Reconciling Invariant Topography with Along-Strike Gradients in Climate and Tectonics in the Greater Caucasus Mountains

板块构造的概念描述了山带的大规模构造形成。然而，形成活跃山脉地形的更基本的过程还没有完全被理解。特别是，构造变形或气候是否控制了产生山体地形的侵蚀？尽管有许多不同类型的研究，但构造和气候在控制侵蚀速度和地形方面的相对重要性仍未确定。这项研究利用了大高加索山脉(阿塞拜疆和格鲁吉亚)这一有趣的例子，那里的地形是恒定的，但年平均降水量(气候)和阿拉伯与欧亚大陆(构造)之间的碰撞速率沿山脉长度变化。通过测量山脉沿线的侵蚀速率，研究小组将评估构造和气候在这一活跃变形的山脉地形发展中的相对重要性。该项目有可能通过以下方式造福社会或促进预期的社会成果：(1)通过开发学习材料和实验室模块，改善STEM教育；(2)通过更好地了解自然灾害，改善社会个人的福祉；(3)通过培训本科生和外国研究生，以及支持早期职业研究人员，发展具有竞争力的STEM劳动力；以及(4)通过国际合作增加伙伴关系。尽管在气候、会聚速度、结构几何、地壳结构和裸露岩石类型上存在显著的沿走向梯度，但大高加索的地形显著不变。山脉西端为以单侧、南向为主的造山带，基底腹地裸露，经历板片拆离，现代会聚速率较低，为1-4 mm/a，年平均降水量为1-2m/a。与之相反，该山脉的东端是一条双向造山带，没有基底暴露，被俯冲板块覆盖，其会聚速率为8-12毫米/年，年平均降水量仅为0.1-0.5m/年。气候和辐合的梯度本身预测了高降水、低辐合西部的窄而低海拔范围和少降水、高辐合的东部的宽而高的造山带。然而，非常相似的最大海拔、2.5公里的尺度起伏、造山带宽度和沿山脉走向的横截面面积却是大高加索实际地形的特征。该项目验证了这样一种假设，即地形中的这种沿走向的相似性反映了造山带沿走向的侵蚀通量的相似性。具体地说，构造是对大高加索地形形态的主要控制，因此汇聚速度和构造样式的变化结合在一起，使造山带产生类似的吸积速率，从而产生类似的岩石抬升和沿走向的侵蚀速率。这一假设将通过测量大高加索南侧沿线的盆地平均侵蚀速率来检验，方法是使用从现代河流沉积物中采样的石英中10Be的宇宙放射性核素测年，以测量这些盆地平均侵蚀速率--这是一种成熟且经过时间验证的方法，可以测量千年尺度的集水区平均侵蚀速率。现有的历史气候和河流流量数据将被用来评估径流变化对调节沿线侵蚀效率变化的潜在影响。该项目得到了构造计划、地貌和土地利用动态计划以及NSF国际科学与工程计划的支持。

The concept of plate tectonics describes the large scale structural formation of mountain belts. However, the more fundamental processes that create the topography of an active mountain range are not fully understood. In particular, does the tectonic deformation or climate control the erosion that generates the mountain topography? Despite many different types of studies, the relative importance of tectonics versus climate in controlling erosion rates and topography remains unresolved. This study takes advantage of the interesting case of the Greater Caucasus Mountains (Azerbaijan and Georgia) where the topography is constant but the mean annual precipitation (climate) and the collision rate between Arabia and Eurasia (tectonics) change along the range length. By measuring erosion rates along the range, the research team will assess the relative importance of tectonic versus climate in topographic development of this actively deforming mountain range. The project has potential to benefit society or advance desired societal outcomes by: (1) improved STEM education through development of learning materials and lab modules; (2) improved well-being of individuals in society through better understanding of natural hazards; (3) development of a competitive STEM workforce through the training of undergraduate students and a foreign graduate student plus support for an early career researcher; and (4) increased partnerships through international collaboration.The Greater Caucasus Mountains are a young predominantly east-west striking orogen that lie between the Black and Caspian Seas and represent the locus of northeast-southwest directed convergence in the central Arabia-Eurasia collision zone. Despite significant along-strike gradients in climate, convergence rate, structural geometries, crustal structure and exposed rock types, the topography of the Greater Caucasus is remarkably invariant. The western end of the range is a predominantly one-sided, south-directed orogen, with hinterland exposures of basement, that experienced slab-detachment, has a low modern convergence rate of 1-4 mm/yr and a high mean annual precipitation of 1-2 m/yr. In contrast, the eastern end of the range is a doubly-vergent orogen, is devoid of basement exposures, is underlain by a subducting slab, and experiences a convergence rate of 8-12 mm/yr and mean annual precipitation of only 0.1-0.5 m/yr. On their own, the gradients in climate and convergence predict a narrow and low elevation range in the high-precipitation, low-convergence west and a wide and high elevation orogen in the low-precipitation, high-convergence east. However, remarkably similar maximum elevations, 2.5 km scale relief, orogen width, and cross-sectional area along the strike of the range instead characterize the actual topography of the Greater Caucasus. This project tests the hypothesis that this along-strike similarity in the topography reflects a similarity in erosional flux out of the orogen along-strike. Specifically, tectonics is the primary control on the topographic form of the Greater Caucasus such that the combination of variations in convergence rate and structural style combine along-strike to produce similar rates of accretion into the orogen, and thus similar rates of rock uplift and erosion along-strike. The hypothesis will be tested by measuring basin averaged erosion rates along the southern flank of the Greater Caucasus using cosmogenic radionuclide dating of 10Be in quartz sampled from modern river sediments to measure these basin averaged erosion rates - a well-developed and time-proven method to gauge millennial-scale catchment mean erosion rates. Available historical climate and river discharge data will be used to assess the potential influence of runoff variability on modulating changes in erosional efficiency along-strike.This project is supported by the Tectonics Program, the Geomorphology and Land Use Dynamics Program, and NSF International Science and Engineering.