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

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)

DE MIN, ANGELO
2016

Abstract

The first results of Pb isotope compositions of the high-Ti Mesozoic dykes of the Southern Espinhaço are presented. the results do not show large variations and are significantly more radiogenic than the Pb isotope compositions of the high-Ti tho- leiites from the Paraná Continental Flood Basalts.the data com- bined with published geochemical and Sr-Nd isotope results rule out crustal contamination processes in the genesis of the dykes, requiring magma generation in metasomatized subcontinental li- thospheric mantle with the involvement of HIMU-type and car- bonatite components.The magmas may have been also derived from a mantle source containing ~4 – 5% of pyroxenite and ~1% of carbonatite melts, agreeing with published Os isotope composi- tions of high-Ti rocks from the Paraná Continental Flood Basalts. These metasomatizing agents could be responsible for mantle sour- ce refertilization, as was also proposed in the literature to explain the characteristics of xenoliths of the Goiás Alkaline Province, whi- ch also occurs in the border of the São Francisco Craton. Additio- nally, to evaluate the risks of Pb contamination during sample pre- paration for analysis, several experimental tests were accomplished, which indicate the need of sawed surface removal and a careful washing of small-sized rock fragments before powdering, especially for rocks with [Pb] < 7 μg/g.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11368/2848197
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