Evolution of the Gállojávri ultramafic intrusion from U-Pb zircon ages and Rb-Sr, Sm-Nd and Lu-Hf isotope systematics

The Karasjok–Central Lapland Greenstone Belt is one of the largest Palaeoproterozoic greenstone belts in Fennoscandian Shield and includes multiple (ultra)mafic intrusions, some with notable ore reserves, formed during three episodes at 2.44, 2.22 2.05 Ga. This study presents new mineralogical, geochronological isotopic data for Gállojávri ultramafic intrusion, Karasjok Belt, northern Norway. Previous petrogenetic modelling suggests that intrusion was emplaced as a conduit system open influx melt signs polybaric fractionation assimilation. Zircon U-Pb geochronology yields an age 2051 ± 8 Ma, interpreted to reflect magmatic crystallisation. Large variations signature over decimetres metres indicate incomplete magma mixing. In bulk samples, ?Nd(t) ranges from ?15 4. ?Hf(t) ?14 ?1. Bulk 87Sr/86Sr(t) shows apparent range 0.5041 0.7072: anomalously low values general alteration indicates 87Sr/86Sr non-primary, whereas less mobile Sm-Nd/ Lu-Hf systems are represent primary signatures. We ascribe large Nd Hf signatures local melting or dissolution xenoliths variably contaminated into semi-consolidated chamber, consistent model involving variable replenishment crustal interaction. most evolved cannot be accounted by interaction Archaean basement, indicating presence unidentified components depth. many similarities other c. Ga intrusions Central Belt.