『Abstract
Clay mineralogy and major-element geochemistry of 35 surface
sediment samples collected in 21 major to moderate rivers of Luzon,
Philippines are used to evaluate the present chemical weathering
process. The clay mineral assemblage consists mainly of smectite
(average 86%) with minor kaolinite (9%) and chlorite (5%) and
very scarce illite (1%9, and does not show strong island-wide
differences. The major element results of both bulk and clay-fraction
sediments indicate that the formation of clay minerals is accompanied
by leaching of Ca and Na first and of Fe and Mn thereafter during
the chemical weathering process. A low-moderate chemical weathering
degree of bulk sediments and a moderate-intensive degree of clay-fraction
sediments are obtained in Luzon rivers based on proxies of chemical
index of alteration (CIA) and smectite crystalinity. It is suggested
that the majority of andesitic-basaltic volcanic and sedimentary
rocks along with the tectonically active geological setting and
sub-tropical East Asian monsoon climate are responsible for the
predominance of smectite in the clay mineral assemblage.』
1. Introduction
2. Geological and hydrographic settings
3. Sampling and analytical methods
4. Results
4.1. Clay minerals
4.2. Major elements
5. Discussion
5.1. Formation of smectite
5.2. Chemical mobility and weathering trends
6. Conclusions
Acknowledgments
References