Prolonged (629–578 Ma) post-collisional syenite–monzonite magmatism on the verge of the post-orogenic period: the Arroio do Silva Pluton, southernmost Brazil

Post-collisional magmatism is reported in the northwestern portion of the Dom Feliciano Belt (DFB), southernmost Brazil. Syenite and monzonite, with subordinate diorite, along either transpressive or transtensive sites of the Passo das Canas Shear Zone, are produced for c. 50 Myr. Early syenite magmatism is emplaced at c. 640 Ma along gently or steeply dipping planes. The following period (from 629 to 578 Ma) features the Arroio do Silva Pluton (ASP) construction through an autophagic system of syenite–monzonite magmas emplaced along a transtensive stepover. Therefore, the system starts with monzonite incorporating zircon grains from the high-grade host rocks. The next syenite pulses (at 620–617 Ma) have no zircon xenocrysts but show autocrysts from the previous ones, and the same happens with the 597 and 578 Ma quartz syenite magmas. The three first ASP magmatic pulses were emplaced under extension-dominated transtension, while quartz syenites record an extensional regime. At c. 600 Ma, the conditions shifted to extensional, accommodating the last quartz syenite pulses. The Passo das Canas Shear Zone is considered a translithospheric structure that has focused transport and emplacement of magmas from the metasomatized mantle regions. The change in the deformation regime at 600 Ma marks the shift from the post-collisional to post-orogenic period.