The eastern border of the Sa˜o Francisco craton is characterized by widespread Mesoproterozoic (1.0 Ga) tholeiitic dykes and minor analogues of Early Cretaceous age (130 Ma). The Mesoproterozoic dykes (Salvador, Olivenc¸a, Espinhac¸o, Diamantina) show large elemental and Sr–Nd isotopic variations that suggest different parental melts related to a small-scale heterogeneous mantle of depleted residua and enriched components (Statistical Upper Mantle Assemblage, SUMA), responsible for plume- and crust-type signatures. The Mesoproterozoic intrusions, compatible with early stages of Rodinia breakup, may represent the initial breakup of the Sa˜o Francisco– Congo junction. Early Cretaceous dykes (Espinhac¸o) reveal normal and reversed polarities, indicating two distinct intrusive periods. These intrusions have elemental and Sr–Nd isotopic compositions similar to those of the coeval (132 Ma) high-TiO2 tholeiites from southern Parana´ Basin (Urubicı´-type, Brazil) and northern Etendeka (Khumib-type, Namibia). The genesis of these tholeiites requires lithospheric mantle components, as represented by K-alkaline (and carbonatitic) rocks from the Asuncion-Sapucai graben (Paraguay), that highlight the intriguing Pb-isotope relationships involving the Urubicı´-Khumib tholeiites. The essential role of the Tristan plume is difficult to determine. The spatial distribution of such uncommon high-TiO2 tholeiites reveals that similar lithospheric components may exist in different cratonic blocks and associated mobile belts.
Genesis and Geodynamic Significance of Mesoproterozoic and Early Cretaceous Tholeiitic Dyke Swarms from the São Francisco Craton (Brazil).
DE MIN, ANGELO;
2007-01-01
Abstract
The eastern border of the Sa˜o Francisco craton is characterized by widespread Mesoproterozoic (1.0 Ga) tholeiitic dykes and minor analogues of Early Cretaceous age (130 Ma). The Mesoproterozoic dykes (Salvador, Olivenc¸a, Espinhac¸o, Diamantina) show large elemental and Sr–Nd isotopic variations that suggest different parental melts related to a small-scale heterogeneous mantle of depleted residua and enriched components (Statistical Upper Mantle Assemblage, SUMA), responsible for plume- and crust-type signatures. The Mesoproterozoic intrusions, compatible with early stages of Rodinia breakup, may represent the initial breakup of the Sa˜o Francisco– Congo junction. Early Cretaceous dykes (Espinhac¸o) reveal normal and reversed polarities, indicating two distinct intrusive periods. These intrusions have elemental and Sr–Nd isotopic compositions similar to those of the coeval (132 Ma) high-TiO2 tholeiites from southern Parana´ Basin (Urubicı´-type, Brazil) and northern Etendeka (Khumib-type, Namibia). The genesis of these tholeiites requires lithospheric mantle components, as represented by K-alkaline (and carbonatitic) rocks from the Asuncion-Sapucai graben (Paraguay), that highlight the intriguing Pb-isotope relationships involving the Urubicı´-Khumib tholeiites. The essential role of the Tristan plume is difficult to determine. The spatial distribution of such uncommon high-TiO2 tholeiites reveals that similar lithospheric components may exist in different cratonic blocks and associated mobile belts.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
