Granitoid magmatism of the Chokhchuro-Chekurdakh zone (north of the Verkhoyansk-Kolyma orogen)

This article presents findings from research conducted on the Mesozoic intrusive magmatism within the ChokhchuroChekurdakh zone (CCZ). This zone extends in a submeridional direction across the Primorskaya (Yano-Indigirka) lowland, from the Bakyn massif of the Northern batholith belt in the south to Cape Svyatoy Nos on the Laptev Sea in the north. All granitoid massifs of this series intrude upon the folded strata of the Late Jurassic and Early Cretaceous periods. Their location is controlled by a regional deep fault zone, indicating that the massifs formed during the postcollision stage of the tectonic stretching process. Available data suggest a close timeframe for their formation, estimated at 105–109 million years ago, as determined by the 39 Ar– 40 Ar dating method. Petrography, mineralogy and petro-geochemical features of rocks, forming the massifs of the zone and their associated dikes are examined. The P–T parameters of the generation for parent melts and the crystallization of granitoids are calculated. It has been determined that the granitoids of the massifs of the northern part of the zone belong to I type granitoids, which formed in a suprasubduction environment. In contrast, the massifs of the southern part of the zone and the postgranitic dikes of rhyolite-porphyry are defined as A-type granites, formed under the conditions of the continental margin (granites of massifs) and close to the continental rift-related one (dikes of rhyolite-porphyry). The temperatures and pressures during magma generation are close for all massifs in the zone, indicating a change in the composition of magma-forming substrates along the zone from north to south. Geochemical criteria correspond to the crustal origin of the granitoids, whereas the high temperatures of magma generation (1000–1200 °C) and the beginning of crystallization (900– 1150 °C) require the inflow of juvenile heat to begin melting crustal substrates.