Spectral variations in serpentine and saponite 2.7 µm band due to heating under vacuum.
S. Sidhu1, D. Applin1, E. A. Cloutis1, and A. Maturilli2
1
Centre for Terrestrial and Planetary Exploration, University of Winnipeg, Winnipeg, Manitoba, R3B 2E9, Canada.
2Institute for Planetary Research, German Aerospace Center DLR, Rutherfordstr. 2, 12489 Berlin, Germany
Introduction: Carbonaceous chondrites (CCs) are scientifically significant as they present a window into the early Solar System.
Many classes of meteorites are considered primitive and provide an opportunity to study early solar system chemistry [1].
Carbonaceous chondrites in the sub-group CM2 likely underwent aqueous alteration to various degrees, resulting in formationof alteration minerals such as phyllosilicates [2]. Here we present a heating experiment conducted on two phyllosilicates and asimple two-component phyllosilicate + carbonaceous phase spectral analogue powder created at the Centre for Terrestrial andPlanetary Exploration (C-TAPE) at the University of Winnipeg, Canada.
Methods: Samples of saponite (C-TAPE ID: SAP104), serpentine (C-TAPE ID: ASB267), and CC spectral analogue, createdin-house, MUD008 (C-TAPE ID) were heated up to 900˚C under vacuum (~0.07 mbar) in 100°C increments for 1 hour at eachtemperature increment. Heating was conducted using an induction heating system in the external emissivity chamber at thePlanetary Spectroscopy Lab (PSL) at DLR, Berlin. Samples were allowed to cool in the vacuum chamber and then removed
from vacuum and transferred to the spectrometer. The sample was then evacuated down to ~0.1 mbar prior to the spectral
measurements. Data were collected using a Bruker Vertex 80v FTIR spectrometer using the Bruker A513 bi-directionalreflectance accessory. Reflectance data were collected over the VISNIR (0.4 – 1.1 µm) and MIR (1.1 – 20 µm), however for thepurposes of this report, only results up to 5 µm are discussed and displayed in the figures below. A new sample was used foreach temperature increment.
Results: Progressive heating of SAP104 generally displays a decrease in reflectance values as temperatures increase in theVISNIR (0.4 – 1.1 µm). In the MIR (1.1 – 20 µm), the spectra brighten slightly up to 300°C, after which the reflectance starts todecrease. The H2O absorption feature ~2.7 µm decreases in depth with increasing temperature, displaying qualitatively thedeepest band at the room temperature observation and the shallowest band at 900°C (see Figure 1).

Figure 1: MIR (1-5 µm) reflectance spectra of SAP104 (top), MUD008 (middle), and ASB267 (bottom) heated up to 900°C for 1 hour at each
100°C increment under vacuum.

ASB267 displays a similar trend upon heating as SAP104’s spectra regarding reflectance values: generally, decreases
in the VISNIR and slightly increases then decreases in the MIR with increasing temperature. Also, similar to SAP104, the ~2.7
µm absorption feature systematically decreases in depth as a function of increasing temperature.

MUD008 (90 wt.% SAP105 saponite, <45 µm grain size + 10 wt.% LCA101 carbon lampblack, <0.021 nm grain size)
gets spectrally brighter as a result of heating in both the VISNIR and the MIR, which may be due to the volatilization of carbon.
MUD008 displays a slight ~2.7 µm feature which gets shallower with increasing temperature, consistent with the spectra ofSAP104 and ASB267 (serpentine).
Other OH/H2O related features ~1.4 and 1.9 µm are observable in both SAP104 and ASB267 spectra. After exposure
to high temperatures, these absorption features also decrease in depth, consistent with the ~2.7 µm feature. Metal-OH featuresnear ~2.3 µm are also visible in both phyllosilicate samples. By 900°C, the absorption features are drastically reduced in depth.

Figure 2: VISNIR (0.4 – 1.1 µm) reflectance spectra of SAP104 <45 µm (top), MUD008 <45 µm (middle), and ASB267 <45 µm (bottom)
heated under vacuum up to 900°C in 100°C increments. Spectral artifact at ~0.64 µm.

Discussion: Our spectra show that several OH/H2O absorption features at ~1.4, ~1.9, and ~2.7 µm become shallower withincreasing temperature in SAP104 and ASB267. In addition, the Mg-OH features near ~2.3 µm also decrease in strength withincreasing temperature in both saponite and serpentine samples. These results are part of an on-going study investigating thespectral and mineralogical variations in saponite, serpentine and MUD008 due to thermal exposure under vacuum conditions.
Future work includes collecting X-ray diffraction data on the heated samples presented in this study and relate any
mineralogical changes to the spectral variations observed.
Acknowledgements: This project has received funding from the European Union’s Horizon 2020 research and innovation
programme under grant agreement No 871149. Thanks are due to the Canadian Space Agency (CSA), the Natural Sciences andEngineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), the Manitoba ResearchInnovation Fund (MRIF) and the University of Winnipeg for supporting this study.
References[1] McSween. H. 1979. Reviews of Geophysics & Space Physics 17:5. [2] Rubin. A. E. et al. 2007. Geochimica et
Cosmochimica Acta 71:9.