Collaborative Research: A Structural, Thermochronologic, and Provenance Investigation of a Hypothesized Transition From Subduction to Slab Breakoff in the Greater Caucasus

板块剥离是指板块从俯冲板块上剥离并下沉到地幔中，它对碰撞造山带的地球动力学演化起到一级控制作用，因为板块剥离从根本上改变了会聚边缘的作用力。模拟结果表明，碰撞造山带内断裂的可观测特征包括碰撞前洋盆的俯冲、岩带加速岩石和地表抬升的瞬时脉冲、断裂后汇聚速率的降低以及板块保持连接的相邻部分上方的增大。然而，在大陆碰撞带内对这一过程的地质观察并没有很好的记录。加州大学戴维斯分校和密歇根大学的这个研究小组与他们的国际合作伙伴合作，探索了大高加索(黑海和里海之间)最近的地质史是这一过程的结果这一观点。该项目将通过以下方式促进预期的社会成果：(1)通过培训几名美国研究生，培养一支具有全球竞争力的STEM工作队伍，让本科生参与研究，以及培训来自格鲁吉亚、亚美尼亚和阿塞拜疆的研究生；(2)增加学术界与碳氢化合物行业的伙伴关系，加强现有的合作伙伴关系，并与亚美尼亚和格鲁吉亚、台湾和加拿大的科学家发展新的合作关系。该项目将为研究生提供丰富的国际研究经验。该项目得到了构造计划和NSF国际科学与工程计划的支持。这项研究计划将检验这样一种假设，即大高加索地区反映了最近在山脉西段下方板块断裂的瞬时地球动力学响应。这一事件是在渐新世至上新世闭合一个残存洋盆之后发生的，目前该洋盆的俯冲作用仍在山脉的东半部下方进行。研究小组将对这一鲜为人知的造山带进行野外调查，使用构造制图和平衡剖面，使用碎屑锆石的U-Pb分析来研究沉积物来源，使用磷灰石的(U-Th)/He分析，基岩低温计时和新构造调查。他们的目标是限制沿三个造山带垂直剖面横跨大高加索的新生代缩短的幅度，并从低温热力学计时法得出大高加索和小高加索的折返历史。将这些数据与相邻沉积盆地的碎屑物源和滞后时间分析相结合，将捕捉到对瞬时地球动力学事件的地质响应，并可能记录下活动造山带俯冲-碰撞转变过程中板片拆离的第一个证据。

Slab breakoff, in which a slab detaches from a subducting plate and sinks into the mantle, exerts a first-order control on the geodynamic evolution of collisional orogenic belts because breakoff fundamentally alters the forces along the convergent margin. Modeling indicates that observable characteristics of breakoff within a collisional orogen include subduction of an ocean basin before collision, a transient pulse of accelerated rock and surface uplift in the belt, a decrease in convergence rate over the breakoff and an increase above adjacent parts of the slab that remain attached. However, geologic observations of this process within continental collision zones are not well documented. This University of California Davis and University of Michigan research team, in collaboration with their international partners, in explores the idea that the recent geological history of the Greater Caucasus (between the Black Sea and the Caspian Sea) is a consequence of this process. The project will advance desired societal outcomes by: (1) development of a globally competitive STEM workforce through the training of several U.S. graduate students, involvement of undergraduate students in research, and training of graduate students from Georgia, Armenia, and Azerbaijan; (2) increased partnerships between academia and the hydrocarbon industry and strengthening of existing collaborations and the development of new collaborations with scientists in Armenia and Georgia, Taiwan, and Canada. The project would provide the graduate students with rich international research experiences. The project is supported by the Tectonics Program and NSF's International Science and Engineering program.This research project will test the hypothesis that the Greater Caucasus reflects the transient geodynamic response to recent slab breakoff beneath the western portion of the range. This event follows the Oligocene to Pliocene closure of a remnant ocean basin, subduction of which presently continues beneath the eastern half of the range. The research team will carry out a field investigation of this little-studied orogen using structural mapping and balanced cross-sections, sediment provenance studies using U-Pb analyses of detrital zircons and (U-Th)/He analyses of apatite, bedrock low-temperature thermochronometry, and neotectonic investigations. They aim to constrain the magnitude of Cenozoic shortening across the Greater Caucasus along three orogen-perpendicular sections, and to derive the exhumation history of the Greater and Lesser Caucasus from low-temperature thermochronometry. Integration of these data with detrital provenance and lag time analyses of adjacent sedimentary basins will capture the geologic response to a transient geodynamic event and record perhaps the first evidence for slab detachment at the subduction-to-collision transition in an active orogen.