The central Andes of northern Chile and northwestern Argentina developed in a largely autochthonous, intracontinental setting during Proterozoic and Paleozoic time through a recurrent sequence of extensional and compressional tectonic regimes. The exposed pre-Andean crust consists of tectonically isolated outcrops of: (1) metamorphosed basement, (2) plutonio bodies, and (3) slightly metamorphosed volcanic and sedimentary strata resting upon and intruded by multiple plutonic units. U-Pb and Nd-Sm geochronology indicates the existence of a Precambrian foundation for the central Andes dating from at least middle Proterozoic time. Three episodes of Precambrian/Paleozoic deformation/magmatism are recognized: (1) the Panamerican at the Precambrian/Cambrian transition, (2) the Caledonian at the Ordovician/Silurian boundary, and (3) the Variscan during the Carboniferous. Intrusive units can be grouped into synorogenic (S-type) and anorogenic (A-type) rocks based on structural, petrographic, and geochemical relations. Mafic lavas of middle Proterozoic to lowerCarboniferous age likely were generated during episodes of crustal dilatation.

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The tectonic evolution of the proto-Andean

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The palaeo-Pacific margin of Gondwana in the present-day south-central Andes is marked by tectonic activity related to subduction and terrane accretion. We present detrital zircon U-Pb data encompassing the Palaeozoic era in northern Chile and northwestern Argentina. Cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase. The main age clusters for these zircon grains are Ediacaran to Palaeozoic with an additional peak at 1.3-0.9 Ga and they can be correlated with 'Grenvillian' age, and the Brasiliano, Pampean, and Famatinian orogenies. The zircon data reveal main transport from the nearby Ordovician Famatinian arc and related rocks. The Silurian sandstone units are more comparable with Cambrian units, with Brasiliano and Transamazonian ages (2.2-1.9 Ga) being more common, because the Silurian deposits were situated within or east of the (extinct) Famatinian arc. Hence, the arc acted as a transport barrier throughout Palaeozoic time. The complete suite of zircon ages does not record the accretions of exotic terranes or the Palaeozoic glacial periods. We conclude that the transport system along the palaeoPacific margin of Gondwana remained stable for c. 0.3 byr and that provenance data do not necessarily reflect the interior of a continent. Hence, inherited geomorphological features must be taken into account when detrital mineral ages are interpreted.

We here present the first systematic description of Devonian plant fossils from Chile. The material was collected from the Upper Devonian El Toco Formation in the Coastal Cordillera of northern Chile. Plant fossils occur as impressions of lycopsid axes in marine turbiditic greywacke beds and comprise Haplostigma furquei (Frenguelli) Gutiérrez, Malanzania cf. nana Archangelsky, Azcuy and Wagner, and further unidentifiable remains. The biostratigraphic ranges of these taxa agree well with previous age assessments for this sequence, based on conodonts and radiometric data. Haplostigma was widely distributed in the middle-to-high latitude, cool-temperate biome of southern Gondwana, providing further evidence that Middle to Late Devonian extra-tropical floras of Gondwana were dominated by low-diversity associations of herbaceous lycopsids.