Petrology and geochronology (U[sbnd]Pb) OF the Caapucú suite – Southern Paraguay: POST-TECTONIC magmatism of the Paraguari belt

Abstract

The Caapucú Suite (CS), the focus of this study, includes Precambrian rocks that form the Alto Caapucú Block, located at the northern edge of the Rio de La Plata Craton in southern Paraguay. This is an acidic plutonic to volcanic magmatic suite, hosted in metavolcanic-sedimentary rocks of the Paso Pindó Group, which are in tectonic contact with the Villa Florida Metamorphic Suite of the Alto Caapucú Block. Based on the field and petrographic data of the CS, plutonic and volcanic lithotypes of this suite were identified, characterized and grouped into four petrographic facies: the rapakivi porphyritic syenogranite facies (RPSF), the monzogranite to alkali-feldspar microgranite facies (MAMF), the rhyolite facies (RF) and the ignimbrite facies (IF). These are underformed rocks of monzogranitic to syenogranitic composition with very-fine-to-medium grained crystals and inequigranular-to-porphyritic granophyric textures. The facies show circular-to-ring configurations with a large difference in relief in the area in which hypabyssal facies are partly surrounded by volcanic facies. The lithochemical analysis shows a limited compositional variation within this suite, which may be classified as acidic rocks, according to a silica content ranging from 73.9 to 79.2%. This corresponds to A-type granitoids that formed from metaluminous-to-slightly peraluminous ferrous magmatism in a post-collisional magmatic arc environment. The UPb (LA-ICPMS) geochronological data collected from zircon crystals suggest magma crystallization ages for the RPSF and IF of 563 ± 7.9 Ma and 565 ± 11 Ma, respectively. Based on these data, magmatism of the CS likely originated from Paraguari belt generated by agglutination of the Paranapanema and Rio de La Plata cratons. The CS presumably developed in the post-collisional stage of the Brasiliano/Pan-African Cycle during the formation of Western Gondwana. Considering the lithostratigraphic and structural framework of the CS, in addition to the collection of geochronological ages presented here and those previously available, the tectonic-magmatic correlation between the CS and the post-tectonic igneous events of the Ribeira and/or Dom Feliciano belts of the Mantiqueira Province is suggested.