Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4724621 | Precambrian Research | 2006 | 19 Pages |
Abstract
The evolution of the basement of southern Madagascar north and south of the Ranotsara shear zone was investigated using (UÂ +Â Th)/Pb electron probe monazite age dating in combination with petrographic constraints. Several monazite grains show a stepwise progression of younger ages towards the rim indicating partial and complete resetting during tectonic, metamorphic and/or fluid events. The oldest ages, ranging from 630-2400Â Ma, occur relatively rare in relic cores. A first, clear age-population is dated at 550-560Â Ma. Most ages fall in two populations at 420-460 and 490-500Â Ma, which in some samples overlap in error. We interprete these ages as dating low-pressure and high-temperature metamorphism. We have also clear evidence for Carboniferous (300-310Â Ma) monazite overgrowth rims, which can not directly be related to macroscopic structures or metamorphic parageneses. In combination with literature data, we propose that the observed monazite age populations are related to Gondwana amalgamation and subsequent rifting events during the break up of Gondwana. Our study confirms that only the electron or ion microprobe yields sufficient spatial resolution to date individual shells of multiple zoned monazites in the polymetamorphic basement of Madagascar.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
A. Berger, E. Gnos, G. Schreurs, A. Fernandez, M. Rakotondrazafy,