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

造山带的地层特征的性质仍然是一个有争议的问题，在许多情况下，造山带开始的地层估计大大落后于基于结构，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范例，中部安第斯山脉为检验同造山期地层演化的相互矛盾的模型提供了机会。该项目涉及安第斯山脉的一个基本方面-由于地壳缩短和增厚而形成的初始山脉的时间。为此，来自亚利桑那大学、德克萨斯大学和怀俄明州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纪盆地的演化。盆地演化的三种模式正在进行测试：（1）裂谷后热沉降，（2）前陆盆地沉降，（3）安第斯前陆构造破坏期间山间盆地的发展。每个模型都对沉积环境、沉积物分布模式、物源、盆地结构、沉降和热历史做出了具体的预测。该研究小组正在收集大约3万平方公里区域内古近纪地层的沉积学数据（岩相、厚度、古水流方向、物源）和年代学数据（40 Ar/39 Ar凝灰岩年龄、孢粉学、U-Pb锆石和磷灰石年龄以及磷灰石裂变径迹年龄）。该研究的预期成果包括阿根廷西北部古近纪地层的综合数据集，以及两种新方法（碎屑锆石和磷灰石U-Pb地质年代学）在安第斯山脉中部新生代早期构造问题中的协调应用。安第斯山脉被广泛认为是大洋岩石圈俯冲到大陆之下而形成的山脉带的典型区域，基于安第斯山脉的模型经常被用来理解地球仪周围古老山脉带的发展。然而，安第斯山脉的一个基本方面-由于地壳缩短和增厚而形成的初始造山年龄-仍然存在争议。通过应用新的分析技术和解释沉积记录，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新的方法来确定地质历史中主要造山活动的时间。

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.