Behavior of lithosphere and asthenosphere in slab window environments

岩石圈和软流圈之间的相互作用控制着地球演化的许多方面，包括火山活动、地震和造山运动。 岩石圈是坚硬的，覆盖在软流圈上，并被分成许多构造板块。 在某些板块边界处，一个岩石圈板块滑到另一个岩石圈板块之下，并下降到软流圈中。 这些边界被称为俯冲带，其特征是沿着弯曲带（例如太平洋火环）进行剧烈的火山活动。我们对俯冲带的理解中的一个重大差距是岩石圈和软流圈在板片窗口处的行为，板片窗口是俯冲岩石圈的缺口，主要由撕裂或山脊俯冲引起。 目前地球上有几个板窗活动，特别是沿着美洲西缘、西南太平洋和地中海东部。 火山通常位于板窗上方，它们的分布和组成是俯冲岩石圈和环境软流圈的位置和行为的代理。拟议的研究将包括在加拿大和土耳其的关键地点以研究生为中心的调查。 第一个将测试一个假设，即南不列颠哥伦比亚省已从一个板窗口环境转移到一个板目前的情况，并返回到一个板窗口环境在过去的55百万年。 在这项研究中，一名博士生将研究始新世火山岩和深成岩，一名硕士生将研究第四纪熔岩，一名荣誉学士生将研究渐新世火山岩。 第二个将测试一个假设，土耳其是由俯冲岩石圈的非洲板块，在新近纪分裂。 一名博士生将通过研究卡帕多西亚带的新第三纪到全新世火山来验证这一想法。 这项工作将与土耳其一所大学的教师合作进行。 这两项调查将涉及实地研究和实验室分析，以确定板片和软流圈的当前和过去的分布和行为。 敏感的硼和铍同位素将用于跟踪板块和俯冲沉积物的地球化学贡献，并对地下过程进行独立评估。 在第三项调查中，一名博士生将测试这样一个假设，即板片窗口处的板片熔融和碎裂在地质时代对地壳和地幔的组成产生了重大影响。 通过汇编来自世界各地的板窗火成岩的信息，并开发一种方法来描述板边缘的行为，我的研究将提供第一个板窗的全球影响的时间综合视图。 总的来说，这项研究将提高我们对板窗如何影响加拿大西部和中东火山活动的理解，并有助于自板块构造开始以来地球的成分演变。

Interactions between the lithosphere and the asthenosphere control many aspects of Earth evolution including volcanism, earthquakes and mountain building. The lithosphere is rigid, overlies the asthenosphere and is divided into numerous tectonic plates. At some plate boundaries, one lithospheric plate slides beneath another and descends into the asthenosphere. These boundaries, called subduction zones, are characterized by violent volcanic activity along curved belts such as the Pacific Ring of Fire.One significant gap in our understanding of subduction zones is the behavior of lithosphere and asthenosphere at slab windows, which are breaches in the subducting lithosphere caused mainly by tearing or ridge subduction. Several slab windows are currently active on Earth, particularly along the western margin of the Americas, in the southwest Pacific and the eastern Mediterranean. Volcanoes are commonly located above slab windows and their distribution and composition are proxies for the position and behavior of subducted lithosphere and ambient asthenosphere.The proposed research will consist of graduate student-centered investigations in key locations in Canada and Turkey. The first will test a hypothesis that southern British Columbia has shifted from a slab window environment to a slab-present situation and back to a slab window environment during the past 55 m.y. In this investigation, a PhD student will study Eocene volcanic and plutonic rocks, an MSc student will examine Quaternary lavas and a BSc Honors student will study Oligocene volcanic rocks. The second will test a hypothesis that Turkey is underlain by subducted lithosphere of the African plate that fragmented in the Neogene. A PhD student will test this idea by examining Neogene to Holocene volcanoes of the Cappadocia belt. The work will be carried out in collaboration with faculty at a Turkish university. These two investigations will involve field research and laboratory analysis to define the current and past distribution and behavior of slab and asthenosphere. Sensitive boron and beryllium isotopes will be used to track geochemical contributions from the slab and subducted sediment and provide an independent assessment of the subsurface processes. In the third investigation, a PhD student will test the hypothesis that slab melting and fragmentation at slab windows has significantly affected the composition of the crust and mantle through geologic time. By compiling information on igneous rocks from slab windows worldwide, and developing a methodology to describe slab-edge behavior, my research will provide the first time-integrated view of the global effects of slab windows. Overall, the research will improve our understanding of how slab windows are affecting volcanism in western Canada and the Middle East, and have contributed to the compositional evolution of Earth since the onset of plate tectonics.