Post-collisional alkaline magmatism on the Taquarembo Plateau: A well-preserved Neoproterozoic-Cambrian plutono-volcanic association in southern Brazil

The Taquarembo Plateau plutono-volcanic association (TPPVA), a magmatic ass ociation related to a silica-saturated alkaline series, represents a portio n of the last episode of post-Brasiliano/Pan-African collisional magmatism in southern Brazil. It was preceded by a post-collisional high-K calc-alkal ine and shoshonitic magmatism, which is more pronounced near the collisiona l belt. The TPPVA is a sequence of volcanic, volcaniclastic, and volcanogen ic sedimentary deposits with hypabyssal associated rocks, lying on Paleopro terozoic granulites. Isotope data suggest that this alkaline post-collision al magmatism occurred over the period from 580 to 537 Ma. Two sequences of magmatic liquids, which evolved by mineral fractionation from low-Ti-P and high-Ti-P basaltic magmas, were identified. The former includes mildly alka line silica-saturated basalts, metaluminous monzodioritic intrusions, and r hyolitic lavas, whereas the second includes hawaiites, mugearites, syenitic intrusions, and peralkaline to intermediate lava flows of comenditic affin ity. Trace-element and isotope data suggest that both parental magmas were produced from the same EM1-type mantle sources, representing different melt fractions, which preserve the trace-element signature inherited from metas omatism caused by a previous (similar to 780 to 700 Ma) crustal subduction.