Electron microprobe U-Th-Pb monazite dating of the Transamazonian high-grade metamorphic overprint on Archean rocks from Amapa block, southeastern Guiana Shield, Northern Brazil
Résumé
The previous termAmapánext termprevious termBlocknext term, previous termsoutheasternnext termprevious termGuiananext termprevious termShieldnext term, represents an previous termArcheannext termprevious termblocknext term involved in a large Paleoproterozoic belt, with evolution related to the previous termTransamazoniannext term orogenic cycle (2.26 to 1.95 Ga). previous termHighnext term spatial resolution previous termdatingnext term using an previous termelectronnext term-probe microanalyzer (EPMA) was employed to obtain previous termUnext term-previous termThnext term-previous termPbnext term chemical ages in previous termmonazitenext term of seven previous termrocknext term samples of the previous termArcheannext term basement from that tectonic previous termblocknext term, which underwent granulite- and amphibolite-facies metamorphism. previous termPbnext term-previous termPbnext term zircon previous termdatingnext term was also performed on one sample. previous termMonazitenext term and zircon ages demonstrate that the previous termmetamorphicnext term overprinting of the previous termArcheannext term basement occurred during the previous termTransamazoniannext term orogenesis, and two main tectono-thermal events were recorded. The first one is revealed by previous termmonazitenext term ages of 2096 ± 6, 2093 ± 8, 2088 ± 8, 2087 ± 3 and 2086 ± 8 Ma, and by the zircon age of 2091 ± 5 Ma, obtained in granulitic previous termrocksnext term. These concordant ages provided a reliable estimate of the time of the granulite-facies metamorphism in the southwest of the previous termAmapánext termprevious termBlocknext term and, coupled with petro-structural data, suggest that it was contemporaneous to the development of a thrusting system associated to the collisional stage of the previous termTransamazoniannext term orogenesis, at about 2.10-2.08 Ga. The later event, under amphibolite-facies conditions, is recorded by previous termmonazitenext term ages of 2056 ± 7 and 2038 ± 6 Ma, and is consistent with a post-collisional stage, marked by granite emplacement and coeval migmatization of the previous termArcheannext term basement along strike-slip shear zones.