Birth of the East African Rift System: Nucleation of magmatism and strain in the Turkana Depression
Birth of the East African Rift System: Nucleation of magmatism and strain in the Turkana Depression
复制标题
东非裂谷系统的诞生：图尔卡纳凹陷的岩浆成核和应变
作者：
S. Boone;B. Kohn;A. Gleadow;C. Morley;C. Seiler;D. Foster
肯尼亚北部和埃塞俄比亚南部的图尔卡纳洼地含有大量与羽流相关的玄武岩，这些玄武岩标志着古近纪——近代东非裂谷系统（EARS）在大约 1977 年开始形成。 45马。因此，图尔卡纳凹陷对于理解陆内裂谷的起源至关重要。然而，图尔卡纳早期裂谷盆地形成的精确年代却很难确定。我们提供了来自南北走向的洛基查尔盆地边缘基底岩石的磷灰石裂变径迹和 (U-Th-Sm)/He 热年代学数据，这些数据限制了与裂谷相关的冷却的开始。这些数据文件的热历史模型表明，盆地边界的洛基查断层下盘经历了始新世到中新世的剥蚀冷却。这些结果，以及洛基查断层上盘中保存的约 7 公里的古近纪至中中新世同裂谷地层，表明洛基查盆地的形成早在大约 1977 年就开始了。 45–40 Ma。继承自早期中生代裂谷和始新世地幔柱岩浆作用的先前存在的岩石圈异质性可能促进了图尔卡纳凹陷中广泛同时发生的应变成核，时间长达~15 m.y.。早于其他地方的 EARS 启动。洛基查尔盆地和图尔卡纳其他地区的晚古近纪伸展明显早于东非中新世明显的羽流相关地形的形成，这表明其他机制，例如远场应力或地幔基底阻力，可能在 EARS 起始过程中发挥了关键作用。
The Turkana Depression of northern Kenya and southern Ethiopia contains voluminous plume-related basalts that mark the onset of the Paleogene–recent East African Rift System (EARS) at ca. 45 Ma. Thus, the Turkana Depression is crucial to understanding the inception of intracontinental rifting. However, the precise chronology of early rift-basin formation in Turkana is poorly constrained. We present apatite fission-track and (U-Th-Sm)/He thermochronology data from basement rocks from the margins of the north-south–trending Lokichar Basin that constrain the onset of rift-related cooling. Thermal history modeling of these data documents pronounced Eocene to Miocene denudational cooling of the basin-bounding Lokichar fault footwall. These results, along with ∼7 km of Paleogene to middle Miocene syn-rift strata preserved in the Lokichar fault hanging wall, suggest that formation of the Lokichar Basin began as early as ca. 45–40 Ma. Preexisting lithospheric heterogeneities inherited from earlier Mesozoic rifting and Eocene plume magmatism likely facilitated the broadly concurrent nucleation of strain in the Turkana Depression, up to ∼15 m.y. earlier than EARS initiation elsewhere. Late Paleogene extension in the Lokichar Basin and other parts of Turkana significantly predate the Miocene creation of pronounced plume-related topography in East Africa, suggesting that other mechanism(s), such as far-field stresses or mantle basal drag, likely played a critical role during EARS inception.