Magmatic and hydrothermal evolution of mafic pegmatites and their host basalts, Paraná Large Igneous Province, Brazil

Gomes, Allan; Vasconcelos, Paulo M.; Ubide, Teresa; Vasconcellos, Eleonora Maria Gouvêa

doi:10.1016/j.lithos.2021.106547

Cited by 2 publications

(1 citation statement)

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“…Possibly due to its expressive volume and depth of emplacement, and consequent slow cooling rates, the CJS preserved important structures of melt segregation in form of subhorizontal lenses and eye-shaped pockets of medium-to coarse-grained mesocratic rocks of gabbroic composition that are injected in the host finegrained diabase, mostly at the upper parts of the sill. Similar segregations have been reported in recent works on thick basaltic flows in the PCFB (Oliveira et al, 2020, Gomes et al, 2022 and fractionated, coarse-grained gabbros and monzogabbros are recognized as more differentiated rocks derived from diabase in intrusive bodies occurring near the CJS (Limeira Sill; Oliveira and Dantas, 2008;Farias, 2012, Lino et al, 2018, Lino and Vlach, 2021. In this scenario, the CJS offers an excellent opportunity to study the mechanisms of melt segregation in large basaltic bodies and their geochemical and morphologic relationships with regional analogous PCFB occurrences.…”

Section: -Introduction and Justificationsupporting

confidence: 82%

The Campinas Jaguariúna Sill, NE Paraná Continental Flood Basalt Province, Brazil: insights on the mechanisms of emplacement and differentiation from geochemical and magnetic data

Vasconcelos¹

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The Paraná Continental Flood Basalt Province (PCFB), one of the largest magmatic provinces in Planet Earth, is composed of lava flows, dike swarms and sills that occupy thousands of kilometers across central-eastern South America. The Campinas-Jaguariúna Sill (CJS) is a large (<50 m thick and >100 km 2 ) diabase intrusion showing frequent medium to coarse-grained gabbroic segregations and was emplaced at the interface between the Precambrian basement and sedimentary rocks in the northeastern Paraná Basin. This paper applies aeromagnetic and geochemical modeling to help understand the emplacement mechanisms and petrological evolution of the CJS. Magnetic field filtering techniques demonstrates that the CJS continues for tens of kilometer in the subsurface; analogous features are shown to be associated with other neighbor diabase occurrences, creating lobe-shaped structures that seem to freeze their original geometry and are not fully exposed by the current erosion levels. Petrological modeling indicates that the parental magma of the CJS was emplaced at ~1 kbar, 1000 ppm H 2O and oxygen fugacity near FMQ-1. The gabbroic segregations, exposed as cm-to dm-sized sheets and eyeshaped lenses, are more evolved than the host diabase and can be shown by geochemical modeling to correspond to residual melts formed by crystal fractionation in a closed-system. The parent magma of the CJS is akin to the more primitive Paranapanema magma-type of the PCFB and we tested the possibility that sills intruding upper sedimentary layers may be part of a single sill complex. For this purpose we used geochemical data from the well-studied Limeira Sill, which is akin to the more evolved Pitanga magma-type. Our modeling shows that under crystal fractionation in the representative system condition a CJS starting compositions cannot generate the Limeira rocks.

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