Geochemistry of zircon in granulites of the Daldynskaya series, Anabar Shield
Sergeeva L. Yu., Skublov S. G., Gusev N. l., MeInik A. E.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 6. P. 20-44
Full text is available
Language: Russian
Abstract
The study of zircon geochemistry has been carried out for the main types of granulite-facies rocks in Daldyn series of the Anabar shield; and it has shown that contents of REE and trace elements in zircons depend significantly on the type of zircon’s domain (magmatic core or metamorphic rim). Cores of all zircons of the Archean age have similar characteristics of geochemical features—such as REE spectra with highly differentiated distribution of the summary REE content, presence of the negative Eu- and positive Ce-anomalies, and the Th/U ratio not lesser than 0.5. Cores of zircon of the magmatic origin from garnet-orthopyroxene amphibolites (sample 166) are distinguished by reduced Ce-anomaly (Ce/Ce* ~ 6.15), appearance of the positive Eu-anomaly (Eu/Eu* = 1.01—2.50) and elevated values of the Th/U ratio (~ 0.81). Rims of zircons from both biotite-hypersthene crystalline schist (sample 508) and garnet-orthopyroxene amphibolites (sample 166) have, in general, geochemical features of zircon of the hydrothermal origin (Hoskin, 2005). On the other hand, zircons from these two rocks also have differences in distribution of trace elements and REE. For instance, a distinctive feature of zircons from garnet-orthopyroxene amphibolite (sample 166) is an evident positive Eu-anomaly (Eu/Eu* ~ 3.95) which could indicate for an intensive alteration of this amphibolite by a fluid in non-equilibrium conditions. The most ancient zircon (3012±15 Ma) from biotite-hypersthene crystalline schist (sample 508) has the magmatic origin, and its age seems to be the time of formation of the magmatic protolith of the Daldyn series crystalline schists. Analysis of the internal structure, distribution of trace elements and REE in zircons from two-pyroxene plagiogneiss (sample 169-1) allows to assume its age 2990 Ma. The age of the magmatic protolith of garnet-orthopyroxene amphibolites (sample 166) is determined as 2890 ±26 Ma. The Palaeoproterozoic stage of metamorphism, widely spread in territory of the Daldyn series occurrence, is fixed by rims of zircon with the U-Pb age corresponding to interval from 2050 to 1970 Ma (samples 508 and 166).
Key words: zircon, granulites, Anabar shield, REE, U-Pb age.
