Sr-Nd constraints and trace-elements geochemistry of selected Paleo and Mesoproterozoic mafic dikes and related intrusions from the South American Platform: Insights into their mantle sources and geodynamic implications

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• 作者：V.A.V. Girardi^a ; ^{girardi@usp.br} ; W. Teixeira^a ; M. Mazzucchelli^b ; P.C. Corrê ; a da Costa^c
• 关键词：Mafic dikes ; South American platform ; Amazonian craton ; Sã ; o Francisco craton ; Mantle composition ; Geochemistry
• 刊名：Journal of South American Earth Sciences
• 出版年：2013
• 出版时间：January, 2013
• 年：2013
• 卷：41
• 期：Complete
• 页码：65-82
• 全文大小：565 K

文摘

The study of selected mafic intrusions from cratonic areas of the South American Platform shows considerable differences among their mantle sources and geodynamic features, particularly regarding the dikes from the SW Amazonian and S?o Francisco Cratons. The tholeiites from the SW Amazonian Craton, which belong to the Serra da Provid¨ºncia Intrusive Suite (1.55?Ga), the Nova Lacerda swarm (1.44?Ga), the Colorado Complex (1.35?Ga), and the Nova Brasilandia Group (1.10?Ga), originated from a mantle source composed mainly of a N-MORB end-member, with a variable addition of slab fluids (up to 30 % , according to the adopted model) from oceanic lithosphere due to episodic subductions during the Mesoproterozoic. Mafic intrusions from Nova Lacerda swarm and Colorado Complex are related to arc settings formed during the 1.47-1.35?Ga closure of the oceanic domain separating the Amazonian Craton and the Paragu¨¢ Terrane, whereas the tholeiites from the Serra da Provid¨ºncia Intrusive Suite and the Nova Brasilandia Group are considered intracratonic. The dike swarms of the S?o Francisco Craton are associated with intra-plate events. The inferred composition of the mantle source of the Lavras swarm (1.9?Ga) has a predominant E-MORB signature, and a modest contribution of up to 10 % of an OIB component. The mantle composition underwent considerable changes during the Proterozoic, as indicated by the sources of the younger dikes, represented by the Diamantina (0.93?Ga) and the Salvador-Oliven?a swarms (0.92?Ga), to which considerable amount of slab derived fluids, probably from recycled crustal material, and OIB component were added. Changes in mantle composition and dikes intrusions could be related to the initial disruption of the Rodinia Supercontinent. The Florida (1.79?Ga) and Tandil (2.0?Ga) dikes are associated with extensional events of the Rio de La Plata Craton. In spite of the similarities between the tectonic framework of these swarms and that of Lavras (1.9?Ga), the composition of the Paleoproterozoic mantle of both cratons is very different. The parent mantle of the Florida dikes is more enriched and more heterogeneous than the others, probably due to the recycling of old crusts and OIB metasomatism. Isotopic data from the Tandil dikes also suggest an enriched original source, which could be a characteristic feature of the mantle of the Rio de La Plata Craton in Paleoproterozoic times. The Crix¨¢s-Goi¨¢s (2.49?Ga) swarm originated from a very heterogeneous mantle source, probably contaminated by OIB metasomatic fluids and crustal addition, suggesting that crustal recycling has occurred since Archean times.