四国東部および紀伊半島西部の三波川帯の苦鉄質・超苦鉄質貫入岩について:(その2)紀伊半島西部の三波川帯の苦鉄質・超苦鉄質貫入岩と三波川帯四国区での三波川帯の形成と貫入岩との関係について [in Japanese] On the mafic to ultramafic intrusive rocks of the Sambagawa zone in the Eastern Shikoku and the Western Kii Peninsula:Part 2. The Western Kii peninsula-with special reference to the relations between the formation of the Sambagawa zone and intrusive rocks in the Eastern Shikoku and the Western Kii peninsula [in Japanese]
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The Sambagawa zone of this area can be divided into the following three regions. a) Northern region with igneous activity b) Central region with no igneous activity c) Southern region with igneous activity In the northern region with igneous activity on the southern bank of the Kinokawa, the Shibuta and linori formations are composed largely of basic volcanic ejecta, overlain by the Ryumon formation which consists chiefly of pelitic schist. As the geologic map (Fig. 4) indicates, these formations do not extend indefinitely in the strike direction, near the town of Kudoyama the limori formation pinches out. In this region the intrusion of igneous rocks took place during the erogenic movement, as proven by the occurrence of mafic to ultramafic rocks. These igneous rocks are distributed in the direction of the strike of the sedimentary rocks. The mode of intrusion is conformable with the surrounding sedimentary rocks. The mafic to ultramafic rock comprise dunite, cortlandite, syenitic gabbro, serpentinite and meta-gabbro. The larger ultramafic body consists of dunite, wehrlite, and gabbro occurs near the summit of Ryumondake, and recrystallized olivines are found in dunite. The ultramafic rocks of this region are mostly characterized by the presence of cortlandite which consists of titaneierous augite, kaersutite, olivine, and titanobiotite. Also in this region syenitic mafic rocks occur in two localitites. In the southern igneous activity region excepting so-called Mikabu zone the ultramafic rocks are mostly cortlandite. Mafic intrusive rocks conformably intruded into the surrounding sedimentary rocks. Whether these rocks can not be determined mostly alkaline or non-alkaline by the chemical composition of the clinopyroxene, but in one locality, the mafic rock is found to be an alkaline rock by the chemical composition of the clinopyroxene and the rock. The rock is composed to titanaugite, kaersutite, plagioclase and olivine. The locality is situated in the southern part of the southern igneous activity region. In the central non-igneous activity region, cortlandite is rarely found as lenticular bodies parallel to axial plane cleavage in pelitic schist. In the northern and southern igneous activity regions, the transformation of the subsided area into the upheaval area with gentle folding structure is attributed to the intrusion of the ultramafic and mafic igneous rocks. The formation of higher grade metamorphic rock in the upper horizon of the Sambagawa Zone is related to the intrusion of the mafic and ultramafic intrusive rocks. Namely, the author assumed that the reversal thermal structure originate in the combination of the presence of impermiable bed and heat transfar with evaporation of water in the sedimentary rocks due to intrusion of intrusive rocks, excepting the contact metamorphism by intrusion and emplacement of the mafic to ultramafic rocks.
- Earth Science (Chikyu Kagaku)
Earth Science (Chikyu Kagaku) 37(6), 312-328, 1983
The Association for the Geological Collaboration in Japan