Subduction plagiogranites of Rudny Altai: Age and composition characteristics

Abstract

The spatial-temporal relationships and the pecu liarities of petrogenesis of extrusive and intrusive rocks that make up large igneous belts, as well as their con nections to the concentration of ores, are areas of inquiry that perennially attract the attention of researchers. This interest continues because answers to these questions, on the one hand, may provide a fuller understanding of the nature of magmatic pro cesses and, on the other hand, may favor development of new criteria for prospecting ore deposits. The most acute questions are in the areas of diachronous volca nism and intrusive magmatism.One of prominent examples of geological struc tures of the type mentioned is the Hercynian system of Rudny Altai which was formed during the DevonianEarly Carboniferous evolution of the active margin of the Siberian Craton [1-6] (Fig. 1A). There, as a result of two pulses of the Devonian volcanism, thick vol cano-sedimentary members were formed: they are hosts to numerous deposits and ore nodes of sulfidebase metal formation. During the first pulse (EmsianEarly Fransian), the Melnichno Sosnovsky rhyolite (D 1-2 ) and the Davydov-Kamenevsky basalt-dac ite-rhyolite (D 2-3 ) complexes have been formed: those build up large central-type volcanoes and hypabyssal intrusives [4]. The majority of sulfide-base metal deposits were formed during this pulse [7]. In the second pulse (Late Fransian-Famennian) of vol canism in Rudny Altai, some subaerial extrusive, pyroclastic, and subvolcanic rocks of the Pikhtovsky basalt-dacite-rhyolite (D 3 ) complex were formed: they constitute a chain of volcano-tectonic structures along the western edge of the Rudny Altai block.Furthermore, the Rudny Altai area is permeated with intrusive igneous rocks, the major proportion of which is represented by gabbros, plagiogranite, and granite of the Zmeinogorsky complex (D 3 ) (378 ± 6 and 371 ± 2 Ma, SHRIMP II zircon U-Pb age) [8]. Those plutons have been intruded in the tectonic set ting of the transform margin [9] practically simulta neously with the Pikhtovsky volcanic complex (D 3 ).The most important for the question of the igneous geology of Rudny Altai is the presence or absence of granites older than the Late Devonian, synchronous to suprasubduction volcanism per se and syngenetic with subvolcanic porphyry, which are accompanied by sul fide-base metal mineralization. This question has been debated for many years. In the second half of the twentieth century, V.S. Kuzebny [10] compiled systematic observations of the relation between granites and fossiliferous volcano sedimen tary rocks: he concluded there was an absence of such rocks in the northern part of Rudny Altai. However subsequent researchers noted the presence of plagiog ranite pebbles in basal conglomerates of stratified members (beginning from the Emsian) along with the occurrence of leucocratic plagiogranite xenoliths in the Late Devonian granites. Those observations allowed them to assume the presence of pre-Late Devonian plagiogranites in Rudny Altai, rocks of which have been...

Leading genetic types of base metal deposits of Rudny Altai

“…As seen, the main industrial pyritic deposits of the Rudny Altai were formed in a riftogenic geodynamic setting and, ac cording to metallogenic zoning, are combined into a large Rudny Altai copperpolymetallic belt of regional significance, which is a part of the general geological structure of the Great er Altai [6,7].…”