First evidence for expressive neoproterozoic intraplated mafic rocks and magma mixing in post-collisional A-PA type granites, Southern Brazil: Geochemistry and U-Pb (zircon), Nd-Sr-18O(zircon) isotope investigations

New and recent geological investigations around Pien-Tijucas suture zone, between Luis Alves and Curitiba Microplates (Basei et al.2000) led to mapping of Palermo, Agudos do Sul and Rio Negro A-PA type Granites with expressive expositions of alkaline felsic ans mafic rocks and, associated mafic and felsic hybrid rocks. The suture zone is formed by subduction arc-related Pien-Mandirituba deformed calc-alkaline I-type granite belt and serpentinized supra subduction zone (SSZ) obducted mantle rocks with intrusive Neoproterozoic (650-630 Ma) very high Cr and Ni tholeitic gabbros. The Pien-Mandirituba calc-alkaline I-type Granite Belt is constituted by three main granite suites. The older emplaced pre-collisional suite is constituted by deformed to highly deformed amphibole and biotite-rich, magmatic epidote-absent quartz-monzodiorites and granodiorites formed between 620 and 610 Ma. The second sincollisional granite suite is constituted by deformed and slightly deformed low content amphibole-biotite-magmatic epidote-bearing, quartz-monzodiorites, granodiorites and leucogranodiorites emplaced between 605 and 595 Ma. The third, also sincollisional, granite suite is deformed to highly deformed biotite ± amphibole monzogranites. The deformation age of the three non-cogenetic granite suites of this granite belt is between 605-595 Ma. The granite rocks of the Pien-Mandirituba Granite Belt are meta-aluminous to slightly peraluminous, high K calc-alkaline, generally with high Ba, high Sr and low Rb contents. Palermo, Agudos do Sul and Rio Negro Granites are components of the expressive Neoproterozoic volcanic and plutonic alkaline-peralkaline Serra do Mar Suite (Kaul 1997), emplaced in extensional post-collisional and anorogenic settings along the central portion and northern border of the Luis Alves Microplate and southern border of the Curitiba Microplate. Magma mixing evidence is rare ou absent in the other components of the Serra do Mar volcanic and plutonic suite. The Palermo Granite, formed between 595-585 Ma, is mainly constituted by medium to coarse grained, non deformed A-type amphibole-biotite and biotite monzo-syenogranites, and subordinately slightly peralkaline (PA-type) quartz-monzonites/quartz-syenites with sodic amphibole and pyroxene, intraplated alkaline mafic rocks and associated felsic and mafic hybrid granite rocks. The Rio Negro Granite, formed between 595-585, Ma is mainly constituted by mafic and felsic hybrid granite rocks and associated alkaline mafic rocks and non deformed A-type biotite monzo-syenogranites. The peralkaline rocks are absent in the Rio Negro Granite. The A-type monzo-syenogranites of Palermo and Rio Negro and, A-type leucogranodiorites of Agudos do Sul Granite are high silica (SiO2 70-80%), aluminous (meta-aluminous to slightly peraluminous) with low Sr, low Ba, high Rb content and high Ga, Zr, Hf, Nb and Y contents and, high LREE and HREE with high Eu negative anomalies. The slightly peralkaline quartz-monzonites/quartz-syenites (SiO2 = 60-65 %) of Palermo Granite presents very low Sr, low Ba, high Rb, very high Zr, Hf and Y, and LREE and HREE enrichment with high Eu negative anomalies. The alkaline mafic rocks emplaced within Palermo and Rio Negro Granites forms, by mixing with the adjacent A-type monzo to syenogranites, a great variety of mafic (hybrid monzodiorites/hybrid monzogabbros, hybrid quartz-monzodiorites to hybrid quartz-monzonitos) and felsic (hybrid quartz-monzodiorites, hybrid quartz-monzonitos to hybrid monzogranitos) hybrid rocks. The mafic and felsic hybrid rocks are mainly characterised by the presence of typical mixing textures such as, quartz-ocelli with or without interstitial perthite mantled by pyroxene, amphibole and biotite, chaotic acicular apatite, rounded and elliptical mafic (biotite, amphibole/pyroxene) concentrations. The mixing textures are absent in the alkaline mafic rocks. The lithochemical and 18O isotope investigations on these hybrid rocks and the mixing components suggest no genetical links between monzo-syenogranites and alkaline mafic rocks (au)