Summary: | The rich Archean geological records in southern West Greenland offer valuable insights into the tectonic evolution of the early Earth. Specifically, the well-preserved metavolcanic and ultramafic rock assemblages in the Nuuk region potentially represent co-genetic lithologies, thereby aiding in clarifying their petrogenetic context as well as intricate geological relationships. This thesis extensively examines three suites of metavolcanic and ultramafic rock assemblages from this region: the Narssaq Ultramafic Body (NUB), Bjørneøen Supracrustal Belt (BSB), and Storø Supracrustal Belt (SSB). They represent rock records from the Eoarchean, Mesoarchean, and Neoarchean, respectively, providing an opportunity to comprehend the complete geological history of the Archean Eon (4.0-2.5 Ga) in SW Greenland. The >3.81 Ga NUB is a small outcrop of ultramafic rocks distributed in the Itsaq Gneiss Complex (IGC). It mainly consists of peridotite and is spatially associated with some tholeiitic amphibolites. The NUB ultramafic rocks were previously interpreted as the oldest preserved mantle peridotites, formed in an Eoarchean subduction setting. However, the geochemical data presented in this thesis suggest that these ultramafic rocks are consistent with a cumulate origin. As demonstrated by thermodynamic modeling, they formed through the fractional crystallization of the NUB amphibolites. Therefore, the NUB ultramafic rocks cannot provide support for the operation of plate tectonics in the early Earth. The BSB contains a series of tholeiitic amphibolites, calc- alkaline andesitic leucoamphibolites, and ultramafic rocks. Zircon dating of the leucoamphibolite yielded an age of 3077 ± 6 Ma, aligning with the previously identified volcanic arc activity at 3070 Ma. In addition, several models based on thermodynamics and partition coefficients indicate that the BSB ultramafic rocks reflect open system cumulate processes at shallow depths, while the andesitic leucoamphibolites are compatible with binary magma mixing processes. ...
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