Collaborative Research: Quantifying crustal hydration effects in the Colorado Plateau from xenoliths

美国西部的科罗拉多高原包括壮观的自然景观，如大峡谷、锡安和拱门国家公园。这一地区在1亿年前处于海平面，现在海拔约2公里。然而，该地区地表高度增加的原因还不是很清楚。该项目将调查在过去几十年中引起了相当大的争论的几个拟议机制之一的可行性。具体地说，这项研究将探讨太平洋板块俯冲碎片产生的水对地壳的水化作用是否会降低其密度并导致地表上升。这是基于相同的原则，即控制不同密度的木块在水中漂浮的高度。这项研究的结果可能会产生深远的影响，因为更广泛的落基山脉地区和高平原(包括丹佛，“英里高地城市”)高海拔的原因机制可能是由于过程也影响了其他山区，如安第斯山脉。该项目所有活动的共同教育主题包括研究生和本科生教育和培训，与法国研究人员的国际合作，以及加强地球科学中未被充分代表的少数民族学生。该项目将调查以下假设：含水蚀变改变了科罗拉多高原下地壳的矿物组成和相关的密度结构，并通过均衡调整对其2公里的表面隆起做出了重大贡献。这项研究将整合新的岩石学、地质年代学和稳定氢同位素研究，这些研究来自大约2500万年前的纳瓦霍火山田的一套地壳包体。将开发一个科罗拉多高原中部地壳的水化后(现在)模型，其中纳入了来自捕虏体的新观测结果，并确保与现代地震和其他地球物理数据相一致。这将与地壳的预水化模型一起进行评估，该模型基于详细的捕虏体分析。水化前和水化后模型密度的计算差异将被用来限制潜在的均衡变化响应。该项目由地球科学部的构造计划和岩石学和地球化学计划联合资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Colorado Plateau in the western United States incorporates spectacular natural landscapes, such as Grand Canyon, Zion, and Arches National Parks. This region was at sea level 100 million years ago and now sits at an elevation of about 2 kilometers above sea level. However, the reasons why surface elevations in this region increased are not well understood. This project will investigate the viability of one of several proposed mechanisms that have generated considerable debate over the last several decades. Specifically, this research will address whether hydration of Earth’s crust by water derived from a subducted fragment of the Pacific oceanic plate reduced its density and caused the ground surface to rise. This is based on the same principles that govern how high blocks of wood with different densities will float in water. The results of this research could have far-reaching implications because causal mechanisms for high elevations in the broader Rocky Mountain region and High Plains (including Denver, the “Mile High City”) may be due to processes that also affect other mountainous regions such as the Andes. Common educational themes among all of the activities in this project include graduate and undergraduate education and training, international collaborations with researchers in France, and enhancement of underrepresented minority students in Earth science.This project will investigate the hypothesis that hydrous alteration changed the mineralogical makeup and associated density structure of the Colorado Plateau lower crust and contributed significantly to its 2 kilometers surface uplift via isostatic adjustment. This research will integrate new petrologic, geochronologic, and stable hydrogen isotopic studies of a suite of crustal xenoliths from the approximately 25-million-year-old Navajo Volcanic Field. A post-hydration (present-day) model of the central Colorado Plateau crust will be developed that incorporates new observations from xenoliths, and ensures compatibility with modern seismic and other geophysical data. This will be evaluated along with a pre-hydration model for the crust that is based on detailed xenolith analyses. Calculated differences in pre-and post-hydration model densities will be used to constrain the potential isostatic response to alteration.This project is jointly funded by the Tectonics program and the Petrology & Geochemistry program in the Division of Earth Sciences.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.