PETROLOGIC COMPARISON BETWEEN PALEOZOIC BASEMENT FROM TWO DIFFERENT LOCALITIES IN NORTHEASTERN MEXICO: CABALLEROS CANYON, TAMAULIPAS AND ARAMBERRI UPLIFT, NUEVO LEON
In Caballeros Canyon (CC) GS crops out as a NW-SE trending narrow band. Here the schist is massive, black to gray, with interstratifications of pelitic to psammitic lithologies. The mineralogical assemblage is dominated by quartz, muscovite, albite, graphite, chlorite, tourmaline, and minor biotite. The pelitic levels are strongly deformed, while the psammitic beds are more competent and display brittle deformation. Quartz segregations are more abundant in the pelitic levels, where they are parallel to the main schistosity and commonly folded, recording the deformation phases. At least four events are preserved: three schistosities with 150/55, 320/60, 99/58° and a mesoscopic folding trending 240/54°.
AU shows massive schists that vary from gray to greenish, greenish to black, and red to greenish tonalities. The lithology is dominated by phyllite, quartzphyllite, talc schist, soapstone, metashale, metagraywacke, metavolcanic and metadiabase rocks. They develop more quartz segregations, is less deformed, more competent and more fractured than GS in CC. The main schistosity trends 330/20° NE-SW.
AU represents a more complex unit than CC, where the lithology is much more constant. This can be interpreted by quite different environments. In CC GS protoliths were deposited in a deep basin along a distal acrecional prism. On the other hand AU involves mafic-ultramafic, siliciclastic and volcanic lithologies. The metamorphism age (≈ 330±30 Ma) and metamorphic conditions (greenschist) of both localities could be similar.