Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil) Neoproterozoic crust recycling constrained by elemental and isotope (Sr Nd Pb) geochemistry
Abstract Whole rock elemental and Sr Nd isotope geochemistry and in situ K feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810 580 Ma) and is dominated by crust derived relatively low T (850 750 degC, zircon saturation) biotite granites to biotite muscovite granites. Two Cryogenian plutons show the least negative eNd t 8 to 10) and highest mg# (30 40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI 1.2) ~660 Ma Serra do Quebra Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI 0.96 1.00) 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ~810 Ma. The predominant Ediacaran (595 580 Ma) plutons have a spread of compositions from biotite granites with SiO 2 as low as ~65% (e.g. Itapeti, Maua, Sabauna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ~75% SiO 2 eNd T are characteristically negative 12 to 18) with corresponding Nd T DM indicating sources with Paleoproterozoic mean crustal ages (2.0 2.5 Ga) The Guacuri and Santa Branca muscovite granites have the more negative eNd t highest 87 Sr/ 86 Sr t (0.714 0.717) and lowest 208 Pb/ 206 Pb and 207 Pb/ 206 Pb, consistent with an old metasedimentary source with low time integrated Rb/Sr. However, a positive Nd Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Maua granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The Ediacaran granites are coeval with profuse granite magmatism attributed to continental arc magmatism in northern Ribeira and Aracuai belts. However, their evolved compositions with low mg# and dominantly peraluminous character are unlike those of magmatic arc granites, and they are more likely products of post collisional magmatism or correspond to an inner belt of crust derived granites.