{"title":"Propagating rifts: the roles of crustal damage and ascending mantle fluids","authors":"Folarin Kolawole, Rasheed Ajala","doi":"10.5194/se-15-747-2024","DOIUrl":null,"url":null,"abstract":"Abstract. We investigate the upper-crustal structure of the Rukwa–Tanganyika rift zone in East Africa, where the Tanganyika rift interacts with the Rukwa and Mweru-Wantipa rift tips, evidenced by prominent fault scarps and seismicity across the rift interaction zones. We invert earthquake P-wave and S-wave travel times to produce 3D upper-crustal velocity models for the region and perform seismicity cluster analysis to understand strain accommodation in rift interaction zones and at the propagating rift tips. The resulting models reveal the occurrence of anomalously high Vp/Vs (primary-to-secondary wave velocity) ratios in the upper crust beneath the Rukwa and Mweru-Wantipa rift tips – regions with basement exposures and sparse rift sedimentation. We detect distinct earthquake families within the deeper clusters which exhibit a temporal evolution pattern characterized by an upward linear trend that suggests triggering caused by upward fluid migration and creep failure. A spatial transition from proximal tip zones dominated by a thinned crust and through-going crustal and upper-mantle seismicity to distal tip zones with a thick crust and dominantly upper-crustal seismicity indicates an along-axis variation in the controls on rift tip deformation. Overall, the collocation of basement faulting, crustal and upper-mantle seismicity, and high upper-crustal Vp/Vs ratios suggests a mechanically weakened crust at the rift tips, likely accommodated by brittle damage from crustal-bending strain and thermomechanical alteration via ascending fluids (mantle-sourced volatiles and hydrothermal fluids). These findings provide new insights into the physics of the propagation, linkage, and coalescence of continental rift tips – a necessary ingredient for initiating continental-breakup axes.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.2000,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Solid Earth","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.5194/se-15-747-2024","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Abstract. We investigate the upper-crustal structure of the Rukwa–Tanganyika rift zone in East Africa, where the Tanganyika rift interacts with the Rukwa and Mweru-Wantipa rift tips, evidenced by prominent fault scarps and seismicity across the rift interaction zones. We invert earthquake P-wave and S-wave travel times to produce 3D upper-crustal velocity models for the region and perform seismicity cluster analysis to understand strain accommodation in rift interaction zones and at the propagating rift tips. The resulting models reveal the occurrence of anomalously high Vp/Vs (primary-to-secondary wave velocity) ratios in the upper crust beneath the Rukwa and Mweru-Wantipa rift tips – regions with basement exposures and sparse rift sedimentation. We detect distinct earthquake families within the deeper clusters which exhibit a temporal evolution pattern characterized by an upward linear trend that suggests triggering caused by upward fluid migration and creep failure. A spatial transition from proximal tip zones dominated by a thinned crust and through-going crustal and upper-mantle seismicity to distal tip zones with a thick crust and dominantly upper-crustal seismicity indicates an along-axis variation in the controls on rift tip deformation. Overall, the collocation of basement faulting, crustal and upper-mantle seismicity, and high upper-crustal Vp/Vs ratios suggests a mechanically weakened crust at the rift tips, likely accommodated by brittle damage from crustal-bending strain and thermomechanical alteration via ascending fluids (mantle-sourced volatiles and hydrothermal fluids). These findings provide new insights into the physics of the propagation, linkage, and coalescence of continental rift tips – a necessary ingredient for initiating continental-breakup axes.
摘要我们研究了东非鲁夸-坦噶尼喀断裂带的上地壳结构,坦噶尼喀断裂与鲁夸和姆韦鲁-万提帕断裂尖端相互作用,突出的断层疤痕和跨越断裂相互作用区的地震活动证明了这一点。我们反演了地震 P 波和 S 波的传播时间,为该地区建立了三维上地壳速度模型,并进行了地震群分析,以了解裂谷互动区和传播裂谷尖端的应变容纳情况。由此产生的模型揭示了鲁克瓦和姆韦鲁-万蒂帕裂谷顶端--基底暴露和裂谷沉积稀少的区域--下方上地壳出现异常高的 Vp/Vs(一次波速与二次波速)比。我们在较深的地震群中发现了不同的地震家族,这些地震家族的时间演化模式以上升的线性趋势为特征,表明触发地震的原因是流体向上迁移和蠕变破坏。从地壳变薄、贯穿地壳和上地幔地震为主的近端尖区到地壳较厚、上地壳地震为主的远端尖区的空间过渡,表明裂谷端部变形的控制存在沿轴变化。总体而言,基底断裂、地壳和上地幔地震以及上地壳高Vp/Vs比值的搭配表明,裂谷尖端的地壳机械性减弱,很可能是由地壳弯曲应变的脆性破坏和通过上升流体(地幔源挥发物和热液)产生的热机械改变所造成的。这些发现为了解大陆裂谷尖端的传播、联系和凝聚的物理学原理提供了新的视角--这是启动大陆断裂轴的必要因素。
期刊介绍:
Solid Earth (SE) is a not-for-profit journal that publishes multidisciplinary research on the composition, structure, dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. The journal invites contributions encompassing observational, experimental, and theoretical investigations in the form of short communications, research articles, method articles, review articles, and discussion and commentaries on all aspects of the solid Earth (for details see manuscript types). Being interdisciplinary in scope, SE covers the following disciplines:
geochemistry, mineralogy, petrology, volcanology;
geodesy and gravity;
geodynamics: numerical and analogue modeling of geoprocesses;
geoelectrics and electromagnetics;
geomagnetism;
geomorphology, morphotectonics, and paleoseismology;
rock physics;
seismics and seismology;
critical zone science (Earth''s permeable near-surface layer);
stratigraphy, sedimentology, and palaeontology;
rock deformation, structural geology, and tectonics.