Generation of block-and-ash flows at the onset of silicic volcanism in the Paraná Magmatic Province (Brazil): evidence from photoanalysis of Caxias do Sul breccias - Guimarães, Letícia Freitas; Hornby, Adrian; Kueppers, Ulrich; Alves, Adriana; Janasi, Valdecir de Assis; Dingwell, Donald B. (Bulletin of Volcanology, 2019)