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| Detailed Reference Information |
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Edmond, J.M., Palmer, M.R., Measures, C.I., Grant, B. and Stallard, R.F. (1995). The Fluvial Geochemistry and Denudation Rate of the Guayana Shield in Venezuela, Colombia, and Brazil. Geochimica et Cosmochimica Acta 59(16): 3,301-3,325. doi: 10.1016/0016-7037(95)00128-M. |
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The Guayana Shield is composed of Early to Mid-Precambrian igneous and metamorphic basement rocks with a quartzitic platform cover. The complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment. Total erosion rates are extremely slow, similar to 10 m/m.y., with equal contributions from the dissolved and suspended loads. However, the former is largely silica with ratios of Si to total cation equivalents [Si:TZ(+)] ranging to in excess of three. Weathering is ''complete'' to kaolinite and gibbsite, i.e., the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate. In basins of relatively homogeneous lithology, Rb/Sr isochrons constructed from the river data agree with the whole-rock ages from the drainages; thus, all the common, refractory, Rb-containing minerals( K-feldspar, mica) are completely dissolved. The thick, lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other Southern Hemisphere Shields. In the absence of active tectonics or greatly accelerated mechanical erosion, the weathering rates of these basement rocks must be quite insensitive to environmental change. |
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| BACKGROUND DATA FILES |
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Sampling & Analytical |
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Keywords
river water, precipitation chemistry, isotope geochemistry, weathering processes, dissolved inputs, imataca complex, carbon-dioxide, drainage-basin, south-america, guiana shield |
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Publisher
Elsevier Science
P.O. Box 211
1000 AE Amsterdam
The Netherlands
(+31) 20 485 3757
(+31) 20 485 3432
nlinfo-f@elsevier.com |
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