1070 ISSN 1028-334X, Doklady Earth Sciences, 2006, Vol. 410, No. 7, pp. 1070–1074. © Pleiades Publishing, Inc., 2006. Original Russian Text © V.A. Lebedev, I.V. Chernyshev, A.S. Avdeenko, A.A. Nosova, A.Ya. Dokuchaev, T.I. Oleinikova, Yu.V. Gol’tsman, 2006, published in Doklady Akademii Nauk, 2006, Vol. 410, No. 1, pp. 95–100. Late Miocene subalkaline granite magmatism in the Caucasian Mineral Waters (CMW) region is related to the first stage of Late Cenozoic magmatic activity in the Caucasian segment of the Alpine foldbelt. The young age and presence of uranium mineralization, as well as other factors including easy availability, promoted detailed study of these intrusions in geological [1, 2], mineralogical, petrographical, geochemical, and physi- cochemical aspects [3–7]. The CMW region known as Mineral’nye Vody (Fig. 1) is confined to the ring struc- ture in the northern termination of Transcaucasus Transverse Uplift. The intrusions typically form stocks with deep subvertical contacts, and their exposures are no more than 5 km 2 in area. The presence of granite pebbles at the base of Late Miocene sedimentary sequence unambiguously indicates the Post Paleogene age of the subalkaline magmatism in the region. The massifs are made up of leucogranite–granite and alkaline granite–granosyenite–syenite series [1, 7]. The granitoids typically exhibit porphyritic texture and consist of phenocrysts and fine-grained groundmass. Syenites and granosyenites contain phenocrysts of sanidine, plagioclase, phlogopite, and clinopyroxene. In granites which also contain quartz, clinopyroxene is replaced by hornblende. Phenocrysts in leucogranites occur as quartz and feldspars. In terms of geochemical characteristics, subalkaline rocks of the CMW region are classified as latite (shoshonite) granites typical of late collisional and postcollisional stages of the evolu- tion of foldbelts [7]. The geology, composition, and crystallization conditions of granitoids of the CMW region are considered in detail in [1, 7]. The problem of age and chronology of CMW gran- itoid massifs remains debatable. Available K–Ar and 39 Ar– 40 Ar datings do not always coincide and span only part of the known massifs. Of special interest is their formation history, especially in view of the recognition of two or even three phases for some massifs in petro- logical works [1, 7]. The first K–Ar determinations were performed 30 years ago and ranged within 10.5–8 Ma [3, 8] which unambiguously confirmed their Late Miocene age pre- viously inferred from geological data. In later studies, the granites were dated by analytically improved K–Ar method at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (Moscow) [9] and for the first time by the 39 Ar– 40 Ar method at Heidelberg University [5, 6]. K–Ar datings on five phlogopite samples from the Kinzhal, Sheludivaya, Ostraya, Zmeika, and Verblyud massifs are reported in [9]. Three datings are within 8.40–8.25 Ma, while two others fall around 9.3 Ma. No correlation was found between the age and composition of the rocks, while K–Ar data were interpreted as the uplift time, i.e., exhumation of the host crustal blocks above the 300°C isograd. These authors believed that the intrusions are slightly older than 9 Ma. Based on our more detailed K–Ar data, we shall show that the appar- ent different ages of the CMW massifs noted in [9] can be interpreted in a different way. An incremental step heating 39 Ar– 40 Ar method was applied by Hess, Paul, and others to date these massifs [5, 6]. They studied three sanidine–phlogopite mineral pairs from rocks of the Razvalka, Kinzhal, and Zmeika massifs and two sanidine samples from rocks of the Ostraya and Zolotoi Kurgan massifs. All dated samples define plateau age spectra, indicating rapid cooling and subsequent closure of the K–Ar isotope mineral sys- tem. The obtained data are plotted in a narrow range of 8.4–8.1 Ma, which allowed the authors to conclude that the age of CMW massifs is ~8.25 Ma. It should be Heterogeneity of Ar and Sr Initial Isotopic Composition in the Coexisting Minerals from Miocene Hypabyssal Granitoids in the Caucasian Mineral Waters Region V. A. Lebedev, Corresponding Member of the RAS I. V. Chernyshev, A. S. Avdeenko, A. A. Nosova, A. Ya. Dokuchaev, T. I. Oleinikova, and Yu. V. Gol’tsman Received April 6, 2006 DOI: 10.1134/S1028334X06070154 Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017 Russia e-mail: leb@igem.ru GEOCHEMISTRY