CONDITIONS OF ELDJURTA GRANITE FORMATION IMPLIED FROM O-ISOTOPIC AND SR-ISOTOPIC DATA ALONG THE VERTICAL PROFILE

Rb and Sr concentrations and Sr and O isotopic composition in samples from 5 km vertical cross-section of Eldjurta granite are presented as well as in some country rocks: marble, gneiss, skarn, and ore metasoma tite from Tyrnyauz W-Mo deposit. Upper part of the granite exhibits co nstant initial Sr isotopic composition near 0,70685, and smooth decrea sing of delta(18)O from +9,1 parts per thousand at depth 2,5 km to +6, 6 parts per thousand at the top endocontact. The absence of pronounced postmagmatic alterations and high O-isotopic equilibrium temperatures (660-770 degrees C) between quartz and biotite suggest penetration of meteoric waters into Eldjurta magma chamber from above. The water pen etration was terminated immediately after the granite was crystallized . Meteoric water/magma ratio is evaluated from 0,1-0,8 at the top endo contact to 0,007-0,03 on 2,5 km below it. The granite located just bel ow have concurrently decreasing Sr-87/Sr-86 (from 0,70741 to 0,70673) and delta(18)O (from +9,1 parts per thousand to +7,0 parts per thousan d) as depth increase. These data, as well as Sr concentrations, are co nsistent with a model including assimilation of about 6% crust rocks b y granitic melt during crystallization with ratio assimilation to crys tallization rates about 1:10. Sr and O isotopic compositions in ore me tasomatite (0,70810 and +5,4 parts per thousand), skarn (0,70897 and 6,0 parts per thousand) and marble (0,70823 and +17,7 parts per thousa nd) suggest that main transport medium in ore formation was meteoric w ater, likely the same that washes the upper part of the granitic body.