『Abstract
Physical and chemical weathering of primary minerals of granitic
till in the proglacial area of Morteratsch (Switzerland) was investigated
using cathodoluminescence (CL), Nomarski differential interference
contrast (DIC) microscopy and scanning electron microscope (SEM-EDX).
The investigated time-span ranges from 0 to 140 years of sediment
exposure. For the very early stage of weathering or soil formation
only little information is available. The main aim of our investigation
was consequently to see whether weathering of primary minerals
can be detected in such a short time-span using for the first
time for soils well-established methods as CL and Nomarski DIC
microscopy in geo- and material science such. For that purpose,
the fine earth fraction (<2 mm) of topsoil samples was investigated.
Some physical weathering had taken place within 140 years. The
delamination of biotite seems to increase with time. SEM and CL
analyses also demonstrate early weathering of quartz by evidencing
edge pits and structural bonds - such as Si-O-Si in quartz - that
start to break and to transform into free radicals. K-feldspar
and plagioclase contain Fe. When using Fe3+ as reference
point (680-700 nm) to standardise the CL spectra, the Al-O--Al
defects of K-feldspar exhibit a relative decrease with time; this
was not the case for plagioclase. The CL measurements showed that
the investigated apatite contained REE (rare earth elements) in
the crystal structure. However, none of the other techniques (DIC,
SEM-EDX) was helpful in detecting any specific weathering features
for apatite. In the time span of 140 years, epidote weathering
was evidenced using XRD in a previous investigation and here using
DIC microscopy (morphologic changes). Several mineral changes
could be traced within a very short weathering sequence using
the applied techniques. These changes include physical (e.g. biotite),
chemical or crystal structure 'K-feldspar, biotite) feature. Such
an analytical combination is promising, therefore, for the detection
of chemical, physical and mineralogical characteristics and changes
in very young glacial sediments.
Keywords: Cathodoluminescence; Nomarski DIC microscopy; SEM-EDX;
Weathering; Quartz; Apatite』
1. Introduction
2. Study area
3. Material and methods
3.1. Soil sampling and preparation
3.2. SEM-EDX
3.3. Cathodoluminescence
3.4. Nomarski DIC microscopy
3.5. Total element analysis
4. Results
4.1. Quartz
4.1.1. SEM-EDX
4.1.2. CL
4.1.3. Nomarski DIC microscopy
4.2. Feldspar
4.2.1. SEM-EDX
4.2.2. CL
4.2.3. Nomarski DIC microscopy
4.3. Biotite
4.3.1. SEM-EDX
4.3.2. CL
4.3.3. Nomarski DIC microscopy
4.4. Apatite (accessory phase)
4.4.1. SEM-EDX
4.4.2. CL
4.4.3. Nomarski DIC microscopy
4.5. Epidote
4.5.1. SEM-EDX
4.5.2. CL
4.5.3. Nomarski DIC microscopy
5. Discussion
6. Conclusions
Acknowledgements
References