Frederico Meira Faleiros

The inventory of geological heritage of the state of São Paulo, Brazil: Methodological basis, results and perspectives

An inventory of geological sites based on solid and clear criteria is a first step for any geoconservation strategy. This paper describes the method used in the geoheritage inventory of the State of São Paulo, Brazil, and presents its main results. This inventory developed by the geoscientific community aimed to identify geosites with scientific value in the whole state, using a systematic approach. All 142 geosites representative of 11 geological frameworks were characterised and quantitatively evaluated according to their scientific value and risk of degradation, in order to establish priorities for their future management. An online database of the inventory is under construction, which will be available to be easily consulted and updated by the geoscientific community. All data were made available to the State Geological Institute as the backbone for the implementation of a future state geoconservation strategy.

Geoquímica e petrogênese de metabasitos do grupo Votuverava (Terreno Apiaí, Cinturão Ribeira Meridional): evidências de uma bacia retroarco calimiana

O Grupo Votuverava (ca. 1500 - 1400 Ma) faz parte do Terreno Apiai, um segmento do Cinturao Ribeira Meridional. E constituido por turbiditos distais com expressivo magmatismo basico representado por lentes concordantes de metabasito. Vinte amostras de metabasito foram investigadas por meio de analises geoquimicas (elementos maiores e tracos). Tres grupos (G1, G2, G3) foram distinguidos com base em assinaturas Ti/V, padroes de elementos terras raras e perfis multielementos normalizados pelos valores de basaltos de dorsais meso-oceânicas (MORB). Todas as amostras apresentam assinaturas toleiticas. O G1 mostra assinatura de arco vulcânico, com razao Ti/V de 15 - 20, enriquecimento em ions litofilos de grande raio ionico (LILE) e empobrecimento em elementos de alta forca de campo (HFSE) relativos ao MORB. O padrao dos elementos tracos indica importante contribuicao do componente de subduccao. O G2 apresenta composicao geral semelhante ao MORB, com Ti/V de 22 - 28. Contudo, o comportamento dos elementos tracos sugere uma pequena contribuicao do componente de subduccao. O G3 apresenta assinatura de basaltos do tipo MORB enriquecido, com razao Ti/V ao redor de 40 e enriquecimento em LILE e HFSE. A variabilidade entre as razoes TiO2/Yb e Nb/Yb sugere que as rochas G1 e G2 foram geradas por fusao rasa (fontes mantelicas tipo MORB normal e enriquecido, respectivamente). As rochas G3 sao enriquecidas em Ti e Nb, sugerindo interacao entre fontes do tipo MORB e pluma. A coexistencia de metabasitos com composicoes de basaltos toleiticos de arcos vulcânicos e basaltos de dorsais meso-oceânicas, os padroes geoquimicos de forma geral e o ambiente de sedimentacao do Grupo Votuverava sao consistentes com um ambiente de bacia retroarco.

Key Dolerite Dyke Swarms of Amazonia: U-Pb Constraints on Supercontinent Cycles and Geodynamic Connections with Global LIP Events Through Time

presented for mafic dykes from selected swarms in two important Amazonian regions: the Carajás Province in the east, and the Rio Apa block in the southwest – areas separated by over 1500km. The new ages reveal four significant episodes of intraplate magmatism (ca. 1880, ca. 1110, 535, and 200 Ma), and provide additional opportunities for assessing supercontinents cycles and correlating associated Large Igneous Province (LIP) events. Recent U-Pb studies in Amazonia have documented two widespread magmatic episodes: the 1795Ma Avanavero and the 1110Ma Rincón del Tigre–Huanchaca LIP events. Both have “barcode” matches with global LIP events in the context of the Nuna and Rodinia reconstructions, respectively. Additionally, a third event, more clearly mantle plume-driven, has an important component preserved in Amazonia, linked with the 200 Ma Central Atlantic Magmatic Province (CAMP). The Carajás Province (part of the Archean core of Amazonia) is bounded to the east by the Araguaia belt which records assembly of Amazonia and West Africa in Gondwana times. Dyke swarms intrude the Carajás country rocks, and subordinately the ca. 1.88 Ga Carajás anorogenic suite. Dyke subswarms mainly strike NW-SE and NE-SW, with the longest dykes (mafic and felsic) belonging to the prominent NW-trending Tucumã swarm. N-S trending dykes are subordinate. A representative NWtrending, basaltic dyke yields a U-Pb baddeleyite age of 1880 ± 2 Ma; a second sample, from a NE-trending, basaltic dyke gives a provisional, slightly older, age of ca. 1885 Ma. These two ages confirm previously published UPb SHRIMP zircon dates from rhyolitic members of the Tucumã bimodal swarm at 1881 ± 3 and 1882 ± 4 Ma (Silva, 2015). They are synchronous with the timing of the Carajás anorogenic suite, and with nearby, undeformed volcanics of the Iriri Group (1874 ± 8 Ma; Santos et al., 2002). All of these magmatic activities could be related to thermal perturbations in the upper mantle, which drove limited crustal extension and contemporaneous intraplate plutonism and volcanism. Potential barcode matches exist with dykes and sills in North China, Kaapvaal and Zimbabwe cratons, and Laurentia, Baltica, Australia and Siberia, suggesting global-scale connections within Nuna supercontinent at ca. 1.8Ga. The Rio Apa block is bounded by the intervening Neoproterozoic Paraguay-Tucavaca belts. It comprises Paleoproterozoic metamorphic basement and granitoid intrusions partly covered by a supracrustal association (1.81 Ga). These rocks are intruded by EWand NWtrending dykes and sills (andesitic basalts of tholeiitic affinity) of the Rio Perdido suite (Lacerda Filho et al., 2016 and references therein). A recent LA-ICPMS U-Pb study of zircon (Faleiros et al., 2015) from a N85°Wtrending subvertical Rio Perdido dyke suggested an igneous crystallization age of 1589±44 Ma, although inheritance of older zircon was clearly present (at ~1800, 2200 and 2600 Ma). We subsequently recovered baddeleyite from this same microgabbronorite dyke sample (4220-FM-R-173), analysis of which has provided a robust conventional ID-TIMS U-Pb age of 1110Ma. Therefore the zircons previously analyzed from this dyke are xenocrystic in origin. The new age has a precise match with the 1110 Ma Rincon del Tigre-Huanchaca LIP event (Teixeira et al., 2013), occurring ca. 500-800 km to the northwest in the SW Amazonian craton, therefore significantly increasing the known regional expanse of this late Mesoproterozoic LIP. From a global perspective, the 1110 Ma LIP event defines mantle plume activity predating Rodinia breakup, and has a rigorous, narrow age match with intraplate mafic magmatism in the Congo, Kalahari and Indian cratons, and the Keweenawan event of central Laurentia. Wilson TEIXEIRA, Mike A. HAMILTON, Vicente A. V. GIRARDI, Frederico M. FALEIROS, 2016. Key Dolerite Dyke Swarms of Amazonia: U-Pb Constraints on Supercontinent Cycles and Geodynamic Connections with Global LIP Events Through Time. Acta Geologica Sinica (English Edition), 90(supp. 1): 84-85.