|Title||Aspects of mineral transformation during weathering of volcanic materials : the microscopic and submicroscopic level|
|Source||Agricultural University. Promotor(en): N. van Breemen; P. Buurman. - S.l. : Jongmans - ISBN 9789054852797 - 143|
|Department(s)||Laboratory of Soil Science and Geology|
|Publication type||Dissertation, internally prepared|
|Keyword(s)||vulkanische gronden - andepts - andosols - bodemvorming - fysische eigenschappen - mechanische eigenschappen - natuurlijke hulpbronnen - vulkanische gesteenten - basalt - vulkanische lava - pedologie - bodemmicromorfologie - volcanic soils - andepts - andosols - soil formation - physical properties - mechanical properties - natural resources - volcanic rocks - basalt - volcanic lava - pedology - soil micromorphology|
Mineral transformation at the earth surface is a complex process. In volcanic ejecta, such transformations tend to be fairly rapid. Many weathering studies on volcanic materials have been carried out at different scales of observations, mostly using bulk samples. However, to get a proper understanding of the mechanisms of weathering of primary minerals and formation secondary minerals it is necessary to obtain data of undisturbed material at the scale of observation that micromorphology and submicroscopy deal with. Weathering studies at the micrometre scale with help of micromorphology showed the heterogenous character of mineral weathering and the co- existence of different secondary minerals.
The main objective of papers in this thesis was to characterize and explain alteration of primary minerals and formation of secondary minerals at the particle level in volcanic soils in relation to (micro) environmental conditions.
In a chronosequence of Quaternary terraces of the Allier in France, micromorphological and sub microscopical analyses showed:
A technique is described to isolate undisturbed microparts of pedofeatures from thin sections. Such microparts can subsequently be analysed by Transmission Electron Microscopy. This technique allows performance of micromorphological, mineralogical and chemical analyses on one undisturbed micro sample at micrometre to nanometre scales.
Isotropic coatings in the C horizon of a young Hapludand in Guadeloupe and in the C and R horizons of an old Hapludand in Costa Rica, both developed on andesitic volcanic materials were allophanic. Isotropic coatings present in the Bw horizons of both soils contain allophane and imogolite. The Al/Si molar ratios in the coatings in the Bw horizons are higher than those in the coatings of the C and R horizons. Anisotropic coatings are wholly gibbsitic and occur only in the Bw horizon of the older Costa Rican Hapludand. The gibbsitic coatings show a gradual transition to isotropic coatings and both types looks alike in plane polarized light suggesting a genetic relationship. The allophane coatings resulted from initial weathering of the parent materials, whereas the gibbsite coatings represent the ultimate stage of secondary mineral formation. The differences in chemical and mineralogical composition of the coatings are thought to be the result of different leaching conditions at the macro and micro scale.
2:1 Phyllosilicates in Hapludands on Holocene andesitic beach ridges in Costa Rica occur as clay pseudomorphs after primary minerals. They are inherited from hydrothermally altered parent material from which the beach ridges were derived, and are not due to post depositional soil formation. Weathering and biological activity affect the clay pseudomorphs which leads to clay- sized particles consisting of 2:1 phyllosilicates. They are incorporated in the allophanic groundmass that results from actual soil formation in the Hapludands.
Isotropic coatings also found in a West Java (Indonesia) Oxisol on andesitic volcanic parent materials are probably due to weathering of airborne ash additions. The coatings recrystallize to anisotropic coatings suggesting a neoformed genesis. Both types of coatings appear to be common in three andesitic catenas in Indonesia. The amount of coatings and the crystallinity tend to increase as the dry season become more pronounced. The anisotropic coatings can easily be confused with illuviation coatings.