Original paper
The Archean Peraluminous Gouveia Granite, its structure, geochemistry, and phase petrology (Serra do Espinhaço, Minas Gerais, Brazil)
Hoffmann, Christoph
Neues Jahrbuch für Mineralogie - Abhandlungen Band 146 Heft 2 (1983), p. 151 - 169
67 references
published: May 17, 1983
DOI: 10.1127/njma/146/1983/151
ArtNo. ESP154014602002, Price: 29.00 €
Abstract
Granites of 2700 m. y. minimum ages and greenschist grade metasedimentary rocks form the basement of younger Archean sedimentary cover rocks of the Serra do Espinhaço. Structural features of the granites (xenolith- and K-feldspar megacryst orientations) are cut by the greenschist schistosity contrary to the tectonic relationships described from many “greenstone belts”. The granite is of palingenic origin (peraluminous chemistry, Na/K relation, paragenic xenoliths, prevailing of rounded zircons). Primary muscovite and K-feldspar megacrysts allow to bracket the condition of granite solification to 3.5-4 kb/680-660°C. Later metamorphic overprints led to a phyllonitisation of parts of the granites and to a redistribution and reordering of elements, e. g.: highly ordered low temperature feldspars, low paragonite contents of newly formed sericite, low Ti content of biotites. The data presented for this area and for that time do not confirm the view of an unusually thin crust, of unusual chemical compositions of Archean granites nor of an unusually shallow intrusion.
Keywords
Peraluminous granite • two mica granite • granodiorite • petrofabrics • modal analyses • geochemistry • palingenesis • Archean (2700 my) • Minas Gerais (Gouveia granite)