Spectral Characteristics of Pillow Lava Series Rock units in the
Near-IR (1300-2500nm) Range, Troodos Massif, Cyprus
Spectral Characteristics of Pillow Lava Series Rocks and Soils
Spectral curves of the soil and rock samples collected from Troodos pillow lava series rock units were recorded using the PIMA-II spectrometer. When re cording the spectral curves, several precautionary measures were taken to minimize the errors due to secondary sources and to get smooth curves. However, some of the resultant curves were slightly noisy as a result of surface roughness of the sample. The resultant spectral curves were analyzed using the PIMAVIEW software package, available with the instrument.
Spectral Features of Upper Pillow Lavas (UPL)
Spectra of UPL rocks and soils are displayed in Figures 1 & 2 respectively. All the samples which were used to record the above spectra are composted of a mixture of both pinkish and grayish portions of the UPL. The reflectance values of spectra are occupied in a very narrow zone which indicates the similar reflectance behaviour in all samples. In addition, they show identical absorption features having equal depths. The broad absorption bands at 1400 and 1900 nm positions are due to the presence of poorly ordered molecular water in all samples. These bands, especially the one at 1900 nm, are sharply enhanced due to the weathering effect.
A characteristic weak absorption feature is observed in the 2170-2270 nm range and it appears to be a result of combination vibrations involving the OH stretch and Al-OH bend of smectites (montmorillinite) or molecular water absorption of zeolites (natrolites). Apart from that, a very weak absorption band is observed at 2270-2330 nm in most of the samples and is due to CO
32- absorption to calcites, associated with vesicular fillings and inter pillow materials. In some samples, especially one at win 4-4, this feature is somewhat clear due to presence of pseudomorphs of olivine phenocrysts which are now replaced by iron stained calcites.
Similarity of reflectance and absorption features of both UPL rock and soil units indicate that the soils developed on Upper Pillow Lavas reflect the spectral signature of the parent UPL materials and their weathered products.
In some areas, UPL do not display any pinkish appearance and are solely comprised of gray coloured UPL. By overlapping the digitized geological boundaries of the published maps on the processed images, it is observed that some parts of the UPL succession appear similar in colour as LPL units. With the intention of resolving these features, spectra were recorded separately from pinkish inter pillow material, grayish pillow fragments and limey fragments of the inter pillow material of UPL, collected near the Agrokipia mine. These graphs are displayed in Fig. 3.
In the sample of pink inter pillow material, carbonates also occur at a minor constituent. The spectrum of pink inter pillow material exhibits two absorption bands. Out of these, the one at 2170-2265 nm range is broad and it may be due to bending of the Al-OH bond in montmorillonite or molecular water absorption of zeolites (natrolites). The other is a very weak which is observed at 2270-2370 nm wavelength region. It occurs as a result of CO
32- ions, associated with the pink inter pillow material. The reflectance values and absorption features of the spectrum of pink inter pillow material is almost identical to that of all UPL rock and soil units (Fig. 1 and 2). This indicates that the spectrum of UPL unit is influenced by the pink inter pillow materials.
The spectrum of limey materials was made by choosing a cream coloured lime fragment in the inter pillow materials. In this sample, apart from the carbonates, a scattered pink staining is also visible in lesser amounts. The spectrum shows considerable high overall reflectance due to its bright colour. Absorption bands of this sample are dominated by planner CO
32- ions, which results a sharp feature at 2275-2380 nm region. A very weak absorption at 2175-2260 nm region is either due to Al-OH bend of smectite or molecular water absorption of zeolites (natrolites) present in the pink stainings of the fragments.
However, except for vesicular fillings, this type of white limey fragments are not widespreaded in the UPL sequence and are restricted to minor associations within the pink inter pillow materials. Therefore overall absorption features of pinkish UPL are appeared to be influenced by the absorption bands due to clay minerals (smectites) or zeolites (natrolites) occurring within the pink inter pillow materials. However, a minor features at 2270-2380 nm region occurring in most of the samples in due to the presence of lesser amount of carbonates.
The other spectrum was recorded by selecting only the grayish coloured potion of upper Pillow Lavas. In this samples, considerable amounts of calcites occur as vesticular fillings. In addition, weathered olivine phenocrysts which are now replaced by iron stained calcites are also presents in considerable amounts. Therefore, the band at 2265-2365 nm of this material is solely due to the combination and overtone bands of the CO
32- ions occurring in the near IR region.
It is clear that when the pinkish inter pillow materials are absent in the UPL samples, the absorptions are influenced only by CO
32- ions. When comparing this spectrum with that of the LPL, it shows that both are similar in reflectance as well as in absorption features. So, when the pinkish inter pillow materials are absent in UPL, the discrimination of UPL and LPL is somewhat difficult. This may be the reason for UPL to appear in the same colour as in LPL in some parts of the processed images.
