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An exotic Cretaceous kimberlite linked to metasomatized lithospheric mantle beneath the southwestern margin of the S?o Francisco Craton,Brazil

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Geoscience Frontiers 2022年第1期13卷 182-203页

作者： Luísa D.V.Carvalho Tiago Jalowitzki Ricardo Scholz Guilherme O.Gonçalves Marcelo Peres Rocha Rogério Silvestre Pereira Cristiano Lana Marco Paulo de Castro Gláucia Queiroga Reinhardt A.Fuck Universidade Federal de Ouro Preto(UFOP) Escola de MinasDepartamento de GeologiaCampus Morro do Cruzeiro35400-000 Ouro PretoMGBrazil Universidade de Brasília(UnB) Instituto de GeociênciasCampus Universitário Darcy Ribeiro70910-900 BrasíliaDFBrazil Independent Geologist Consultant

We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals(titanite,calzirtite,anatase,baddeleyite and pyrochlore)of a newly discovered Late Cretaceous kimberlite(U-Pb zircon age 90.0±1.3 Ma;2σ)named Osvaldo Franca 1,located in the alto paranaíba igneous province(APIP),southeastern Brazil.Pyrope grains are lherzolitic(Lherz-1,Lherz-2 and Lherz-3),harzburgitic(Harz-3)and wehrlitic(Wehr-2).The pyrope xenocrysts cover a wide mantle column in the subcratonic lithosphere(66–143 km;20–43 kbar)at relatively low temperatures(811–875°C).The shallowest part of this mantle is represented by Lherz-1 pyropes(20–32 kbar),which have low-Cr(Cr_(2)O_(3)=1.74–6.89 wt.%)and fractionated middle to heavy rare earth elements(MREE-HREE)pattern.The deepest samples are represented by Lherz-2,Lherz-3,Harz-3,and Wehr-2 pyropes(36–43 kbar).They contain high-Cr contents(Cr_(2)O_(3)=7.36–11.19 wt.%)and are characterized by sinusoidal(Lherz-2 and Wehr-2)and spoon-like(Lherz-3 and Harz-3)REE patterns.According to their REE and trace elements,pyrope xenocrysts have enriched nature(e.g.,Ce and Yb vs.Cr_(2)O_(3)),indicating that the cratonic lithosphere has been affected by a silicate melt with subalkaline/tholeiite composition due to their low Zr,Ti and Y concentrations.Besides minerals with typical kimberlitic signatures,such as ilmenite and zircon,the exotic compositions of phlogopite and ulvöspinel suggest an enriched component in the magma source.The formation of rare mineral phases with strong enrichment of light-REE(LREE)and high field strength elements(HFSE)is attributed to the late-stage kimberlitic melt.We propose a tectonic model where a thermal anomaly,represented by the low-velocity seismic anomaly observed in P-wave seismic tomography images,supplied heat to activate the alkaline magmatism from a metasomatized cratonic mantle source during the late-stages of Gondwana fragmentation and consequent South Atlantic Ocean opening.The metasomat

关键词： Osvaldo França 1 kimberlite alto paranaíba igneous province Metasomatized cratonic lithosphere Zircon U-Pb geochronology

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