Ductile deformations of opposite vergence in the eastern part of the Guerrero Terrane (SW Mexico)

Abstract

The Teloloapan volcanic arc in SW Mexico represents the easternmost unit of the Guerrero Terrane. It is overthrust by the Arcelia volcanic unit and is thrust over the Guerrero–Morelos carbonate platform. These major structures result from two closely related tectonic events: first, an eastward verging, ductile deformation (D1) characterized by an axial-plane schistosity (S1) supporting an E–W trending mineral stretching lineation (L1) and associated with synschistose isoclinal, curvilinear folds (F1). Numerous kinematic indicators such as asymmetrical pressure-shadows, porphyroclast systems, and micro-shear bands (S–C structures) indicate a top-to-the-east shear along L1. This first deformation was followed by another ductile event (D2) that produced a crenulation cleavage (S2) associated with westward overturned folds (F2), hence showing that the vergence of D2 is opposite to that of D1. Regionally, both D1 and D2 deformations have been identified east and west of the Teloloapan unit, in the Arcelia volcanic rocks as well as in the Mexcala flysch of Late Cretaceous age overlying the Guerrero–Morelos platform. This implies that all three units were deformed and thrust simultaneously, during the Late Cretaceous or Paleocene, prior to the deposition of the overlying, undeformed Eocene red beds of the Balsas group.