Isotopic and chemical systematics of river waters
The isotopic composition of Nd and Sr and the concentration of the rare earth elements (REE), Rb, and Sr are reported for the dissolved and suspended load of rivers from North America, Australia, Japan, the Philippines, South America, and Pakistan. Nd and light REE are mobilized in solution in rivers of low pH, whereas Sr concentrations are generally determined by the degree of chemical weathering of source rocks. The REE pattern of the dissolved load of rivers is sensitive to pH, with heavy REE enrichments and negative Ce anomalies for alkaline rivers. The isotopic composition of Nd and Sr in the dissolved load of rivers is mainly controlled by the age of materials in a drainage basin and preferential weathering of marine precipitates. Rivers appear to be the dominant source of these elements in the oceans. Estuarine removal processes lower the actual river flux of dissolved REE to the oceans by 70% for the light REE and 40% for the heavy REE. A Sr isotopic mass balance for modern seawater yields a hydrothermal water of 2.9 x 10/sup 16/ g/yr. Suspended load data directly reflect the Sm-Nd isotopic systematics and REE systematics of upper continental crust exposed to weathering. Average Sm-Nd parameters estimated for the upper crust are: Sm = 5.7 ppm. Nd = 30.0 ppm, epsilon/sub Nd/ = -15.4, and T/sub DM//sup Nd/ = 2.0 Ga. An overall relationship between epsilon/sub Nd/ and /sup 87/Sr//sup 86/Sr in river suspended loads directly reflects the relationship of these parameters in upper crust and suggests that crustal additions have become progressively depleted in incompatible elements through time. The implications of these data for interpretation of the record of Nd and Sr isotopes and REE abundances in ancient erosion products are briefly discussed.
- Research Organization:
- Harvard Univ., Cambridge, MA (USA)
- OSTI ID:
- 7056176
- Country of Publication:
- United States
- Language:
- English
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54 ENVIRONMENTAL SCIENCES
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580400 -- Geochemistry-- (-1989)
AGE DEPENDENCE
ALKALI METALS
ALKALINE EARTH METALS
ASIA
AUSTRALASIA
AUSTRALIA
CHEMISTRY
DEVELOPING COUNTRIES
DISPERSIONS
DISSOLUTION
ECOLOGICAL CONCENTRATION
ELEMENTS
EROSION
GEOLOGIC HISTORY
ISLANDS
ISOTOPE RATIO
JAPAN
LATIN AMERICA
METALS
NEODYMIUM
NORTH AMERICA
PAKISTAN
PH VALUE
PHILIPPINES
RARE EARTHS
RIVERS
ROCKS
RUBIDIUM
SEAS
SEDIMENTARY ROCKS
SOUTH AMERICA
STREAMS
STRONTIUM
SURFACE WATERS
SUSPENSIONS
WATER CHEMISTRY
WEATHERING