Browsing by Author "Martinez, Juan Cruz"
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- Unprecedented U-Pb-Th SHRIMP and Lu-Hf isotopic data in zircon from Tandilia basement rocks, Argentina: new insights into Palaeoproterozoic and Neoproterozoic crustal reworking of the Rio de la Plata cratonPublication . Angeletti, Melisa; Chichorro, Martim Afonso; Castro, Antonio; Frisicale, María Cristina; Solá, A. Rita; Dimieri, Luis Vicente; Martinez, Juan CruzABSTRACT: We present new geochronological zircon data from the Siempre Amigos Hill (SAH), a small but representative portion of Tandilia Terrane within the R & iacute;o de la Plata Craton (RPC). U-Pb-Th SHRIMP data indicate a heterogeneous Palaeoproterozoic (Rhyacian) crust. A garnet-bearing granite (2165 +/- 16 Ma) hosts felsic (2108 +/- 13.6 Ma) to intermediate gneiss protolith (2104 +/- 8 Ma), andesite with a sanukitoid signature (2094 +/- 47 Ma) and granulites or charnockites. Additionally, calc-alkaline granitoids (2092 +/- 13 Ma) intruded, as a result of differentiation from an igneous mafic sanukitoid source. Localised low-temperature shear zones affected the sequence. Lu-Hf isotopic data for the post-orogenic stage (< 2.1 Ga) complement previous results, showing progressive negative epsilon Hf-(t) values. These isotopes suggest post-orogenic transtension. New Neoproterozoic ages (652 +/- 37 Ma, 618.4 +/- 11.2 Ma and 686 +/- 60 Ma) from granites, with low-to-very low zircon Th/U ratios, are presented as evidence of U-Th-Pb systems overprinting by Neoproterozoic (Cryogenian) thermal-hydrothermal events. Those Neoproterozoic ages are, within analytical uncertainty, equivalent to the 656 +/- 19 Ma metamorphic age obtained for the Palaeoproterozoic granulite. These new Neoproterozoic ages, suggests a thermal perturbation linked either to the collision of the Nico Perez Terrane against the passive margin of RPC, or the Neoproterozoic evolution of the Ventania System basement during the Brasiliano/ Pan-African orogeny.