Pb, Nd, Sr, AND Os ISOTOPIC SYSTEMATICS OF BRAZILIAN CRETACEOUS POTASSIC ROCKS

Abstract

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.

Cretaceous Na‐Alkaline Magmatism from the Misiones Province (Paraguay): Its Relationships with the Paleocene Na‐Alkaline Analog from Asunción and Geodynamic Significance

“…These model ages indicate that some notional distinct series of metasomatic events may have occurred during Paleoproterozoic to Neoproterozoic times (1.8-0.6 Ga) as a precursor to the alkaline and tholeiitic magmas in Eastern Paraguay (see CominChiaramonti et al 1995CominChiaramonti et al , 1997CominChiaramonti et al , 1999, and they are also supported by the plumbotectonic model of Hawkesworth et al (1986) for the Paraná tholeiites and by Re-Os systematics for the Alto Paranaíba kamafugites (Carlson et al 1996;Araú jo et al 2001). This conclusion is distinct from the proposal by Gastal et al (2005), who suggest that the major events of metasomatism in the region took place mainly during the Neoarchean-Paleoproterozoic.…”

Mineralogia e Petrologia de xenólitos mantélicos da Província Kimberlitica de Juína, MT

“…A Província Geocronológica Rio Negro -Juruena (Tassinari, 1981;Teixeira et al, 1989;Tassinari et al, 1996;Sato & Tassinari, 1997) O Grupo Parecis (Barros et al, 1982) -Lauar et al, 1994;206 Ma, Barros et al, 2006) como as províncias kimberlíticas de Paranatinga (122,6 -126,3 Ma;Heaman et al, 1998), Juína (91,6 -94,6 M.a;Heaman et al, 1998) et al, 1980;Schultz Filho, 1981), que já havia descoberto kimberlitos na província de Paranatínga, MT (Lopes, 1976;Fragomeni, 1976). Davis (1977a, b) obteve idades (U-Pb em zircão) entre 80,1 -79,2 Ma para os kimberlitos das intrusões denominadas Juína-5 e 6 (J-5 e J-6; PKDJ, MT) e idades entre 120 -121,1 Ma para o kimberlito Batovi-9 (Província de Paranatinga, MT).…”

Mantle xenoliths and new constraints on the origin of alkaline ultrapotassic rocks from the Alto Paranaíba and Goiás igneous provinces, Brazil

“…The Alto Paranaíba and Goiás Alkaline Provinces, located in southern Brazil (Figure 1) are composed mainly by kamafugites (Danni & Gaspar 1994;Sgarbi et al 1995;Gibson et al 1995;Sgarbi 1998;Araujo et al 2001aAraujo et al , 2001b. In the Alto Paranaíba Province the kamafugites are associated with kimberlites (Araujo et al 2001a) and carbonatites (Brod et al 2000).…”