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Lead isotope constraints on the mantle sources involved in the genesis of Mesozoic high-Ti tholeiite dykes (Urubici type) from the São Francisco Craton (Southern Espinhaço, Brazil)

By Leila Marques, Eduardo Rocha-Júnior, Marly Babinski, Karine Carvas, Liliane Petronilho and Angelo De Min

Abstract

The first results of Pb isotope compositions of the \ud high-Ti Mesozoic dykes of the Southern Espinhaço are presented. \ud the results do not show large variations and are significantly more \ud radiogenic than the Pb isotope compositions of the high-Ti tho-\ud leiites from the Paraná Continental Flood Basalts.the data com-\ud bined with published geochemical and Sr-Nd isotope results rule \ud out crustal contamination processes in the genesis of the dykes, \ud requiring magma generation in metasomatized subcontinental li-\ud thospheric mantle with the involvement of HIMU-type and car-\ud bonatite components.The magmas may have been also derived \ud from a mantle source containing ~4 – 5% of pyroxenite and ~1% \ud of carbonatite melts, agreeing with published Os isotope composi-\ud tions of high-Ti rocks from the Paraná Continental Flood Basalts. \ud These metasomatizing agents could be responsible for mantle sour-\ud ce refertilization, as was also proposed in the literature to explain \ud the characteristics of xenoliths of the Goiás Alkaline Province, whi-\ud ch also occurs in the border of the São Francisco Craton. Additio-\ud nally, to evaluate the risks of Pb contamination during sample pre-\ud paration for analysis, several experimental tests were accomplished, \ud which indicate the need of sawed surface removal and a careful \ud washing of small-sized rock fragments before powdering, especially \ud for rocks with [Pb] < 7 μg/g

Topics: Mafic dyke swarms, Paraná Continental Flood Basalts, Large Igneous Provinces, Pb isotope analysis.
Year: 2016
DOI identifier: 10.1590/2317-4889201620150010
OAI identifier: oai:arts.units.it:11368/2848197

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