Geochemical and tectonic setting of mafic dike swarms of the Juruena-Teles Pires mineral province, southwestern Amazonian craton, Brazil

Abstract

The present study provides a comprehensive set of whole-rock geochemical, petrographic, and mineral chemistry data on diabase dike swarms that crosscut the Archean/Paleoproterozoic basement of the Peixoto de Azevedo domain, located in the central-western part of the Juruena-Teles Pires mineral province, in the southwestern portion of the Amazonian Craton. The dike swarms are classified into two groups based on TiO₂ concentration: high-Ti (HTi, >2 wt.%) and low-Ti (LTi, <2 wt.%). In the Peixoto de Azevedo domain, LTi dikes, with an undetermined crystallization age, predominantly exhibit N30-40E strikes. In contrast, in the central-western Juruena-Teles Pires province, the ~1.8 Ga fissure-controlled HTi dikes are systematically aligned along shear zones and fault systems, with strikes varying from E-W to WNW-ESE, predominantly crosscutting Orosirian/Statherian granitic rocks. Mineral assemblages in LTi dikes are dominated by clinopyroxene (augite) and plagioclase, the latter sometimes exhibiting a Ca-rich core (An_63-74) and a Na-enriched rim (An_26-43), with minor Fe-Ti oxides, apatite, and biotite. Conversely, HTi dikes contain labradorite, augite (±olivine), magnetite, and ilmenite, with common accessory minerals such as biotite and apatite. Both groups exhibit low Ni contents, which, in conjunction with the observed CaO-MgO correlations, indicate fractional crystallization likely controlled by plagioclase and clinopyroxene. The HTi and LTi dikes are tholeiitic and classified as continental flood basalts, displaying distinct geochemical features. LTi dikes have Mg# values ranging from 0.32 to 0.58 and are enriched in Ba, K, Rb, Sr, Ce, and Y, with low to moderate MgO, Ni, and Cr contents, and moderate LREE enrichment. In contrast, HTi dikes have relatively low Mg# (31–49) and are slightly more evolved than the LTi diabase dikes. Additionally, they exhibit higher concentrations of TiO₂, P₂O₅, Ba, Rb, Sr, Th, Ce, Y, Zr, as well as both LREE and HREE. The relationship between typical crustal elements in the chemical composition of the studied diabases, such as Ba, Rb, La, Ce, and Nb-Ta, supports the presence of a crustal component in the source of both HTi and LTi dikes. These geochemical characteristics suggest that crustal contamination and fractional crystallization may have influenced their magmatic evolution. The probable occurrence of lithospheric delamination, accompanied by crustal thinning and mantle uplift followed by mantle melting, likely culminated in the generation of intraplate continental tholeiitic magmatism, often marking significant geodynamic events in the southwestern portion of the Amazonian craton.