Evolution of sand and silt injection and effusion around the rim and depocenter of Paraná volcanic province

Abstract

The Novo Hamburgo Complex (NHC) occurs widespread in the 1 million km2, Early Cretaceous Paraná volcanic province. Integrated field work with zircon dating and whole rock geochemistry supported the investigation. We used the sensitive high-resolution ion microprobe (SHRIMP II) to determine the U-Pb age of zircon from eight sandstones from pairs of parent Botucatu Formation (1.2 million km2, largest paleoerg in geological history) (n = 3) and injectites, extrudites (n = 5), total = 718 analyses. Samples were collected from south to northeast to northwest of the complex. Integrated age peaks (in Ma) occur at 151 (one grain), 236 (minor), 280–288 (significant), 528-536-544-626-628 (approximate 520–630; highest peak at 544), 1043–1057 (approximate 900–1300), 1734, 1968, 2046–2098, 2691, and 3300 (one grain). U-Pb age distribution barcode is similar for both parent sandstones and injectites, extrudites. No zircon from the Cretaceous Serra Geral Group of basalt and rhyodacite (134 ± 2 Ma) was dated in the sandstones. Differences between parent sandstones and injectites, extrudites originated by elutriation in 1–1700 m-high injection columns. Textural characteristics are bimodal, medium to fine grained in parent beds, and unimodal, fine grained in injectites, extrudites. Chemical differences are increase in Al, K, Na, Ca, Rb, Sr, Ba, ETR, Cu, U, Th in injectites, extrudites compared to parent beds. We conclude that the injected sandstone and contained zircon originated in the Botucatu Formation paleoerg ascending through the volcanic lavas in a sand (estimated 70 vol%) and water (30 vol%) slurry. This is a prime, unique example of paleoerg sand remobilization after aquifer heating and volcanic rock sealing in a huge injection complex.