Ya. Kostitsyn et En. Altukhov, Subalkali and Li-F granites of the central Cis-Sayan region: Rb-Sr age andSr isotopic composition, GEOCHEM INT, 38(5), 2000, pp. 429-435
Results of Rb-Sr isotopic study of subalkali and alkali granitic rocks from
the central Cis-Sayan region are reported. The isochron for the rocks of t
he Bugul'ma, Sopkol, Pravaya Kamenka, and Tarta plutons gave an age of 427
+/- 7 Ma and initial Sr isotope ratio of 0.70476 +/- 14. Regardless of the
tectonic setting of the granitic rocks, they have a low initial isotope rat
io indicative of the origin by melting of crustal rocks under the effect of
mantle-derived melts. The Li-F granite of the Khoroi pluton and dikes cutt
ing the Bugul'ma pluton have the Rb-Sr isochron age of 403 +/- 5 Ma and the
initial Sr isotope ratio of 0.7102 +/- 4 Ma. A difference in Sr isotopic c
omposition, geochemistry, and age between the Khoroi and Bugul'ma granitic
rocks prevent us from their affiliation to a genetically related associatio
n of one intrusive complex.