Tectonic wedges and offset Laramide structures along the Polochic Fault of Guatemala and Chiapas, Mexico: Reaffirmation of large Neogene displacement

Abstract

Fault wedges along the Polochic fault of northern Guatemala and Chiapas, Mexico record left‐lateral slip of from 20 to 65 km that accompanied documented Neogene slip of 130 km across this North American—Caribbean plate boundary fault. Wedges can be correlated to source areas consistent with left‐lateral displacement along the Polochic fault. They occur adjacent to restraining bends in three areas where changes in strike of the fault have been mapped. These wedges, which have been previously interpreted as allochthons emplaced along low‐angle reverse faults, are bounded by high‐angle faults. Folds that terminate against the Polochic fault are part of a regional fold belt that originated during the Campanian through Paleocene (Laramide) orogenic event. A previous contention that some of these major folds are secondary and related to fault movement is shown to be incorrect. The 130 km model of left‐lateral offset across the Polochic fault is reviewed along with evidence for and against a Neogene time of major displacement. Additional evidence for the model is presented: (1) Late Cretaceous granitoid rocks from near Motozintla, Chiapas, Mexico (northern fault block), are correlated with granitic rocks of the Santa Maria Batholith in the region of Huehuetenango, Guatemala (southern block), (2) mineralization at the contacts of the granitoid intrusives of the two areas is correlated, (3) points of deflection of Laramide structural axes are correlated across the fault, (4) a major thrust sheet similar to that of the Sierra de Santa Cruz in eastern Guatemala is reassembled by reversing 130 km of left‐lateral slip which has offset serpentinites north of the fault in western Guatemala and those south of the fault in central Guatemala.