Ponta do Morro

The Ponta do Morro alkaline complex is located in the state of Mato Grosso of west-central Brazil. It consists of a crescent-shaped, silica-saturated to over-saturated granite-syenite association covering an area of ~7 km2, intruding the metasediments of the Upper Precambrian Cuiabá Group. Granitic lithologies dominate, displaying graphic intergrowths of quartz and mesoperthite, with alkali amphiboles (barroisite to winchite) and subordinate Na-bearing clinopyroxene (aegirine-augite). Syenites are subordinate and exist in both one and two feldspar varieties, with notable minerals including aegirine/aegirine-augite pyroxenes and riebeckite-arfvedsonite amphiboles and accessory fayalite, aenigmatite and astrophyllite. The main body is intruded by 30-40 cm thick trachytic and rhyolitic dykes, concentrated along the eastern border. Geochemical data, including whole rock major and trace element, mineral chemical, and Rb-Sr isotopic can be found in Souza et al. (2005) and Souza (1997).