Los mármoles cálcicos de El Escorial (Formación Cushamen), macizo Nord-Patagónico: caracterización isotópica de 87Sr-86Sr y probable edad de sedimentación

EDGARDO GASPAR BALDO; JUAL ALBERTO MURRA; CARMEN GALINDO; SEBASTIÁN OSVALDO VERDECCHIA

San Miguel de Tucumán

Congreso; 20º Congreso Geológico Argentino.; 2017

Asociacíon Geologica Argentina

Inthis communication the first isotopic values of Sr of the marbles correspondingto the member El Escorial of Cushamen F. (Province of Chubut, Argentina). Thesemarbles are of calcite composition (calcite > 95 %, I.R.: 0.5 to 2.5 %), andthe isotopic values obtained are 87Sr/86Sr =0.70768-0.70825 (n = 10). Considering the higher ratios (~ 0.70821), those thatbest reflect the original isotopic relationship of seawater, and therefore themost adequate to limit the age of sedimentation. It is not possible tounequivocally defines the sedimentation age as a function of the secularevolution curves due to the fluctuations present for the Paleozoic. In spite ofthis, the inheritance ages obtained from detrital zircons from thesiliciclastic units of the Cushamen F. in its type locality allow the maximumage of sedimentation to be limited to the Visean (ca. 335 Ma). On the other hand, the metasedimentary rocks from CushamenF. are intruded by post-metamorphic granites of 286 and 261 Ma, so that thesedimentation age and the main metamorphic event would be bounded between theVisean and the early Permian. According to this, the relationship between the 87Sr/86Sr= 0.70818-0.70825 obtained corresponded to the characteristic secular variationof the medium to upper Carboniferous period (330-310 Ma).