The dyke swarms of Tandil and Azul are groups of dykes of Proterozoic age located in Buenos Aires Province, Argentina. The dyke swarms consists of two groups: 2000 million year old dykes of calc-alkaline type and 1600 million year old dykes of tholeiitic type.[1]
The tholeiitic dykes are made up of diabase and titanium-rich basalt, in contrast the calc-alkaline dykes are made up of andesite and rhyolite.[2] The dyke swarms intrude the southern part of the Río de la Plata Craton, much the same way the Uruguayan dyke swarms intrude the northeastern part of the craton.[1]
The calc-alkaline dykes intruded in a period of transtensional tectonics during the Transamazonian orogeny, while the tholeiitic dykes intruded during the period of extensional tectonics that succeeded the orogeny.[1]