Chemical and Sr isotopic compositions of beryl crystals in the Ebrahim-Attar pegmatite, NW Iran, indicate melting of the upper continental crustal source

抄録

Here we focus on the Ebrahim-Attar beryl-bearing granitic pegmatite in NW Iran. The granitic pegmatite is highly peraluminous and contains small prismatic beryl crystals. Pale green to white beryl minerals are crystallized in the rim and central parts of the granitic body. In order to reveal the source and genesis of the beryl minerals, we carried out the chemical and Sr isotopic analyses of the beryl minerals. The result of beryl geochemistry indicates low contents of alkali oxides (Na2O = 0.24-0.41 wt.%, K2O = 0.05-0.17 wt.%, Li2O = 0.03-0.04 wt.%, and Cs2O = 0.01-0.03 wt.%) and high value of Be2O (10.0 to 11.9 wt.%). The REE abundances are low (total REE= 1.21 to 5.41 ppm). The beryl chemical formula was calculated based on 18O, as ch(Na0.054,K0.014,Cs0.001)T2(Be2.412,Li0.013)2.412O(Al2.145,Fe0.04,Mn0.0004,Mg0.003)2.188T1Si6.372O18. The low ratio of Na/Li (apfu) (2.94 to 5.75) and the high variation of FeO (0.28-1.18 wt.%) suggest that the beryl minerals originated from the less evolved granites. The high 87Sr/86Sr(i) ratios (0.739 ±0.036) for the beryl grains indicate that partial melting of the upper continental crust (UCC) is the source of the magma and sufficiently support.