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Central Argentina from the Pampean flat‐slab segment to northern Patagonia (27°–41°S) represents a classic example of a broken retroarc basin with strong tectonic and climatic control on fluvial sediment transport. Combined with previous research focused on coastal sediments, this actualistic provenance study uses framework petrography and heavy‐mineral data to trace multistep dispersal of volcaniclastic detritus first eastwards across central Argentina for up to ca. 1,500 km and next northwards for another 760 km along the Atlantic coast. Although detritus generated in the Andes is largely derived from mesosilicic volcanic rocks of the cordillera, its compositional signatures reflect different tectono‐stratigraphic levels of the orogen uplifted along strike in response to varying subduction geometry as well as different character and crystallization condition of arc magmas through time and space. River sand, thus, changes from feldspatho‐litho‐quartzose or litho‐feldspatho‐quartzose in the north, where sedimentary detritus is more common, to mostly quartzo‐feldspatho‐lithic in the centre and to feldspatho‐lithic in the south, where volcanic detritus is dominant. The transparent‐heavy‐mineral suite changes markedly from amphibole ≫ clinopyroxene > orthopyroxene in the north, to amphibole ≈ clinopyroxene ≈ orthopyroxene in the centre and to orthopyroxene ≥ clinopyroxene ≫ amphibole in the south. In the presently dry climate, fluvial discharge is drastically reduced to the point that even the Desaguadero trunk river has become endorheic and orogenic detritus is dumped in the retroarc basin, reworked by winds and temporarily accumulated in dune fields. During the Quaternary, instead, much larger amounts of water were released by melting of the Cordilleran ice sheet or during pluvial events. The sediment‐laden waters of the Desaguadero and Colorado rivers then rushed from the tract of the Andes with greatest topographic and structural elevation, fostering alluvial fans inland and flowing in much larger valleys than today towards the Atlantic Ocean. Sand and gravel supply to the coast was high enough not only to promote rapid progradation of large deltaic lobes but also to feed a cell of littoral sediment transport extending as far north as the Río de la Plata estuary. [ABSTRACT FROM AUTHOR]

We here review in terms of tectono-magmatic setting and Quaternary landscape dynamics what is known about the provenance of Argentine dune fields and their fluvial feeder systems draining the Andean Cordillera. The detrital signatures of these eolian sediments were previously investigated based on either framework petrography and heavy minerals or detrital-zircon geochronology, and their peculiar volcaniclastic nature was long recognized. Compositional variability, however, was only broadly evaluated, and quantitative provenance analysis based on a systematic multimethod approach across the entire region was not carried out so far. For this reason, here we integrate original and previously obtained petrographic, heavy-mineral, and detrital-zircon geochronology data to present the first comprehensive provenance study of dune fields stretching for 1000 km across central Argentina from the Andean piedmont to the Atlantic Ocean. In dune fields along the Andean retroarc basin, sediment composition defines a steady northward decrease in volcanic detritus. This reflects active magmatism in the Southern Volcanic Zone and Payenia province (38°-34°S), in contrast with the ~600-km-long Pliocene-Quaternary magmatic gap in the Pampean flat-slab segment (33°-27°S), where sediment is derived from deeper-seated tectono-stratigraphic levels of the continental arc and uplifted blocks of retroarc-basin basement. In distal Pampean lowlands extending across the bulge and backbulge depozones, instead, sand dunes display notably homogeneous compositional signatures, indicating that detritus was mostly generated north of 34°S and transported by a paleo-Desaguadero trunk river that formed during southward-progressing diachronous uplift of the Sierras Pampeanas since the late Miocene. In contrast with huge African and Arabian deserts that contain multiply recycled quartzose to pure quartzose sand, even very fragile volcanic clasts, plagioclase feldspar, and unstable ferromagnesian minerals are widespread, testifying to largely first-cycle volcanic provenance and only minor effects of mechanical breakdown and chemical weathering in the Pampean Sand Sea. During the Late Pleistocene, after a first southward shift of the Desaguadero trunk river possibly induced by increased water and sediment discharge at the end of the penultimate glacial maximum, tectonic uplift eventually outpaced stream power during the last glacial period. Paleo-rivers were thus forced to shift farther southwards, leading to the formation of an integrated paleo-Desaguadero+Colorado drainage system. During the latest Pleistocene-early Holocene, such a large trunk river fostered the rapid progradation of a wide delta and littoral sand transport all along the shores of the Buenos Aires Province. Climate change and repeated waxing and waning of glaciers through the Quaternary have left a prominent mark on sediment distribution, dominated by fluvial processes during periods of high fluvial discharge but alternating with arid phases characterized by limited transport capacity and vegetation cover, extensive wind deflation of floodplains, and sand accumulation in the dune fields. [ABSTRACT FROM AUTHOR]