Lu-Hf isotope composition of zircon as an indicator of the sources for Paleoproterozoic collisional granites (Sharyzhalgai uplift, Siberian craton)

Abstract

We present geochemical characteristics of rocks and results of local dating and Lu-Hf isotopic analysis of zircons from two plutons of Paleoproterozoic collisional granitoids in the northwest of the Sharyzhalgai uplift. The rocks of the Alar pluton in the Bulun terrane correspond in major- and trace-element composition to I-type potassic granites. The Alar granites formed at ~780 °C and <5-8 kbar through melting of predominantly graywacke (volcanosedimentary) source rocks with the contribution of melt from plagiogneisses of tonalite-trondhjemite complex. The age and Lu-Hf isotopic similarity between inherited zircon core (3.3-3.0 and 2.85-2.6 Ga) in these granites and zircons from the Paleo- and Mesoarchean rocks of the Bulun terrane suggests that the latter are the most likely crustal sources of the granites. The more radiogenic isotope composition of the Paleoproterozoic (1.85 Ga) magmatic zircons from the granites as compared with the Archean crustal rocks of the Bulun terrane testifies to the contribution of juvenile material to the granite formation. Highly ferroan granodiorites and granites of the Shumikha pluton in the Onot terrane are enriched in HFSE and correspond to A-type granites. They probably derived by the melting of crustal sources of intermediate-felsic (tonalitic) and mafic composition at >860 °C. The Hf isotope composition of magmatic (1.86 Ga) and inherited (ca. 2.5 Ga) zircons indicates that the granites formed from ancient crustal source (model Hf age is >3.0 Ga) with the contribution of Neoarchean juvenile, probably mafic material.