UNRAVELING SW-GONDWANA NEOPROTEROZOIC TO EO-PALEOZOIC TECTONICS WITH PRECISE GEOCHRONOLOGY – A BRAZILIAN CASE-STUDY

More than a decade ago, the amalgamation of SW-Gondwana was considered by several authors as one major tectonic event: the Brasiliano Cycle (for South America), or the Pan-African Cycle (for Africa). Detailed mapping and precise geochronology brought another perspective, unraveling numerous tectonic events, related to rifting, intraoceanic subduction, Andean-type subduction, accretion and collision processes. These events are registered in distinct terranes that were previously related or not. One case-study is the Cabo Frio Terrane, located in the southeastern Brazilian margin, attached to the Ribeira Belt. It´s constituted by a Paleoproterozoic orthogneissic basement interleaved tectonically with Neoproterozoic metasedimentary and metavolcanic rocks from an ancient basin, the Buzios-Palmital Basin. These Precambrian units collided during Mid-Cambrian with the Ribeira belt terranes, a collision event defined as the Búzios Orogeny. U-Pb dating (ID-TIMS) in zircons from leucosome within all units gave a time interval of 525 to 515 Ma for the metamorphic peak, coeval with main D1-D2 deformational phases related to thrust tectonics. Monazite, sphene and rutile U-Pb data provided a cooling curve for this terrane, considered now the record of the youngest Brasiliano tectono-metamorphic pulse. Furthermore Sm-Nd data together with U-Pb SHRIMP data confirmed the existence of a Neoproterozoic ocean floor, which partially subducted prior to collision. This Cambrian collision event is coeval with other well documented orogenies in SW-Gondwana, dated in Africa (Damara and Mocambique belts), in South America (Cuchilla Dionisio Terrane) and other parts of Gondwana (Antarctica and Australia). A late-kinematic map is coherent with the final adjustments of Gondwanan terranes and closure of the last Neoproterozoic oceans. In conclusion a single Wilson´s Cycle is not the key answer for Brasiliano-Pan-African complexity, but rather a multi-phase terrane puzzle which might be better constrained with geochronology of structurally controlled elements.