Tectonic evolution of an Early Cryogenian late-magmatic basin in central Madagascar

Abstract

 Early Cryogenian basin with volcanoclastic contribution in Central Madagascar  Three distinct tectonic models for Late Tonian-Early Cryogenian  Extensional intracontinental magmatic setting related to an outboard subduction  A transform continental setting resolves the tectonic Cryogenian paucity  Continental collision dated with 550 Ma metamorphic rims on zircons ABSTRACT Central and southern Madagascar comprise a number of distinctive Archaean crustal blocks (the Antongil-Masora and Antananarivo domains) overlain by Proterozoic supracrustal sequences, preserved in the East African Orogen. Here, we present U-Pb and Lu-Hf isotopic data for two supracrustal units from detrital and metamorphic zircon grains. The lower sequence is comprised of quartzite and calcsilicate units with a major Palaeoproterozoic detrital zircon source and a minor Archaean contribution with a maximum depositional age of ca. 1780 Ma. This sequence reflects a stable shelf sedimentation within the Antananarivo Domain and is correlated with the Itremo Group. U-Pb and Hf data are equivocal in determining the direct sources for the Archaean and early Palaeoproterozoic detrital zircon grains. However, the abundant ca. 2.3-1.8 Ga detrital grains are correlative with the Congo-Tanzania-Bangweulu Block and as these are close to the inferred age of the Itremo Basin, these are interpreted to be single cycle detritus. This implies that the Congo-Tanzania-Bangweulu craton was close to central Madagascar at ca. 1.8-1.6 Ga and the lower sequence would correspond to an originally contiguous late Palaeoproterozoic to early Mesoproterozoic sedimentary basin across central