5:15 PM - 7:15 PM
[SGL23-P05] NNE-SSW compressive stress during the intrusion of andesite dikes into the granite of the San-in Belt
Keywords:Paleo-stress, Dike, Andesite, Cretaceous, Paleogene
Introduction
It is known that the igneous activity of the southwest Japan arc from the Cretaceous to the Paleogene followed a pattern of active terms before 60 Ma, a hiatus from 60 to 46 Ma, and a resumption after 46 Ma, reflecting characteristic tectonics such as the subduction of the oceanic ridge (Yamaoka & Wallis, 2023; Imaoka et al., 2011, etc.). The history of these igneous activities has been revealed mainly through the chemical composition and dating of igneous rocks.
On the other hand, data on the changes in stress that drive these igneous activities is still scarce. In this study, we will estimate the paleo-stress from the attitude data of the dikes that intrude into the granites in the Misasa area of Tottori Prefecture, which is located in the San-in region where granites from the Late Cretaceous to the Paleogene are widely distributed, in order to constrain the stress field around 60 Ma.
Geological setting
The Chugoku region, which is located in the inner zone of southwestern Japan, is widely distributed with granite, and is divided into the Ryoke, Sanyo, and San-in belts. Solidification ages of these granites show a systematic tendency to become younger from west to east, and also show a tendency to become younger in the order of the Ryoke, Sanyo, and San-in belts (Nakajima, 2018). The Cretaceous to Paleogene granites are distributed in the study area. Zircon U-Pb ages of granites near the study area is reported to be 66-64 Ma (Iida et al., 2015), but the solidification ages of the volcanic dikes that intrude the granite have not been measured, and the timing of the intrusion of these dikes is unknown.
Results
The survey identified 17 dikes intruded into the granite, and rock samples were collected and the orientations of the dikes were measured. The elemental composition of the rock samples was determined using X-ray fluorescence analysis. Based on the results of plotting the obtained elemental composition data based on the lithology classification diagram of Winchester & Floyd (1977), we identified 15 samples as non-alkaline andesite to basalt and 2 samples as dacite. A zircon U-Pb age of 63.0 ± 0.2 Ma was obtained from the dacite dike. The dacite and andesite-to-basalt dikes have similar attitudes, so we will treat them as intruded at the same time.
We estimated the paleo-stress using attitude data for 15 dikes that were identified as andesite to basalt. As a result, we detected NNE-SSW compressional strike-slip faulting stress. Paleo-stress during the Cretaceous to Paleogene was estimated using the attitudes of andesite dikes in the Hida and Tono areas of the Chubu region. The attitude of the dikes intruding at approximately 60 Ma indicates either E-W compression or N-S tension (Niimura et al., 1994; Oikawa et al., 2006), which is different from the stress detected in the Misasa area. In the Yanahara area, which is located about 40 km southeast of our survey area, a maximum horizontal compressive stress axis in the N-S direction was detected from the quartz porphyry dikes of approximately 54 Ma (Masumoto and Wadatsumi, 1983). In order to discuss the spatiotemporal variation of the stress in the period, it is necessary to expand the attitude data of dikes with age constraints.
References
Yamaoka & Wallis, (2023), EPS, 10:62. Imaoka et al., (2011), JAES, 40, 509-533. Nakajima, (2018), JGSJ, 124(8), 603-625 (in Japanese). Iida et al., (2015), IAR, 24, 205-220. Winchester & Floyd, (1977), Chemical Geology, 20, 325-343. Niimura et al., (1994), JMPEG, 89, 285-293 (in Japanese). Oikawa et al., (2006), JGSJ, 112(10), 616-619 (in Japanese). Masumoto & Wadatsumi, (1983), JGSJ, 89(2), 87-97 (in Japanese).
Acknowledgments
This study was partly funded by the METI, Japan, as part of its R&D supporting program titled “Establishment of Technology for Comprehensive Evaluation of the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste” (grant no. JPJ007597; fiscal year 2023–2024).
It is known that the igneous activity of the southwest Japan arc from the Cretaceous to the Paleogene followed a pattern of active terms before 60 Ma, a hiatus from 60 to 46 Ma, and a resumption after 46 Ma, reflecting characteristic tectonics such as the subduction of the oceanic ridge (Yamaoka & Wallis, 2023; Imaoka et al., 2011, etc.). The history of these igneous activities has been revealed mainly through the chemical composition and dating of igneous rocks.
On the other hand, data on the changes in stress that drive these igneous activities is still scarce. In this study, we will estimate the paleo-stress from the attitude data of the dikes that intrude into the granites in the Misasa area of Tottori Prefecture, which is located in the San-in region where granites from the Late Cretaceous to the Paleogene are widely distributed, in order to constrain the stress field around 60 Ma.
Geological setting
The Chugoku region, which is located in the inner zone of southwestern Japan, is widely distributed with granite, and is divided into the Ryoke, Sanyo, and San-in belts. Solidification ages of these granites show a systematic tendency to become younger from west to east, and also show a tendency to become younger in the order of the Ryoke, Sanyo, and San-in belts (Nakajima, 2018). The Cretaceous to Paleogene granites are distributed in the study area. Zircon U-Pb ages of granites near the study area is reported to be 66-64 Ma (Iida et al., 2015), but the solidification ages of the volcanic dikes that intrude the granite have not been measured, and the timing of the intrusion of these dikes is unknown.
Results
The survey identified 17 dikes intruded into the granite, and rock samples were collected and the orientations of the dikes were measured. The elemental composition of the rock samples was determined using X-ray fluorescence analysis. Based on the results of plotting the obtained elemental composition data based on the lithology classification diagram of Winchester & Floyd (1977), we identified 15 samples as non-alkaline andesite to basalt and 2 samples as dacite. A zircon U-Pb age of 63.0 ± 0.2 Ma was obtained from the dacite dike. The dacite and andesite-to-basalt dikes have similar attitudes, so we will treat them as intruded at the same time.
We estimated the paleo-stress using attitude data for 15 dikes that were identified as andesite to basalt. As a result, we detected NNE-SSW compressional strike-slip faulting stress. Paleo-stress during the Cretaceous to Paleogene was estimated using the attitudes of andesite dikes in the Hida and Tono areas of the Chubu region. The attitude of the dikes intruding at approximately 60 Ma indicates either E-W compression or N-S tension (Niimura et al., 1994; Oikawa et al., 2006), which is different from the stress detected in the Misasa area. In the Yanahara area, which is located about 40 km southeast of our survey area, a maximum horizontal compressive stress axis in the N-S direction was detected from the quartz porphyry dikes of approximately 54 Ma (Masumoto and Wadatsumi, 1983). In order to discuss the spatiotemporal variation of the stress in the period, it is necessary to expand the attitude data of dikes with age constraints.
References
Yamaoka & Wallis, (2023), EPS, 10:62. Imaoka et al., (2011), JAES, 40, 509-533. Nakajima, (2018), JGSJ, 124(8), 603-625 (in Japanese). Iida et al., (2015), IAR, 24, 205-220. Winchester & Floyd, (1977), Chemical Geology, 20, 325-343. Niimura et al., (1994), JMPEG, 89, 285-293 (in Japanese). Oikawa et al., (2006), JGSJ, 112(10), 616-619 (in Japanese). Masumoto & Wadatsumi, (1983), JGSJ, 89(2), 87-97 (in Japanese).
Acknowledgments
This study was partly funded by the METI, Japan, as part of its R&D supporting program titled “Establishment of Technology for Comprehensive Evaluation of the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste” (grant no. JPJ007597; fiscal year 2023–2024).