Jadeite-K-Feldspar Rocks and Jadeitites from Northwest Turkey

Aral I. Okay
İTÜ, Maden Fakültesi, Jeoloji Bölümü, Ayazağa 80624, İstanbul, Turkey

Abstract: Blueschist-facies rocks with jadeite-K-feldspar-lawsonite paragenesis occur as exotic blocks in Miocene debris flows in the blueschist belt of northwest Turkey. The jadeite-K-feldspar rocks have a very fine grain size and although recrystallized locally retain a relict porphyritic volcanic texture. The former nepheline microphenocrysts, recognized from their characteristic shapes, are pseudomorphed by jadeite and K-feldspar, while the relict magmatic aegirine has rims of jadeite. The matrix of the rock consists of very fine-grained aggregates of jadeite, K-feldspar and lawsonite. In some blocks, jadeite makes up >60% of the mode. Jadeite, K-feldspar and lawsonite in the blocks are essentially pure end-member in composition. P-T estimates for these rocks are 8 ± 2 kbar and 300 ± 50°C. The preserved volcanic texture, relict aegirine and the bulk rock composition indicate that these rocks represent metamorphosed phonolites. The paragenesis in these rocks shows that jadeite-K-feldspar is a stable mineral pair in blueschist-facies P-T conditions.

Keywords: jadeite • K-feldspar • lawsonite • jadeitite • blueschist • Turkey

Mineralogical Magazine; December 1997 v. 61; no. 409; p. 835-843; DOI: 10.1180/minmag.1997.061.409.06
© 1997, The Mineralogical Society
Mineralogical Society (www.minersoc.org)