Sources of Terrigenous Clastic Material of the Pechenga Ore-Bearing Structure from Data of Detrital Zircon Isotopic Analysis (SIMS SHRIMP-Ⅱ, LA-ICPMS)

摘要

The research results were received from studying the Pechenga ore-bearing Paleoproterozoic structure, which is located on the northwestern part of the Kola region. The U-Th-Pb zircon age was determined by Secondary Ion Mass Spectrometry (SIMS) on the Sensitive High-Resolution Ion microprobe (SHRIMP-II) spectrometer and Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICPMS) on the ThermoQuest Finnigan MAT Neptune instrument. Basalt conglomerates of the Televi Formation, red gritstones of the Luchlompolo Formation, and high-siliceous turbidites from the middle part of the Matert Formation were tested. On the U-Pb concordia diagram, the part of analytical points for zircon from conglomerates are approximated by the discordia with a top intercept at 2792 +/- 7 Ma. All zircon grains from gritstone are located on the concordia. Most of the values of their ages lie within 2700-2820 Ma, and the lesser part of the age values lies within 2840-3000 Ma. Single grains have an age from 3037 +/- 4 Ma to 3698 +/- 8 Ma. The concordant value of the Pb-207/Pb-206 age, which is 2640 +/- 16 Ma, was established for turbidite zircon. Rocks of the basement at the northern rim of the Pechenga structure: gneisses of the Kirkenes, Varanger, and Svanvik complexes (2715, 2803, and 2825 Ma) and high-aluminous gneisses (2798-2830 Ma) were sources of zircon for conglomerates and gritstones. Granitoids from the southern flank of the structure were sources of zircon for turbidites. The predominant role of the zircon group with an age of 2.7 Ga proves the global increment of the continental crust during this period. The ancient age of zircon (3.0-3.7 Ga) of red-colored gritstones is related to deeper erosion of the basement and exposure of the Eoarchaean and Mezoarchaean rocks at the northern rim during the period of the first global "Oxygen revolution" (2.4-2.3 Ga).