Horokanai Ophiolite Fm
Period:
Jurassic
Age Interval:
Province:
Hokkaido
Type Locality and Naming
Sorachi-Yezo Belt (Yezo Main Zone)
Synonym:
Lithology and Thickness
Although significantly disrupted, it shows an ophiolite succession from serpentinized peridotite via gabbro, amphibolite and MORB-like basalt, to cherty (or tuffaceous) siliceous sedimentary rocks which are conformably overlain by clastic rocks of the Yezo Group. The base of the peridotite is in fault contact with crystalline schists of the Kamuikotan metamorphic rocks. Among these, basalt and siliceous sedimentary rocks are correlated with the Sorachi Group. The peridotite consists mainly of harzburgite and dunite (both with highly depleted chemical characteristics: Katoh & Nakagawa 1986) and serpentinites, and is intruded by numerous gabbro and diorite dykes with chilled margins (Igarashi et al. 1985).
Lithology Pattern:
Volcanics
Relationships and Distribution
Lower contact
No data
Upper contact
Lower Sorachi Gr (conformable)
Regional extent
Sorachi-Yezo Belt (Yezo Main Zone). The Horokanai Ophiolite (Asahina & Komatsu 1979; Ishizuka 1980, 1981, 1985, 1987) typically occurs in the Horokanai area in the north-central part of the Sorachi-Yezo Belt.
GeoJSON
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Fossils
Chert overlying the basalt layer yields Late Jurassic radiolarians (Ishizuka et al. 19836; Kawabata 1988; Kiminami et al. 1992a).
Age
Age Span:
Beginning stage:
Bajocian
Fraction up in beginning stage:
0
Beginning date (Ma):
170.90
Ending stage:
Kimmeridgian
Fraction up in the ending stage:
0
Ending date (Ma):
154.78
Depositional setting
Depositional pattern:
Additional Information
Compiler:
Hayato Ueda. 2g Hokkaido. in Moreno, T., WALLIS, S., Kojima, T. & Gibbons, W. (Eds) 2016. The Geology of Japan. Geological Society. London. 201-220.