Linking metamorphic P-T conditions to a determined age is crucial in reconstructing the thermal evolution of orogens. Traditionally, datable minerals are extracted from the host rock, whereas P-T conditions are obtained independently from whole-rock geochemistry and EPMA geochemical data. Mineral extraction frequently results in a time-consuming process that implies removing a textural context and may result in a sample cross-contamination increase. In this work, we present LA-ICP-MS U-Pb ages and cathodoluminescence imagery from a petrographic section of a high-amphibolite facies anatectic gneiss collected from La Secreta mylonites unit at the Santa Marta Massif. Our results reveal widely variable zircon morphologies, in which euhedral neoformed crystals hint at a major recrystallization event at ca. 250 Ma. Textural relations among minerals indicate equilibrium between the Triassic sectors and the Grt-Hbl+Plg paragenesis from which the Hbl+Pl+Qtz pairs hint to peak conditions at 11.8 kb and 750 °C. In a few cases, Triassic zircons preserve Ordovician (ca. 470 Ma) and Permian (ca. 270 Ma) inherited cores. Outer rims in euhedral crystals yield ages between 230-218 Ma. In contrast, anhedral and highly resorbed sectors present as zircon aggregates display Jurassic ages between 200-175 Ma. In-situ petrochronology indicates that Triassic and Jurassic growth sectors mantling Ordovician and Permian cores occurred by anataxis. Whereas, Jurassic recrystallization was induced by fluid alteration, dissolution and reprecipitation of zircon. Furthermore, textural relations and phase equilibria discard a detrital reworking of grains, instead indicating multiple metamorphic events coeval with ages determined in other localities of Gondwanan affinity as the Mérida Andes. In-situ thin section petrochronology of zircon is essential for reconstructing P-T-t histories of metamorphic complexes and differentiate between detrital recycling Vs. recrystallization, particularly when analyzing medium-to high-grade metamorphic complexes.

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  • Piraquive, Alejandro; Contreras Fayad, David; Muñoz Rocha, Jimmy Alejandro; Jimenez Triana, Carolina; Villamizar Escalante, Nicolas; Bedoya Mejia, Alejandra; Peña Urueña, Mary Luz
  • apiraquive@sgc.gov.co