Petrology and geochemistry of the ~2.9 Ga Itilliarsuk banded iron formation and associated supracrustal rocks, West Greenland:source characteristics and depositional environment

• Published in: Precambrian Research
• Main Authors: Haugaard, Rasmus, Frei, Robert, Stendal, Henrik, Konhauser, Kurt
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Greenland
• Online Access: https://curis.ku.dk/portal/da/publications/petrology-and-geochemistry-of-the-29-ga-itilliarsuk-banded-iron-formation-and-associated-supracrustal-rocks-west-greenland(4b7a8380-fbf6-4d0b-bea5-9a41140011a0).html; https://doi.org/10.1016/j.precamres.2012.04.013

Here we present new field, petrographic and geochemical data from the ∼2.9 Ga Itilliarsuk banded iron formation (BIF) and associated lithologies within the Itilliarsuk supracrustal belt, south-eastern Nussuuaq, West Greenland. The supracrustals represent a volcanic–sedimentary sequence, which rests unconformably on a basement of tonalite–trondhjemite–granodiorite (TTG) lithologies. Felsic metagreywackes, meta-semipelites and thinly bedded ferruginous shales were identified intercalated with the Itilliarsuk BIF. Other associated rocks include metapelites, acidic metavolcanics and metagabbroic sills. The supracrustals have experienced amphibolite-facies metamorphism, which has resulted in complete resetting of the U–Pb system with an apparent age of 1895 ± 48 Ma. This tectono-metamorphic event corresponds well with the Paleoproterozoic Rinkian orogeny known from this region. The Itilliarsuk-(oxide-facies) BIF has been divided into two segments on the basis of major and trace elements chemistry: a shaley-BIF with a strong clastic component and a more chemically pure BIF. The shaley-BIF contains high terrigenous influx as reflected by elevated Al2O3 (up to 12 wt.%), TiO2, high field strength elements (HFSE) and transition metals. The chemically pure BIF is characterised by alternating high iron (∼68 wt.%) and high silica (∼64 wt.%) bands with low total rare earths and yttrium (REY), Al2O3, TiO2 and HFSE contents, suggesting a low detrital component. The least altered bands of the BIF record diagnostic Archaean seawater features with Post-Archaean Average Shale (PAAS)-normalised positive La- and Eu-anomalies, enrichment in heavy rare earth elements (HREE) relative to light rare earth elements (LREE) [(Pr/Yb)PAAS < 1], and absence of Ce-anomalies which suggests deposition from an anoxic water column. Sm–Nd isotopes of the chemically pure silica-rich bands record TDM model ages of 3.23–2.85 Ga and initial ɛNd (ɛNd(i)) values in the range of +0.43 to +4.05, average of +1.35. In contrast, the chemically pure Fe-rich ...