DETRITAL ZIRCON PROVENANCE STUDIES AT CACHOEIRA AND IGUAPE METASEDIMENTARY SEQUENCES FROM CURITIBA AND COSTEIRO TERRANES – SOUTHERN RIBEIRA BELT (SÃO PAULO STATE)

In the southeast region of the State of São Paulo, a distinct set of tectonic domains belonging to the Neoproterozoic Southern Ribeira Belt are delimited by important shear zones. Among these blocks, the Curitiba Terrane (Registro and Itatins Complexes), and the Costeiro Terrane (Paranaguá/Iguape Domains), are separated by the Serrinha Shear Zone. These terranes respectively comprise the Cachoeira and Iguape Metasedimentary Sequences. These units’ maximum sedimentation ages and provenance were unknown and not yet constrained, even though they could be significant to understanding terrane accretion at the Southern Ribeira Belt. To fulfill the objectives of contributing new isotopic and petrological data about both sequences, detrital zircon U-Pb analyses were performed by LA-ICP-MS on two samples of each sequence, and petrographic analyses were carried on many samples from the studied terranes. The Cachoeira Sequence (K-40 and K-56 dated samples) are represented by garnet-biotite paragneisses, garnet-biotite-sillimanite paragneisses, orthoquartzites and garnet-biotite schists with a metamorphic peak between amphibolite and granulite facies, on the Second Sillimanite Zone. U-Pb analysis on sample K-40 revealed maximum deposition ages at approximately 750 Ma and metamorphism age at 597 Ma. On sample K-56 the maximum deposition age obtained was approximately 740 Ma and the metamorphism age between 600 and 620 Ma. The provenance age distribution ranges between Neoproterozoic and Paleoproterozoic sources. Iguape Sequence (K-152 and K-162 dated samples) are represented by low-to-medium grade metamorphism biotite-sericite fine schists, meta-rhythmites, metamarls, and quartzites, at greenschist facies, on the Biotite Zone. U-Pb analysis on sample K-152 revealed maximum deposition ages from 600 to 610 Ma and metamorphism age at 575 Ma. On sample K-162 the maximum deposition age obtained was of approximately 603 Ma. The provenance age distribution ranges between Neoproterozoic and Mesoarchean. Hf isotopic analysis were also carried within the samples, and εHf preliminary results indicate Cachoeira Sequence’s Neoproterozoic zircons crystallized mainly from crustal sources but older zircons mainly from mantle sources. In contrast, Iguape Sequence detrital zircons show greater variability, originating from different sources, although there is a tendency of mantle origin for the Mesoproterozoic zircons. From the detrital zircon spectra applying discriminant diagrams on tectonic environments, there is a suggestion that the Cachoeira sequence has been deposited in a convergent tectonic environment as a backarc basin and the Iguape Sequence originated from a collisional tectonic environment as a foreland basin. New detrital zircon samples from both sequences are being prepared for LA-ICP-MS U-Pb dating and Hf data is being refined. In addition, fluid inclusion microthermometry is being carried out to better constrain metamorphism conditions.