Collaborative Research: Consequences of flat slab subduction on the chemical, structural, and dynamic evolution of continental lithosphere

这个项目将扩大我们对一个特定的构造环境，平板俯冲，如何影响我们生活的大陆的理解。当一个海洋板块通常以恒定的倾角进入地幔时，它改变了几何形状，只下沉到50英里左右的深度，然后在大陆下面水平移动数百英里，然后回到地球深处的内部，就会发生平板俯冲。据信，美国西部的一段平坦板块俯冲期不仅造成了落基山脉的形成和科罗拉多矿带的大量矿床，而且还造成了广泛的火山爆发，在3600万至1800万年前，美国西部爆发了50万立方千米的硅岩浆（相比之下，圣海伦斯火山喷发了1万立方千米）。这种火山活动被认为是由于平板的移动和正常俯冲几何形状的恢复所造成的影响，但由于这种情况发生在美国西部已经过去了很长时间，而且在此之前存在的平板的几何形状也不确定，因此很难进行研究。在哥伦比亚，有一个独特的环境，曾经广阔的平板被分成两部分，其中一部分仍然是平坦的，另一部分最近才沉没并恢复到正常的俯冲几何形状。虽然这块平板比影响美国西部的那块要小得多，但研究人员将研究哥伦比亚的造山、矿床和火山灾害的过程，以更好地了解大陆是如何随着时间的推移而演变的，以及这些类型的火山事件是如何与这种特定的构造环境相关的。该项目包括由卡内基科学教育学院（CASE）领导的嵌入式教师培训计划，将涉及六名教师，每个PI城市（华盛顿特区、奥斯汀和凤凰城）两名教师。在整个项目中，教师将参加培训、实地考察和全体会议，并制定可通过STEM教师网络共享的双语课程计划。pi将与教师和CASE密切合作制定这些课程计划，并将访问教师教室直接与学生互动并提供反馈。此外，该项目汇集了一个多元化的团队，包括两名女性pi和四名国际合作者。本研究旨在利用哥伦比亚独特的构造环境来评估平板俯冲和随后的沉降对大陆岩石圈地球化学、构造和动力演化的影响。在大多数洋陆辐合边缘发现了平板俯冲，并被用来解释中国的拉拉米造山运动、高原演化、板内变形和火山作用等主要构造事件。哥伦比亚的安第斯山脉北部为评估平板效应提供了一个理想的位置，因为哥伦比亚中部的弧后地区直接将现代平板与约4 Ma重新变陡的部分并置。研究人员将对平板和正常俯冲进行比较和对比，从而对岩浆作用、地壳结构、岩石圈交代作用、盆地沉降和造山带隆升的记录进行横向和纵向比较。为了实现这些目标，研究团队将包括多个学科，如地质年代学、地球化学、地震学、盆地分析、构造学、构造学、热年代学和地球动力学。项目pi和合作者将1)对平板和正常倾斜的板块区域以及两者之间的过渡进行地震成像，以获得平板俯冲对上覆岩石圈的发展和持续影响的证据；2)通过分析平板上方和平板沉降区产生的火成岩产物，研究平板俯冲对上覆岩石圈的岩浆和地球化学影响；3)通过对Magdalena和Llanos盆地以及中部和东部科迪勒拉盆地的沉积和热年代学分析，研究与平板沉降和隆升相关的时空格局及其沉降；4)将这些约束因素整合到地球动力学模型中，这将提高我们对控制平板动力学和俯冲动力学的条件和参数的理解。该奖项由极端事件预测和恢复能力（PREEVENTS）项目共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will expand our understanding of how a specific tectonic setting, flat slab subduction, affects the continents on which we live. Flat slab subduction occurs when an oceanic plate that normally descends into the Earth`s mantle at a constant angle of dip changes its geometry and instead sinks only to ~50 miles depth and then travels horizontally for hundreds of miles beneath the continent before returning to the deep Earth`s interior. An episode of flat slab subduction beneath the western United States is believed to be responsible not only for the formation of the Rocky Mountains and the extensive ore deposits of the Colorado Mineral Belt, but also for wide spread explosive volcanism that erupted ~500,000 km3 of silicic magma across the western United States between 36 and 18 million years ago (Mt. St. Helens erupted ~1 km3 for comparison). This volcanism is believed to be due to the effects of the removal of the flat slab and the resumption of a normal subduction geometry, but it has been difficult to study because of the amount of time that has passed since this occurred in the western United States, and because of uncertainty about the geometry of the flat slab that existed before that. In Colombia, there is a unique setting where a once extensive flat slab has split into two parts, one of which remains flat, and one that has comparatively recently foundered and returned to a normal subduction geometry. While this flat slab is much smaller than the one that affected the western United States, the researchers will study the processes responsible for the mountain building, ore deposits, and volcanic hazards in Colombia to gain a better understanding about how continents evolve over time and how these types of volcanic events are related to this specific tectonic environment. This project includes an embedded teacher training initiative led by the Carnegie Academy for Science Education (CASE) which will involve six teachers, two from each PI city (DC, Austin, and Phoenix). Teachers will participate in training, fieldwork, and all-hands meetings throughout the project, and will develop bilingual lesson plans that can be shared through STEM teacher networks. PIs will work closely with the teachers and with CASE in the development of these lesson plans, and will visit teacher classrooms to interact directly with students and to provide feedback. In addition, this project brings together a diverse team that includes two female PIs, and four international collaborators. This research seeks to take advantage of Colombia`s unique tectonic setting to evaluate the effects of flat slab subduction and subsequent foundering on the geochemical, structural, and dynamic evolution of continental lithosphere. Flat slab subduction has been identified along most ocean-continent convergent margins, and has been invoked to explain major tectonic events including the Laramide Orogeny, the evolution of the Altiplano Plateau, and intraplate deformation and volcanism in China. The northern Andes of Colombia provide an ideal location to assess flat slab effects as the retroarc region in central Colombia directly juxtaposes a modern flat slab with a segment that re-steepened over ~4 Ma. The investigators will compare and contrast flat slab and normal subduction, allowing for both across-strike and along-strike comparison of the records of magmatism, crustal structure, lithospheric metasomatism, basin subsidence, and orogenic uplift. To accomplish these objectives, the research team will include multiple disciplines like geochronology, geochemistry, seismology, basin analysis, structure, tectonics, thermochronology, and geodynamics. Project PIs and collaborators will 1) seismically image both the flat and normally dipping slab regions, and the transition between the two, to obtain evidence of the developing and persistent effects of flat slab subduction on the overriding lithosphere; 2) study the magmatic and geochemical effects of flat subduction on the overriding lithosphere through time by analyzing the resulting igneous products, both above the flat slab and along the region of flat slab foundering; 3) investigate the spatial and temporal patterns of subsidence and uplift associated with flat slabs and their foundering through sedimentary and thermochronologic analyses of the Magdalena and Llanos basins and flanking Central and Eastern Cordilleras in both settings, and 4) integrate these constraints into geodynamic models that will improve our understanding of the conditions and parameters that control the dynamics of flat slabs and subduction in general. This award is cofunded by the Prediction of and Resilience against Extreme Events (PREEVENTS) program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.