Zirconium-Bearing Amphiboles from the Igaliko Dyke Swarm, South Greenland

N. J. G. Pearce*
Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE
*Present address: Dept. of Geology, The University College of Wales, Aberystwyth, Dyfed SY23 3DB, Wales.

Abstract: Sodic-calcic and alkali amphiboles from benmoreitic members of the Igaliko Dyke Swarm contain up to 4.13 wt. % ZrO2. It is proposed that Zr enters the amphiboles by a coupled substitution of ZrC4++AlT3+⇌FeC3++SiT4+ (where C = octahedral site and T = tetrahedral site) to produce the richest Zr-bearing amphiboles so far identified, with compositions ranging up to K 0.48 Na 2.30 Ca 0.32 [ Ti 0.00 Fe 0.38 3+ Fe 3.95 2+ Mn 0.14 Mg 0.25 Zr 0.33 ] Si 7.58 Al 0.36 O 22 (OH) 2 These amphiboles crystallize at a late stage from magmas which were Zr-rich, highly peralkaline and hydrous, with an fo2 close to the synthetic QMF buffer. The incorporation of Zr in to the amphibole is a consequence of the failure of other Zr-bearing phases (such as zircon, baddeleyite, eudialyte) to crystallize.

Keywords: Zr-bearing amphiboles • amphiboles • Igaliko Dyke Swarm • Greenland

Mineralogical Magazine; March 1989 v. 53; no. 369; p. 107-110; DOI: 10.1180/minmag.1989.053.369.12
© 1989, The Mineralogical Society
Mineralogical Society (www.minersoc.org)