 61–68. doi: https://doi.org/10.2138/am-1997-1-208 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Compressibility data of clinozoisite and zoisite were measured by single-crystal X-ray diffraction in a diamond-anvil cell up to a pressure of about 50 kbar. In both polymorphs, the unit cell parameters varied linearly with pressure but in an anisotropic pattern: βa = 2.1(1) × 10–4, βb = 2.8(1) × 10–4, βc = 3.3(1) × 10–4 kbar–1 for clinozoisite, and βa = 2.3(2) × 10–4, βb = 2.9(1) × 10–4, βc = 3.7(2) × 10–4 kbar–1 for zoisite. The principal coefficients of the strain ellipsoid of clinozoisite are β1 = 2.0 × 10–4, β2 = 2.7 × 10–4, β3 = 3.3 × 10–4 kbar–1; β1 and β3 were symmetrically oriented in the (010) plane with an angle of about 12° between β1 and the a axis, whereas β2 coincides with the b axis. Bulk moduli calculated as the reciprocal of cell-volume compressibility were 1300(20) kbar for the monoclinic and 1140(20) for the orthorhombic polymorph. K0, determined by fitting the unit-cell parameters with a third-order Birch-Murnaghan equation of state, was 1270(45) kbar, with K′ = 0.5(2) for clinozoisite and 1020(65) kbar with K′ = 4.8(4) for zoisite.Structural refinements of clinozoisite performed at 0.5, 19.4, and 42 kbar, and also under ambient conditions, showed that the compression mechanism included both shrinking of the polyhedra (i.e., octahedra and Ca polyhedra) and tilting of the Si2O7 group, with reduction of the Si-O-Si angle. The different effect of these mechanisms explains the anisotropic compressional pattern in clinozoisite and the similar behavior observed in the two polymorphs.Comparison of high-pressure and high-temperature data for clinozoisite showed that a given increase in pressure produced structural effects very similar to those seen after a proportional decrease in temperature. The calculated volume-expansivity–to–compress-ibility ratio of 38 bar/K indicates that the cell volume of clinozoisite remains unchanged with geothermal gradients of about 10 °C/km. The crystallographic data support the results of experimental petrology in indicating that epidote is a good candidate for transporting H2O in down-going subduction slabs. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.