HR: 0830h
AN: V51H-0386    [PDF]
TI: Rare Earth Element Geochemistry of Atacama Desert Soils
AU: * Sutter, B
EM: bsutter@mail.arc.nasa.gov
AF: NASA Ames Research Center, MS 245-3, Moffet Field, CA 94035-1000 United States
AU: Ewing, S
EM: saewing@nature.berkeley.edu
AF: UC Berkeley, 151 Hilgard Hall Div. Ecosystems Sci., Berkeley, CA 94720 United States
AU: Amundson, R
EM: earthy@nature.berkeley.edu
AF: UC Berkeley, 151 Hilgard Hall Div. Ecosystems Sci., Berkeley, CA 94720 United States
AU: McKay, C
EM: cpmckay@nasa.gov
AF: NASA Ames Research Center, MS 245-3, Moffet Field, CA 94035-1000 United States
AB: The Atacama Desert of northern Chile is one of driest deserts in the world, with a hyper-arid climate that arguably has persisted since the Miocene. Soils in the driest parts of the Atacama record the effects of long-term hyperaridity, retaining atmospherically-derived elements in quantities rarely seen on Earth. Recent work has demonstrated that the hyper-arid environment allows Atacama soils to accumulate large amounts of sulfate (e.g., anhydrite, gypsum), nitrate (NaNO$_{3}$), and chloride (halite) that result in radical volumetric expansion of the soil. Possible salt sources include eolian redistribution from Atacama playas and/or marine aerosols. The objective of this work is to examine the rare earth element (REE) geochemistry of Atacama soils in order to understand how these trace elements chemically behave as soil water decreases to nearly zero. Two soils developed on fluvial landforms were examined along a south to north transect (Copiapo to Yungay) that coincides with decreasing moisture levels ($\sim$15mm to $\sim$2 mm yr$^{-1}$, south to north). Both soils have likely been undergoing soil formation since the Plio-Pleistocene. REE mass balance determinations were conducted on both soils through a comparison to that of the granitic alluvium from which they formed. An apparent net loss of REE relative to the granitic alluvium (10 to 30% Yungay; 15 to 65% Copiapo) has been calculated for these soils. The apparent loss of REE in both soils suggests that REE have been removed by some process or they have been have been diluted by dust and aerosols that have lower REE levels. Atmospheric deposition of marine and non-marine salts is the likely cause for the net loss of REE in the most arid soil, while weathering and leaching losses are a likely cause in the more humid endmember. Salts of marine origin are known to have low REE levels. Chondrite-normalized REE diagrams of the soils and parent materials are examined to determine if variations in local parent materials are evident. Europium anomalies, La/Yb, Gb/Yb, and Sm/Nd ratios are also presented to assess variations between soil horizons and parent materials.
DE: 1020 Composition of the crust
DE: 1045 Low-temperature geochemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting