Other
Scientific paper
Apr 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997gecoa..61.1653n&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 61, Issue 8, p. 1653-1670.
Other
34
Scientific paper
The bulk composition and mineralogy of the Toorongo Granodiorite, Australia, are similar to average upper continental crust (AUCC). Weathering characteristics of the Toorongo profile consequently provide insight into large-scale chemical weathering of the upper crust. In situ weathered materials of the profile do not reflect parent granodiorite composition in quartz-plagioclase-K-feldspar (Q-P-K) or in quartz-feldspar-rock fragment (Q-F-L) compositional space. Intensive in situ weathering precludes sands, derived from mature weathering profiles through erosion, from reflecting their provenance. Where intensive chemical weathering has occurred, clay minerals and oxyhydroxides of the profile, and by inference muds derived therefrom, contain much more chemical information about provenance than do associated sands. Actinides, rare earth elements (REEs), many transition metals, and metalloids have accumulated in deep parts of the weathering profile at concentrations much greater than observed in the fresh granodiorite. Mass balance considerations require the bulk of these elements to have been derived from previously weathered, and now eroded, granodiorite. These elements were, and are, continually cycled from the intensely weathered uppermost soil zone to deeper, less weathered, zones of the profile where they accumulate. The profile therefore represents a large, continental elemental storage reservoir, the storage capacity of which has increased over time. Wherever erosion is sufficiently slow and chemical weathering sufficiently rapid, mature weathering profiles may become large, long-term storage reservoirs for actinides, REEs, and many other elements. The total REE contents of extremely weathered soil material are somewhat less than in the parent granodiorite, but they are enriched twofold to threefold in the zone of intermediate weathering relative to parent. Similar variations in total REEs are observed in some muds when normalized to their source (AUCC). These differences are attributed to a combination of chemical weathering and selective mass wasting of profiles. Homogenization of detritus in large sedimentary basins, however, produces muds with REE patterns and total REE contents similar to source (AUCC). Nd/Sm ratios are not influenced by chemical weathering, although both elements are mobilized by weathering and become enriched by over 200% relative to parent rock. Constancy of Nd/Sm in the profile indicates that Nd-Sm model ages derived from soils and sediments are not affected by chemical weathering. The least mobile trace elements of the profile are Sc, Cu, Nb, and Ta, but others are more mobile. Thorium, for example, is mobilized during weathering of the Toorongo Granodiorite and displays a twofold increase in the profile, as does the Th/Sc ratio. The ratio, however, varies by more than a hundredfold in major rock types so that Th/Sc (and other ratios) provides valuable information about provenance, although sensitivity is diminished somewhat by the effects of chemical weathering.
Markovics G.
Nesbitt Wayne H.
No associations
LandOfFree
Weathering of granodioritic crust, long-term storage of elements in weathering profiles, and petrogenesis of siliciclastic sediments does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Weathering of granodioritic crust, long-term storage of elements in weathering profiles, and petrogenesis of siliciclastic sediments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Weathering of granodioritic crust, long-term storage of elements in weathering profiles, and petrogenesis of siliciclastic sediments will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1317907