Famatinian inner arc: Petrographical observations and geochronological constraints on pegmatites and leucogranites of the Comechingones pegmatitic field (Sierras de Córdoba, Argentina)

DEMARTIS, MANUEL; JUNG, STEFAN; BERNDT, JASPER; ARAGÓN, EUGENIO; SATO, ANA MARÍA; RADICE, STEFANIA; MAFFINI, MARÍA NATALIA; CONIGLIO, JORGE ENRIQUE; PINOTTI, LUCIO PEDRO; D'ERAMO, FERNANDO JAVIER; AGULLEIRO INSÚA, LEONARDO ALFREDO

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2017 vol. 79 p. 239 - 253

0895-9811

TheComechingones pegmatitic field comprises granitic pegmatites and leucograniteshosted by mylonitic rocks from the Guacha Corral shear zone. Pegmatites consistof variably sized, internally zoned bodies, with late replacement units.Leucogranites are fine-grained rocks that form small bodies with tabular- tolens-like shapes. Field relationships and petrographic observations suggest asynkinematic emplacement of both rock types with respect to the maindeformational event of this shear zone. U-Pb LA-ICP-MS analyses on zirconcrystals indicate crystallization ages of 473.8 ±3.9 and 474.8 ± 12.2 Ma forthe granitic pegmatites and leucogranites, respectively, suggesting that theyoriginated coevally at around 474 Ma. This age provides a first-order timeconstraint on the deformation of the Guacha Corral shear zone. Using ages andpressure estimations, along with an average pressure gradient of 1GPa/35 km forthe continental crust, an exhumation rate of approximately 0.1 mm/a and 10.5 kmof total amount of exhumation were calculated for the time span between the earlyOrdovician and the late Devonian in this part of the Sierras Pampeanas. Theinherited ages obtained in zircon crystals from the leucogranites display adistribution pattern that strongly resembles those of the metasedimentary rocksof the Pampean metamorphic belt, suggesting that equivalents of these rocksshould have been involved in the melting processes that originated theleucogranites.