Seminário: Genesis and evolution of the Neoproterozoic Galiléia batholith, Araçuaí Orogen, SE Brazil

Data: 
21/11/2019 - 16:30
Local: 
Auditório P217 do IAG (Rua do Matão, 1226, Cidade Universitária)

O seminário do Departamento de Geofísica será apresentado pelo Dr. Francesco Narduzzi (IAG/USP).

 

Resumo:

The Araçuaí orogen (SE Brazil) formed during the assembling of West Gondwana and is one of the largest (350,000 km2) and long-lived (ca. 630 – 480 Ma) granitic province in the world. The central part of its crystalline core is mostly represented by the weakly deformed, medium- to high-K calc-alkaline metaluminous Galiléia batholith (15.000 km2) characterized by the widespread occurrence of grossular-rich garnet (Grs25-43) and epidote (Ps9–23) both indicating crystallization at pressures above 0.6 GPa (≥15 km depth). Furthermore, from nine samples, zircon crystals have been dated through U-Pb method showing that for each sample, the age variability of magmatic zircons reach up to 50 Ma, spanning the entire lifetime of the batholith (ca. 630 – 580 Ma). However high-precision CA-ID-TIMS U-Pb dates on eleven zircon grains gave a well-defined weighted mean age at 581.39 ± 0.26  Ma, interpreted as the age of final batholith assembling. Zircons older than 590 Ma are from centres showing inherited magmatic textures thus representing grains repeatedly recycled from older magma batches. εHf(t) from all magmatic zircons span from -6.0 to -15 suggesting either an isotopically homogenous source through time or a process where each new magma pulse was capable of re-melting the previous one until final crystallization and cooling at ca. 581 Ma. Overall, these data indicate that the Galiléia batholith assembled in the mid- to lower crust consistent with models indicating that the Araçuaí orogen is a hot orogen with limited pre-collisional subduction.