Collaborative Research: Determining Triggers for Subduction Accretion and Tectonic Erosion in a Mesozoic Accretionary Complex, Alaska

当沉积物在俯冲的大洋板块的下行边缘被收集(即，吸积)并复杂变形时，就形成了吸积棱柱。吸积棱柱在地质记录中提供了会聚的证据，是大陆地壳生长的重要机制。俯冲带中的一些吸积棱柱经历了长时间的侵蚀，而不是吸积，这导致PI建议研究吸积与侵蚀的触发因素。长期以来，阿拉斯加的丘加赫地体一直被认为是吸积棱柱的典型例子。PI将把吸积棱柱中的岩石类型变化与北美的主要构造事件联系起来。构造地质学和碎屑锆石年龄将被用来确定这些变化是代表不同的增积幕还是代表连续的增积。他们将研究复理石，以限制其增长历史，使用区域地质学作为沉积物供应的替代。这个项目将阐明俯冲侵蚀的过程，这些过程影响了地球内部地球化学循环的一般模型。地质学家早就认识到，地球的许多特征，以及自然灾害的原因，都与大型构造板块在俯冲过程中进入地球内部的过程有关。俯冲导致火山活动，如在喀斯喀特看到的那样，俯冲导致了有史以来最大的地震，如1964年在阿拉斯加发生的地震。研究俯冲板块上方的沉积将有助于我们了解这种俯冲过程。此外，吸积棱柱有可能容纳矿藏，并可能提供甲烷的来源，从而加剧全球变暖。该项目还将帮助我们了解阿拉斯加的历史，并为美国西南部少数民族服务机构的本科生和研究生提供教育。

Accretionary prisms form as sediments are collected (i.e., accreted) and complexly deformed at the down-going edge of a subducting oceanic plate. Accretionary prisms provide evidence of convergence in the geologic record and are a significant mechanism for the growth of continental crust. Some accretionary prisms in subduction zones experience long periods of erosion, rather than accretion, which has led the PIs to propose investigating the triggers for accretion vs. erosion. The Chugach terrane in Alaska has long been considered as a type example of an accretionary prism. The PIs will relate rock-type variations in the accretionary prism to major tectonic events in North America. Structural geology and detrital zircon ages will be used to determine if these variations represent distinct accretionary episodes or a continuum of accretion. They will study the flysch to constrain its accretionary history using regional geology as a proxy for sediment supply. This project will elucidate processes of subduction erosion that impact general models of geochemical cycling in the Earths interior. Geologists have long realized that many of the features of the Earth, as well as the causes of natural hazards, are related to the processes by which the large tectonic plates move into the interior of the Earth during subduction. Subduction leads to volcanism, such as that seen in the Cascades, and subduction caused the largest earthquakes ever recorded, such as in Alaska in 1964. Studying the sediment accreted above the subducting plate will help us understand this subduction process. In addition, accretionary prisms have the potential to host mineral deposits and could provide a source of methane that would enhance global warming. This project will also help us to understand the history of Alaska and provide for the education of undergraduate and graduate students at minority-serving institutions in the southwest U.S.