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MAJOR- AND TRACE-ELEMENT COMPOSITION OF OLIVINE, PEROVSKITE, CLINOPYROXENE, Cr–Fe–Ti OXIDES, PHLOGOPITE AND HOST KAMAFUGITES AND KIMBERLITES, ALTO PARANAÍBA, BRAZIL

Leone Melluso^1,, Michele Lustrino², Excelso Ruberti³, Pietro Brotzu⁴, Celso de Barros Gomes⁵, Lucio Morbidelli⁶, Vincenzo Morra⁷, Darcy P. Svisero⁸ and Fosco d’Amelio⁹

¹ Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Via Mezzocannone 8, I–80134 Napoli, Italy
² Dipartimento di Scienze della Terra, Università degli Studi di Roma "La Sapienza", P.le Aldo Moro 5, Roma, Italy and CNR Istituto di Geologia Ambientale e Geoingegneria (I.G.A.G.) c/o Università di Roma "La Sapienza", I–00185 Roma, Italy
³ Instituto de Geociências, Universidade de São Paulo, Rua do Lago, São Paulo, SP, Brazil
⁴ Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Via Mezzocannone 8, I–80134 Napoli, Italy
⁵ Instituto de Geociências, Universidade de São Paulo, Rua do Lago, São Paulo, SP, Brazil
⁶ Dipartimento di Scienze della Terra, Università degli Studi di Roma "La Sapienza", P.le Aldo Moro 5, Roma, Italy and CNR Istituto di Geologia Ambientale e Geoingegneria (I.G.A.G.) c/o Università di Roma "La Sapienza", I–00185 Roma, Italy
⁷ Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Via Mezzocannone 8, I–80134 Napoli, Italy
⁸ Instituto de Geociências, Universidade de São Paulo, Rua do Lago, São Paulo, SP, Brazil
⁹ Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Via Mezzocannone 8, I–80134 Napoli, Italy

E-mail address: melluso{at}unina.it

An integrated whole-rock petrographic and geochemical study has been carried out on kamafugites and kimberlites of the Late Cretaceous Alto Paranaíba igneous province, in Brazil, and their main minerals, olivine, clinopyroxene, perovskite, phlogopite, spinels and ilmenite. Perovskite is by far the dominant repository for light lanthanides, Nb, Ta, Th and U, and occasionally other elements, reaching concentrations up to 3.4 x 10⁴ chondrite values for light lanthanides and 10⁵ chondrite for Th. A very strong fractionation between light and heavy lanthanides (chondrite-normalized La/Yb from ~175 to ~2000) is also observed. This is likely the first comprehensive dataset on natural perovskite. Clinopyroxene has variable trace-element contents, likely due to the different position of this phase in the crystallization sequence; Sc reaches values as high as 200 ppm, whereas the lanthanides show very variable enrichment in light over heavy REE, and commonly show a negative Eu anomaly. The olivine, phlogopite (and tetra-ferriphlogopite), Cr–Ti oxide and ilmenite are substantially barren minerals for lanthanides and most other trace elements, with the exception of Ba, Cs and Rb in mica, and V, Nb and Ta in ilmenite. Estimated mineral / whole-rock partition coefficients for lanthanides in perovskite are similar to previous determinations, though much higher than those calculated in experiments with synthetic compositions, testifying once more to the complex behavior of these elements in a natural environment. The enormous potential for exploitation of lanthanides, Th, U and high-field-strength elements in the Brazilian kamafugites, kimberlites and related rocks is clearly shown.

Keywords: trace elements in minerals, perovskite, clinopyroxene, phlogopite, kamafugites, kimberlites, Alto Paranaíba, Brazil.