Armalcolite in crustal paragneiss xenoliths, central Mexico

Abstract

Other| August 01, 1995 Armalcolite in crustal paragneiss xenoliths, central Mexico Jodie L. Hayob; Jodie L. Hayob University of Michigan, Department of Geological Sciences, Ann Arbor, MI, United States Search for other works by this author on: GSW Google Scholar Eric J. Essene Eric J. Essene Search for other works by this author on: GSW Google Scholar Author and Article Information Jodie L. Hayob University of Michigan, Department of Geological Sciences, Ann Arbor, MI, United States Eric J. Essene Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 1995 by the Mineralogical Society of America American Mineralogist (1995) 80 (7-8): 810–822. https://doi.org/10.2138/am-1995-7-817 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 Jodie L. Hayob, Eric J. Essene; Armalcolite in crustal paragneiss xenoliths, central Mexico. American Mineralogist 1995;; 80 (7-8): 810–822. doi: https://doi.org/10.2138/am-1995-7-817 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 Aluminous armalcolite has been found in two sillimanite-bearing xenoliths that were recently exhumed from the lower crust of central Mexico. The ranges of compositions are (Fe0.58−0.662+Mg0.18−0.28Al0.15−0.18V0.06−0.103+Fe0.00−0.063+Ti1.84−1.864+)O5 and (Fe0.20−0.512+Mg0.18−0.29Al0.16−0.19-V0.02−0.063+Fe0.30−0.813+Ti1.49−1.714+)O5⁠. The occurrence of armalcolite is unusual in crustal para-gneisses because most terrestrial armalcolite occurs in volcanic rocks that are derived from partial melting in the Earth's mantle. Textures suggest that armalcolite is a late product formed by the reaction rutile + ilmenitess = armalcolitess during rapid transport of the xenoliths to the surface. Phase equilibria in the system MgO-FeO-Fe2O3-TiO2, which indicate that armalcolite is stable in the crust at 900–1200 °C, are consistent with this interpretation.Thermodynamic properties are estimated for oxides in the system MgO-FeO-Fe2O3-TiO2 to constrain activity-composition relations for armalcolite and conditions of formation. Activity coefficients calculated for armalcolite range from 0.27 to 1.36, depending on the ilmenite model used, at temperatures between 1000 and 1300 °C. Depth of formation of armalcolite in the crust is not well constrained. Thermodynamic calculations at 800–1200 °C for the compositions observed indicate that the armalcolite in one xenolith would have been in equilibrium with rutile at values of fO2 between the hematite + magnetite buffer (HM) and the fayalite + magnetite + quartz (FMQ) buffer, and that armalcolite in the other xenolith would have been in equilibrium with rutile and ilmenite at values of fO2 between FMQ and two log units below the FMQ buffer. 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.