Geology applications of Fourier transform infrared spectroscopy
Fourier transform infrared spectroscopy (FTIR) is a spectroscopic technique that has been used for analyzing the fundamental molecular structure of geological samples in recent decades.
The intrinsic physicochemical property of each particular molecule determines its corresponding IR absorbance peak, and therefore can provide characteristic fingerprints of functional groups (e.g. C-H, O-H, C=O, etc.).
[4] The fundamental components of a Fourier transform spectrometer include a polychromatic light source and a Michelson Interferometer with a movable mirror.
[4] The modified Beer-Lambert Law equation is commonly used in geoscience for converting the absorbance in the IR spectrum into the species concentration:
Water is thought to have significant role in affecting mantle rheology, either by hydrolytic weakening to the mineral structure or by lowering the partial melt temperature.
[15] The presence of hydrous components within NAMs can therefore (1) provide information on the crystallization and melting environment in the initial mantle; (2) reconstruct the paleoenvironment of early terrestrial planet.
[9] By coupling a synchrotron light source to the FTIR spectrometer, the diameter of the IR beam can be significantly reduced to as small as 3 μm.
[3] By incorporating the other parameters, (i.e. temperature, pressure and composition), obtained from micro thermometry, electron and ion microprobe analyzers, it is able to reconstruct the entrapment environment and further infer the magma genesis and crustal storage.
The above approach of FTIR has successfully detect the occurrence of H2O and CO2 in numbers of studies nowaday, For examples, the water saturated inclusion in olivine phenocryst erupted at Stromboli (Sicily, Italy) in consequences of depressurization,[3] and the unexpected of occurrence of molecular CO2 in melts inclusion in Phlegraean Volcanic District (Southern Italy) revealed as the presence of a deep, CO2-rich, continuous degassing magma.
The evolution of vesiculation can be summarized in these steps:[16] In order to understand the eruption process and evaluate the explosive potential, FTIR spectromicroscopy is used to measure millimeter-scale variations in H2O on obsidian samples near the pumice outcrop.
[16] The diffusive transfer of water from the magma host has already completed in the highly vesicular pumice which volatiles escapes during explosion.
[16] The maximum H2O content measured from FTIR spectrometer is substituted into the diffusion equation as the initial value that resembles a volatile supersaturated condition.
The duration of the vesiculation event can be controlled by the decrease of water content across a distance in the sample as the volatiles escape into the bubbles.
[5] They share similarity to cells or organelles with different origins listed below: Acritarchs samples are collected from drill core in places where Proterozoic microfossils have been reported, e.g. Roper Group (1.5–1.4 Ga) and Tanana Formation (ca.
[4][5] Comparison of the chain length and presence of structure in modern eukaryotic microfossil and the acritarchs suggests possible affinities between some of the species.
For example, the composition and structure of the Neoproterozoic acritarch Tanarium conoideum is consistent with algaenans, i.e. the resistant wall of green algae made up of long-chained methylenic-polymer that can withstand changing temperature and pressure throughout the geological history.
[5][21] Both of the FTIR spectra obtained from Tanarium conoideum and algaenans exhibit IR absorbance peaks at methylene CH2 bend (c. 1400 cm−1 and 2900 cm−1).
[6][7] For example, the well-preserved cuticle of cordaitales fossils, an extinct order of plant, found in Sydney, Stellarton and Bay St. George shows similar FTIR spectra.
