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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Stability of the Upper Nile drainage network (Ethiopia) deduced from (U-Th)/He thermochronometry: implications for uplift and erosion of the Afar plume dome
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Stability of the Upper Nile drainage network (Ethiopia) deduced from (U-Th)/He thermochronometry: implications for uplift and erosion of the Afar plume dome

机译：从（U-Th）/ He温度计时推论得出的上尼罗河排水网络（埃塞俄比亚）的稳定性：对阿法尔羽毛穹顶隆起和侵蚀的影响

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One of the best places to investigate the role of a mantle plume in creating topography at the onset of continental breakup is the Ethiopian volcanic province since it is the youngest and best preserved case of a large igneous province dissected by a system of rifts. In the center of the volcanic province, the northwestern Ethiopian plateau which surrounds the Afar depression displays the highest topography and experienced more than 1 km of surface uplift. Because hydrology and physiography are genetically linkekd, understanding the long-term evolution of these upper basins has implications regarding the morphotectonic evolution of the plateau as well as the paleo-hydrological evolution of the whole Nile River. We report the results of a combined thermochronological and morphological study aimed at understanding the long-term stability of the upper Blue Nile drainage network. Apatite and titanite He ages have been determined for crystalline basement samples collected below the lava pile, in various key sites of the drainage network. Titanite He ages, which range from 213 to 520 Ma, are in good agreement with published K-feldspar Ar-Ar data and most likely reflect post-Pan-African cooling of the Ethiopian basement. Apatite He ages, which range from 45 to 107 Ma, display a trend of decreasing age with increasing crustal depth in the Blue Nile gorge, which is interpreted as partial resetting of pre-existing ages due to basement burial because of the thick pile of flood lavas erupted 30 Ma ago. Simulations of apatite He age partial resetting suggest that erosion initiated in the Blue Nile canyon as early as 25-29 Ma ago, whereas erosion would have started after 11 Ma along the present retreat scarp. The early onset of erosion in the Blue Nile canyon suggests that: (i) volcanic and uplift-related tectonic divides represent long-lived (20 - 30 Myr) pre-breakup divides, and (ii) the elevated plateau physiography, which controls most of the present-day Nile hydrology, has existed since the Oligocene. We propose that the plateau represents the preserved part of a large uplifted dome, related to Afar plume impingement, and/or to massive underplating triggered by Oligocene continental flood basalt differentiation. In this case, the topographic development of the western Afar margin, which is related to extension and drift of the Arabian plate, would be mainly the result of the collapse of the Afar area from an initially elevated region.
机译：埃塞俄比亚火山省是研究大陆破裂开始时地幔柱在形成地形中作用的最佳地点之一，因为它是裂谷系统剖开的大型火成岩省的最年轻且保存最完好的案例。在火山省的中心，环绕阿法尔凹陷的西北埃塞俄比亚高原地势最高，经历了超过1 km的地表隆升。因为水文和生理学是遗传上的联系，所以了解这些上游盆地的长期演化对高原的构造构造演化以及整个尼罗河的古水文演化具有重要意义。我们报告了结合热年代学和形态学研究的结果，旨在了解上部Blue Nile排水网络的长期稳定性。已经确定了在排水网络的各个关键位置采集到的熔岩堆下面的结晶基底样品的磷灰石和钛矿的He年龄。钛铁矿的年龄范围在213至520 Ma之间，与已发表的K长石Ar-Ar数据非常吻合，并且很可能反映了泛非对埃塞俄比亚地下室的冷却作用。磷灰石的He年龄范围为45至107 Ma，在青尼罗河峡谷中，随着地壳深度的增加，年龄呈降低趋势，这被解释为由于大量洪水淹没了地下埋藏而部分重置了先前存在的年龄30 Ma以前的熔岩喷发了。磷灰石He年龄部分复位的模拟表明，侵蚀始于25 N-29 Ma之前在Blue Nile峡谷中开始，而侵蚀将在沿目前的退缩陡坡11 Ma之后开始。青尼罗河峡谷的侵蚀开始较早，这表明：（i）火山和隆升相关的构造鸿沟代表着长寿命的（20-30 Myr）破裂前鸿沟，以及（ii）高原生理学控制了大部分自渐新世以来，尼罗河水文学已经存在。我们建议高原代表大隆起的穹顶的保留部分，与阿法尔羽撞击和/或由渐新世大陆洪水玄武岩分化引发的大规模地下活动有关。在这种情况下，西阿法尔边缘的地形发展与阿拉伯板块的扩展和漂移有关，这主要是阿法尔地区从最初升高的地区坍塌的结果。

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