Publication Date:
2022-03-22
Description:
We investigated mid‐infrared reflectance spectra of anorthosite samples from Mt. Briand near the Manicouagan impact structure. Microprobe analyses of the plagioclase minerals reveal that they have a similar chemical composition (labradoritic), which is corroborated by the location of the Christiansen Feature at around 7.96 μm (1256 cm−1). However, their respective spectral shapes differ from each other in the region of the reststrahlen bands. This is linked to the degree of Al,Si order within the plagioclase minerals, which also correlates with the previously assumed distance of the sample site to the impact melt. Powdering and sieving led to remarkable changes in the spectra resulting from different mechanical stability of minerals contained in the sample. Our data show that even very weakly shocked (6–10 GPa, shockstage S2) anorthosites could show spectra of Al,Si disordered plagioclase which we attribute to post shock heating after the impact shock. Consequently, the degree of Al,Si order has to be taken into account in the interpretation of remote sensing data. A comparison of synthetic linear mixture with an average Mercury spectrum reveals the possible presence of more or less anorthositic material with reduced degree of Al,Si order of the plagioclase component on Mercury's surface. The results of our study are helpful for the interpretation of data returned by space missions, especially for MERTIS ‐ an infrared spectrometer on its way to Mercury.
Description:
Plain Language Summary:
The studied rocks, which contain predominantly the feldspar mineral plagioclase, are very common in our Solar System, for example, on the Moon and probably also on Mercury. The surface of planets without atmosphere, like Moon and Mercury are constantly the target of asteroid impacts. These impacts cause changes in the constituents of the rocks. The studied samples are from the area near a meteorite crater and show weak effects of the former meteorite impact. The infrared spectra of the samples have different shapes. This shape does not correlate with the chemical composition, but with the distribution of aluminum and silicon ions in the plagioclase components of the investigated samples. This distribution is often underestimated in remote sensing. Our study shows that this distribution of these ions is related to a previously assumed distance of the sample location from the impact. The results are useful for interpreting remote sensing data coming back from space missions. In our case, in particular, from an infrared spectrometer on its way to the planet Mercury called MERTIS. The study also presents a spectrum calculated from various mineral spectra comparable to the samples analyzed. This spectrum shows similarities to an average Mercury surface spectrum and suggests that the feldspars on the Mercury surface have a very disordered ion distribution.
Description:
Key Points:
Low impact shock with proposed impact melt influences Al,Si order of plagioclases.
Grinding of rocks leads to modal changes of the minerals.
Potential plagioclases with reduced degree of Al,Si order on the surface of Mercury.
Description:
Deutsches Zentrum für Luft‐ und Raumfahrt (DLR)
http://dx.doi.org/10.13039/501100002946
Language:
English
Type:
doc-type:article
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