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The Caloris group is a set of geologic units on Mercury. McCauley and others〔McCauley, J. F., Guest, J. E., Schaber, G. G., Trask, N. J., and Greeley, Ronald, 1980, Stratigraphy of the Caloris Basin, Mercury: Icarus, 1980〕 have proposed the name “Caloris Group” to include the mappable units created by the impact that formed the Caloris Basin and have formally named four formations within the group, which were first recognized and named informally by Trask and Guest. Like the Imbrium and Orientale Basins on the Moon, Caloris Basin is surrounded by an extensive and well-preserved ejecta blanket〔〔Guest, J. E., and O’Donnell, W. P., 1977, Surface history of Mercury: A review: Vistas in Astronomy, v. 20, p. 273–300.〕 As on the Moon, where ejecta from the better preserved basins was used to construct a stratigraphy, the ejecta from the Caloris Basin also can be used as a marker horizon. This ejecta is recognizable to a distance of about one basin diameter in the Tolstoj quadrangle and the adjacent Shakespeare quadrangle to the north. Undoubtedly, the ejecta also influences a large part of the terrain to the west that was recently photographed by MESSENGER. A stratigraphic and structural comparison between the Orientale and Caloris Basins has been made by McCauley.〔McCauley, J. F., 1977, Orientale and Caloris: Physics of the Earth and Planetary Interiors, v. 15, no. 2–3, p. 220–250.〕 McCauley and others〔 have proposed a formal rock stratigraphy for the Caloris Basin that we have adopted on the present map. This stratigraphy is patterned after that used in and around the Orientale Basin on the Moon〔Scott, D. H., McCauley, J. F., and West, M. N., 1977, Geologic map of the west side of the Moon: U.S. Geological Survey Miscellaneous Investigations Series Map I-1034, scale 1:5,000,000.〕 and should aid in the future recognition of pre- and post-Caloris events over a broad expanse of the surface of Mercury. Crater degradation chronologies, such as the one modified from Trask,〔 and correlations between plains units on the basis of crater frequency may aid in tying much of the remainder of the surface of Mercury to the Caloris event. Unlike the Imbrium-related stratigraphy of Shoemaker and Hackman,〔Shoemaker, E. M., and Hackman, R. J., 1962, Stratigraphic basis for a lunar time scale, in Kopal, Zdenek, and Mikhailov, Z. K., eds., The Moon: International Astronomical Union Symposium, 14th, Leningrad, U.S.S.R., 1960: London, Academic Press, p. 289–300.〕 that devised for Mercury is a rock rather than a time stratigraphy. It recognizes the existence of an orderly, in essence isochronous sequence of mappable units around Caloris that are similar in character to those recognized around the better preserved impact basins of the Moon such as Orientale, Imbrium, and Nectaris. The four formations are described in order of occurrence from the rim of Caloris Basin outward: ==Caloris Montes Formation== (詳細はscarp or ring of the Caloris Basin and grade outward into smaller blocks and lineated terrain. The Caloris Montes Formation is very similar in morphology to and is considered the equivalent of the massif facies of the Montes Rook Formation around the Orientale Basin.〔〔 The Caloris Montes is interpreted as basin rim deposits consisting of ejecta from deep within Caloris that is mixed with but generally overlies uplifted and highly fractured prebasin bedrock.〔 A gap is present in the Caloris Montes toward the southeast; its origin is unknown, but it is somewhat similar to the gap on the east side of the Imbrium Basin, where the mountain ring cuts the edge of the Serenitatis Basin. On Mercury, however, we have no evidence for the presence of a preexisting basin east of Caloris. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Caloris Group」の詳細全文を読む スポンサード リンク
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