SUMMARY OF ORIGIN AND ACCRETION OF THE ARGENTINE PRECORDILLERA TERRANE

The Argentine Precordillera is an exotic terrane in the eastern foothills of the Andes in northwestern Argentina.  The Precordillera was rifted from the Ouachita embayment of the Iapetan margin of Laurentia in Early Cambrian time and was accreted to western Gondwana in Middle-Late Ordovician time.

A palinspastic location of the Precordillera on the Laurentian margin is documented by: (1) Early Cambrian olenellid trilobite fauna and Salterella; (2) Grenville-age basement rocks with Pb isotopic ratios like those of Laurentian Grenville; (3) Early Cambrian synrift redbeds and evaporites; (4) Sr isotopic ratios, indicating coeval, similar depositional environments of Early Cambrian synrift evaporites in Precordillera and southern Laurentia; (5) detrital-zircon populations in Early Cambrian synrift sandstones, indicating similar provenance for Precordillera and southern Laurentia; (6) Early Cambrian through Early Ordovician thick passive-margin carbonate successions; (7) complementary asymmetry of Early Cambrian to Early Ordovician post-rift thermal subsidence on conjugate rift margins of Precordillera and Texas promontory of Laurentia; and (8) Early Cambrian paleomagnetic pole of Precordillera in palinspastic location, corresponding to Laurentian pole.

Accretion of the Precordillera by subduction beneath western Gondwana and the Ocloyic orogeny are documented by: (1) Ordovician metamorphic overprint on Grenville-age basement rocks and younger synrift igneous rocks in the Sierra de Pie de Palo and Sierra de Valle Fertil east of the Precordillera; (2) top-to-west shear zones associated with the Ordovician metamorphic rocks; (3) Ordovician magmatic continental-margin arc in the Sierra de Famatina east of the Precordillera; (4) flexural subsidence of a foreland basin, drowning of the passive-margin carbonate platform, and deposition of black shale, beginning in early Middle Ordovician and progressing westward; (5) westward prograding Middle-Late Ordovician synorogenic clastic wedge filling the foreland basin; (6) west-verging thin-skinned thrust belt propagating synchronously with deposition of the clastic wedge; and (7) numerous bentonite beds, geochemically and temporally linked to the Famatina arc, within the uppermost carbonate beds and lower part of the clastic wedge.