Blue quartz as an indicator of strongly deformed rocks: an example from Guayaguás hill, San Juan province, Argentina

CASTRO DE MACHUCA, BRÍGIDA

Rio de Janeiro

Congreso; 31º International Geological Congress; 2000

International Union of Geological Sciences (IUGS)

Deformed blue quartz veins from a ductile shear zone have been examined by conventional optical microscopy and scanning electron microscope (SEM). A sequence of progressive deformation from intact rock to mylonite and ultramylonite can be established for samples from Guayaguas Hill, Western Sierras Pampeanas. From detail observation of the quartz grains, it became evident that this mineral has experienced strong ductile deformation. This study demonstrates a direct relationship between the colour of quartz and the degree of deformation. The colour is induced by interference processes and/or light spectrum differential absorption (Rayleigh scattering) due to dislocations in the crystalline structures. Thus, the presence of blue quartz can be used as an indicator of high-strain zones in metamorphic basement rocks.