The monazite record of (ultra)high-temperature metamorphism in southern Madagascar: Gondwana terrane correlations and structural trapping of hot middle crust

Ancient orogens eroded to midcrustal levels provide insight into strain accommodation, metamorphism and melting in Himalaya-type continent–continent collisions. This study focuses on the Neoproterozoic–Cambrian Eastern Africa–Kuunga orogen exposed in Madagascar, where uncertainty about the terrane correlations, and therefore structural framework, of the orogen persists. We present a comprehensive dataset of monazite petrochronology and thermobarometry across the southern Madagascar basement to quantify the regional and temporal variability of metamorphism. We argue that the ultrahigh-temperature Anosyen domain and associated Androyen domain have a shared geological history, recording two successive tectonic events at 630–600 and 580–500 Ma. Other Madagascar domains record primarily the former (Vohibory domain to the west) or latter (all other domains to the NE) event. From this inference, we discuss terrane correlations with Africa and India, then present a structural framework for the orogen in which the Anosyen–Androyen domain was structurally confined in a central, lithosphere-scale transpressional shear system between divergent, diachronous thrust belts. By limiting exhumation, extrusion and collapse, the structural trapping of the Androyen–Anosyen domain facilitated longer-lasting, higher- T metamorphism than associated rocks in the adjacent nappe systems. Such structural trapping may be an important control on high- T metamorphism in the cores of Himalaya-type orogens in general.