SUBDUCTION-RELATED INTRUSIVE MAGMATISM IN THE URALS

Abstract

In the Silurian-Carboniferous (440-330 Ma), the Urals was involved in suprasubduction magmatism. The following subduction-related intrusive magmatites are recognized here: 1. Volcanic, mainly high-level complexes including: a) Silurian gabbro-granitoid and gabbro-syenite series of the Tagil volcanogenic zone; b) Middle-Late Devonian gabbro-granitoid series of the Magnitogorsk volcanic zone (360 Ma). 2. Early Silurian anorthosite-plagiogranite series of the Pt-bearing) belt. 3. Silurian layered wehrlite-gabbro-plagiogranite complexes and accompanying parallel spreading dikes associated with ophiolites (Akkermanovka and Kirpichnaya Massifs on the eastern and western periphery of the Khabarny ophiolite and Reft Massif in the Central Urals). 4. Deep-level and medium-level tonalite-granodiorite complexes dated to 355-360 Ma (Chelyabinsk complex) and 320-340 Ma (Verkhisetsk complex). The subduction is responsible for many peculiarities of the Urals magmatites of this age: high content of water in magmatic melts, which increased during the evolution of the mobile belt; calc-alkalic composition of the rocks; predominantly hornblende type of gabbroids; wide occurrence of primary epidote and sphene; positive anomalies of large-ion lithophile elements (Ba, Sr) and negative anomalies of HFSE (Nb, Zr, Hf, Ti) on spidergrams, typical of most S-C2 Urals igneous rocks of basic and normal compositions. These regularities are disturbed only in those series that are related to taphrogenic structures and disjoining, though the latter, most likely, resulted from subduction.