The early Ordovician Aguada de la Perdíz Formation in the Puna of Antofagasta, N Chile, revisited: stratigraphy, provenance and regional plate-tectonic setting
Abstract
The Ordovician Aguada de la Perdíz Formation exposed in the Puna de Antofagasta of northern Chile is one of the oldest non-metamorphosed sedimentary units on continental Chilean territory. Graptolites indicate a late Floian to early Dapingian age of the formation at the Aguada de la Perdíz type locality and small nearby outcrops in Chile. Correlative outcrops on the Argentinian side at Huaitiquina, Filo Pircas, Sierra de Guayaos and Lever Mucar range from the late Floian to the Darriwilian. Graptolites are associated with scarce occurrences of brachiopods and conodonts in some outcrops. In the Argentinian Puna the correlative units were assigned to the Coquena Formation.
The lithological assemblage in all outcrops comprises of bimodal lavas, breccias and mostly reworked felsic tuffs. The main part of the successions consists of volcaniclastic turbidites and lutite flow deposits. The lithological assemblage reflects deposition in a marine volcaniclastic apron located on the eastern flank of the Famatinian magmatic arc.
In view of the common characteristics of the respective outcrops on both sides of the political border we propose to group them in the Aguada de la Perdíz Formation thus respecting precedence of the first definition of the formation by Garcia et al. (1962).
New U-Pb detrital zircon ages of a sample (n=124) from the Huaitiquina locality range between 3530 Ma and 550 Ma and reflect a common polycyclic provenance from older Amazonian mountain belts. It is noteworthy that the youngest U-Pb zircon age belongs in the Ediacaran and predates the biostratigraphically defined depositional age by c. 80 Myr. This means that the synsedimentary Famatinian felsic volcanism, otherwise common in coeval units, is not reflected in the detrital zircon age record at Huaitiquina. The absence of Famatinian ages may indicate that sediment delivery from the Famatinian arc bypassed this site and that erosion in the source region of the arc had locally dissected the volcanic edifices and had progressed to broach the pre-Pampean Neoproterozoic arc basement.
The lithological assemblage in all outcrops comprises of bimodal lavas, breccias and mostly reworked felsic tuffs. The main part of the successions consists of volcaniclastic turbidites and lutite flow deposits. The lithological assemblage reflects deposition in a marine volcaniclastic apron located on the eastern flank of the Famatinian magmatic arc.
In view of the common characteristics of the respective outcrops on both sides of the political border we propose to group them in the Aguada de la Perdíz Formation thus respecting precedence of the first definition of the formation by Garcia et al. (1962).
New U-Pb detrital zircon ages of a sample (n=124) from the Huaitiquina locality range between 3530 Ma and 550 Ma and reflect a common polycyclic provenance from older Amazonian mountain belts. It is noteworthy that the youngest U-Pb zircon age belongs in the Ediacaran and predates the biostratigraphically defined depositional age by c. 80 Myr. This means that the synsedimentary Famatinian felsic volcanism, otherwise common in coeval units, is not reflected in the detrital zircon age record at Huaitiquina. The absence of Famatinian ages may indicate that sediment delivery from the Famatinian arc bypassed this site and that erosion in the source region of the arc had locally dissected the volcanic edifices and had progressed to broach the pre-Pampean Neoproterozoic arc basement.
Keywords
Ordovician; stratigraphy; sedimentology; Chile; Argentina; detrital zircon ages; tectonic setting;
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