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

IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of African Earth Sciences Pub Date : 2024-06-21 DOI:10.1016/j.jafrearsci.2024.105326
Netsanet Mulugeta , Tesfaye Kidane , Kahsay Nugsse , Geramu Fufa , Demise Tadessa , Ameha A. Muluneh
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引用次数: 0

摘要

在埃塞俄比亚主断裂带(MER)中部布塔吉拉火山链的 27 个地点共采集了 208 个古地磁岩芯样本,为了解构造旋转提供了依据。岩芯样本取自埃塞俄比亚中部裂谷西缘的火成岩(1.7-2.54Ma)、玄武岩和砂岩单元(<1.6Ma)。每个岩芯样本都使用双试样进行分析,并采用分步交替场(AF)和热(Th)退磁技术。此外,每个地点的单个样本都被用于岩石磁性实验。详细的岩石磁性实验确定了钛磁铁矿、磁铁矿和赤铁矿为剩磁载体磁性矿物。自然剩磁(NRM)方向分析显示了两个成分:1)低温(300 °C)和低场(20 mT)去除的低稳定性(LS)成分;2)加热 300 °C或 20 mT 增量的高稳定性(HS)成分,其矢量指向图的原点,表明了特征剩磁(ChRM)。除一个位点外,所有位点都显示出反向极性 NRM。根据 19 个点位计算出的倾斜校正平均方向为 Do = 355.7°,Io = 9.9°(N = 19,K = 22.9,α95 = 7.3°),表明逆时针方向为 6.2° ± 6.相对于稳定非洲的参考偶极地磁场方向 2Ma Dx = 1.9°, Ix = 15.5° (N = 32, K = 105.6, α95 = 2.5°),逆时针(CCW)构造旋转 2° (Besse and Courtillot, 2003)。研究区域边界断层的斜向断裂和纯垂向滑动运动学特征可能导致了这种轻微的逆时针旋转,这与 Corti 等人 2013 年的模拟模型预测一致。
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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.

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来源期刊
Journal of African Earth Sciences
Journal of African Earth Sciences 地学-地球科学综合
CiteScore
4.70
自引率
4.30%
发文量
240
审稿时长
12 months
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.
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