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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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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
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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 regio
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.
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