講演情報
[T7-P-14]島根県隠岐道後におけるカタクラスティックな断層の構造解析とテクトニックな意義
*桑原 一平1、スリハリ ラクシュマナン1、向吉 秀樹1 (1. 島根大学)
キーワード：
隠岐島後、断層、カタクレーサイト、日本海、テクトニクス
The Oki Dogo, an island located in the southwestern part of the Sea of Japan comprises Proterozoic to Cenozoic Oki metamorphic rocks, and unconformably overlayed by volcanic and sedimentary rock strata from the late Oligocene to Miocene. Based on their age, the Oki metamorphic rocks are considered to be fragments of the continental crust (Kawabata et al., 2022), and are expected to record the geologic history prior to the opening of the Japan Sea and also tectonic process after that.
Recent studies focused on metamorphism and geochronology of the Oki Dogo, but studies intend to describe the fault activities are limited. Based on our detailed field surveys cataclastic fault zones are identified in the vicinity of the Oki metamorphic rocks.
In this study, we describe the location, structural evolution and tectonic significance of these cataclastic fault rocks. Fault outcrops are mainly identified in the metamorphic rocks along Araki river, Oku river and Nakamura river outcrops. Overall, ENE–WSW and WNW–ESE strike is prominent along the identified faults. The E–W, NE–SW, and NW–SE strike is also present in some locations. Most of the fault outcrops dip south, dip angle ranges between 40° to 70°. The width of the damage zone varies from 1–8 m. Reverse sense of movement predominant in the cataclasites, but in few locations normal and right lateral sense is also observed. In the Araki and Oku rivers, where fault outcrops observed, rhyolite intrusions are also identified in the near vicinity of the fault outcrops. Notably intrusive rocks are not affected by the fault activity, and we propose that the cataclasite faulting is possibly associated with these rhyolitic intrusions.
Our study found fault outcrops only in the metamorphic rocks, not in any other lithologies. This limitation makes it difficult to determine the relative age of the faulting. To address this challenge and better understanding of the stress fields associated with fault activities, we plan to conduct detailed fieldwork in the future. Identifying faults in Cenozoic strata and comparing them with those observed in this study will be crucial for clarifying the timing and nature of fault formation.
Reference: Kawabata et al., 2022, J. Metamor. Geol., 40, 257-286.
Recent studies focused on metamorphism and geochronology of the Oki Dogo, but studies intend to describe the fault activities are limited. Based on our detailed field surveys cataclastic fault zones are identified in the vicinity of the Oki metamorphic rocks.
In this study, we describe the location, structural evolution and tectonic significance of these cataclastic fault rocks. Fault outcrops are mainly identified in the metamorphic rocks along Araki river, Oku river and Nakamura river outcrops. Overall, ENE–WSW and WNW–ESE strike is prominent along the identified faults. The E–W, NE–SW, and NW–SE strike is also present in some locations. Most of the fault outcrops dip south, dip angle ranges between 40° to 70°. The width of the damage zone varies from 1–8 m. Reverse sense of movement predominant in the cataclasites, but in few locations normal and right lateral sense is also observed. In the Araki and Oku rivers, where fault outcrops observed, rhyolite intrusions are also identified in the near vicinity of the fault outcrops. Notably intrusive rocks are not affected by the fault activity, and we propose that the cataclasite faulting is possibly associated with these rhyolitic intrusions.
Our study found fault outcrops only in the metamorphic rocks, not in any other lithologies. This limitation makes it difficult to determine the relative age of the faulting. To address this challenge and better understanding of the stress fields associated with fault activities, we plan to conduct detailed fieldwork in the future. Identifying faults in Cenozoic strata and comparing them with those observed in this study will be crucial for clarifying the timing and nature of fault formation.
Reference: Kawabata et al., 2022, J. Metamor. Geol., 40, 257-286.
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