Sources of Pechenga structure terrigenous layers clastic material according to detrital zircon isotopic analysis data (SIMS SHRIMP-II, LA-ICP MS)

The results of Pechenga ore-bearing Paleoproterozoic structure, located on the northern-western part of Kola region, research, are presented in this article. Secondary ions mass-spectrometry (SIMS) was used for U-Th-Pb-zircon age definition, on SRHIMP-II device and mass spectrometry with inductively associated plasm with LA-ICPMS ablation on ThermoQuest Finnigan MAT Neptune device. Televi Formation basalt conglomerates, Luchlompo Formation red colored gravelites and middle part Matert Formation high siliceous turbidites were tested. On U-Pb diagram with Concordia part of analytical points for zircon from conglomerates are approximated by Discordia with the top intersection 2792 ± 7 Ma. All gravelite zircon grains are located on Concordia. The main part of their age values is within interval 2700-2820, the lesser - 2840-3000 Ma (with the maximums 2718, 2779, 2854, 2972). The single grains have the age from 3037 ± 4 up to 3698 ± 8 Ma. Concordant value ²⁰⁷Pb/²⁰⁶Pb age 2640 ± 16 Ma is fixed for turbidite zircon. The sources of zircon for conglomerates and gravelites were the rocks of Northern zone Pechenga structure basement: gneisses of Kirkenes, Varanger and Svanvik Complexes (2715, 2803 and 2825 Ma) and high aluminous gneisses (2798-2830 Ma), for turbidites - Southern slope granitoides. The dominating role of zircon group with 2. 7 billion years proves a global growth of continental crust in this period. Ancient values of zircon age (3.0-3.7 billion years) of red colored gravelites are connected with the deeper erosion of the basement and outcrop of Eoarchaean and Mezoarchaean age rocks on erosive surface in Northern zone within the period of the first global “Oxygen revolution” (2.4-2.3 billion years).