北上山地の白亜紀-古第三紀火成作用に関する2,3の問題

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Cretaceous-Paleogene igneous activity in the Kitakami Mountains is shown as follows; [Table] Niitsuki volcanics is composed of hornblende-augite andesite and augite andesite, and Kanaegaura volcanics is composed of augite basalt, olivine-augite basalt and augite andesite. Most of andesites are calc-alkali rock series, however some of basalts are slightly alkalic. ？olcanic rocks of the Harachiyama formation are calc-alkali andesite and dacite. Massive dacites of the Pacific coast side were called quartz keratophyre because of enrichment of Na_20 and may be intrusive rocks heavily altered by auto-metamorphism. Andesitic and basaltic rocks are altered to low grade metamorphic rocks showing prehnite-pumpellyite facies. Orikabe-Taro type granitic masses, which intruded before intrusion of large granitic masses such as Senmaya and Miyako masses, are adamellite to quartz monzonite and accompany granite porphyry. These granitic rocks are epizonal and are closely associated with the early Cretaceous volcanic rocks. The Taro type granites and massive dacites form a intrusive-tectonic zone in the Taro belt. Contact aureoles around the masses are generally narrow. Inner side of the aureole is characterized by biotite and amphibole and outer side by hydrothermal alteration minerals such as calcite, epidote and chlorite, however pyroxene hornfels often occurs in the innermost side. Character of contact metamorphism is resemble to that of the Tertiary granitic rocks.
日本地質学会の論文
1979-09-20

著者

島津光夫
新潟大学理学部地質鉱物学教室

北上山地の白亜紀-古第三紀火成作用に関する2,3の問題

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