Geology and Geochemistry of Synplutonic Dykes in the Chelyabinsk Granitoid Massif, South Urals

Abstract

We present the results of geological, petro-geochemical and mineralogical studies of synplutonic intrusive formations in the Chelyabinsk granitoid massif, South Urals. Numerous synplutonic intrusions in the study area are in early phases, composed of quartz diorites and granodiorites of the Late Devonian-Early Carboniferous. Such intrusions are represented by a bimodal series of rocks from gabbro-diorite to plagioleic granite. Both the mafic and salic members of the series form separate independent dykes and, jointly, compose the dyke bodies of complex structures. With respect to the relationships with host rocks, two types of the studied dykes are distinguished: (1) 'classical' synplutonic dykes with monolithic bodies that are split along strike by the enclosing granodiorite into separate fragments; and (2) 'post-granite' dykes that clearly break through the host quartz diorites and granodiorites that are older that the dykes, but show similar isotope ages: the U-Pb-Shrimp ages of zircon in the samples taken from the dyke and the host quartz diorite are 362±4 и 358±5 Ma, respectively. The first group includes the dyke of melanocratic diorite, the second-granitoid dykes and dykes of gabbro-diorites and diorites. The intrusion of acid rocks preceded the basites and was completed after their formation. As a result of the nearly simultaneous intrusion of both, the dykes of complex structures were formed. The material compositions of mafic rocks in these two groups are significantly different. The 'post-granite' dioritoids are moderately alkaline. Melanodiorite in the synplutonic dyke belongs to normal alkaline rocks. It has a very high content of MgO (12.5 mass %) and is sharply enriched with chromium (~700 ppm vs. 100-350 ppm in the 'post-granite' dykes). It is thus closer to sanukitoids. The acid 'post-granite' dykes vary in composition from plagoleic granite and adamellite to tonalite. They are normal-alkaline. Their chemical compositions often do not correspond to cotectic ones. The dioritoids have nearly zero values of Nd (from +1 to-2), and the values of (87 Sr/ 86 Sr)I vary from 0.70485 to 0.70571. The granitoids are typically characterized by negative values of Nd (from-2 to-5) and, generally, more radiogenic strontium ((87 Sr/ 86 Sr)i=0.70517-0.70567). The established isotopic compositions of Nd and Sr in the synplutonic dykes of the Chelyabinsk Massif give evidence of different sources for the coexisting salic and mafic melts, but do not fit a model of simple mixing of the two components.

Trace-element geochemistry of molybdenite from porphyry Cu deposits of the Birgilda-Tomino ore cluster (South Urals, Russia)

“…Numerous diorite and andesite porphyry stocks of the Birgilda–Tomino Igneous Complex, dated as 428 ± 3 Ma and 427 ± 6 Ma (Grabezhev et al ., 2013), are believed to have produced both porphyry and epithermal-style mineralization (Grabezhev et al ., 1998; Puzhakov, 1999). The Chelyabinsk Pluton, located in the northernmost part of the area, comprises several Late Devonian to Permian intrusive phases (Kallistov, 2014).

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Zircon in High‐mg Diorite of the Chelyabinsk Massif (South Urals): Morphology, Geochemical Signature, and Petrogenesis Implications

“…Более кислые разности (граниты и лейкограниты) преимущественно слагают центральную и юго-восточную часть массива, а также представлены в западном эндоконтакте (гнейсированные граниты). Основные черты строения и состава Челябинского массива рассмотрены в работах [Fershtater et al, 2004;Kallistov, 2014;Kallistov, Osipova, 2017].…”

“…Подробнее петролого-минералогические особенности и химический состав высокомагнезиального диорита из Челябинского массива охарактеризованы в работах [Kallistov, Osipova, 2017Pribavkin et al, 2019].…”

“…Возраст, определенный вторым кластером, не совпадает ни с одной датировкой более молодых пород Челябинского массива. По имеющимся на сегодня данным, он не фиксируется U-Pb изотопной системой в цирконе ни из вмещающего дайку гранодиорита, ни в какой-либо другой породе слагающих Челябинский массив интрузивных комплексов [Fershtater et al, 2004;Kallistov, 2014;Kallistov, Osipova, 2017]. Соответственно, значение возраста, определяемое этим кластером, не представляется возможным связать с каким-либо тектонотермальным событием на этой территории.…”