The Neoarchaean Storø Supracrustal Belt, Nuuk region, southern West Greenland : an arc-related basin with continent-derived sedimentation

摘要: We present new major and trace element data, as well Sm–Nd isotope compositions for Archaean supracrustal rocks a gabbro-anorthosite complex from the island of Storo in Godthabsfjord, southern West Greenland. also provide U–Pb data zircon extracted these rocks. The have experienced amphibolite facies metamorphism, entire sequence forms an east-dipping frontal thrust ramp tectonic contact with Mesoarchaean (‘Nuk’) gneisses to west Eoarchaean (‘Itsaq’) east. These orthogneisses record regional accretion history, established by previous work. study aims at explaining geochemical features Supracrustal Belt (SSB), which comprises metavolcanic metasedimentary that are situated within this collisional zone. SSB has maximum age ca. 2800 Ma, constrained youngest detrital population found unit. minimum is 2707 ± 8 defined previously published Re–Os data. tholeiitic basaltic composition, relatively flat primitive mantle-normalised patterns generally negative Nb-anomalies (Nb/Nb* 0.30–0.90). They plot above mantle array Th/Yb-Nb/Yb space, consistent subduction zone affinity, proposed studies. A thin fault separates (formally here ‘Storo Anorthosite Complex’), 3050 Ma. suggest, contamination crustal source was isotopically similar Complex (SAC). This turn suggests SAC could formed basement younger volcanic or alternatively contaminated melts derived SAC-aged crust sediments. show mixed mafic–felsic component variable degrees maturity. Highly mature metasediments contain several populations regionally well-known magmatic events, thus support significant local provenance. Furthermore, documented unit rocks, thereby shows close proximity subaerially exposed continental (i.e. back-arc environment) not distal arc setting proposed. Finally, suggests, cool lower crust, capable supporting subaerial mountains, existed least locally during Meso- Neoarchaean.