17:15 〜 18:30
[MIS12-P03] 火星オリンポス山山頂カルデラの地形・地質学的検討
キーワード：火星、カルデラ、惑星火山
The Olympus Mons, located in the northwestern part of the Tharsis Highlands on Mars, is the largest volcano in the Solar System. It has a basal width of 840 × 640 km (Plescia, 2004), and an elevation of 21,241 m (MOLA DEM data). Olympus Paterae are located in the northern part of the summit and are divided into six calderas (Mouginis-Mark, 2019). In this research, we reconsider the formation of Hames Patera based on the geological and morphological study. The Hermes Patera, located in the center of the western part of Olympus Paterae, has diameters of ~40 km. It could be divided into the western (Hermes Patera-1) and the eastern patera (Hermes Patera-2)(Fig. 1. Hermes Patera-1 and 2).
The floor of Hermes-Patera-2 is ~ 200 m deeper than that of Hermes Patera-1. The boundary of them is a north-south-strike cliff in the central area of the Patera recognized by a 10 m-interval topographic map that has been recognized as a wide ridge by Mouginis-Mark (2018). The elevation of the east side of the cliff is ~200 m lower than that of the west side. This landform constitutes a cliff topography with a dense concentration of contour lines on the 10 m interval contour map. The cliff shows an arc shape that curves northeast-trend at the north and southeast-trend at the south end of the cliff. The entire floor of the western part slopes toward the east. In contrast, the eastern floor is circular and slopes toward the northeast. The eastern shows a circularly enclosed topography, it is necessary to consider the different landforms of the western and eastern parts. Consequently, it is necessary to consider different collapses in Hermes Patera-1 and 2. The cliffs deserve the Hermes Patera-2 caldera rim. In addition, circumferential graben (Zuber and Mouginis-Mark, 1992) are distributed in Olympus Patera. Above all, we Focus on the west of Zeus patera and the graben of Hera patera. This graben surrounding Hermes Patera-is divided in Graben-1 and 2 based on its circumferential curvature. The Graben-1 restricted to the floors of the Hera Patera (Fig. 1. Graben-1). It has a curvature that is subparallel to the western rim of the Hermes Patera-1. The Graben-2 exists along the eastern margin of Hermes Patera-2 (Fig. 1. Graben-2). It has a smaller curvature than Graben-1, and each one is smaller in size. These graben were cut by Hermes Patera-1 and 2, and don't extend to the subsequent collapse of Patera.
Patera and graben are considered to have been formed in the following formation order. Hermes Patera-2 shows a lower elevation than Hermes Patera-1, and thus Hermes Patera-1 considered to have subsidence before Hermes Patera-2. The first, Graben-1 formed on the floors of Hera Patera, which is the subsidence of Hermes Patera-1. Subsequently, Hermes Patera-2 did subsidence of the caldera floors. Graben-2 formed on the floors of Zeus Patera, which is the subsidence of Hermes Patera-2. It can be estimated that these graben were formed at the same time as Hermes Patera-1 and 2 on the geological time scale.
Therefore, we need to reconsider Hermes Patera-1n the present proposed formation sequence of the Olympus Patera.
The floor of Hermes-Patera-2 is ~ 200 m deeper than that of Hermes Patera-1. The boundary of them is a north-south-strike cliff in the central area of the Patera recognized by a 10 m-interval topographic map that has been recognized as a wide ridge by Mouginis-Mark (2018). The elevation of the east side of the cliff is ~200 m lower than that of the west side. This landform constitutes a cliff topography with a dense concentration of contour lines on the 10 m interval contour map. The cliff shows an arc shape that curves northeast-trend at the north and southeast-trend at the south end of the cliff. The entire floor of the western part slopes toward the east. In contrast, the eastern floor is circular and slopes toward the northeast. The eastern shows a circularly enclosed topography, it is necessary to consider the different landforms of the western and eastern parts. Consequently, it is necessary to consider different collapses in Hermes Patera-1 and 2. The cliffs deserve the Hermes Patera-2 caldera rim. In addition, circumferential graben (Zuber and Mouginis-Mark, 1992) are distributed in Olympus Patera. Above all, we Focus on the west of Zeus patera and the graben of Hera patera. This graben surrounding Hermes Patera-is divided in Graben-1 and 2 based on its circumferential curvature. The Graben-1 restricted to the floors of the Hera Patera (Fig. 1. Graben-1). It has a curvature that is subparallel to the western rim of the Hermes Patera-1. The Graben-2 exists along the eastern margin of Hermes Patera-2 (Fig. 1. Graben-2). It has a smaller curvature than Graben-1, and each one is smaller in size. These graben were cut by Hermes Patera-1 and 2, and don't extend to the subsequent collapse of Patera.
Patera and graben are considered to have been formed in the following formation order. Hermes Patera-2 shows a lower elevation than Hermes Patera-1, and thus Hermes Patera-1 considered to have subsidence before Hermes Patera-2. The first, Graben-1 formed on the floors of Hera Patera, which is the subsidence of Hermes Patera-1. Subsequently, Hermes Patera-2 did subsidence of the caldera floors. Graben-2 formed on the floors of Zeus Patera, which is the subsidence of Hermes Patera-2. It can be estimated that these graben were formed at the same time as Hermes Patera-1 and 2 on the geological time scale.
Therefore, we need to reconsider Hermes Patera-1n the present proposed formation sequence of the Olympus Patera.