ISOTOPE (U-Pb, Sm-Nd, Rb-Sr) GEOCHRONOLOGY OF ALKALI-BASIC PLUTONS OF THE KUZNETSK ALATAU
V.V. Vrublevskii1, I.F. Gertner1, G. GutiГ©rrez-Alonso2, M. Hofmann3, O.M. Grinev1, P.A. Tishin1
1Tomsk State University, prosp. Lenina 36, Tomsk, 634050, Russia
2Area de Geodinamica Interna Departamento de Geologia, Universidad de Salamanca, 37008, Salamanca, Spain
3Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Königsbrücker Landstraße 159, 01109 Dresden, Germany
Keywords: Alkaline magmatism, isotope geochronology, plume-lithosphere interaction, Kuznetsk Alatau, Central Asian Fold Belt
Abstract
On the northeastern slope of the Kuznetsk Alatau, small differentiated alkaline basic intrusive massifs form an isometric area ~100 km across. They are composed of subalkalic and alkali gabbroids, basic and ultrabasic foidolites, nepheline and alkali syenites, and carbonatites. Results of complex (U-Pb, Sm-Nd, and Rb-Sr) isotope dating suggest that alkaline basic magmatism developed at two stages in the Middle Cambrian-Early Ordovician (~510-480 Ma) and in the Early-Middle Devonian (~410-385 Ma). Finding of accessory zircons (age 1.3-2.0 Ga) in alkaline rocks suggests that the ascent of mantle plume was accompanied by the melting of fragments of Proterozoic mature continental crust composing the basement of the Caledonian orogen of the Kuznetsk Alatau. Probably, parental Cambrian-Ordovician alkaline mafic melts initiated metasomatism and lithosphere erosion. During the next melting of lithosphere substrate in ~100 Myr, this caused the generation of magmas of similar composition with inherited isotope parameters (εNd(T) ≈ +4.8 to +5.7, TNd(DM) ≈ 0.8-0.9 Ga) pointing to the similar nature of their matter sources in the moderately depleted mantle.
DOI: http://dx.doi.org/10.1016/j.rgg.2014.10.002
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