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Abstracts 12° South American Symposium on Isotope Geology (SSAGI) - U-Pb AND Lu-Hf DATA OF A LATE DEVONIAN GRANITE FROM BAJO DE LA LEONA, EASTERN DESEADO MASSIF, SOUTHERN PATAGONIA (ARGENTINA)
Congress
Authorship:
Ballivián Justiniano, Carlos A. ; Basei, Miguel A.S. ; Oriolo, SebastiánDate:
2022Publishing House and Editing Place:
Editorial board 12° South American Symposium on Isotope Geology (SSAGI)Summary *
Themiddle to late Paleozoic orogenic evolution of Patagonia is well-documented byDevonian to Permian magmatism in the North Patagonian and Deseado massifs, andfurther west along the Andes. This evolution has been explained by collisionalor accretionary models (e.g., Ramos et al. 2020; Rapela et al. 2021). Inparticular, Devonian intrusions are mainly exposed in the North Patagonian Andesand the western North Patagonian Massif along a NNW-SSE-striking belt, thoughrelics of coeval, mainly juvenile magmatism are also recorded to the west inChile (e.g., Rapela et al. 2021; Serra-Varela et al. 2021). In the easternsector of the Deseado Massif, high- to medium-grade metamorphic rocks,gabbro-diorites, and granites were included into the Río Deseado Complex. Theserocks crop out in Bajo de la Leona and the Dos Hermanos, Tres Hermanas, ElSacrificio, and El Laurel farms. SHRIMP U-Pb isotopic dating of zircons fromgranites of the Río Deseado Complex yielded ages between ca. 450 Ma (DosHermanos Granite) and ca. 344 Ma (Mina La Leona Granite) (e.g., Pankhurst etal. 2003). In Bajo de la Leona, migmatites, gneisses, schists, and granitoids ofthe Río Deseado Complex (pre-Permian) crop out. In addition to the Mina LaLeona Granite, another Paleozoic granite crops out in the area, whose coupledLA-ICP-MS U-Pb and Lu-Hf isotopic data in zircons are here presented.Concentration, separation, and U-Pb and Lu-Hf analyses of zircons were done atthe Centro de Pesquisas Geocronológicas (CPGeo) of the Universidade de SãoPaulo, Brazil. The analytical data were obtained with a Thermo Fisher NeptuneLA multicollector ICP-MS equipped with a 193 Photon laser system, following theanalytical method described by Souza et al. (2017). The studied sample is ahigh-K calc-alkaline and peraluminous granite mainly composed of quartz,K-feldspar, biotite, and Na-plagioclase. Twenty-three zircons from this granitewere analyzed. They are mainly prismatic and show magmatic oscillatory zoning.The best estimate U-Pb concordia age for the crystallization of the studiedsample (24 spots) is ca. 362 Ma (Famennian). Regarding the Lu-Hf isotopic data,results show variable subchondritic (εHf(t) = –15/–1; TDM-Hf = 2.0-1.3 Ga) tosuprachondritic (εHf(t) = 0/+6; TDM-Hf = 1.3-0.9 Ga) compositions. Results showa geochemical and isotopic fingerprint comparable to coeval intrusions exposedbetween the North Patagonian Andes and the North Patagonian Massif, thusindicating that the Bajo de la Leona magmatism might have represented thesouthernmost expression of the Devonian continental magmatic arc. Information provided by the agent in SIGEVAKey Words
PATAGONIARIO DESEADO COMPLEXDEVONIAN ARC