1991 Fiscal Year Final Research Report Summary
Greenstone and terrigeous clastics in the Hidaka Supergroup, northern Hokkaido
| Project/Area Number |
02640600
|
|---|
| Research Category |
Grant-in-Aid for General Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
地質学一般
|
|---|
| Research Institution | Yamaguchi University |
|---|
Principal Investigator |
KIMINAMI Kazuo Fac. of Sci., Yamaguchi Univ., Assistant Prof., 理学部, 助教授 (20127757)
|
|---|
| Project Period (FY) |
1990 – 1991
|
| Keywords | accretionary prism / greenstone / melange / collision of active ridge / Hidaka Supergroup / Rurochi Formation |
|---|
| Research Abstract |
I have gained the following results through the research.
1). The Rurochi Formation. which occurs in the northern part of Hokkaido. consists mainly of black shale, alternating beds of sandstone and snale, and greenstones. Black shale and exotic blocks of green siliceous shale withi in the formation yield Eocene radiolarian assemblages. The greenstones are composed of massive basalt, pillow basalt and basic tuff. Basalts have been intruded frequently into black shale. Glassy chilled margins of basalt and baked parts of black shale confirm the primary nature of these igneous contacts. Argillaceous xenoliths in the basaltic rock, and pillow lavas with inter-pillow black shale are also common.
2). The Makimine Formation is made mainly up argillite and greenstones. The greenstones comprise dolerite, massive basalt, pillow basalt and basic tuff. Some dolerite sills with double chilled margins less than a few centimeters in thickness are interlayered with black shale. In most cases the black shale shows gradational alteration to light-colored baked rock over a range of a few centimeters from dolerite contacts, due to the thermal effect of dolerite emplacement. - Dolerites commonly contain xenoliths of black shale. These facts indicate that the basaltic rocks were intruded into and extruded upon unconsolidated fine-grained clastic sediments.
3). The Mugi Formation is represented by argillite and greenstones. Some of the basalt lavas with chilled margins are in immediate contact with black shale, which has locally suffered thermal effects along its contact. Xenoliths of black shale occur locally in the basalts.
4). The basaltic rocks in the formations were generated at a spreading ridge on the basis of their chemical features. In this context, we therefore conclude that the greenstones were emplaced in connection with a ridge-forearc collision.
|
Research Products
(10 results)
