Internal structure and formation of the Cape Sukoton doleritic intrusion, Rebun Island, Hokkaido, Japan

Accession number;03A0594928
Title;Internal structure and formation of the Cape Sukoton doleritic intrusion, Rebun Island, Hokkaido, Japan
Author;HIRAHARA YUKA(Niigata Univ., Graduate School of Sci. and Technol., JPN)   SHUTO KENJI(Niigata Univ., Fac. Sci., JPN)   
Journal Title;Journal of the Geological Society of Japan
Journal Code:F0528A
ISSN:0016-7630
VOL.109;NO.8;PAGE.442-458(2003)
Figure&Table&Reference;FIG.15, TBL.2, REF.24
Pub. Country;Japan
Language;Japanese
Abstract;The outcrop of the Cape Sukoton intrusion, a constituent of Miocene doleritic sill swarm in the northern part of Rebun Island, north Hokkaido, is 1,600*600m wide and more than 240m thick, and dips gently eastward. It can be lithologically divided into three zones; the upper Columnar Joint Zone, middle Banded Structure Zone, and lower Massive Zone. The appearance of columnar joints is remarkable in doleritic rocks of the Columnar Joint Zone. Banded structures and columnar joints are also well developed in the doleritic rocks of the Banded Structure Zone, whereas both banded structures and columnar joints are not observed in porphyrites of the Massive Zone. Based on structural analysis of columnar joints, lithological descriptions of rocks in each zone, and the presence of interlayered sill-sediment structure at the boundary between the intrusion and sedimentary rocks, the Cape Sukoton intrusion is infered to have formed in the following main three stage magmatic events. 1) first stage (formation of the Columnar Joint Zone); intrusion of a basaltic magma into wet and poorly consolidated sediments, and melanocratic to leucocratic dolerites and leucocratic andesitic veins were generated during subsequent cooling contraction and crystallization of magma, and columnar joints were formed throughout the body, 2) second stage (formation of the Banded Structure Zone); intrusion of a new basaltic magma into the Columnar Joint Zone and wet poorly consolidated sediments. During cooling of the magma, banded structures composed of stratified vesicular and non-vesicular layers have been formed in melanocratic dolerites, and 3) third stage (formation of the Massive Zone); intrusion of another magma into the Banded Structure Zone, prior to the complete cooling of the Banded Structure Zone.... (author abst.)