Geology, petrology and U-Pb geochronology of Serra da Rajada Granitic Pluton: implications about ediacaran magmatic evolution in NE portion of the Rio Piranhas-Seridó Domain (NE of Borborema Province)

• Published in: Geologia USP. Série Científica Vol. 15; no. 3-4
• Main Authors: Alan Pereira da Costa, Marcos Antonio Leite do Nascimento, Antônio Carlos Galindo, Alexandre Ranier Dantas
• Format: Journal Article
• Language: English
• Published: Universidade de São Paulo 01.12.2015
• Subjects: Borborema Province; Geochronology; Lithochemical; Petrographic; Serra da Rajada Granitic Pluton
• ISSN: 2316-9095
• DOI: 10.11606/issn.2316-9095.v15i3-4p83-105

The Ediacaran plutonic activity, related to the Brasilian/Pan-African orogeny, is one of the most important geological features in the Borborema Province, formed by batholiths, stocks and dikes. The Serra da Rajada Granitic Pluton (SRGP), located in the central portion of the Rio Piranhas-Seridó Domain, is an example of these bodies. This site is the target of cartographic, petrographic, lithochemical and geochronological studies. Its rocks are described as monzogranites consisting of K-feldspar, plagioclase (oligoclase-An23-24%), quartz and biotite (main mafic), having as accessory minerals opaque, titanite, allanite, apatite and zircon. Chlorite, white mica and carbonate are alteration minerals. Lithochemical data from 15 samples show quite evolved rocks (SiO2 , 69% to 75%), rich in alkalis (Na2 O + K2 O ≥ 8.0%), depleted in MgO (≤ 0.45%), CaO (≤ 1.42%) and TiO2 (≤ 0.36%), and displaying moderate levels of Fe2 O3 t (2.16 to 3.53%). These rocks present a transitional nature between metaluminous and peraluminous (predominance of the latter) and have subalkaline/monzonitic affinity (high-K Calc-alkaline). Harker diagrams represent negative correlations in Fe2 O3 t, MgO and CaO, indicating fractionation of mafic and plagioclase.The REE spectrum show enrichment of light in relation to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in Eu (Eu/ Eu* = 0.70 to 10.13) suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows correlating the SRGP rocks with those described as Equigranular high-K Calc-alkaline Suite. The U-Pb geochronology and Sm-Nd isotope dating indicate that the biotite monzogranite have a crystallization age of 557 ± 13 Ma and TDM model age of 2.36 Ga, respectively, and εNd value of - 20.10 for the crystallization age, allowing to infer a crustal source for the magma generated in the Paleoproterozoic age.