METAMORFISMO Y DEFORMACIÓN DEL SECTOR NOR-ORIENTAL DE LA SIERRA DE VELASCO, LA RIOJA

VILA TELLO, M; LARROVERE, M.A.; ROCHER, R.; MORENO, G.; ALASINO, P.H.

Congreso; XX Congreso Geológico Argentino; 2017

Metamorphism and deformation of the northeastern region of the Sierra de Velasco, La Rioja. The basement of the northeastern region of the Sierra de Velasco comprises metasedimentary and mylonitic units. The metasedimentaryunit is composed of metaquarzite, phyllite and banded schist exhibiting to the west a metamorphic prograde from low to medium metamorphic grade. Temperature calculated in banded schist range from 513 to 549 °C and from 431 to 529 °C (Ti-in-Biotite and Ti-in-Muscovite thermometry respectively) consistent with greenschist facies conditions. The mylonitic unit is composed of mylonites and ultramylonites derived from granites. Based on microstructures, estimated metamorphic conditions suggest that temperature during ductile deformation exceeded 450- 500 °C. This ductile shear zone shows C planes that strike NNW and dip toward the W. The kinematic is reverse, with top to the NE displacements. The metasedimentary unit could be correlated with the Ordovician La Cébila Metamorphic Complex whereas the mylonitic unit with others syn- to post-Ordovician ductile shear zones recognized in Sierra de Velasco. This suggests that the evolution of the metasedimentary succession from northeastern Sierra deVelasco would be linked to the regional high temperature ? low pressure metamorphism and ductile deformation developed during the Famatinian Orogen.