Stability relations and Al content of tremolite and talc in CMASH assemblages with kyanite + zoisite + quartz + H2O
European Journal of Mineralogy Volume 7 Number 2 (1995), p. 353 - 362
published: Mar 29, 1995
manuscript accepted: Dec 5, 1994
manuscript received: Nov 2, 1993
ArtNo. ESP147050702010, Price: 29.00 €
Abstract The discontinuous reaction zoisite + talcss = tremolitess + kyanite + quartz + H2O was investigated experimentally using synthetic phases in the CaO-MgO-Al2O3-SiO2-H2O (CMASH) system. Reversed runs constrain a phase boundary at20kbar/700-743gC, 15kbar/676-7179C, 10 kbar/626-7109C. The Al content of tremolite and talc is controlled by the continuous reactions 8 tremolite + 7 kyanite + 2 zoisite + 1 H2O = 10 hornblende + 7 quartz and 2 talc + 3 kyanite + 1 H2O = 3 Tschermak’s talc + 2 quartz. Their time dependent approach towards equilibrium was demonstrated in separate runs starting with Al-free and Al-bearing phases as well as zoisite, kyanite and quartz. Microprobe and X-ray data show that the Al contents are in the range 0.5–1.1 for tremolite (f.u. 23 0) and 0.12-0.24 for talc (f.u. 11 O), the lower values corresponding to higher pressure.