Dislocation formation and albitization in alkali feldspars from the Shap Granite

Abstract

Other| June 01, 1997 Dislocation formation and albitization in alkali feldspars from the Shap Granite Martin R. Lee; Martin R. Lee University of Edinburgh, Department of Geology and Geophysics, Edinburgh, United Kingdom Search for other works by this author on: GSW Google Scholar Ian Parsons Ian Parsons Search for other works by this author on: GSW Google Scholar Author and Article Information Martin R. Lee University of Edinburgh, Department of Geology and Geophysics, Edinburgh, United Kingdom Ian Parsons Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online Issn: 1945-3027 Print Issn: 0003-004X Copyright © 1981 by the Mineralogical Society of America American Mineralogist (1997) 82 (5-6): 557–570. https://doi.org/10.2138/am-1997-5-616 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Martin R. Lee, Ian Parsons; Dislocation formation and albitization in alkali feldspars from the Shap Granite. American Mineralogist 1997;; 82 (5-6): 557–570. doi: https://doi.org/10.2138/am-1997-5-616 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 Orthoclase-rich alkali feldspars in the Lower Devonian Shap granite, northwest England, contain two generations of albite-rich feldspar. These have partially replaced earlier exsolution microtextures consisting of albite lamellae (coarse semicoherent albite films and fine coherent albite platelets) in tweed orthoclase. The earlier generation of replacive albite-rich feldspar (~Ab90An9OrI) occurs together with orthoclase-rich feldspar (~Ab10Or90) in veins that crosscut exsolution microtextures throughout grain interiors. This episode of recrystallization was mediated by magmatic fluids at ~410 °C (estimated from two-feldspar geothermometry) and was driven by stored elastic strain energy, which was relatively homogeneously distributed throughout the microtextures. The later generation of replacive albite-rich feldspar, which is restricted to grain margins and is compositionally pure (Ab>99), was produced by magmatic-hydrothermal fluids at ~370 °C. This generation of albite-rich feldspar does not crosscut exsolution microtextures and has selectively replaced volumes of highly elastically strained feldspar surrounding edge dislocations along semi-coherent albite films. Marked differences in controls of the localization of the two generations of replacive albite-rich feldspar by pre-existing exsolution microtextures indicate that significant numbers of edge dislocations developed along albite films after the first phase of fluid-feldspar interaction and associated albitization but before the second phase. This relation indicates that edge dislocations formed between 410 and 370 °C. These observations have important implications for understanding the factors that control the interaction of alkali feldspars with fluids both in cooling igneous rocks and in clastic sedimentary rocks during diagenesis. 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.