The San Blas Pluton: An Example of the Carboniferous Plutonism in the Sierras Pampeanas, Argentina

DAHLQUIST, J.A., PANKHURST, R.J., RAPELA, C.W., CASQUET, C., FANNING, C.M., ALASINO, P.H., BAEZ, M.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier Science Ltd

Lugar: Oxford. England; Año: 2006 vol. 20 p. 341 - 350

0895-9811

New U-Pb zircon sensitive high-resolution ion microprobe (SHRIMP) data is obtained from the San Blas Pluton (SBP), in the northeastern Sierra de Velasco, Sierras Pampeanas. A precise Carboniferous age (340 ± 3 Ma) is established for the SBP, which intrudes Ordovician granitoids developed during the Famatinian orogeny, confirming previous field observations that indicated later emplacement of the SBP. The SBP illustrates several petrological and geochemical characteristics of previously reported Carboniferous granitoids in the Sierras Pampeanas. Their generation is consistent with a regional reheating of the crust at 342 Ma, resulting in the formation of relatively large amounts of granitic melts, which were emplaced into higher crustal levels along master fractures (reactivated older master shear zones of  Lower Paleozoic age). The SBP can be chemically defined as  a typical  A -type granitoid  related to post-collisonal  or post-orogenic magmatism. Its high REE content and extraordinarily high U and Th concentrations may have economic significance. Many previously published Devonian and Carboniferous K-Ar dates probably are reset Ordovician ages, but the existence of other Carboniferous bodies in the Sierra de Velasco cannot be discounted until detailed mapping and dating of the whole Sierra is completed.