Isotope (U–Pb, Sm–Nd, Rb–Sr) geochronology of alkaline basic plutons of the Kuznetsk Alatau

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 (ε Nd (T) ≈ +4.8 to +5.7, T Nd (DM) ≈ 0.8-0.9 Ga) pointing to the similar nature of their matter sources in the moderately depleted mantle.

Geochemistry, isotope triad (Nd–Sr–O), and 40Ar–39Ar age of Paleozoic alkaline mafic intrusions of the Kuznetsk Alatau (by the example of the Belaya Gora pluton)

“…Asterisk marks the compositions of mafic foidolite and nepheline syenite of the Belaya Gora pluton. d, Composition fields of Paleozoic Kuznetsk Alatau igneous complexes (1-4): 1, alkaline rocks and carbonatites (T ≈ 509 Ma) of the Upper Petropavlovka intrusion; 2, Devonian (~385-400 Ma) alkaline mafic intrusions; 3, gabbro-monzodioritesyenite association (~485-500 Ma); 4, Cambrian and Silurian-Devonian granitoids, including Gornaya Shoria and Gorny Altai (Kruk et al, 2001;Rudnev, 2013;Vrublevskii et al, 2003Vrublevskii et al, , 2005Vrublevskii et al, , 2012bVrublevskii et al, , 2014b. The mantle array domain and the position of the PREMA, MORB, HIMU, EM I, and EM II reservoirs are given in accordance with their modern isotope parameters, after Zindler and Hart (1986).…”

“…Here, small (1-2 km 2 ) differentiated alkaline mafic intrusive massifs are widespread, which are composed of subalkalic and alkali gabbro, mafic and ultramafic foidolites, and nepheline and alkali syenites in different proportions. The available Sm-Nd and U-Pb isotope dates suggest that the intrusion took place in two stages: the Middle Cambrian-Early Ordovician (480-510 Ma) and EarlyMiddle Devonian (385-410 Ma) (Vrublevskii, 2015;Vrublevskii et al, 2003Vrublevskii et al, , 2014bVrublevsky et al, 2004). Rock associations that formed at the Devonian stage are the most abundant.…”

Polygenesis of mafic–ultramafic complexes: Isotope-geochronological and geochemical evidence from zircons of the Berezovka massif rocks (Sakhalin Island)

“…In recent time, an advance in this field has been made owing to the elaboration of methods for dating zircon grains with application of high-resolution secondary-ion mass spectrometers (SHRIMP-II). Today, these methods are used for isotope dating of not only zircons from granitoids (Rudnev et al, 2012), alkaline igneous rocks (Vrublevskii et al, 2014), and metamorphic rocks (Turkina et al, 2014) but also zircons from gabbroids (Bortnikov et al, 2008;Krasnobaev et al, 2007;Ledneva et al, 2012;Skolotnev et al, 2010;Tsukanov and Skolotnev, 2010) and ultramafites (Badanina and Malich, 2012;Fershtater et al, 2009;Knauf, 2008;Lesnov et al, 2010;Malitch et al, 2009;Oh et al, 2012;Ronkin et al, 2013).…”

Features of geology and composition of rocks from the alkaline-gabbroic University massif (N-E Kuznetsky Alatau ridge, Siberia)

“…Such expression of alkaline magmatism in this region took place exclusively in western part of Mariinsk Taiga and was recorded in alkaline-gabbroid association of UpperPetropavlovsk Massif [11]. Dating alkaline rocks by Sm-Nd isotope method nowadays is quite complicated because variations in 147 Sm/…”