Evidence of Gondwana early rifting process recorded by Resende-Ilha Grande Dike Swarm, southern Rio de Janeiro, Brazil

• 40Ar/39Ar data for Resende-Ilha Grande Tholeiitic Dike Swarm point to early extensional episode ca. 156-144 Ma.
• The event precedes the onset of Paraná LIP and the Gondwana break-up.
• Three high-TiO2 magmatic suites identified using geochemistry and Nd and Sr isotopic data.
• TDM ages suggest basement contamination and are similar to mafic rocks interlayered with Neoproterozoic basement.
• The swarm represents the precise onshore projection of Pelotas-Santos rift propagator, in the N–S direction.

Continental flood basalts and dike swarm have been related to continental breakup process through geological time. The Resende – Ilha Grande Dike swarm (RIGDS) located in the southeast Brazil, is related the Gondwana breakup and composed of dikes/sills intruded in Precambrian gneiss. The dikes have three distinguish orientations: NNW more inland; NS-NNE in the central segment and NE orientation in the coast line, consistent with Precambrian structural lineaments. The swarm comprises high-TiO2 tholeiitic basalts divided into three suites based on REE and Sr and Nd isotope data. The Resende and Volta Redonda suites present higher initial 87Sr/86Sr ratios between 0.7077 and 0.7065, while Angra dos Reis suite presents values of 0.7066 to 0.7057. Geochemical and isotopic data support the sub-continental lithospheric mantle (SCLM) as the main source for the high-TiO2 basalts. The suites heterogeneities are explained by different compositions of SCLM in accreted Precambrian terranes and/or different degree of partial melting and fractional. 40Ar/39Ar data indicate age interval between ca. 156 to 144 Ma for the swarm, older than the average for Gondwana breakup (ca. 130-120 Ma). The age interval places the RIGDS between the Karoo magmatism (181-178 Ma) and the Paraná-Etendeka magmatism (133–134 Ma) and indicates that extensional process affected the supercontinent prior the break-up.

Age comparison between samples from Resende-Ilha Grande dike swarm and other magmatic events related to the Gondwana breakup. 1) Resende-Ilha Grande Dike swarm (this work): Resende suite (VR-ELS-8 and RE–II–22), Volta Redonda suite (NSA-ELS-05), Angra dos Reis suite (VR-ELS-06, VR-ELS-9 and BAN-ELS-10); 2) Santos Basin (Fodor et al., 1983); 3) Paraná continental flood (Thiede and Vasconcelos, 2010); 4) PGDS – Ponta Grossa dike swarm (Renne et al., 1996); 5) Campos basin (Misuzaki et al., 1988); 6) SMDS – Serra do Mar dike swarm – high TiO2 Rio de Janeiro (Vieira, 2009); 7) FLDS – Florianopolis Dike swarm (Raposo et al., 1998); 8) SMDS – Serra do Mar dike swarm –São Paulo (Regelous, 1993). The error bars represent only values higher than 6 Ma. Map modified from Almeida (1986).Figure optionsDownload as PowerPoint slide