Analytical Identification and Characterization of the Major Geochemical Terranes of Mercury's Northern Hemisphere

Abstract

Principal component analysis of Mercury chemical composition maps provide analytically robust identification of distinct geochemical terranes on Mercury. The results reveal a wide diversity of terrane types, including previously identified terranes like the high-Mg terrane and northern terranes, as well as a new terrane not identified in prior studies, the intermediate composition, high-K (IHK) terrane. We propose that the IHK is material excavated from beneath the Borealis planitia by the Rustaveli-basin-forming impact. In addition to the new IHK terrane, Caloris-basin-like materials are recognized outside of the basin rim for the first time. This indicates that the terrane type found within the Caloris basin is not a unique consequence of the Caloris impact event. Geochemical modeling of terrane compositions facilitates interpretation of the principal components in terms of mineral end-members, making the individual principal component maps also a measure of the relative variability of pyroxenes, olivine, and plagioclase. Our mineralogical modeling also confirms the low-viscosity nature of the lava that flooded Mercury's surface to produce the present-day crust, consistent with the geomorphology of Mercury's extensive volcanic plains units.