Isotope-geochronological study of Ingozero massive (the Kola peninsula)

The Ingozero massive composed of Archeaen gneisses and granitoids is situated in the north-eastern part of the Belomorian mobile belt. The Ingozero massive petrochemical and geochemical characteristics are similar to those of tonalite-trondhjemite-granodiorite (TTG) complexes established on other Archean shields. High concentrations of Na, Ca, and low of K characterize the gneisses of the Ingozero massif and the samples points lie on the tonalite and trondhjemite fields on the Ab-An-Or diagram. The high content of light rare earth elements and the absence of Eu anomalies indicate the origin of rocks from enriched sources without the essential role of fractional crystallization. The isotope U-Pb single zircon grains dating of the biotite gneisses yielded the oldest age for the Ingozero gneisses magmatic protolith at 3 149 ± 46 Ma. Model Sm-Nd ages have shown the formation of the gneisses protolith initial melt occurred at 3.1-2.8 Ga. The ages of metamorphic processes were determined by isotope U-Pb dating (ID TIMS): biotite gneisses - 2 697 ± 9 Ma; amphibole-biotite gneisses - 2 725 ± 2 and 2667 ± 7 Ma; and biotite-amphibole gneisses - 2 727 ± 5 Ma. The ages for granitoids, which cut the deformed gneisses are 2 615 ± 8 Ma and 2 549 ± 30 Ma for plagiogranites and pegmatoid veins in gneisses respectively.