Upper Cretaceous weakly to strongly silica-undersaturated alkaline dike series of the Mantiqueira Range, Serra do Mar alkaline province: Crustal assimilation processes and mantle source signatures

Autor(es)

Azzone, Rogerio Guitarrari ^[1] ; Ruberti, Excelso ^[1] ; Lopes da Silva, Julio Cesar ^[1] ; Gomes, Celso de Barros ^[1] ; Enrich Rojas, Gaston Eduardo ^[1] ; Bezerra Maia de Hollanda, Marla Helena ^[1] ; Gaeta Tassinari, Colombo Celso ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, Sao Paulo, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: BRAZILIAN JOURNAL OF GEOLOGY; v. 48, n. 2, p. 373-390, APR-JUN 2018.
• Citações Web of Science: 2

Resumo

ABSTRACT: Three series of alkaline dikes are characterized in a restricted area of the Mantiqueira Range: a weakly silica-undersaturated series (normative ne < 7), of potassic character, represented by basanite, tephrites, alkali basalts, basaltic trachyandesites, phonotephrites, tephriphonolites, and trachyandesites, an intermediate series (7 > normative ne > 13), of potassic character, consisting only of basanites and tephrites, and a strongly silica-undersaturated series (normative ne > 13), of sodic character, consisting of basanites, tephrites, phonotephrites, and phonolites. Ar-Ar data for biotite from a tephriphonolite dike yielded an average age of 85.4±0.4 Ma. All three series show similar evolution trends controlled mainly by early-fractionation of olivine, spinel and clinopyroxene and, secondly, fractionation of plagioclase and apatite. Different degrees of crustal assimilation are suggested for each series. Assimilation processes are responsible for the wide 87 Sr/ 86 Sr i (0.70447-0.71172) and 143 Nd/ 144 Nd i (0.51237-0.51244) ranges, for the increased K 2 O/Na 2 O, Ba/Sr and Rb/Sr ratios, and for the reduced Ce/Pb ratios. In general, a significant contribution from partially melted host rocks is associated to the weakly silica-undersaturated potassic series. A phlogopite-bearing carbonate-metasomatized heterogeneous peridotite source accounts for the main chemical variations in the least contaminated samples of each series. Geochemical signatures of the strongly sodic alkaline series indicate a greater contribution from carbonated pyroxene-rich veins in the mantle source. (AU)

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