The Argentine Precordillera: its odyssey from the Laurentian Ouachita margin towards the Sierras Pampeanas of Gondwana

Abstract

Abstract The Argentine Precordillera (Cuyania terrane) and the Marathon/Solitario basin (west Texas), both underpinned by Grenvillian Laurentian basement, evolved together during Early Cambrian to Mid-Ordovician times. Ages, Pb-isotope and geochemical data for Precordilleran and for west-central Texas basement (including the Llano uplift) are strikingly similar. Carbonate platform sequences developed on both sides (e.g., El Paso and Chica de Zonda) of the Marathon/Solitario outer-shelf to slope basin and hosted homologous reef organisms which were unique to the Laurentian Ouachita margin. The Marathon/Solitario basin received sediments from both north and south; much detritus came from the northern shelf, including olistoliths bearing shelf fauna. Erosional vacuities on the platforms correlate with coarse detrital basin deposits. Cuyania constituted the long-sought southern source. Stratigraphy and structures of the Precordillera/Marathon/Solitario basin are consonant with plate reconstructions that place southern Laurentia near western Gondwana from Late Cambrian into mid-Ordovician time. During Caradoc time, Cuyania moved beyond range of faunal exchange with Laurentia, and tholeiitic basalts were intruded into off-shelf turbidites in the western Precordillera. The attenuated, thermally weakened, Laurentian slab broke apart with continued extension and right-oblique separation of Laurentia and Gondwana. Severance of Cuyania from Laurentia was complete before the onset of Taconic or Ocloyic orogenesis.