GEOCHEMICAL STRUCTURE OF THE EARLY CARBONIFEROUS VOLCANIC COMPLEXES OF THE SOUTHERN URALS

Abstract

In this paper, the concept of a geochemical structure (Yaroshevskii, 2004) was applied to describe chemical variations in the Early Carboniferous volcanic complexes and their distribution over the tectonic zones of the Southern Urals and Transuralian region in order to clarify the geodynamic settings of their formation. The cluster analysis of a geochemical dataset including 325 analyses of volcanic rocks from the Magnitogorsk, Southern Ural, Transuralian, and Valer’yanovskii tectonic zones allowed us to reduce the geochemical diversity of rocks to eight large geochemical groups. Based on average compositions, these geochemical groups (clusters) can be classed with the following rocks: (1) low-K tholeiitic basalts, (2) high-Ti subalkaline basalts, (3) high-Al subalkaline basalts, (4) subalkaline andesites, (5) subalkaline rhyolites, (6) Na subalkaline rhyolites, (7) potassic subalkaline rhyolites, and (8) high-Al potassic trachyandesibasalts. The distribution of these clusters in tectonic zones of the Southern Urals and Transuralian makes it possible to organize these complexes into four groups. The first group includes a differentiated series from high-Ti subalkaline basalts to sodic subalkaline rhyolites with the predominance of aluminous subalkaline basalts and subalkaline andesites. This group is most widespread in the Magnitogorsk and Valer’yanovskii zones. The second group corresponds to a differentiated series from low-K basalts to Na subalkaline rhyolites with a strong prevalence of high-Ti subalkaline basalts and less abundant aluminous subalkaline basalts. This group is widespread in the Eastern Ural zone. The third group includes subalkaline andesites and rhyolites with subordinate ultrapotassic rhyolites and trachyandesibasalts, which compose the Uya-Novoorenburg suture. The fourth group comprises high-Ti subalkaline basalts occurring in the Transuralian zone. Such a distinct distribution of the geochemical types of volcanic rocks is well consistent with concepts on the formation of the Southern Ural volcanic belts at the East European paleocontinent margin in a Californian-type setting. The Valer’yanovskii belt was formed at the active margin of the Kazakhstan paleocontinent.