MESOZOIC GRANITES OF THE CHUBACHIN MASSIF, TUKURINGRA COMPLEX, DZHUGDZHUR-STANOVOI FOLDBELT: NEW GEOCHEMICAL, GEOCHRONOLOGICAL, AND ISOTOPIC-GEOCHEMICAL EVIDENCE

Abstract

The Chubachin Massif in the central part of the Dzhugdzhur-Stanovoi foldbelt is dominated by biotite and biotite-muscovite granites and belongs to the Tukuringra Complex, which is traditionally considered to be Early Proterozoic. Newly obtained geochronologic data (U-Pb on zircon) indicate that the age of the massif is 138 ± 4.8 Ma. The most typical geochemical features of the rocks of the Chubachin Massif are as follows: (1) they belong to the moderately and low alkaline petrochemical types of the calc-alkaline series with broad variations in the Na2O/K2O ratios; (2) the rocks are very low in HFSE and most LILE, except Ba and Sr; and (3) they are low in REE and are characterized by fractionated patterns of these elements with a relative enrichment in LREE and strong depletion in HREE at the absence of Eu anomalies. The parental melt of the granitoids was most probably produced by the partial melting of acid-intermediate rocks in an environment saturated with water. This process resulted in amphibole-enriched residue. Sm-Nd isotopic data [TDM(2-st) = 2.5-2.1 Ga, εNd from -18.5 to -14.0] suggest that the parental melt of the Chubachin granites was derived from a mixed source, which consisted of rocks of the Early Proterozoic juvenile and Archean continental crust. The granitoids of the Tukuringra Complex were produced in a collisional environment as a consequence of collision between the Amur microplate and the Siberian craton or the immediate docking of the Barguzin-Vitim superterrane to the Siberian craton along the Zhuin-Dzhudgzhur suture.