The Betsiaka Group in northern Madagascar: a palaeoproterozoic terrane along the northern margin of the Bemarivo Domain

Abstract

The Betsiaka Group, located on the northern edge of the Bemarivo Domain in northern Madagascar, consists of metamorphic felsic rocks, amphibolite, and impure marbles. These rocks are overlain by the Permo-Triassic sedimentary cover to the NW and are separated by a normal fault from the Neoproterozoic volcanic rocks of the Bemarivo Domain to the SE. This study aims to determine the provenance and geodynamic evolution of the Betsiaka Group. Orthoamphibolites are associated with siliciclastic sedimentary rocks and exhibit geochemical characteristics of back-arc basin basalts. A quartzite from the Betsiaka Group contains detrital zircon with a youngest single grain U–Pb age of 1771 ± 28 Ma, with peaks at 2500 and 1850 Ma. An orthogneiss intruding this group has concordant zircon grains interpreted to date the protolith's crystallization at 841 ± 3.2 Ma. The detrital zircon age pattern corresponds to that of the Aravalli Craton in India, suggesting that the northern Madagascar crustal fragment may have been formed off the coast of NW India between 1770 and 1000 Ma. This fragment could have been connected with other crustal fragments, now part of the SE Arabian plate, showing similar detrital zircon patterns in Neoproterozoic sedimentary rocks and sharing a calc-alkaline magmatism around 840 Ma.