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RESUMOFoi cnc on rradc mn nodu le COlli imcrc resc nrcmo gra fico ihn cuit a -clin opiroxcmc e m tcsrcn umbo de sou dagcm de 111 11/ ' ;1' (' de kimberlite da pro vincia dinnuuuffcru de J uma (MTJ. a xcnolitc rem for madiscoidc . COlli apro ximadamcnre 2,0 x 1,5 em. A le xlura Cg rufica COlli corea de 2Ql k de ihrcnim cmhnrelas de I mm de cspcss ura. Pclc gccte rmcnctro quc utiliza o coc ficieruc de dislli bui\'ao fc't-Mg pode-sc infcnr qcc esse nodul e foi forumdocm tcmpc mnuu clc vada ( 12M -1308" C) 1 "1I~1 uma prcss;i tl l. 'Slim

ABSTRAC~Malic potassic rocks of the Alto Pummuba (Minas Gerais), Paruuatinga (Goins). Jurnu (Mmo Grosso) , uud Pimemu Bueno (Mute Grosso) provmccs belong to a large Iincumcut of rods that crosses from western to southeastern Brazil and have been associated to a hot spot track by severa l authors. These provin ces intruded the Neoprot erozoic Bra sflia and Paraguay fold belts (Alto Parunafba. Pcrauatin ga j. and the Mesopro rcrozoic Rio Ncgro-Jurueua bell (Jufua. Purcuta Bueno). Pb isotopic compositions ofthe studied provim.. xs show a wide variation. : !<"Pb':!<>IPb o f kimbcrlitcs (18.47-19.23) and knmafugites (17 .79-18.7 1) fromthe Alto Pamnaiha Province arc dose 10the Trisnuvwnlvis Ridge composition. The : !<"'PW:!<>I pb of the Pnmnmingu (19.38-19.67) and Pimcnm Bueno (11).78-21.00) provinces arc similar 10the So uth African Gro up I kimberlite compositicnnl Iields. while Jufnn is displaced 10 higher Ph isotopic ralios (2 1.38-22.26). dose 10those shown by IIIMU ocean island basalts (OIB). Although the Ph isotopic composition Il l' the more IJOl1hcI'lI alkalic provinces ranges towards the values seen for Ill r vIU O IB. the SI'and Nd isotopic co mposition of these samples is 1I0t like IIIMU. nor illcombination with Ph. like any other ocean island basalt. With the exception of'thc kimbcrlites from the Aho Paranafbu, which range to quite unrndiogcnic compositions. most ofthe sam ples have IK'Os/"C"OS between 0.13 and 0. 15. The Nd model ages of Juina kimberlites v:uy from 1.70• 1.73Ga. and could be indicating a prior accret ion period iurcrbc mobile bell. Nd model ages for Parancunga k~lllberl~tes vary between 0.56 and O.64Ga and PinwmuBueno kimbcrtitcs from 0.72 to 1.05Ga. Minimum Re dcplcriou model ages for Puranminga kimbcrtitcs vary between 0.74 and 0.93 and Pimcuta Bueno kimbcrhrcs from 0.9 10 I.JGa. indicating that the Nd isotopic signcnncs could have been affected by mcmsonunic overprint in Necrorcrozolc.

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