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Material Sources, Chemical Weathering, and Physical Denudation in the Chubut River Basin (Patagonia, Argentina): Implications for Andean Rivers

Pasquini, Andrea I. and Depetris, Pedro J. and Gaiero, Diego M. and Probst, Jean-Luc Material Sources, Chemical Weathering, and Physical Denudation in the Chubut River Basin (Patagonia, Argentina): Implications for Andean Rivers. (2005) The Journal of Geology, vol. 113 (n°4). pp. 451-469.

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Official URL: http://dx.doi.org/10.1086/430243

Abstract

The Chubut is a medium-size (45,000 km2) river basin that drains the arid-to-semiarid Patagonian scaboard and pours its waters into the southwestern Atlantic Ocean (ca. lat 43°20'S, lond 65°04'W).The materials croded from the continent and deposited in the sea arc scarcely affected by chemical weathering (the chemical index of alteration of rierbed sediments is -55)and bear a typical chemical and mineralogical signature characteristic of volcanic arcs Cleary, Flowing toward a passive margin, tyhe river carries the mineralogical and chemical signature of an active margin. Physically weathered andesites and basalts occupy only about 25% of the drainage area, and therefore most exported material must be supplied by outcropping sedimentary beds of variable age. The Chubut River headwaters are placed in a tectonically active region, soil formation is incipent ("weathering-limited regime"), and the rate of denudation (24,6 t km 2 yr 1) is much lower than the rates exhibited by similar rivers in other parts of the world. The depleted dissolved and particulate load is determined by scare atmospheric precipitations (i.e., the drainage basin is in the Andean rain shadow) and by the protective effect of Cenozoic lava flows that often shield sedimentary formations from denudation. Although the index of chemical variability suggests that materials exported are products of the first denudational cycle, the geological history supports the view that most materials may have passed two or even three times though the exogenous cycle without acquiring a chemical or mineralogical signature indicative of repeated weathering. This is probably also true for other basins in temperate Andean climates

Item Type:Article
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > Universidad Nacional de Cordoba - UNC (ARGENTINA)
French research institutions > Institut de Recherche pour le Développement - IRD
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
French research institutions > Centre National de la Recherche Scientifique - CNRS
Other partners > Université Louis Pasteur-Strasbourg I - ULP (FRANCE)
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Deposited By: Florence Amor

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