{"title":"埃塞俄比亚中部主裂谷布塔吉拉火山区早更新世逆时针旋转的古地磁证据","authors":"Netsanet Mulugeta , Tesfaye Kidane , Kahsay Nugsse , Geramu Fufa , Demise Tadessa , Ameha A. Muluneh","doi":"10.1016/j.jafrearsci.2024.105326","DOIUrl":null,"url":null,"abstract":"<div><p>A total of 208 paleomagnetic core samples were collected from twenty-seven sites within the Butajira volcano chains of the central Main Ethiopian rift (MER), providing insights into tectonic rotation. Core samples were taken from ignimbrite (∼1.7–2.54Ma), basalt, and trachyte rock units (<1.6Ma) along the western margin of the central MER. Each core sample underwent analysis using twin specimens subjected to stepwise alternate field (AF) and thermal (Th) demagnetization techniques. Furthermore, a single specimen from every site was employed for rock-magnetic experiments. Detailed rock magnetic experiments identified titano-magnetite, magnetite, and hematite as the remanence carrier magnetic minerals. The natural remanent magnetization (NRM) directional analysis revealed two components:1) a low-stability (LS) component removed by low-temperature (<300 °C) and low-field (<20 mT) and 2) a high-stability (HS) with heating >300 °C or 20 mT increments showed vectors pointing to the plot's origin, indicative of the characteristic remanent magnetization (ChRM). All sites, except one, displayed reverse polarity NRM. The tilt-corrected mean direction calculated from 19 sites, yielded D<sub>o</sub> = 355.7°, I<sub>o</sub> = 9.9° (N = 19, K = 22.9, α<sub>95</sub> = 7.3°), indicates a 6.2° ± 6.2° counterclockwise (CCW) tectonic rotation relative to the reference dipole geomagnetic field direction of 2Ma D<sub>x</sub> = 1.9°, I<sub>x</sub> = 15.5° (N = 32, K = 105.6, α<sub>95</sub> = 2.5°) for stable Africa (Besse and Courtillot, 2003). The oblique rifting and pure-dip slip kinematics that characterize the border faults in the study area could have caused this minor counterclockwise rotation and agrees with analogue model prediction of Corti et al.,2013.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"216 ","pages":"Article 105326"},"PeriodicalIF":2.2000,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Paleomagnetic evidence of early Pleistocene counterclockwise rotation in the Butajira volcanic zone, central Main Ethiopian rift\",\"authors\":\"Netsanet Mulugeta , Tesfaye Kidane , Kahsay Nugsse , Geramu Fufa , Demise Tadessa , Ameha A. Muluneh\",\"doi\":\"10.1016/j.jafrearsci.2024.105326\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>A total of 208 paleomagnetic core samples were collected from twenty-seven sites within the Butajira volcano chains of the central Main Ethiopian rift (MER), providing insights into tectonic rotation. Core samples were taken from ignimbrite (∼1.7–2.54Ma), basalt, and trachyte rock units (<1.6Ma) along the western margin of the central MER. Each core sample underwent analysis using twin specimens subjected to stepwise alternate field (AF) and thermal (Th) demagnetization techniques. Furthermore, a single specimen from every site was employed for rock-magnetic experiments. Detailed rock magnetic experiments identified titano-magnetite, magnetite, and hematite as the remanence carrier magnetic minerals. The natural remanent magnetization (NRM) directional analysis revealed two components:1) a low-stability (LS) component removed by low-temperature (<300 °C) and low-field (<20 mT) and 2) a high-stability (HS) with heating >300 °C or 20 mT increments showed vectors pointing to the plot's origin, indicative of the characteristic remanent magnetization (ChRM). All sites, except one, displayed reverse polarity NRM. The tilt-corrected mean direction calculated from 19 sites, yielded D<sub>o</sub> = 355.7°, I<sub>o</sub> = 9.9° (N = 19, K = 22.9, α<sub>95</sub> = 7.3°), indicates a 6.2° ± 6.2° counterclockwise (CCW) tectonic rotation relative to the reference dipole geomagnetic field direction of 2Ma D<sub>x</sub> = 1.9°, I<sub>x</sub> = 15.5° (N = 32, K = 105.6, α<sub>95</sub> = 2.5°) for stable Africa (Besse and Courtillot, 2003). The oblique rifting and pure-dip slip kinematics that characterize the border faults in the study area could have caused this minor counterclockwise rotation and agrees with analogue model prediction of Corti et al.,2013.</p></div>\",\"PeriodicalId\":14874,\"journal\":{\"name\":\"Journal of African Earth Sciences\",\"volume\":\"216 \",\"pages\":\"Article 105326\"},\"PeriodicalIF\":2.2000,\"publicationDate\":\"2024-06-21\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of African Earth Sciences\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S1464343X24001596\",\"RegionNum\":4,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOSCIENCES, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of African Earth Sciences","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1464343X24001596","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
Paleomagnetic evidence of early Pleistocene counterclockwise rotation in the Butajira volcanic zone, central Main Ethiopian rift
A total of 208 paleomagnetic core samples were collected from twenty-seven sites within the Butajira volcano chains of the central Main Ethiopian rift (MER), providing insights into tectonic rotation. Core samples were taken from ignimbrite (∼1.7–2.54Ma), basalt, and trachyte rock units (<1.6Ma) along the western margin of the central MER. Each core sample underwent analysis using twin specimens subjected to stepwise alternate field (AF) and thermal (Th) demagnetization techniques. Furthermore, a single specimen from every site was employed for rock-magnetic experiments. Detailed rock magnetic experiments identified titano-magnetite, magnetite, and hematite as the remanence carrier magnetic minerals. The natural remanent magnetization (NRM) directional analysis revealed two components:1) a low-stability (LS) component removed by low-temperature (<300 °C) and low-field (<20 mT) and 2) a high-stability (HS) with heating >300 °C or 20 mT increments showed vectors pointing to the plot's origin, indicative of the characteristic remanent magnetization (ChRM). All sites, except one, displayed reverse polarity NRM. The tilt-corrected mean direction calculated from 19 sites, yielded Do = 355.7°, Io = 9.9° (N = 19, K = 22.9, α95 = 7.3°), indicates a 6.2° ± 6.2° counterclockwise (CCW) tectonic rotation relative to the reference dipole geomagnetic field direction of 2Ma Dx = 1.9°, Ix = 15.5° (N = 32, K = 105.6, α95 = 2.5°) for stable Africa (Besse and Courtillot, 2003). The oblique rifting and pure-dip slip kinematics that characterize the border faults in the study area could have caused this minor counterclockwise rotation and agrees with analogue model prediction of Corti et al.,2013.
期刊介绍:
The Journal of African Earth Sciences sees itself as the prime geological journal for all aspects of the Earth Sciences about the African plate. Papers dealing with peripheral areas are welcome if they demonstrate a tight link with Africa.
The Journal publishes high quality, peer-reviewed scientific papers. It is devoted primarily to research papers but short communications relating to new developments of broad interest, reviews and book reviews will also be considered. Papers must have international appeal and should present work of more regional than local significance and dealing with well identified and justified scientific questions. Specialised technical papers, analytical or exploration reports must be avoided. Papers on applied geology should preferably be linked to such core disciplines and must be addressed to a more general geoscientific audience.