ABSTRACT
Previously reported left-lateral slip of 132 ± 5 km across the Polochic fault of Guatemala and Chiapas, Mexico, was based on a match of structures and stratigraphic units. This amount of offset can also be established by a match of present topographies in the region of the Cuchumatanes Mountains of northwestern Guatemala and the once adjacent region in central Guatemala. By moving the blocks back to their pre-slip positions and examining the union of modern topographies, several interesting correlations are noted. In the pre-slip position the present drainage divide of the Cuchumatanes Mountains on the northern block closely matches the present drainage divide between the Polochic and Chixoy Rivers on the southern block. Ridge and drainage trends extend across the fault so that, in the reconstructed position, a missing part is restored to the annular drainage pattern of the Cuchumatanes domal uplift. The Chixoy and Polochic Rivers on the southern block probably flowed into the present Selegua and Cotzal Rivers respectively. Before slip, the region south of the fault drained northward around the highest elevations of the Cuchumatanes Mountains, but after slip the drainage of rivers on the southern block was shunted into the new, fault-controlled Cuilco and eastern Polochic River channels, vastly reducing the discharge across, and erosion of, the northern block. Significantly lower terrane on the southern block is probably due in large part to this erosional factor.
