Ordovician back–arc clastic wedge in the Famatina Ranges: new ages and implications for reconstruction of the proto–Andean Gondwana margin

Ricardo A. Astini; Federico Dávila; Carlos Washington Rapela; Robert John Pankhurst; C. Mark Fanning

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Ordovician back–arc clastic wedge in the Famatina Ranges: new ages and implications for reconstruction of the proto–Andean Gondwana margin

Ricardo A. Astini ^[1] ^[2] ; Federico M. Dávila ^[1] ^[2] ; Carlos W. Rapela ^[2] ^[3] ; Robert J. Pankhurst ^[5] ; C. Mark Fanning ^[4]
1. [1] Universidad Nacional de Córdoba
  
  Universidad Nacional de Córdoba
  
  Argentina
2. [2] Consejo Nacional de Investigaciones Científicas y Técnicas
  
  Consejo Nacional de Investigaciones Científicas y Técnicas
  
  Argentina
3. [3] Universidad Nacional de La Plata
  
  Universidad Nacional de La Plata
  
  Argentina
4. [4] Australian National University
  
  Australian National University
  
  Australia
5. [5] NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, United Kingdom.
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Localización: Serie correlación geológica, ISSN-e 1666-9479, ISSN 1514-4186, Vol. 17, Nº. 1, 2003
Idioma: inglés
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Resumen
- New Early Ordovician (ca. 480 Ma) U–Pb ages have been obtained by ion–microprobe (SHRIMP) analysis of detrital zircon from the La Aguadita Formation of western Argentina, previously considered to be Late Precambrian–Early Cambrian (Durand et al., 1992). Sedimentological observations show that this siliciclastic unit has suffered major overburden and is affected by very low–grade regional metamorphism. It crops out along the eastern slope of the main Sierra de Famatina (in the present day broken foreland), to the west of Angulos in the La Rioja Province, (28º39’46" S, 67º38’00" W, Figure 1). It is composed of an alternation of thick packages (2–5m) of coarse arkoses and rhythmic intervals, where thin– to medium–bedded sandy storm layers punctuate green silty shales. Petrographical and stratigraphic observations on the extremely unsorted, coarse–grained epidote–rich arkoses (feldspathic sandstones) allow interpretation of the La Aguadita Formation as relicts of an Ocloyic clastic wedge (within the Famatinian Cycle) developed in a back–arc setting and representing a younger depositional system than the well dated Early–early Middle Ordovician volcano–sedimentary cycle.