Mathiasite-loveringite and priderite in mantle xenoliths from the Alto Paranaíba Igneous Province, Brazil: genesis and constraints on mantle metasomatism

Abstract

Alkali-bearing Ti oxides were identified in mantle xenoliths enclosed in kimberlite-like rocks from Limeira 1 alkaline intrusion from the Alto Paranaíba Igneous Province, southeastern Brazil. The metasomatic mineral assemblages include mathiasite-loveringite and priderite associated with clinopyroxene, phlogopite, ilmenite and rutile. Mathiasite-loveringite (55-60 wt.% TiO 2 ; 5.2-6.7 wt.% ZrO 2 ) occurs in peridotite xenoliths rimming chromite (∼50 wt.% Cr 2 O 3 ) and subordinate ilmenite (12-13.4 wt.% MgO) in double reaction rim coronas. Priderite (Ba/(K+Ba)< 0 05) occurs in phlogopite-rich xenoliths as lamellae within Mg-ilmenite (8.4-9.8 wt.% MgO) or as intergrowths in rutile crystals that may be included in sagenitic phlogopite. Mathiasite-loveringite was formed by reaction of peridotite primary minerals with alkaline melts. The priderite was formed by reaction of peridotite minerals with ultrapotassic melts. Disequilibrium textures and chemical zoning of associated minerals suggest that the metasomatic reactions responsible for the formation of the alkali-bearing Ti oxides took place shortly prior the entrainment of the xenoliths in the host magma, and is not connected to old (Proterozoic) mantle enrichment events. Keywords

A Plethora of Epigenetic Minerals Reveals a Multistage Metasomatic Overprint of a Mantle Orthopyroxenite from the Udachnaya Kimberlite

“…Inclusions of mantle chromium titanates of the magnetoplumbite and crichtonite groups in enstatite indicate that during its residence in the lithospheric mantle, the orthopyroxenite underwent the influx of a metasomatic liquid charged with high concentrations of Ti and incompatible elements (Stage 1 in Table 1). Crichtonite-group minerals and YIHA series are widely represented in metasomatized mantle xenoliths the world over and are characteristic indicators of metasomatic enrichment of lithospheric mantle assemblages by deep-sourced melts or fluids [17,27,30,[36][37][38][67][68][69][70][71][72][73]. The extreme enrichment of the enstatite-hosted titanates in LILE, HFSE, and REE could have been caused only by the introduction of these elements into the system during the metasomatism [27].…”

Phlogopite-Forming Reactions as Indicators of Metasomatism in the Lithospheric Mantle

“…The authors believe that the second stage of metasomatism was due to the interaction of rocks with ultra-alkaline fluids/melts with low silica activity [96], which is typical for alkaline carbonatite melts. Reactions of phlogopite with relic Cr-rich spinel can form K-bearing titanates at the advanced stage of metasomatic processes (e.g., [99]). However, such reactions have never been modeled experimentally.…”

Micro‐Raman study of crichtonite group minerals enclosed into mantle garnet

“…The members of both groups are present in xenoliths and/or as xenocrysts sampled by kimberlites, lamprophyres, and alkali basalts. [16,34,37,64,[66][67][68][69][70][71] Regarding the Siberian craton, CGM are known as individual inclusions in pyropic garnet xenocrysts from Yakutian kimberlites, that is, Internatsionalnaya, [24,39,72] Zagadochnaya, [73] Sytykanskaya, [74] as well as from ultramafic rocks of the Chompolo and Tobuk-Khatystyr volcanic fields, Aldan shield. [22,72,74] They are described in a series of oriented needles within garnet grains of mantle xenoliths from Udachnaya, Obnazhennaya, and Mir kimberlites.…”