Early Archaean Amîtsoq tonalites and granites of the Isukasia area, southern West Greenland: development of the oldest-known sial

摘要: Amphibolite facies early Archaean Amitsoq gneisses envelop and intrude the c. 3,800 Ma Isua supracrustal belt, Isukasia area, southern West Greenland. Most of these are strongly deformed, but in a 75 km2 augen lower deformation, seen to comprise predominantly 3,750–3,700 tonalitic grey that were intruded first by thin bodies mafic dioritic composition, known collectively as Inaluk dykes, then 3,600 white finally sporadic 3,400 pegmatitic gneiss sheets. The could have formed partial melting crust consisting basic rocks. dykes interpreted fractionated melts mantle origin, contaminated crustal material. consist mostly medium grained granite occur lenses anastomosing sheets throughout their host with subordinate inclusions chemistry compatible formation at depth source dominated gneisses. igneous chemistry, including REE abundances, has been modified varying degrees metasomatism assimilation reactions during crystallisation also subsequent tectonometamorphic events. evidence for considerable reworking anatexis sialic Archaean, 150 100 after its formation. show granitic rocks s.s. important earliest further diversity oldest-known sial.