IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
artículos
Título:
An Alpine-style Ordovician collision complex in the Sierra de Pie de Palo, Argentina: Record of A-subduction of Cuyania beneath the Famatina arc
Autor/es:
VAN STAAL, C.R.,; VUJOVICH G. I.; CURRIE, K.L.,; NAIPAUER, M.
Revista:
JOURNAL OF STRUCTURAL GEOLOGY
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Año: 2011 vol. 33 p. 343 - 361
ISSN:
0191-8141
Resumen:
The Caucete Group and the immediately structurally overlying Pie de Palo Complex in the Sierra de Pie de Palo, Argentina are characterised by two generations of west-verging, inclined to recumbent folds (F1 and F2) and thrust-related shear zones, which formed under metamorphic conditions typical of the high pressure amphibolite facies. Structural analysis suggests that large fold nappes and thrusts formed during both generations of folds. The main shear zone is the Pirquitas thrust, which everywhere separates the Caucete Group from Pie de Palo Complex, and is itself folded by at least the west-verging F2 folds. These structures are interpreted to have formed as a result of a progressive deformation (Dm), generated during Middle Ordovician, east-directed underthrusting of the Cuyania microcontinent beneath the proto-Andean, active Famatina margin. Lithostratigraphic relationships suggest that the predominantly calcareous Caucete Group is a direct correlative of the nearby Cambro-Ordovician platform succession of the Precordillera terrane, whereas geometrical relationships are most simply explained if the Pie de Palo Complex was the basement to the Caucete Group prior to Ordovician orogenesis. Based mainly on the mineralogy and composition of the sediments, we propose that this basement-cover relationship was established during Cambrian extension and rifting of the Cuyania microcontinent from Laurentia, rather than representing the original stratigraphic basement. We cannot rule out the possibility that the Pie de Palo Complex was entirely 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 evidence is preserved in the rocks. Combined, our data provide strong support for the Laurentian-derived Cuyania microcontinent model of earlier workers. The Pirquitas fault may in part have been initiated during Cambrian extension and was a long-lived structure characterised by protracted remobilization as a thrust, during Ordovician Dm-related ductile shearing of the rocks. The structures suggest a deformation history characterised by early strain localization, probably as a result of fabric softening, followed by a more homogeneously distributed non-coaxial flow during F2 and associated peak metmamorphic temperatures. Thermal softening probably dominated over fabric softening during this stage.