COMPOSICIÓN ISOTÓPICA (Sr) DE LOS MÁRMOLES DE LA SIERRA DE VALLE FÉRTIL. EDAD DE SEDIMENTACIÓN E IMPLICANCIAS ESTRATIGRÁFICAS

MURRA, J.A.; CASQUET, C.; GALINDO, C.; VERDECCHIA, S.; RAMACCIOTTI, C.D.; BALDO, E.G.

Congreso; XIII Congreso de Mineralog¨ªa, Petrolog¨ªa Ígnea y Metam¨®rfica y Metalog¨¦nesis; 2019

The chemical age of marbles from the Sierra de Valle F¨¦rtil - La Huerta (SVF-LH; Argentina) based on the Sr-isotope composition, and the stratigraphic significance is established. Marbles were analyzed for Ca ¨C Mg ¨C Mn ¨C Sr - Fe and the 87Sr/86Sr ratio determined. Calcite content is >85% (R.I. = 0.0-13.2 %). A few samples were discarded due to possible post-sedimentary alterations. The 87Sr/86Sr ratio ranges from 0.70837 to 0.70864 (2¦Ò = 0.01 %). Comparing these values with the secular evolution curve of the Sr-isotope composition of oceanic water for the Neoproterozoic-Cambrian, the sedimentation age can be bracketed between ca. 535 and 510 Ma. Moreover, one migmatite gneiss interbedded with marble contains a population (among other ones) of detrital zircon grains which yields a peak of ages at 515 Ma (unpublished data). Further, the age of metamorphic rims (464¡À8 Ma) yields a lower sedimentation age older than the Guandacol orogenic phase of the Famatinian orogeny (ca. 470 Ma). In consequence carbonate sedimentation can grossly be assigned to the Cambrian Series 2 epoch (509-521 Ma; IUGS Chronostratigraphic Chart, Cohen et al., 2018). The SVF-LH marbles and the interbedded gneisses would thus be part of the siliciclastic/carbonated continental platform that existed in southern South America after the Pampean orogeny between 520 and ca. 490 Ma (Ramacciotti et al., 2018)