First geochronological constraint for the Palaeoproterozoic Lomagundi-Jatuli δ13C anomaly in the Tandilia Belt basement (Argentina), Río de la Plata Craton

• Published in: Precambrian research 2019-11, Vol.334, p.105477, Article 105477
• Main Authors: Lajoinie, María Florencia, Sial, Alcides, Ballivián Justiniano, Carlos Alberto, Cingolani, Carlos Alberto, Recio, Clemente, Etcheverry, Ricardo Oscar, Basei, Miguel, Lanfranchini, Mabel Elena
• Format: Article
• Language: English
• Subjects: Carbon isotope; Lomagundi-Jatuli event carbonate; Metamorphism; Transamazonian Orogeny; U-Pb LA-ICP-MS
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2019.105477

•2206 ± 14 Ma is the minimum age for the LJE in the Tandilia Belt basement.•San Miguel marble is older than the Paso Severino Formation.•San Miguel marble and the Montevideo Formation are temporarily correlated.•LJE record in high metamorphic grade marbles. Geochronological data of Palaeoproterozoic carbonates with δ13C values between +5‰ and +16‰ suggest that the positive carbon isotope excursion of the global Lomagundi-Jatuli event (LJE) occurred mostly between 2220 and 2060 Ma. In the southern portion of the Río de la Plata Craton, the LJE was recorded in calcite-diopside marble of the Tandilia Belt basement. The marble was found at the San Miguel area as part of a metamorphic rock assemblage, mainly composed of gneisses and migmatites, formed during the Transamazonian Orogeny. The latter represents the maximum magmatic and metamorphic activity in the Tandilia Belt basement. The marble, derived from a calcareous-siliciclastic sedimentary marine sequence, was intruded by leucogranites that provoked the San Miguel skarn formation. First U-Pb LA-ICP-MS age of 2206 ± 14 Ma, obtained from titanites of the skarn, also placed the metasomatic processes into the Transamazonian Orogeny. In addition, this age corresponds to the minimum age for the marble’s protolith deposition which matches with the beginning of the LJE worldwide. These new data would favor the correlation between the San Miguel marble and the Montevideo Formation marble of the Tandilia Terrane (Uruguay), within the Río de la Plata Craton, and not with the Paso Severino Formation of the Piedra Alta Terrane, which is at least 60 Ma younger. New δ13C determinations in calcite crystals from the marble allowed the lowest and the highest carbon values (+3.19‰ and +6.90‰, respectively) to be obtained. The lowest values are within the range of normal marine carbonates (between −5‰ and +5‰), despite having been altered by contact metamorphism, while the highest values are typical of the LJE carbonates. In this sense, the early deposition of the carbonate protolith within the LJE, together with the effect of post-depositional metamorphic processes would justify the wide range of values shown by the isotopic ratios of C.