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Proterozoic mafic dyke swarms of the Sao Francisco Craton (SE-Bahia State, Brazil); petrology and Sr-Nd isotopes

Giuliano Bellieni, Riccardo Petrini, Enzo M. Piccirillo, Giancarlo Cavazzini, Lucia Civetta, Piero Comin-Chiaramonti, Adolpho J. Melfi, Sara Bertolo and Angelo De Min
Proterozoic mafic dyke swarms of the Sao Francisco Craton (SE-Bahia State, Brazil); petrology and Sr-Nd isotopes
European Journal of Mineralogy (April 1991) 3 (2): 429-449

Abstract

Archaean to Early Proterozoic granulites in the SE-Bahia State (Brazil) are cut by abundant late Proterozoic (1.0-1.1 Ga) unmetamorphosed tholeiitic dykes. These dykes belong to the Sao Francisco Craton, which is the westerly extension of the Congo Craton (W-Africa) according to the pre-Atlantic configuration. Most dykes represent moderately evolved magmas (mg-value usually lower than 0.5). Major and trace element data show the existence of two main groups of basalts, characterized by low or high contents of TiO (sub 2) and incompatible elements, respectively (i.e. TiO (sub 2) < 2 % wt. = LTi, and TiO (sub 2) > 3 % wt. = HTi). Major and trace element variations indicate that HTi - and LTi-dykes are related to different parent melts. If we assume a common source and partial fusion greater than 5 %, batch melting models suggest that garnet peridotite is required for the generation of both LTi- and HTi-basalt types (e.g. LTi-basalts = 30 %, and HTi-basalts = 15 %). Sr-Nd isotope data show that the investigated dykes are related to time integrated depleted mantle sources which experienced Rb-Nd depletion (e.g. basalt extraction) possibly before 1.7 Ga. These isotopically depleted mantle sources were later variably enriched in incompatible elements by "metasomatic processes" shortly before and/or during the melting processes responsible for the generation of the basalt dykes. High- and low-Ti basalt dykes could be related to mantle sources more or less enriched, respectively, in incompatible elements, but having similar Sr and Nd isotopic ratios. All the data indicate that the investigated tholeiitic dyke swarms are representative of intraplate continental magmatism, and that the late Proterozoic mobile belt evolution of the Sao Francisco (and Congo) Craton was probably of ensialic type and not related to suture/collision plate margin processes.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 3
Serial Issue: 2
Title: Proterozoic mafic dyke swarms of the Sao Francisco Craton (SE-Bahia State, Brazil); petrology and Sr-Nd isotopes
Affiliation: Univ. Padova, Dip. Mineral. Petrol., Padua, Italy
Pages: 429-449
Published: 199104
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 2 p.
Accession Number: 1994-002310
Categories: Igneous and metamorphic petrologyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 83 anals., 11 tables, geol. sketch map
S18°19'60" - S08°19'60", W46°40'00" - W37°19'60"
S21°00'00" - S09°00'00", W47°00'00" - W37°00'00"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany
Update Code: 199402
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