Collaborative Research: Stratigraphic Signatures of Orogeny: Assessing the Timing of Initial Andean Crustal Shortening

造山运动的地层特征的性质仍然是一个争论的主题，在许多情况下，对造山运动开始的地层估计明显落后于基于构造、变质和地质年代学数据的估计。作为高海拔弧后冲断带的典型例子，安第斯山脉中部为检验同造山地层演化的矛盾模型提供了机会。本项目研究安第斯造山运动的一个基本方面-由于地壳缩短和增厚而产生的初始造山时间。为此，来自亚利桑那大学、德克萨斯大学和怀俄明大学的一组研究人员与阿根廷科学家合作，正在记录阿根廷西北部古近系盆地的演变。对盆地演化的三种模式进行了验证：(1)裂谷后热沉降模式；(2)前陆盆地沉降模式；(3)安第斯前陆构造断裂期间的山间盆地发育模式。每个模型都对沉积环境、沉积物分布模式、物源、盆地结构、沉降和热历史做出具体预测。研究小组正在收集大约3万平方公里地区的古近系地层的沉积学数据（岩相、厚度、古洋流方向、物源）和年代学数据（40Ar/39Ar凝灰岩年龄、孢粉学、U-Pb锆石和磷灰石年龄、磷灰石裂变径迹年龄）。预计研究成果包括阿根廷西北部古近系地层综合数据集，以及两种新方法（碎屑锆石和磷灰石U-Pb年代学）在安第斯山脉中部早新生代构造问题上的协同应用。此外，研究结果将直接解决如何在地层记录中读取造山特征的问题。安第斯山脉被广泛认为是在大陆板块下海洋岩石圈俯冲作用下形成的山带的典型区域，以安第斯山脉为基础的模式经常被用来理解全球古代山带的发展。然而，安第斯造山运动的一个基本方面——由于地壳缩短和增厚而产生的初始造山时代——仍然存在争议。通过应用新的分析技术和对沉积记录的解释，该项目将解决安第斯山脉中部的这一争议。该项目将为地质学家提供确定地质历史上主要造山事件发生时间的新方法。

The nature of the stratigraphic signature of orogeny continues to be a subject of debate, and in many cases stratigraphic estimates for the onset of orogeny lag significantly behind estimates based on structural, metamorphic, and geochronological data. As the type-example of a high-elevation retroarc thrust belt, the central Andes provide an opportunity to test conflicting models for synorogenic stratigraphic evolution. This project addresses a fundamental aspect of Andean orogeny - the timing of initial mountain building owing to crustal shortening and thickening. To this end, a team of researchers from the University of Arizona, the University of Texas, and the University of Wyoming in collaboration with Argentinean scientists are documenting the evolution of Paleogene basins in northwestern Argentina. Three models for basin evolution are being tested: (1) post-rift thermal subsidence, (2) foreland basin subsidence, and (3) intermontane basin development during tectonic disruption of the Andean foreland. Each model makes specific predictions about depositional environments, sediment distribution patterns, provenance, basin architecture, subsidence, and thermal history. The research team is collecting sedimentological data (lithofacies, thickness, paleocurrent directions, provenance) and chronological data (40Ar/39Ar tuff ages, palynology, U-Pb zircon and apatite ages, and apatite fission track ages) from Paleogene strata in a roughly 30,000 square kilometer region. Expected products of the research include a comprehensive dataset on the Paleogene stratigraphy of northwestern Argentina, and a concerted application of two new methods (detrital zircon and apatite U-Pb geochronology) to early Cenozoic tectonic problems in the central Andes. Moreover, the results will directly address the issue of how to read orogenic signatures in the stratigraphic record.The Andes are widely regarded as the type area for mountain belts formed in response to subduction of oceanic lithosphere beneath continents and models based on the Andes are regularly used to understand the development of ancient mountain belts around the globe. Nevertheless, a fundamental aspect of Andean orogeny - the age of initial mountain building owing to crustal shortening and thickening -remains controversial. Through application of new analytical techniques and interpretation of the sedimentary record, this project would resolve this controversy for the Central Andes. The project would provide geologists with new methods to determine the timing of major mountain building events in the geological past.