Age and metamorphic conditions of the granulites from Capral-Jegessky synclinoria, Anabar shield
- 1 — leading engineer A.P. Karpinsky Russian Geological Research Institute
- 2 — Research Institute of Precambrian Geology and Geochronology RAS
- 3 — Head of Eastern Siberia ores Department A.P. Karpinsky Russian Geological Research Institute
- 4 — Ph.D., Dr.Sci. Chief researcher Institute of Precambrian Geology and Geochronology RAS
- 5 — Junior researcher Institute of Precambrian Geology and Geochronology RAS
Abstract
The paper presents the results of the isotope, geochemical and thermobarometric study of plagio-crystalline schist containing in the Upper Anabar series of the Anabar Shield. Granulite complexes of the paleoplatforms are the most important issue in addressing the fundamental problem of the Earth's crust origin and its composition. The early stages of crust formation which correspond to the deeply metamorphosed rocks of the platform basements, available for study within the shields, are of particular interest. The study of the age and metamorphic conditions of granulites by the case of the Upper Ananbar series allows specifying the stages the Anabar Shield's ancient crust formation. Isotope-geochemical (U-Pb geochronology for zircon and Sm-Nd for garnet-amphibole-WR) and thermoba-rometric (Theriak-Domino) studies of plagio-crystalline schist allowed to identify two Paleoproterozoic metamorphism stages within the territory of the Anabar Shield with an age of about 1997 and 1919 million years. The peak conditions of granulite metamorphism are determined as 775±35 С and 7.5±0.7 kbar, the parameters of the regressive stage are 700 C and 7 kbar. The sequence of the rocks metamorphic transformations can be assumed: high-thermal metamorphism of the granulite facies (T ≤ 810 C) and subsequent sub-isobaric (about 7 kbar) cooling to 700 C with a water activity increase and formation of Grt-Amp paragenesis corresponding to the transition from the granulite to amphibolite facies. Data on the REE and other trace elements distribution in zircon and rock-forming minerals obtained by the ion microprobe analysis contribute significantly to the isotope-geochemical data interpretation.
Funding
The authors are grateful to O.L.Galankina, E.S.Bogomolov (IPGG RAS),S.G.Simakin, E.V.Potapov (IPT RAS) and colleagues of the VSEGEI Institute for analytical studies. The study was carried out with the financial support of the Russian Foundation for Basic Research (grants 17-35-50002, 16-35-60092, 18-35-00229).