STRUCTURE AND TECTONIC SETTING OF THE CHINGALE IGNEOUS RING COMPLEX, MALAWI FROM AEROMAGNETIC AND SATELLITE GRAVITY DATA: IMPLICATION FOR PRECAMBRIAN TERRANES COLLISION AND CENOZOIC - QUATERNARY RIFTING

This presentation examines the structure and tectonic setting of the possibly late Neoproterozoic - early Cambrian Pan-African (henceforth Pan-African) Chingale Igneous Ring Complex (CIRC) in southern Malawi to document its internal emplacement structure and solicit implications for Precambrian terranes collision and Cenozoic – Quaternary rifting. The CIRC is located along the boundary between the Mesoproterozoic – Neoproterozoic Southern Irumide orogenic belt (portion of which has been recently recognized as the Niassa craton) in the northwest (dominantly amphibolite facies metamorphic terrane) and the Unango complex to the southeast (dominantly granulite facies metamorphic terrane). The CIRC is also dissected by the southeastern border fault of the Malawi rift, which represents a segment of the Cenozoic Western Branch of the East African Rift System. This presentation uses aeromagnetic data enhanced through tilt derivative and three-dimensional (3D) magnetic susceptibility modeling to reveal that the CIRC comprises three 7 km to 12 km wide overlapping circular to elliptical ring structures that are aligned in a NE-SW direction along the boundary between the Southern Irumide orogenic belt and the Unango complex. It also uses Bouguer gravity anomalies of the World Gravity model 2012 (WGM 2012) subjected to upward continuation of 2 km and 12 km to show that the CIRC is located along a relatively steep gravity anomaly gradient coinciding with the boundary between the Southern Irumide orogenic belt and the Unango complex. This presentation proposes that the CIRC mark the location of a Pan-African suture zone resulting from the collision of the Southern Irumide orogenic belt (Niassa craton) and the Unango complex and this is named here the Chingale suture zone. The presence of this suture zone facilitated localization of extensional strain during the onset of the Malawi rift allowing it to change its orientation from NNW-trending in its northern part to NE-trending in its southern part. Because igneous ring complexes are hypabyssal intrusions, the exposure of the CIRC within the southern Malawi rift suggest the lack of rift-related subsidence and that much of the ~300 m to ~500 m high topographic escarpment of the southeastern border fault of the rift was the result of rift flank uplift.