Abstract

LOPEZ ISAZA, Julián Andrés et al. PSEUDOTACHYLITES AND THE PALEOSEISMIC CHARACTER OF THE BUCARAMANGA FAULT SYSTEM (BFS) RELIEF, EASTERN CORDILLERA, COLOMBIA. bol.geol. [online]. 2008, vol.30, n.2, pp.79-92. ISSN 0120-0283.

The occurrence of pseudotachylites associated with cataclasites found in "pressure backs" constituted by rocks related to the Bucaramanga Gneiss, developed in the transpressive segments of the Bucaramanga Faults System (BFS) Relief demonstrates the paleoseismic character of this one to the Northeast of the Municipality of Pailitas - Cesar Department, Colombia. The pseudotachylites are characterized to appear as injection, cataclastic and fault veins, petrographycally conformed by lithic clasts, fine grain matrix, optically observable grains and amygdales. The origin from melting for the pseudotachylites is suggested by the textures of the veins, which are characterized to display cooling margins, injection veins, macroscopic and microscopic flow bands, biotite microlites in veins, plagioclase microlites of albitic composition, "glass plate" type fractures, potassium feldspar and plagioclase deformation, and cleared, corroded and concave edges; potassium feldspar and quartz recrystallized; lithics clasts wrapped by the matrix and amygdales.

Keywords : Pseudotachylites; Bucaramanga Faults System; Paleoseismic character; Eastern Cordillera.

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