『Abstract
In the upper catchment of the Kaveri river in the Sahyadri mountains
of southern India, middle to lower crustal Archean granulite grade
mafic and felsic rocks with similar structures and textures are
exposed under the conditions of active tectonics, high rainfall
and thick tropical vegetation. Occurrence of the two major rock
types in close association under identical geological, geographical
and biological conditions provides an uncommon situation for the
study of weathering, elemental mobilization and sediment generation
processes. Field observations, mineralogical and geochemical data
including major, trace and rare earth elements (REE) of fresh
rocks and variably weathered saprolite samples suggest that close
association of mafic and felsic rocks accelerates the denudational
processes by early weathering of mafic minerals in felsic rocks
and mafic rocks in the terrain. Due to differential weathering
of rocks, unweathered to less weathered felsic grains are likely
transferred to the coarser fraction of fluvial sediments deposited
on the floodplains of the river imposing an upper continental
crust (UCC) geochemical signature. It is found that during chemical
weathering, in addition to other factors, weatherability of host
minerals of REE control the mobility of REE in the weathering
profile. It is suggested from the observations on the weathering
process and on the geochemistry of derivative sediments, that
in a tectonically active system with a climate maximum, as in
Sahyadris, an equilibrium could be dynamically maintained between
weathering and erosional regimes. Also we infer from our study
that there exist certain commonalities between surface denudational
and mantle-magmatic geochemical differentiation processes. Similarity
of these processes, therefore, may have implication to common
UCC-like geochemistry of Post Archean sediments.
Keywords: Sahyadri mountains; Weathering; Erosion; Sediment geochemistry;
Rare earth elements; upper continental crust (UCC)』
1. Introduction
2. Geology and climate of the region
2.1. Field aspects
3. Methodology
4. Results
4.1. Mineralogy
4.2. Major and trace elements
4.3. Rare earth elements (REE)
5. Discussion
6. Conclusions
Acknowledgments
References