Department of Earth Sciences University of Windsor

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Department of Earth Sciences University of Windsor The 3075 Ma Ivisaartoq Greenstone Belt, SW Greenland: Supra-subduction Zone Mesoarchean Oceanic Crust Ali Polat Department of Earth Sciences University of Windsor

The 3075 Ma Ivisaartoq greenstone belt Nuuk region, SW Greenland and The 3075 Ma Ivisaartoq greenstone belt

Age of the belt Zircons from volcanoclastics yielded an age of 3075 Ma (Friend and Nutman, 2005)

Conclusions The Mesoarchean Ivisaartoq greenstone belt is composed of well-preserved pillow lavas, ultramafic cumulates, peridotites, gabbros, anorthosites, and cherts. Pillow lavas and cumulates are compositional comparable to modern island arc picrites (e.g., Solomon Islands). Initial Nd isotopic compositions (eNd= +2 to +5) are consistent with a long term depleted mantle source.

Conclusions The Ivisaartoq pillow lavas and gabbros contain epidosite metasomatic assemblage, which typically occur in Phanerozoic ophiolites, recording Mesoarchean seafloor hydrothermal alteration. Given the lithological similarities between the Ivisaartoq belt and the crustal section of Phanerozoic ophiolites, we interpret the belt as Mesoarchean supra-subduction zone oceanic crust.

3075 Ma Ivisaartoq greenstone belt

(c) (a) (d) (b) Rock Types Pillow basalts Gabbro Pillow basalts Cumulate

(a) Pyrite-rich cherts (c) Epidosites (b) Peridotites (d) Epidosites

(a) NW SE (c) (b) SE NW Collision tectonics

Volcanic rocks (a) eNd= +2.1 to +3.1 (b) eNd= +4.2 to +5.0 Pillow lavas Subduction derived (a) eNd= +2.1 to +3.1 Ultramafic cumulates Subduction-derived (b) eNd= +4.2 to +5.0

Anorthositic inclusions (b)

Anorthosite inclusions (b)

Interpreted geodynamic setting for the 3.1 Ga Ivisaartoq

Ontong Java-Plateau-Solomon Islands convergent zone (From Mann and Taira, 2004)

Conclusions The Mesoarchean Ivisaartoq greenstone belt is composed of well-preserved pillow lavas, ultramafic cumulates, peridotites, gabbros, anorthosites, and cherts, representing the crustal section of a supra-subduction zone ophiolite. Geological characteristics of the Ivisaartoq belt in particular and other Archean greenstone belts in general are comparable to Phanerozoic (Cordilleran-Altaid-Japan) accretionary complexes, consistent with the operation of plate tectonics.