北海道の第四紀火山灰および軽石堆積物の粘土鉱物
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概要
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A number of pyroclastic deposits of the late Pleistocene to Recent are widely developed in the southern part of Hokkaido. Their distribution, source, age of eruption and mode of emplacement have been studied in detail by many geologists and pedologists, resident in Hokkaido. However, mineralogical studies on inorganic colloids of them in the light of modern concepts of clay mineralogy are very scanty. In this paper, based on these geological and volcano-stratigraphical studies, the writers have tried to identify the clay minerals found as alteration products from these pyroclastic deposits, and to consider their processes of alteration from volcanic glasses to crystalline materials. For this purpose, 61 specimens (clay fractions) from eight typelocalities of the pyroclastic deposits were investigated by the use of differential thermal analysis, X-ray powder method, chemical composition, infra-red spectra and electron micrographs. The results are summarized as follows: 1) In the Sapporo-Tomakomai lowland district. In the upper horizon, called Tarumai a and b pumice-fall deposits (less than 300 yrs. B.P.), and volcanic glasses are not altered to allophane. It seems that gel-like substances and nonaltered glass fragments are the dominant components in the clay fraction. In Tarumai c and d pumicefall deposits, "allophane A" described by FIELDES is rich, and downwards in Eniwa a and b horizons (more than 5,000 yrs. B.P.), hydrated halloysite becomes remarkable. In the late Pleistocene deposits, namely in the Shikotsu pumice-flow and Shikotsu pumice-fall (20,000 yrs. B.P.), hydrated halloysite is predominant. 2) In the Tokachi district. The upper horizon is rich in allophane, while downwards, in Tokachi c_2 ash deposit (more than a few thousands years ago), it is characteristic that an irregular mixed layer of hydrated halloysite and halloysite is predominant. 3) In the Nemuro district. There is exceptional irregularity of alteration of allophane to hydrated halloysite. Namely in the upper Mashu f pumice-flow deposit (3,000-5,000 yrs. B.P.), the dominant clay mineral is allophane, that of Mashu k ash deposit is hydrated halloysite, and in the lower Mashu 1 pumice-fall deposit (more than 5,000 yrs. B.P.), allophane is dominant. These facts seem to suggest that an alteration process of allophane to hydrated halloysite is determined not only by the time factor, but is also influenced by the length of the weathering of the deposits and by the size of particles of the parent materials.
- 地学団体研究会の論文
- 1962-09-30