Collaborative Research: Caught in the Act- The Petrology of Modern Lower-Crust Formation and Foundering in the North Andean Arc

地球的大陆被认为主要形成于会聚的构造边界，在那里，俯冲板块将含水流体输送到深处，使上地幔熔融，并产生岩浆，最终有助于上覆地壳的生长。然而，负责驱动弧区产生的原始岩浆的组成，这是玄武岩，对大部分组成的特点，地球的大陆，这是安山岩的过程，仍然存在激烈的争论。理解这些“分异”过程以及它们如何与会聚大陆边的其他一级特征相结合的一个主要困难是，这些岩浆活动区的深根很少暴露在地球中。s表面。然而，火山爆发有时能够运送深源岩石碎片？这些被称为“捕虏体”的物质被带到地球表面，为地球科学家提供了对大陆深处发生的过程的独特一瞥，否则很难研究。在安第斯造山带的北方部分（哥伦比亚南部），一次罕见的火山喷发从最近的火山口运送了大量捕虏体碎片，这些捕虏体碎片来自弧的深根和它下面的地幔部分。因此，这个地方提供了一个独特的机会，有助于解开在岩浆活跃地区（如安第斯山脉）建造大陆地壳期间的物理和化学过程。该奖项支持两位职业生涯早期的助理教授和一名女博士生对这些独特的捕虏体以及将它们带到地表的罕见喷发进行详细的地球化学、岩石学和地质年代学研究。特别是，这项研究的重点是弧的“重力不稳定”的根源，地壳的一部分（即，化学分异）岩石，其密度大于下伏地幔，以石榴石辉长岩、角闪石岩和含石榴石辉石岩等岩性为代表。机械去除密度不稳定的根形成弧的基础，这一过程被称为岩石圈沉降（又名脱层），不仅被认为是解释地球大陆化学的关键过程，而且被认为能够引起表面海拔的快速变化，例如驱动安第斯高原中部快速的新近纪隆起。由于发生在下造山地壳的过程是至关重要的了解山脉的隆升历史，大陆的地球化学，地球物理成像的岩石圈深部，从这次调查的结果将有重要的意义，我们的地球化学，结构和构造历史的安第斯型板块边缘的理解。除了从这次调查中获得的科学研究成果外，PI还将与罗切斯特博物馆和科学中心（RMSC）合作开展活动，这些活动将：1）向纽约州北部的公众解释弧火山的起源和物理化学原理; 2）继续组织RMSC“下一级科学”夏令营的高中参与者参观校园，该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Earth's continents are thought to have mainly formed in convergent tectonic boundaries, where hydrous fluids transported to depth by subducting plates enable melting of the upper mantle and produce magmas that ultimately contribute to the growth of the overlying crust. Nevertheless, the processes responsible for driving the composition of primitive magmas generated in arc regions, which are basaltic, towards the bulk composition that characterizes Earth's continents, which are andesitic, remain intensely debated. A major difficulty in understanding these 'differentiation' processes, and how they may couple with other first-order features of convergent continental margins, is the fact that the deep roots of these magmatically-active regions are rarely exposed in the Earth?s surface. However, volcanic eruptions are sometimes capable of transporting deep-sourced rock fragments ?known as 'xenoliths'- to the Earth's surface, providing Earth scientists with unique glimpses of processes occurring deep within the continents that are otherwise difficult to study. In the northern segment of the Andean orogen (southern Colombia), a rare eruption from a recent volcanic vent transported an extraordinary cargo of xenolith fragments sourced from the deep roots of the arc and mantle section beneath it. Therefore, this locality presents a unique opportunity to help unravel the physical and chemical processes that operate during construction of continental crust in magmatically-active regions like the Andes. This award supports two early-career Assistant Professors and a woman who is a PhD student to conduct a detailed geochemical, petrologic and geochronologic study of these unique xenoliths, and the rare eruptions that brought them to the surface. In particular, this research focuses on the 'gravitationally unstable' root of the arc, a section of crustal (i.e., chemically differentiated) rocks with densities greater than the underlying mantle, represented by lithologies such as garnet gabbros, hornblendites, and garnet-bearing pyroxenites. Mechanical removal of density-unstable roots form the base of arcs, a process known as lithospheric foundering (aka, delamination), has not only been identified as a crucial process to explain the chemistry of Earth's continents but is also thought capable of inducing rapid changes in surface elevation, such as those driving the fast Neogene uplift of the Central Andean Plateau. Because the processes taking place in the lower orogenic crust are critical for understanding the uplift history of mountains, the geochemistry of the continents, and the geophysical imaging of the deep lithosphere, results from this investigation will have important implications for our understanding of the geochemical, structural and tectonic history of Andean-type plate margins. In addition to the scientific research products that will result from this investigation, the PIs will collaborate with the Rochester Museum and Science Center (RMSC) on activities that will: 1) explain the origin and physicochemical principles of arc volcanoes to the public of Upstate NY; and 2) continue to organize campus visits for high-school participants of RMSC's 'Next Level Science' summer camps, to provide local students with a direct opportunity to experience college and learn more about upper-level STEM education.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.