NASA’s MESSENGER spacecraft has revealed geochemical diversity across Mercury’s volcanic crust. Near-infrared to ultraviolet spectra and images have provided evidence for the Fe2+-poor nature of silicate minerals, magnesium sulfide minerals in hollows and a darkening component attributed to graphite, but existing spectral data is insufficient to build a mineralogical map for the planet. Here we investigate the mineralogical variability of silicates in Mercury’s crust using crystallization experiments on magmas with compositions and under reducing conditions expected for Mercury. We find a common crystallization sequence consisting of olivine, plagioclase, pyroxenes and tridymite for all magmas tested. Depending on the cooling rate, we suggest that lavas on Mercury are either fully crystallized or made of a glassy matrix with phenocrysts. Combining the experimental results with geochemical mapping, we can identify several mineralogical provinces: the Northern Volcanic Plains and Smooth Plains, dominated by plagioclase, the High-Mg province, strongly dominated by forsterite, and the Intermediate Plains, comprised of forsterite, plagioclase and enstatite. This implies a temporal evolution of the mineralogy from the oldest lavas, dominated by mafic minerals, to the youngest lavas, dominated by plagioclase, consistent with progressive shallowing and decreasing degree of mantle melting over time.
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This research was carried out with financial support from a Marie Curie Intra-European Fellowship (SULFURONMERCURY-327046) to O.N. and the Belspo BRAIN-be program (BR/143/A2/COME-IN). O.N. also acknowledges support from the Belgian Fund for Scientific Research—FNRS for a position of Postdoctoral Researcher (Grant 1.B.341.16). B.C. is a Research Associate of the Belgian Fund for Scientific Research—FNRS. L. Nittler is thanked for providing the most recent XRS maps of Mercury. B. Mandler and V. Honour are thanked for careful editing of the manuscript.
The authors declare no competing financial interests.
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Namur, O., Charlier, B. Silicate mineralogy at the surface of Mercury. Nature Geosci 10, 9–13 (2017). https://doi.org/10.1038/ngeo2860
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