Petrochemistry, geochemistry, and genesis of the Chek-Chikan gabbronorite Massif, southeastern framing of the North Asian craton

The Chek-Chikan Massif is a typical representative of basic magmatism, which is widely spread within the Dzhugdzhur-Stanovoi superterrane. The massif consists of gabbronorites, amphibole gabbros, gabbroanorthosites, and anorthosites. The geochemical similarity of the gabbronorites, amphibole gabbros, and anorthosites suggests their genetic link and allows us to consider them as products of intrachamber differentiation. The main geochemical peculiarity of this rock association is the high degree of the melt fractionation. The rocks of the considered massif are enriched in large ion lithophile elements such as Sr (424-1018 ppm) and Ba (50-754 ppm) and have moderate to low contents of such high-field strength elements as Nb (1-17 ppm), Hf (0.4-1.0 ppm), and Th (0.05-1.14 ppm). According to the model calculations, the initial melt had a basaltic composition and crystallized at a temperature of similar to 1180 A degrees C and pressure up to 4 kbar. The U-Pb zircon age of the massif is 203 +/- 1 Ma. The geochemical peculiarities of the massif and its confinement to the northern framing of the eastern segment of the Mongol-Okhotsk fold belt make it possible to presume that its formation was related to either the activity of the Siberian plume, to one of the stages of closure of the Mongol-Okhotsk paleoocean in the rear part of subduction zone, or to the slab break off.