The Caucete Group and structurally overlying Pie
de Palo Complex in western Argentina are characterised by two generations of west-verging folds and thrust-related shear zones, which formed un
der amphibolite facies conditions. The Caucete Group is separated from the Pie
de Palo Complex by the Pirquitas thrust. These structures are interpreted to have formed as a result of a progressive
deformation, generated during Middle Ordovician, un
derthrusting of the Laurentian-
derived Cuyania microcontinent beneath the active
Famatina margin. Geometrical relationships are most simply explained if the Pie
de Palo Complex was basement to the Caucete Group prior to Ordovician orogenesis. We propose that this basement-cover relationship was established during Cambrian rifting of the Cuyania microcontinent from Laurentia. The Pirquitas fault may have been initiated during this extension prior to its long-lived remobilization as a thrust. We cannot rule out the possibility that the Pie
de Palo Complex was exotic with respect to the Caucete Group, but for this to be possible we have to introduce an extra generation of structures, for which no evi
dence is preserved.
The deformation was characterised by early strain localization followed by a more homogeneously distributed non-coaxial flow during F2. Thermal softening probably dominated over fabric softening during this stage.