Stratigraphical evidence supporting the rifting, drifting and collision of the Laurentian Precordillera terrane of western Argentina

Major stratigraphical evidence points toward initial rifting of the Precordillera terrane of western Argentina during the Early Cambrian from the Ouachita embayment in southeastern Laurentia. A first fully developed rifting episode is suggested from subsidence analysis and the sedimentary record. Restricted graben-fill red-beds and evaporites in the eastern tectofacies, together with coarse arkose and quartz conglomerate preserved as blocks in the western tectofacies, are interpreted as deposits of the initial rift-related brittle extension. Stratigraphical similarities with localities surrounding the Ouachita embayment leads to a model in which the Precordillera was the southern part of the pre-Appalachian Laurentia margin and the conjugate margin of the Texas promontory, separated along the Alabama-Oklahoma transform and the Ouachita rift, respectively. Overstepping of syn-rift facies by a thick succession of Lower Cambrian to Lower Ordovician carbonates indicates completion of rift-to-drift transition and initiation of thermo-tectonic subsidence characteristic of continental terrace passive-margin development. Slope facies, marginal faunal belts and recently dated mafic rocks indicate the development of an ocean basin separating the Precordillera from Laurentia by the Mid-Cambrian. A 20–30 Ma period of drifting and isolation is indicated from faunal and sedimentological evidence. Subsidence-induced incipient drowning and abundant K-bentonites suggest the influence of subduction and the progressive approach of the terrane to western Gondwana. Continuous Mid- and Late Ordovician post-collisional extension brackets the collision, although no clear evidence of shortening has been detected in the preserved former sedimentary bank. Post-collisional extension is separated by >70 Ma from the initial rifting.