DYNAMOMETRIC EFFECTS IN ROCKS OF TWO FAULT ZONES OF; LA CEBILA FORMATlON, LA RIOJA AND CATAMARCA PROVINCES.

Abstract

A new critical study of two fault zones in the Precambrian basement at Quebrada La Cébila in the area of the antimonium mines Santa Margarita, La Morenita and Ruma Supay has enaÍJled the authors to characterize the petrological and structural behaviour of a group of metaquartzites and sclusts m the southern tip of Sierra de Ambato. Rocks were classified in four main types resulting from tectonic movements: metaquartzite breccias, protocataclasites, foliated gouge (foliated cataclasites) and cataclastized metaquartzites. A much rare, fifth tipo was classified as mylonitic (half way towards true mylonites SC 11) associated to zones of feeble non coaxial laminar flow or transient shear. Prevailing physical conditions were also determined as well as the deformation mechanisms corresponding to the elastic frictional type associated to cataclastic flows. From the data it is inferred that global deformation was multiphase and discontinuous. In mylonitic schist, kinematic markers are markers of internal monoclinic symetry and belong to the Passchier and Simpson type a (1986) with feeble shear deformation. Structures enabled the recognition of three phases of internal deformation F 1, F2 and F3, in the basement, corresponding to SI planes parallel to So, S2 and C2 and S3 bandings, respectively. The general style of fold is Precambrian or low Paleozoic. The metamorphism is contemporaneus with folding. The fault system is inverse and Precarbonic; it was reactivated at the end of the Te rti ary . Petrofabrics diagrams were made based on transversal profiles to the fault area, that permited determine one strain gradient that increase to wands the in side of the fault, in an approximately simmetrycal formo The schist sohwn a monoclinic simmetry, near to SC 11mylonites while the quartzites rocks shown a triclinic symmetrys.