Zirconosilicate phase relations in the Strange Lake (Lac Brisson) Pluton, Quebec-Labrador, Canada

Abstract

Other| October 01, 1995 Zirconosilicate phase relations in the Strange Lake (Lac Brisson) Pluton, Quebec-Labrador, Canada Stefano Salvi; Stefano Salvi McGill University, Department of Earth and Planetary Sciences, Montreal, PQ, United States Search for other works by this author on: GSW Google Scholar Anthony E. Williams-Jones Anthony E. Williams-Jones Search for other works by this author on: GSW Google Scholar American Mineralogist (1995) 80 (9-10): 1031–1040. https://doi.org/10.2138/am-1995-9-1019 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Stefano Salvi, Anthony E. Williams-Jones; Zirconosilicate phase relations in the Strange Lake (Lac Brisson) Pluton, Quebec-Labrador, Canada. American Mineralogist 1995;; 80 (9-10): 1031–1040. doi: https://doi.org/10.2138/am-1995-9-1019 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Petrographic observations of subsolvus granites at Strange Lake indicate that the sodium zirconosilicate elpidite crystallized under magmatic conditions, but that the calcium zirconosilicates armstrongite and gittinsite are secondary. This interpretation is consistent with the extensive solid solution displayed by elpidite and the restricted compositions of armstrongite and gittinsite. Both calcium zirconosilicate minerals show textural evidence of having replaced elpidite, and in the case of gittinsite, with major volume loss. In the near-surface environment, gittinsite plus quartz fill the volume formerly occupied by elpidite. At greater depth, gittinsite and armstrongite partially replaced elpidite but are not accompanied by quartz, and abundant pore space is observed where gittinsite is the principal secondary phase. Below 70 m elpidite is generally unaltered. Replacement of elpidite by armstrongite is interpreted to have been a result of the cation-exchange reactionNa2ZrSi6O15⋅3H2O+Ca2+elpidite=CaZrSi6O15⋅3H2O+2Na+armstrongitein which volume is nearly conserved, and replacement by gittinsite is thought to have resulted from the reactionNa2ZrSi6O15⋅3H2O+Ca2++5H2Oelpidite=CaZrSi2O7+2Na++4H4SiO40gittinsitewhich is accompanied by a 65% volume reduction.An alteration model is proposed in which external Ca-rich, quartz-undersaturated fluids dissolved elpidite and replaced it with gittinsite, where aH4SiO40 was buffered mainly by the fluid (high water-rock ratio), and with armstrongite plus gittinsite, or armstrongite alone, where aH4SiO40 was buffered to higher values by the rock (low water-rock ratio). The formation of gittinsite created extensive pore space that was subsequently filled, in the upper part of the pluton, when the fluid became saturated with quartz as its temperature decreased during the final stages of alteration. 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.