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

美国西部的盆地山脉区和格兰德河裂谷是两个构造域，在过去的2500万年里，岩石圈在这两个构造域中慢慢地被拉开。拉伸分布在盆地和山脉的广泛地区，并且更集中于沿着从新墨西哥州南部到北方科罗拉多的格兰德河裂谷的狭窄地带，在许多方面类似于世界各地的其他重要裂谷带。人们提出了多种构造模式来解释这两个领域的伸展。一些模型将其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的目标是区分哪些构造力量驱动了新墨西哥州南部两个省份的延伸。为此，他们将确定该地区许多山脉的隆起年龄，以确定盆地和山脉省和格兰德河裂谷是否经历了相同的伸展历史。通过西班牙裔遗产的学生和研究人员的充分参与，将实现预期的社会成果。虽然它是暴露最充分、研究最彻底的大陆裂谷，但对于它的形成动力以及它形成的原因、时间和地点，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河裂谷是相邻的盆岭省的最东端，但也有人认为它是一个独立的结构实体。尽管观察到南格兰德河裂谷在地貌上类似于邻近的盆地和山脉，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。这些观察结果导致不确定性，这两个结构域是否同时演变，以及不同的解释的根本原因（S）驱动地壳伸展在美国西南部的本项目的目标是限制时间的扩展在该地区，这两个结构域合并到测试模型形成的格兰德河裂谷。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格兰德河裂谷的主要伸展阶段的时间;（2）格兰德河裂谷与盆地和山脉之间伸展样式/时间的差异;以及（3）格兰德河裂谷南部伸展的主要驱动力。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热年代学方法对从亚利桑那州东部，新墨西哥州南部和德克萨斯州西部的格兰德河裂谷盆地和山脉过渡区的13个单独断块隆起中收集的样品进行分析。这些结果将填补盆地和山脉与北方格兰德河裂谷之间的数据空白。对于每个样本，将获得磷灰石和锆石的U和Th分区剖面，并将制作包含所有新的热年代学数据、分区信息以及现有地质约束的逆模型。这些数据将能够对每个样品的时间-温度历史施加非常严格的约束。由此产生的模型将描绘出每个地点从构造静止期到快速折返期的时间，这将是检验扩展模型的主要方法。

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.