The geochemistry of the Serra do Caramuru Ediacaran magmatism, Northeastern Borborema Province, State of Rio Grande do Norte, Brazil
DOI:
https://doi.org/10.11606/issn.2316-9095.v16i3p117-142Keywords:
Serra do Caramuru magmatism, Rio Piranhas-Seridó Domain, Plutonism, Petrology, Geochemistry.Abstract
The Serra do Caramuru and Tapuio stocks (Serra do Caramuru magmatism), located on the northeasternmost part of Rio Piranhas-Seridó Domain (State of Rio Grande do Norte, NE Brazil), are representatives of the Ediacaran to Cambrian plutonism of the Borborema Province. Whole rock chemical analyses (major and trace elements including rare earth elements) of samples coming mainly from the Serra do Caramuru stock allowed the geochemical characterization of this magmatism. The following facies were identified: dioritic, porphyritic granitic, equigranular I granitic, equigranular II granitic, as well as granitic dykes and sheets. The dioritic facies is leucocratic to melanocratic, rich in biotite and hornblende. The granitic facies are hololeucocratic to leucocratic, and contain biotite and sporadically hornblende. Variations of oxide and trace element concentrations suggest fractionation of zircon, apatite, titanite, clinopyroxene (in diorites), biotite, hornblende, allanite, plagioclase, microcline and garnet (in late dykes). The behavior of Zr, La and Yb indicates that the dioritic magma does not constitute the parental magma for the granitic facies. On the other hand, the granitic facies seem to be cogenetic, displaying similar differentiation trends and Rare Earth Element (REE) spectra [12.3≤(La/Yb)N≤190.8; Eu/Eu*=0.30-0.68]. REE patterns [6.96≤(La/Yb)N≤277.84; Eu/Eu*=0.18-0.58] demonstrate that the granitic dykes and sheets are not cogenetically related to the Serra do Caramuru magmatism. The dioritic facies is metaluminous and shoshonitic, whereas the granitic facies are metaluminous to slightly peraluminous and high-potassium calc-alkaline. Diagrams involving oxides and trace elements corroborate a post-collisional environment. The results allow the correlation of the Serra do Caramuru magmatism with the post-collisional, high-potassium, calc-alkaline granites with some shoshonitic associations of the Rio Piranhas-Seridó Domain.
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