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The Andes of western Venezuela have been interpreted as a segment of the plate boundary between South America and the Caribbean. The details of the late Cenozoic history of the Venezuelan Andes do not support the widely held perception that a narrow axial fault zone (the Boconó Fault Zone) has accommodated all of the strike-slip displacement that has occurred between those plates in late Cenozoic time.

Field data not fully considered in previous interpretations include:

  1. An extensive breccia zone, closely related (where exposures reveal its base) to a high-angle thrust fault that rises within the Boconó lineament and rolls over to the northwest to carry rocks as old as Precambrian(?) gneiss, early Paleozoic(?) schist, and late Paleozoic phyllite over a terrane of flat-lying sediments as young as early Miocene.

  2. A deep red, locally bauxitic paleosol that formed near sea level during a long period of relative tectonic stability after emplacement of the thrust sheet, and that has been arched a minimum of 3 km over parts of the Central Venezuelan Andes in late Quaternary time.

  3. A complex system of interrelated high-angle faults along which Quaternary displacement has been well documented, amounting to (a) 3≥250 m of right-lateral strike-slip displacement since deposition of morainal landforms during the penultimate glaciation and (b) at least 3 km of vertical displacement adjacent to a series of linear central grabens.

The grabens have been interpreted as pull-apart basins and may represent evidence of substantial right-lateral strike-slip movement along the Boconó Fault in latest Quaternary time. The post-early Miocene pre-late Quaternary history of the cordillera, however, clearly shows that for much of that interval of time the stress field imposed on the mountain range has been more complex and has included a substantial component of compression.

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