Collaborative Research: Testing Models for Extension in the Rio Grande Rift-Basin and Range Transition Zone of Southern New Mexico

盆岭省和美国西部的里奥格兰德裂谷是岩石圈在过去2500万年里慢慢分裂的两个构造领域。伸展分布在盆地和山脉的大片区域，更多地集中在从新墨西哥州南部到里奥格兰德裂谷科罗拉多州北部的狭窄地带，该裂谷在许多方面与世界各地其他重要的裂谷带相似。人们提出了多种构造模式来解释这两个领域的延伸。一些模型将它们的发展归因于相同的机制，而另一些模型则涉及每个领域的不同机制。在这个项目中，来自德克萨斯大学埃尔帕索分校和新墨西哥州州立大学的一个研究小组旨在区分哪些构造力量推动了新墨西哥州南部合并的两个省的扩张。为此，他们将确定该地区许多山脉的隆升年龄，以确定盆地和山脉省与里奥格兰德裂谷是否经历了相同的伸展历史。通过拉美裔学生和研究人员的充分参与，预期的社会成果将会达到。里奥格兰德裂谷是世界上最好的裂谷之一？S对大陆裂谷进行了最好的揭示和最深入的研究，但对于产生它的动力以及它为什么在何时何地形成，仍然存在相当大的不确定性和争论。许多研究人员认为格兰德裂谷是毗邻的盆地和山脉省的最东端，但也有人认为它是一个独立的结构实体。尽管观察到南里奥格兰德裂谷在地貌上与邻近的盆地和山脉相似，但它可以通过更高的热流、更薄的地壳、更深的盆地和丰富的第四纪正断层来区分。这些观察结果导致了关于这两个构造域是否同时演化的不确定性，以及对推动美国西南部地壳伸展的根本原因(S)的不同解释。该项目的目标是限制这两个构造域合并区域的伸展时间，以检验格兰德裂谷形成的模型。具体而言，该项目的目标是：(1)亚利桑那州东南部/新墨西哥州西南部的盆地和山脉省以及新墨西哥州南部的里奥格兰德裂谷的主要伸展阶段的时间；(2)里奥格兰德裂谷与盆地和山脉在伸展风格/时机上的差异；(3)里奥格兰德裂谷南部的主要伸展驱动因素。为此，研究小组将使用磷灰石(U-Th)/He、磷灰石裂变径迹和锆石(U-Th)/He热年代学方法对来自里奥格兰德裂谷盆地和亚利桑那州东部、新墨西哥州南部和得克萨斯州西部山脉过渡的13个独立断块隆起的样品进行分析。这些结果将填补盆地和山脉与里奥格兰德北部裂谷之间的数据空白。对于每个样品，将获得磷灰石和锆石的U和Th分带剖面，并将产生包含所有新的热年代学数据、分带信息以及现有地质约束的反模型。这些数据将能够对每个样本的时间-温度历史施加非常严格的限制。由此产生的模型将描绘出每个位置的构造静止时间的快速折返时间，这将是在模型之间测试伸展的主要方法。

The Basin and Range province and the Rio Grande rift in the western United States are two tectonic domains where the lithosphere has slowly pulled apart over the past 25 million years. The stretching is distributed across wide areas in the Basin and Range and is more focused along a narrow zone from southern New Mexico to northern Colorado in the Rio Grande rift, which in many ways resembles other significant rift zones around the world. A variety of tectonic models have been proposed to explain the extension in these two domains. Some models attribute their development to the same mechanisms whereas others implicate different mechanisms for each domain. In this project, a research team from the University of Texas El Paso and New Mexico State University aims to distinguish which tectonic forces drive extension in the two provinces where they merge in southern New Mexico. To do so, they will determine the uplift ages for many of the ranges in the region in order to determine if the Basin and Range province and the Rio Grande rift experience the same extension history. Desired societal outcomes will be achieved through the full participation of students and researchers of Hispanic heritage in the research project.The Rio Grande rift is one of the world?s best exposed and most thoroughly studied continental rifts, yet there still remains considerable uncertainty and debate on the driving forces that produced it and why it formed when and where it did. Many researchers view the Rio Grande rift as the easternmost segment of the adjacent Basin and Range province, but others view it as a separate structural entity. Despite the observation that the southern Rio Grande rift physiographically resembles the adjacent Basin and Range, it can be distinguished by higher heat flow, thinner crust, deeper basins, and an abundance of Quaternary normal faults. These observations lead to uncertainty as to whether these two structural domains evolved contemporaneously or not, as well as different interpretations of the underlying causes(s) driving crustal extension in the southwest U.S. The objective of this project is to constrain times of extension in the region where these two structural domains merge to test models for formation of the Rio Grande rift. Specifically, the project aims to be addressed are: (1) the timing of the main phase of extension in the Basin and Range Province of southeastern Arizona/southwestern New Mexico and the southern Rio Grande rift of southern New Mexico; (2) the difference in style/timing of extension between the Rio Grande rift and Basin and Range; and (3) the main driver of extension in the southern Rio Grande rift. To these ends, the research team will use apatite (U-Th)/He, apatite fission-track, and zircon (U-Th)/He thermochronologic methods on samples collected from thirteen individual fault block uplifts in the Rio Grande rift-Basin and Range transition of eastern Arizona, southern New Mexico, and western Texas. These results will fill a data gap between the Basin and Range and the northern Rio Grande rift. For each sample, U and Th zoning profiles will be obtained for apatite and zircon, and inverse models will be produced that incorporate all new thermochronologic data, zoning information, as well as existing geologic constraints. These data will be able to place very tight constraints on each samples' time-temperature history. The resulting models will delineate times of rapid exhumation from times of tectonic quiescence at each location, which will be the principle method for testing between models for extension.