The Bakhuis ultrahigh-temperature granulite belt: I. Petrological and geochronological evidence for a counterclockwise P-T path at 2.07-2.05 Ga.

摘要: The Bakhuis belt, one of the major granulite-facies domains in Guiana Shield, consists a core banded rocks charnockite suite, metamorphosed and migmatized under conditions. Pelitic gneiss intercalations locally show sapphirine-quartz orthopyroxene-sillimanite-quartz assemblages, with up to 10% Al2O3 orthopyroxene. These assemblages point ultrahigh-temperature (UHT) metamorphism. P-T conditions are difficult deduce, because contain Fe3+ sapphirine sillimanite, do not coeval garnet, but spinel, Feand Fe-Ti oxides instead. for peak UHT metamorphism estimated have been 950 °C 8.5-9 kb. An assemblage impure corundum associated quartz may also formed during Unravelling indicates counterclockwise path from an early cordierite-sillimanite via subsequent metamorphic orthopyroxene-sillimanitequartz. Retrogressive isobaric near cooling occurrence. Single zircon Pb-evaporation whole rock Sm-Nd dating were carried out on granulites. Three zircons garnet-sillimanite-bearing yielded age 2072 ± 4 Ma, fourth grain provided increasing ages 2.10 Ga. enderbitic granulite gave range 2.15-2.09 Zircons garnet-bearing defined 2055 3 while those pegmatite layer ranging between 2085 Ma 2058 Ma. A mylonitic orthopyroxene-bearing granite (a true charnockite) furnished Pb-Pb 2065 2 this is first indication that high-grade was (at least locally) melting production magmatic charnockite. two samples discordant recrystallized basic dyke 2060 2056 respectively. sheared vein 2059 In conclusion, 2072–2055 interpreted as Mountains, older than 2.07 Ga, 2.15 considered reflect inherited component Transamazonian protoliths granulite. TDM model 2.40 2.19 data, together positive slightly 175 GEOLOGIE DE LA FRANCE, N° 2-3-4, 2003 GEOLOGY OF FRANCE AND SURROUNDING AREAS, belt (Suriname): I. petrological geochronological evidence at 2.07-2.05 Ga La ceinture de granulites d’ultra-haute temperature des Monts (Suriname) : mise en d’un chemin anti-horaire 2,07-2,05 Geologie la France, 2003, n° 175-205, 12 fig., 6 tabl. Mots cles Roche metamorphique, Facies granulite, Condition pression temperature, Datation, Pb-Pb, Sm-Nd, Zircon, totale, Paleoproterozoique, Suriname, Bouclier guyanais.