Collaborative Research: Magnitude and timing of shortening in the Greater Caucasus: Locus of Late Cenozoic Arabia-Eurasia convergence?

大高加索山脉在黑海和里海之间绵延近1000公里，形成了阿拉伯-欧亚碰撞区的最北端。这个范围长期以来一直被推测在适应碰撞中的斜辐合中起着核心作用。最近的GPS研究表明，大高加索最东端的缩短率为10至13毫米/年，占远场阿拉伯-欧亚大陆辐合总15至20毫米/年的50%至85%。尽管GPS和地震数据清楚地表明，大高加索东部现在在适应阿拉伯-欧亚大陆辐合中起着中心作用，但目前可用的数据不足以自信地确定整个晚新生代的应变是否同样集中。在这个为期三年的项目中，一个由来自美国、阿塞拜疆、格鲁吉亚和俄罗斯联邦的科学家组成的国际团队正在测试以下假设：1)大高加索山脉是由阿拉伯-欧亚大陆碰撞中的应变局部化形成的一级结构系统；2)大约1000万年前，由于阿拉伯-欧亚大陆总辐合的50% - 80%集中在该范围内，地表隆起开始；3)由于范围向东扩展，掘出和缩短的时间和幅度从西向东沿走向有系统地减小；4)大高加索地区的应变局域化可能是晚新生代造山带形成过程中被困的残海盆地消耗的结果，其中黑海和南里海是残海。通过对大高加索山脉和位于格鲁吉亚和阿塞拜疆山脉东南边缘的库拉褶皱冲断带进行实地综合构造、新构造和热年代学研究，对这些假设进行了验证。在板块构造理论出现近40年后，地球科学家仍在争论大陆在两个汇聚的板块之间的边界碰撞时是如何变形的。解决这个问题对于理解在地震中沿着断层突然释放变形的位置、频率和原因，这些断层是如何随着时间的推移形成和表现的，为什么它们在某些地方形成而不是在其他地方形成是很重要的。欧亚大陆和阿拉伯大陆之间持续的碰撞产生了欧洲最高的山脉，也是地球上第二大大陆活跃碰撞区域。这次碰撞的中心是大高加索山脉，它在西部的黑海和东部的里海之间绵延约1000公里。这条山带似乎是在最近的500万到1000万年间形成的，因此为研究大陆变形和造山的初始阶段提供了一个不寻常的机会。这项研究的结果将促进对大陆变形、导致南里海盆地和阿塞拜疆东部形成丰富石油储量的地质条件以及这个人口稠密和经济重要地区的地震灾害的认识。该地区过去曾遭受毁灭性地震的袭击，例如1988年在亚美尼亚发生的地震，造成至少2.5万人死亡。该项目将支持加州大学戴维斯分校和密歇根大学学生的博士研究，同时也为这两所大学的本科生提供重要的教育和研究机会。

The Greater Caucasus Mountains extend for nearly 1000 km between the Black and Caspian seas and form the northernmost margin of the Arabia-Eurasia collision zone. This range has long been speculated to play a central role in accommodating oblique convergence within the collision. Recent GPS studies indicate shortening rates of 10 to 13 mm/yr across the easternmost Greater Caucasus, which represents 50 to 85% of the total 15 to 20 mm/yr of far-field Arabia-Eurasia convergence. Although GPS and earthquake data clearly imply that the eastern Greater Caucasus now plays a central role in accommodating Arabia-Eurasia convergence, current available data are insufficient to confidently determine if strain has been similarly focused in the range throughout the late Cenozoic. In this three-year project, an international team of scientists from the United States, Azerbaijan, Georgia, and the Russian Federation is testing the hypotheses that: 1) the Greater Caucasus range is a first-order structural system that formed by strain localization within the Arabia-Eurasia collision; 2) surface uplift began approximately 10 million years ago due to focusing of 50 to 80% of total Arabia-Eurasia convergence in the range; 3) the timing and magnitude of both exhumation and shortening systematically decrease from west to east along-strike due to eastward propagation of the range; and 4) strain localization within the Greater Caucasus may be the result of the consumption of a relict ocean basin, of which the Black and South Caspian seas are remnants, that was trapped during formation of the orogen in the late Cenozoic. These hypotheses are tested through a field-based, integrated structural, neotectonic, and thermochronologic study of the Greater Caucasus Mountains and the Kura fold-thrust belt, which flanks the southeastern margin of the range in Georgia and Azerbaijan.Almost 40 years after the advent of the theory of plate tectonics, earth scientists are still debating how continents deform when they collide along the boundary between two converging plates. Addressing this question is important for understanding where, how often, and why deformation is suddenly released during earthquakes along faults, how those faults form and behave over time, why they form in some places and not others. The ongoing collision between the Eurasian and Arabian continents produced the highest mountain range in Europe, and the second largest region of active continental collision on Earth. The center of this collision is defined by the Greater Caucasus Mountains, which extend for approximately 1000 km between the Black Sea to the west and Caspian Sea to the east. This mountain belt appears to have formed in only the last 5 to 10 million years, thus providing an unusual opportunity to study the initial stages of continental deformation and mountain building. Results from this research will advance the understanding of continental deformation, the geological conditions in this region that led to the formation of rich oil reserves in the South Caspian basin and eastern Azerbaijan, and the earthquake hazards in this heavily populated and economically important region. This region has been struck by devastating earthquakes in the past, such as an earthquake in 1988 in Armenia that killed at least 25,000 people. The project will support the Ph.D. research of students at the University of California at Davis and the University of Michigan, while also providing important educational and research opportunities for undergraduate students at both universities.