Home – Home – Jornals – Russian Geology and Geophysics 2006 number 1

A specific complex of metaultrabasites and metabasites has been first mapped and comprehensively studied in the central part of the Aldan-Stanovoi Shield. The complex rocks break through granulites (Kurumkan, Nimnyr, and Fedorov Formations) of the Nimnyr terrane of the Paleoproterozoic collision belt. The age of granulite metamorphism is estimated at 2.0-1.9 Ga, and the age of syncollisional granites, at 1907-1920 Ma. The structure of the southern part of the terrane was determined from successive changes of two types of deformational parageneses of collisional genesis, early domal and late slip. It has been established that metabasite and metaultrabasite bodies intruding into syncollisional granites were deformed by asymmetric folds with steep bends formed during slip motions. The metamorphism grade of metabasites and metaultrabasites corresponds to granulite facies. ⁴⁰Ar/³⁹Ar dating of high-temperature amphiboles from two metabasite samples yielded 1903 ± 16 and 1908 ± 15 Ma. In chemical composition the complex rocks correspond to normal rocks of tholeiitic series. The REE pattern (strong enrichment with LREE, La/Yb = 2-9.5), REE ratios, and LILE and HFSE enrichment of these rocks due to the primitive mantle show their similarity to rocks of plume magmatism. Great variations in contents of HREE (3 to 20 times higher relative to chondrite) seem to be due to the melting of compositionally different mantle rock materials with the participation of asthenospheric or lower-crustal matter. Models for the lithosphere delamination and slab detachment are proposed for the explanation of plume magmatism during the collision of Precambrian terranes.