SETTING OF THE ~2560 MA QÔRQUT GRANITE COMPLEX IN THE ARCHEAN CRUSTAL EVOLUTION OF SOUTHERN WEST GREENLAND

摘要: The Archean gneiss complex of West Greenland contains packages unrelated rocks created during relatively short periods time in arc-like magmatic environments, and having similarities to formed at Phanerozoic convergent plate boundaries. terranes new crust were amalgamated by collisional orogeny then partitioned post-assembly tectonic processes. Having summarized the origin this paper focuses on data concerning latest Neoarchean post terrane-assembly "intra-continental" evolution region. Following youngest documented high pressure metamorphism a clockwise P-T-t loop 2650 Ma, attributed thickening crust, there is 150 million year record intermittent production crustally-derived granite, shearing folding under amphibolite facies conditions. This exemplified SSW-NNE orientated Qorqut Granite Complex (QGC) which forms myriad closely spaced coeval sheets NE Nuuk town. SHRIMP U-Pb zircon dating homogeneous gray granite sheet gives age 2561±11 with 3800 3600 3070 2970 Ma xenocrysts. >40 km long Fjringehavn straight belt, lower amphibolite-facies vertical shear zone, runs from QGC's SE margin strongly deformed 2565±8 but cut undeformed dated 2555±12 Ma. >60 Ivisaartoq fault consisting lowermost mylonite northwestern end main mass granite. It post-2630 because granites that are truncated it. Near northeastern extent, 2559±3 granitic lithons folded 2521±72 sheets. At deep structural level northern QGC, neosomes give ages 2567±9 2563±5 Therefore, 2560 within error for non-deformed bodies shows QGC not largely post-kinematic intrusion as previously thought, was zones an important strike slip component, late development regional non-cylindrical upright folds. body appears be essentially only it emplaced node dilation heterogeneous predominantly deformation. Melting may have been triggered meteoric water percolating down dilational fractures, causing metasomatism. these altered gave rise low 18O signature igneous zircons. Due hydrous nature melting event, immediately above its migmatitic generation zone. These region partition disrupt earlier-formed mosaic rocks. Such patterns seen more recently, example Holocene Asian intra-continental tectonics along north side Himalayas.