Petrologia dos diques máficos da província Chapada Diamantina-Paramirim, Bahia, Brasil.

Abstract

Dyke swarms and mafic sills occur intrusive in metasediments of the Paraguaçu Group, in the southern portion of Chapada Diamantina (CHD) and in the Archean basement in the Brumado region (BG). This work presents the lithogeochemical and isotopic results in order to analyze the behavior of the elements during the differentiation process and define the characteristics of the mantle source. The behavior of the major, trace and rare earth elements (REE) show similar magmatic evolution for the two swarms. The REE pattern for both sets demonstrates a similar spatial distribution, typical of tholeiitic magmas, which may suggest a single source, although the BG dykes present a more enriched pattern than those of the CHD, characterizing a more differentiated mantle source. Most samples showed high ɛNd values in relation to CHUR. Analyzing the fractionation factor, the mantle character of these rocks became clear. ɛNd values (t=1.5 Ga) show that the CHD dykes are more primitive than those of the BG, also confirmed by the values of Mg# (CHD = 0.56 to 0.66 and BG = 0.25 to 0 .45) and were more intensely affected by the process of crustal contamination. Integrated analysis of the data shows an increase in Mg# values towards the North of the Study Area (CHD), possibly approaching the origin of the thermal source (plume) that gave rise to magmatism in this sector with high rates of mantle melt. The two sets are typical continental tholeiites differentiated from a “primitive” magma, presenting an iron-rich differentiation trend.