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

• 作者: Luísa D.V.Carvalho Tiago Jalowitzki Ricardo Scholz Guilherme O.Gon(c)alves Marcelo Peres Rocha Rogério Silvestre Pereir Cristiano Lana Marco Paulo de Castro Gláucia Queiroga Reinhardt A.Fuck
• 来源期刊: 地学前缘（英文版）
• 年，卷（期）: 2022,（1）
• 所属期刊栏目: Research Paper
• 页码范围: 182-203
• 页数: 22页
• 语种: 英文

摘要

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 Fran(c)a 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 ℃).The shallowest part of this mantle is represented by Lherz-1 pyropes (20-32 kbar),which have low-Cr (Cr2O3 =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 (Cr2O3 =7.36-11.19 wt.％) and are char-acterized 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.Cr2O3),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 kimber-litic signatures,such as ilmenite and zircon,the exotic compositions of phlogopite and ulv(o)spinel suggest an enriched component in the magma source.The formation of rare mineral phases with strong enrich-ment of light-REE (LREE) and high field strength elements (HFSE) is attributed to the late-stage kimber-litic 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 fragmen-tation and consequent South Atlantic Ocean opening.The metasomatism recorded by mineral phases is a product of long-lived recycling of subducted oceanic plates since the Neoproterozoic (Brasiliano Orogeny)or even older collisional events,contributing to the exotic character of the Osvaldo Fran(c)a 1 kimberlite,as well as to the cratonic lithospheric mantle.