Exploring the formation of Tangará sill: A single-pulse intrusion feeding CAMP lava flows in Parecis Basin, Brazil

Abstract

The Central Atlantic Magmatic Province (CAMP) stands out as a distinctive large igneous province on the Earth. Due to the extensive outcrop area of CAMP and its complex geological setting, the links between the extrusive and intrusive units are not fully understood. In the intracratonic Parecis Basin located in Central Brazil, the CAMP rocks are represented by mafic lava flows at its south (Tapirapuã Formation) and western edges (Anari Formation). Despite the availability of substantial geophysical, petrological and geochronological data, the understanding of CAMP feeder system in this region remains unclear. In this study, our focus is on investigating the Tangará sill, a dolerite intruded into Triassic sedimentary rocks in the South region of the Parecis Basin. Our aim is to contribute to a better understanding of the plumbing system in this area by investigating the Tangará sill and its potential links to the lava flows at the surface. The sill is identified as a tabular feature in seismic data, with a discernible base and top that extend for about 100 km from northeast to southwest. The Tangará sill was drilled by the 6-ANP-MT-02 stratigraphic well, revealing a continuous igneous intrusion with a thickness of 180 m (at depths ranging from 470 to 650 m). The dolerite intrusion is composed by plagioclase, clinopyroxene, opaque minerals and mesostasis (quartz + feldspar intergrowth and apatite). It can be divided into five segments: the upper and basal margins consist of fine-grained dolerite, the central portion comprises coarse-grained gabbro, which includes pegmatoid zones. The central portion is separated from the margins by two sections of medium-grained dolerite. The dolerite is tholeiitic, with low TiO2 content (<2 wt% TiO2) and low La/Yb ratio (average of 4.4). Geochemical and petrographic data indicate that the intrusion was formed by a single magma pulse and underwent differentiation through plagioclase and pyroxene dominated crystal fractionation. Two samples dated by 40Ar/39Ar geochronology using laser step-heating technique, yield plateau ages ranging from 204.0 ± 0.4 Ma to 202.0 ± 0.5 Ma. Sr-Nd-Pb isotopic data suggest a lithospheric mantle source with possible crustal contamination. Our findings suggest an emplacement model in which a thick single-pulse magma intruded the Triassic red beds. Along a NE-SW section, the sill is truncated by faults along the southern border of the basin, near the mapped lava flows of the Tapirapuã Formation. This suggests that the magma propagated from the northeast to the southwest along the sedimentary strata and fed the Tapirapuã volcanism. This example highlights a single-pulse sill feeding lava flows of the Central Atlantic Magmatic Province (CAMP).