| Title | Constraining the age of the Iporanga Formation with SHRIMP U/Pb zircon; implications for possible Ediacaran glaciation in the Ribeira Belt, SE Brazil |
| Author | Campanha, G.A.C.; Basei, M.S.; Tassinari, C.C.G.; Nutman, A.P.; Faleiros, F.M. |
| Author Affil | Campanha, G.A.C., Universidade de Sao Paulo, Instituto de Geociencias, Sao Paulo, Brazil. Other: Australian National University, Australia |
| Source | Gondwana Research, 13(1), p.117-125, . Publisher: Elsevier on behalf of International Association for Gondwana Research, Amsterdam and Kochi, International. ISSN: 1342-937X |
| Publication Date | Jan. 2008 |
| Notes | In English. 45 refs. GeoRef Acc. No: 282423 |
| Index Terms | radioactive age determination; age determination; radioactive age determination; glacial geology; glaciation; sedimentation; spectra; tectonics; Brazil--Parana; Brazil-- Ribeira Belt; Brazil--Sao Paulo; absolute age; ancient ice ages; Apiai Gabbro; Brasiliano Orogeny; Brazil; dates; depositional environment; Ediacaran; facies; faults; felsic composition; Gaskiers Glaciation; glacial sedimentation; greenschist facies; intrusions; ion probe data; Iporanga Formation; Itaoca Granite; Lajeado Subgroup; lithostratigraphy; mass spectra; metamorphic belts; metamorphic rocks; metasedimentary rocks; Neoproterozoic; nesosilicates; orogeny; orthosilicates; paleoenvironment; Pan-African Orogeny; Parana Brazil; Precambrian; Proterozoic; Ribeira Belt; Ribeira Subgroup; Sao Paulo Brazil; shear zones; SHRIMP data; silicates; South America; supracrustals; thrust faults; U/Pb; upper Precambrian; Vendian; volcanism; zircon; zircon group |
| Abstract | The Ribeira belt in SE Brazil is a Neoproterozoic to Early Palaeozoic orogen, whose architecture and history is not yet fully understood. The depositional age of many of the sedimentary sequences in the Ribeira Belt remains unconstrained, and with debate concerning their depositional environment and tectonic setting. In this paper we present SHRIMP zircon U/Pb age constraints for one such problematic unit in the Ribeira Belt--the Iporanga Formation--and discuss the significance of this age with regards to the timing of Neoproterozoic glacial events in southeast Brazil. Using a felsic volcanic unit immediately under the Iporanga Formation and granite cobbles from breccias in its basal parts a reconnaissance SHRIMP U/Pb zircon maximum depositional age of 580 Ma is assigned for the base of this unit. This age is marginally younger than the 625-605 Ma ages for intrusions into the Lajeado and Ribeira subgroups, with which the Iporanga Formation is in tectonic contact. This indicates that the Lajeado and Ribeira subgroups are not stratigraphically equivalent to the Iporanga Formation, as thought previously by some workers. The maximum depositional age of 580 Ma also places a maximum time constraint on the tectonic juxtaposition of the Iporanga Formation with other supracrustal units, and on the greenschist facies metamorphism and isoclinal folding that affected it. The potential glacial origin for the Iporanga Formation, if correct, would place it in the late Ediacaran--provisionally equivalent to the Gaskiers glaciation. |
| URL | http://hdl.handle.net/10.1016/j.gr.2007.05.010 |
| Publication Type | journal article |
| Record ID | 62002803 |