Late Carboniferous Rhyolites of the Amur Fragment of the Nora–Sukhotino Terrane: Geochemistry and Geochronology.

This paper presents the first geochemical, isotope-geochemical (Sm–Nd) and geochronological (U–Pb, LA–ICP–MS) data on acid volcanic rocks collected in the Bogdanikha River basin of the Priamursky fragment of the Nora–Sukhotino terrane in the northeastern South Mongolia–Khingan orogenic belt. In terms of the contents of rock-forming components, the studied volcanic rocks correspond to high-silica and high-alumina rhyolites. The elevated contents of alkalis, Ga, Zr, Nb, and Y, lower concentrations of Ba, Sr, Ti, and Eu, and mantle values of εNd(t) = +3.0...+3.6 allow the rhyolites from the Bogdanikha River basin to be classified as A2-type rhyolites. The concordant age of the youngest zircon population from the rhyolite, according to geochronological (U–Pb, LA—ICP–MS) studies, is 301 ± 4 Ma, which corresponds to the Late Carboniferous. Taking the geochemical features of the studied rhyolites and the existing models for the formation of the South Mongolia–Khingan orogenic belt into account, it is most likely that they formed in a collisional setting as a result of slab break-off. [ABSTRACT FROM AUTHOR]