『Abstract
Rare Earth Element (REE) contents and 87Sr/86Sr
values were measured in rivers and exposed granites and metasediments
of the Australian Victorian Alps to (1) determine how weathering
affected the major and trace element budget of the bedrocks, (2)
constrain the relative contributions from rainfall and mineral
weathering to the river water dissolved load and (3) evaluate
the factors regulating the temporal and spatial variability of
weathering yields to rivers. Victorian granites become relatively
enriched in Ca, Na, P, Mn and Eu during weathering as a result
of sequential precipitation of secondary calcites and Ca and Na
clays and a relative enrichment of the more resistant phosphate
and Mn-oxide minerals. Only minor proportions of the host rock
ΣREE contents are removed during alteration as most of the REEs
remain in the more resistant accessory phases such as muscovite,
titanite and/or apatite as well as in secondary precipitates.
An end-member mixing model using Y/Ho and 87Sr/86Sr
ratios as tracers implies that Victorian Alpine rivers receive
〜19％ of their solutes from atmospheric precipitation; 〜14％ from
carbonate dissolution and 〜67％ from aluminosilicate weathering.
The agreement between the spatial and temporal trends inferred
from the mixing model and major cation (Ca, Mg, Na, K) inversion
studies suggests that high runoff generally enhances aluminosilicate
weathering yields while low runoff favors the dissolution of secondary
carbonate. That the magnitude of aluminosilicate contribution
derived from the mixing model is higher than that inferred from
the major cation inversion is related to significant REE and Y
contribution from the more resistant silicates (i.e.m muscovite
and titanite) and secondary phases. The results of this study
have implications for global assessments of chemical weathering
yields as they are not necessarily a function of lithology and
river discharge, but are rather a result of the complex interplay
of water-rock contact time and the surface of water-rock interaction.
Keywords: Geochemistry; Weathering; Rivers; Runoff; Australia』
1. Introduction
2. The Australian Victorian Alps drainage system
3. Sampling, analyses and models
3.1. Field methods
3.2. Analytical methods
3.3. Chemical modeling
4. Results and discussion
4.1. REE and Sr chemistry of Victorian granites and metasediments
4.1.1. Rock weathering and translocation of elements
4.2. The REE and Sr chemistry of Victorian Alpine rivers
4.2.1. REE behavior during river transport
5. The sources of REE and Sr in Victorian Alpine rivers
5.1. Quantifying the contribution of atmospheric precipitation,
carbonate dissolution and aluminosilicate weathering
5.2. Atmospheric contribution
5.3. Carbonate weathering
5.4. Aluminosilicate weathering
5.5. Uncertainty
6. The effect of runoff and temperature on chemical weathering
7. Summary and conclusions
Acknowledgements
Appendix A
Appendix B
Appendix C
References