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General Geology, Vol. 1 No. 1, December 15, 2017 [full-issue PDF link]

Preface: At launching of a new online journal General Geology [PDF link]
Jinichiro Maeda
General Geology, Vol. 1, Page i.

Geologic age of the Chobushi Formation distributed in the northeast of the Yudonuma, eastern Hokkaido, Japan [PDF link]
Tsumoru Sagayama
General Geology, Vol. 1, Page 1–6.


Three siltstone samples collected from the Chobushi Formation being in northeast of the Yudonuma, eastern Hokkaido, are investigated geologic age by diatom analysis. The most abundant species obtained from three samples is Neodenticula koizumi Akiba et Yanagisawa and common species are Neodenticula kamtschatica (Zabelina) Akiba et Yanagisawa,Thalassiosira jouseae Akiba and Thalassiosira oestrupii (Ostenfeld) Porshkina-Labrenko s.l., suggesting Neodenticula kamtschatica-Neodenticula koizumii Zone (NPD8; 3.5-3.9~2.6-2.7 Ma,Yanagisawa and Akiba, 1998) for the diatom age of the Chobushi Formation. This fossil assemblage coincides with that obtained from a siltstone fragment dredged from sea floor at a depth of 21 m off the Yudonuma. This evidence indicates that the Chobushi Formation extends to the offshore area of the Yudonuma.

K–Ar whole-rock ages of high-Fe/Mg intrusive rocks from northern Hidaka magmatic belt, Hokkaido, Japan [PDF link]
Jinichiro Maeda, Satoru Yoneyama, Shuhei Nakata, Takehiro Matsuda and Kohei Yamashita
General Geology, Vol. 1, Page 7–14.


We present K–Ar whole-rock ages of two high-Fe/Mg intrusive rocks from northern Hidaka magmatic belt: 20.9 ± 1.0 Ma for Ichinohashi fayalite-bearing biotite granodiorite in the Ichinohahsi plutonic complex and 21.4 ± 1.1 Ma for Fujinosawa quartz monzodiorite in the Okushibetsu plutonic complex. It is suggested that high-Fe/Mg magmatism occurred during the Early Miocene (ca. 20 Ma) throught the whole of the Hidaka magmatic belt, central Hokkaido.

Vertical tearing of subducting slabs [PDF link]
Kazuo Kiminami
General Geology, Vol. 1, Page 15–34.


Tearing of subducting slabs is a wide-spread phenomenon in present-day and ancient subduction zones, and resultant upwelling of asthenosphere is partially responsible for generation of specific magmas such as alkaline mafic and adakitic magmas. Here, I review some factors leading to vertical tearing of subducting slabs and their Miocene–Quaternary examples. Segmentation caused by fracturing and/or tearing of the Philippine Sea slab subducting beneath Southwest Japan has been inferred from geophysical data by many authors. I also review the studies on segmentation of the Philippine Sea slab, and tentatively suggest a possibility that the origin of Aonoyama monogenic volcanoes made up of adakite lavas may be related to a possible vertical-tear of the subducting Philippine Sea slab.

Visit for lost streams in Sapporo―“a City of Water”, Sapporo― [PDF link]
Seigo Miyasaka
General Geology, Vol. 1, Page 35–45.

Late Cenozoic strata of the western hills of Sumirnykh (Keton) area in Sakhalin Island, the Russian Federation [PDF link]
Takao Oka
General Geology, Vol. 1, Page 46–70.

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