Hidaka Mountains Research Articles

日高山脈地震 (1970年1月21日) の余震活動

日高山脈地震 (1970年1月21日) の余震活動

The Intra-Yezo Disturbance and Sedimentation of the Middle Yezo Group

To make efficient use of isopach maps and lithofacies maps that are indispensable in oil exploration, it is required that such maps were prepared on the basis of stratigraphic units distinguished by significant time plane.The Cretaceous sediments which are widely distributed in the axial zone of Hokkaido are divided, in descending order, into the Hakobuchi group, the Upper Yezo group, the Middle Yezo group, the Middle Yezo group, the Lower Yezo group, and the Sorachi group. However, since this stratigraphic division is based largely on lithology, the boundaries of the respective groups may sometimes intersect the time plane obliquely. If such is the case, then the maps that were prepared from the stratigrephic division would be meaningless.Therefore, the present writer examined the propriety of the past methods of defining the base of the Middle Yezo group. His aim was to discern the base of the Middle Yezo group as a time plane and clarify the scope and significance of the Intra-Yezo disturbance.The writer has reached the following conclusion : The Intrayezo disturbance took place in a limited period of time during late Albian. It formed the uplifted zone that stretches north-south centering on the Ashibetsu mountains, and also upraised the west marginal area of the Hidaka mountains. This disturbance probably represents a crustal movement in the middle period of the history of development of a sedimentary basin.

Garnet-Cummingtonite Rocks from the Vicinity of Mt. Petegari-dake in the Central Part of the Hidaka Mountain Range, Hokkaido

Garnet-Cummingtonite Rocks from the Vicinity of Mt. Petegari-dake in the Central Part of the Hidaka Mountain Range, Hokkaido

Development of Communication in the Hidaka Mountains

Development of Communication in the Hidaka Mountains

Facies variation of gabbro on the nickeliferous pyrrhotite deposits(I)

The facies variation of the gabbro which is altered country rock of the nickeliferous pyrrhotite deposits, are reported in the present paper. The gabbro which is a member of the igneous rocks of the Hidaka metamorphic zone is distributed throughout the Hidaka Mountain range. The Satsunai-Dake area is situated in its northern part. The whole nickeliferous pyrrhotite deposits of the Hidaka metamorphic zone usually occur in the gabbro bodies. They are the coarsened gabbros owing to a kind of petroblastase. The olivine gabbro series has been distinguished as follows, (1) medium grained ophitic olivine gabbro, (2) coarse grained granoblastic olivine gabbro. Also in the norite series, (1) fine grained norite, (2) medium grained norite, (3) coarse grained granoblastic norite. The original rock of the olivine gabbro series is estimated the medium grained ophitic olivine gabbro (An70-75) and of the latter is the fine grained norite (An 33). These two series are used to be converged into coarse grained granoblastic olivine gabbro and norite with An60 plagioclase. In present investigation the plagioclase compositions are presented in the form of the An composition frequency diagrams. (Figures 4-10)

神居古潭結晶片岩中の特殊鉱物について

The Kamuikotan metamorphic complex develops as irregular long zone between the Mesozoic and Cenozoic formations along the western side of the Hidaka mountain ridge in Central Hokkaido. It runs about 200 km in a direction of nearly north to south, from areas of boundary of Teshio and Kitami Provinces to Hidaka Province.In general the normal Kamuikotan complex is made up the products due to slight regional metamorphism, in which the chief petrological members are black siliceous schists and next comes an abundance of green schists, small amonnts of quartzite, phyllite, mylonite and crysrtalline limestone are intercalated in the complex. From the geological and petrographical points of view, it may reasonably be assumed that the Kamuikotan complex can be readily correlated with the Franciscan formation in California.Comparatively large lenses or belts of the ultra-basic rocks run parallel with the trend of the Kamuikotan complex, being restricted mainly to the tectonic lines is the zone of the complex. It is noticeable that various interesting crystalline schists locally develop between the normal schistose rocks of the Kamuikotan complex and the ultra-basic intrusives, which have attracted special attention because of the presence of some special minerals, especially soda-bearing silicates. These special rocks may be a product brought about by contact metamorphic action due to ultra-basic intrusion and occurrence of the special minerals in them originated from pyrometasomatism, primarily owing to the action of some especially soda-rich hydrothermal solution drived from the ultra-basic intrusions.The subject matter of this paper is an outline of these some special minerals in the pyro-metasomatized rocks, with special reference to the general properties of the following members ; (A) glaucophane and crossite, (B) riebeckite and crocidolite, (C) aegirine-augite, (D) stilpnomelane, (E) piedmontite, (F) garnet, (G) lawsonite, and (H) pumpellyite.

On the diabase at the Meguro district, Hidaka Province, Hokkaido

There is a distinct difference in the distribution of the igneous rocks between the western and the eastern part of the Hidaka metamorphic zone. The peridotites and gabbroic rocks are widely distributed in the western part. The granites mainly occur in the eastern part. Meguro district is situated in the south-eastern part of the Hidaka Mountains. From petrological features, metamorphic zone of this district can be classified into the following six zones. 1. hornfels, 2. schistose hornfels, 3. banded gneiss, 4. cordierite migmatite, 5. gneissose migmatite, 6. granitic migmatite. These metamorphic rocks and migmatites are intruded by dikes of basic igneous rocks, such as diabase, dioritic gabbro, hornblende gabbro and amphibolite. It seems probable that the above-mentioned basic plutonic complexes and the basic dikes are geneticaly related. The diabases which occur as minor dikes (2-3m in average width) are more abundant than the other dike rocks. The diabase may furnish clues that will suggest further data necessary to solve a problem of the mutural relation between the migmatites and the basic igneous complexes. In the present paper, the writer have described the mode of occurrences and the microscopical features on the diabases. Some considerations on the distribution, alteration and intrusion of the diabases are given.

Notes on inclusions associated with migmatites at Saruru River district in Hidaka, Hokkaido

The so-called migmatites at the Saruru River district in the southeastern Hidaka Mountains are divided into two main types according to their petrographic characters, namely, the granitic migmatite and cordierite migmatite. The writer has described, in the present paper, the modes of occurrence and microscopical features of various inclusions in these two migmatites. The inclusions in the granitic migmatite and cordierite migmatite, which may be classified into the following groups, viz., the argillo-siliceous, calcareous and amphibolitic rocks. The gabbroic inclusion is commonly xenolith-like, which is found only in the granitic migmatite. As shown in the geological map the gabbroic inclusion occurs along the special zone. The argillo-siliceous and calcareous inclusions are probably explained as relics of the original country rocks which have escaped granitization. The gabbroic inclusion may be interpreted as a relict dike of the original country rocks which have escaped granitization.

On the Topography around the Hidaka Mountains in Hokkaido

On the Topography around the Hidaka Mountains in Hokkaido

On the Gneisses and Migmatites of the Central Hidaka Metamorphic Zone

Various kinds of Metamorphic rocks which are regarded as the product of the Hidaka Orogeny, constitute a prominent extended zone along the Hidaka mountain range., Around the upper course of the River Satsunai which is in the central part of the zone, argillaceous metamorphic rocks are widely developed., Their many rock facies are distinguishable and each facies is zonally arranged with N-S trend., In the argillaceous metamorphic rocks of this area, the writer has descriminated from east to west across the metamorphic zone, five different zones, viz., 1., hornfels zone, 2., banded gneiss zone, 3., coarse granitic migmatite zone, 4., breccia like quartz dioritic migmatite zone and 5., Plagioclase porphyroblast biotite gneiss zone., In this paper their chief petrographical characteristics are described and some considerations about their chemical compositions are also offered., As to the chemical compositions of these gneisses, the following features are conspicuous : 1) In the banded gneisses, K2O, Al2O3 contents are greater than in the rocks of any other facies., 2) Biotite-gneiss containing plagioclase porphyroblast has the highest Na2O/K2O, and contrasts with the banded gneiss which has high K2O and low Na2O contents., 3) K2O is comparatively more abundant also in the coarse granitic migmatite, this abundance may be due to the presence of much orthoclase in the coarse granitic migmatite., 4) In the breccia like quartz dioritic migmatite (agmatitic migmatite), the containing hornfels is more basic than is the hornfels of the hornfels zone., From the petrographical view-point, the rock forming biotites were studied., Their chemical compositions are varied corresponding to the differences in the bulk composition of the host rocks., Their relation is given in the Al2O -FeO -MgO Diagram., (Fig., 13)

Petrographical Studies on the Peridotite in the Horoman Region at the Southerr end of the Hidaka Mountain Range, Hokkaido

In Hokkaido, there are many ultra-mafic igneous bodies along the two parallel tectonic zones which are named the Kamuikotan zone and the zone respectively., These tectonic zones compose the geological back-bone of Hokkaido, and are regarded as the product of a Cretaceous orogenic movement which is called Hidaka Orogeny., It is believed that the zone may be an orogenic deep core and the Kamuikotan zone its westward over-thrusting zone., Many common characters have been noticed in the ultra-mafic igneous rocks of both tectonic zones., But contrasting features have also been observed in them., One of the most contrasted features is that the ultra-mafic rocks of the Kamuikotan zone are almost wholly serpentinized, on the other hand, those rocks are always in the unaltered peridotitic state in the zone., In the Horoman region, at the southern end of the tectonic zone, occurs the largest peridotite intrusive mass of the zone., The rock-forming minerals of this peridotite have an orientated arrangement, so the flow structure or layered structure are well marked in all parts of the mass., Judging from the arrangement of these flow structures, it seems that a large dome structure has existed at the centre of this peridotite mass, as presented in Fig 1., There are various kinds of rock facies in this peridotite mass, such as dunitic, pyroxene-peridotitic, and plagioclase-peridotitic facies etc., and each rock facies is developed in accordance with the flow structure., So, in a cliff, obvious appearance caused by the alternation of different kinds of rock facies seem clearly to be stratifications., (Plate 1)., -And their mineralassemblodges in each facies follow., 1., Olivine -(dark brown spinel) 2., Olivine -rhombic pyroxene-monoclinic pyroxene-(light brown spinel) 3., Olivine -rhombic pyroxene-monociinic pyroxene -(green spinel) 4., Olivine -monoclinic pyroxene-plagioclase-(black spinel) Optical characters of each mineralare given in Table 1., In this paper, the writer described the petrographical characters of each rock facies as a basis for further development of the knowledge about the Horoman peridotite mass., Further studies, especially concerning the intrusive tectonics, will be published in the near future by collaborators of the present writer.,

On the intrusive Bodies of the Mt. Poroshiri in Hidaka Mountains

On the intrusive Bodies of the Mt. Poroshiri in Hidaka Mountains