Planet Mercury: Volcanism in a theatre of global contraction, with examples from the Hokusai quadrangle

摘要

Mercury's geological history has been dominated by global contraction caused by secular cooling of the planet's interior. This cooling has had a profound effect on the expression of the planet's volcanism and tectonism, and the expressions of these two surface evolutionary processes are deeply intertwined. Here, we use case studies from the Hokusai quadrangle of Mercury to gain insight into the interplay between Mercury's volcanism and tectonism, which we review throughout this paper. We perform the first crater size-frequency analysis of the southernmost extent of Borealis Planitia, Mercury's largest expanse of volcanic plains, and find that it formed-3.8-3.7 Ga. We discuss the importance of "intermediate plains", a widespread unit in the Hokusai quadrangle, as the manifestation of relatively low-volume effusions with an uncertain stratigraphic relationship with Borealis Planitia. Finally, we detail the formation of the Suge Facula pitted ground during the geological history of Rachmaninoff crater, and hypothesise that such textures probably formed more widely on Mercury but have often either been buried by thick lava flows or otherwise obscured. Unanswered questions in this work can be used to drive the next phase of Mercury exploration and research with the arrival of the BepiColombo mission. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).