Los mármoles cálcicos de El Escorial, Macizo Nord-patagónico: Caracterización Isotópica de 87Sr - 86Sr y probable edad de sedimentación

SEBASTIÁN O. VERDECCHIA ; JUAN A. MURRA; CARMEN GALINDO; EDGARDO G. BALDO

Tucuman

Congreso; XX Congreso Geológico Argentino; 2017

Asociación Geológica Argentina

AbstractThe first isotopic values of Sr from marbles of the "El Escorial" corresponding to the Cusahamen formation of the Macizo Nord-patagónico (Chubut Province, Argentina) are reported. They correspond to calcitic marbles (calcite> 95%, I.R. : 0.5 to 2.5%) with lower contents of dolomite ± phlogopite ± quartz ± diopside ± serpentine ± garnet ± graphite. Ten of twenty five samples were selected for Sr isotope yielding two populations of data: 1) 87Sr / 86Sr = 0.70768-0.70793 (average 0.707835; n = 5), and 2) 87Sr / 86Sr = 0.70818 -0.70825 (average; n = 5). The second group of samples shows fewer evidences of post-sedimentary alterations and therefore the most adequate ones to define the original isotopic relation of the sea water. It is not feasible to determine a single sedimentation age of these marbles from the 87Sr/86Sr = 0.70821 ratio, however, considering the age inheritance of detrital zircons of the siliciclastic units of the Cushamen Fm. in its type locality, which restricts the Visean (~ 335 Ma) the maximum age of sedimentation and on the other hand, considering that the Cusahmen Fm are injected by granites of 286 to 261 Ma it is possible to constrain the age of sedimentation and metamorphism between the Visean and the Early Permian. According to this, the 87Sr/86Sr = 0.70818-0.70825 from El Escorial marble corresponded to the secular variation of the medium to Upper Carboniferous period (~ 330-310 Ma).