P-T-t paths, exhumation and cooling rates and Lu-Hf garnet geochronology of hot orogens: a study case on the nova Venécia complex, Araçuaí orogen

Abstract

Orogenic belts characterized by high geothermal gradients at intermediate crustal levels are known as "hot orogens" and are generally associated with geological processes such as fluid/magma transfer, deformation and radioactive decay. The Araçuaí Orogen, located at the northern Mantiqueira Province, Brazil, is an example that exposes rocks from deeper levels of the crust. Near the city of Colatina, Espírito Santo state, different groups of rocks from the Araçuaí Orogen are exposed, including migmatitic paragneisses of the Nova Venécia Complex that are intruded by Ediacaran anatectic rocks and Cambrian gabbro-norite (São Gabriel Norite). The mafic rocks form a diffusive metamorphic aureole within the paragneisses locally, which enables the establishment of a temporal relationship between two distinct metamorphic stages. Considering the different evolutional stages of the Araçuaí Orogen registered in the surrounding outcrops, this work proposes systematic petrographic, geothermobarometric and geochronological studies to understand the geological and metamorphic relationships between the studied rocks, including the definition of P-T-t paths (Pressure-Temperature-time) for this segment of the Nova Venécia Complex and to estimate exhumation and cooling rates for this particular part of the orogen. The exchange research internship aims to enrich the geochronological and thermobarometric studies with garnet Lu-Hf geochronology (to be done at Washington State University - Peter Hooper GeoAnalytical Lab) and the development of pseudosections for specific samples at Western Washington University (Washington, USA) under the supervision of Prof. Sean Mulcahy. These estimates will enrich the discussion related to the evolution of hot orogens using the Nova Venécia Complex and the Araçuaí Orogen as a natural example, as the method can improve the constraints involving possible different garnet generations and textures/reactions. (AU)