RUI: Collaborative Research: Reconstructing Mid-Miocene-to-Recent Paleo-Erosion Rates in the Eastern Andes, Northern Argentina

RUI：合作研究：重建阿根廷北部安第斯山脉东部的中中新世至近代古侵蚀率

• 批准号: 1148233
• 负责人: William Amidon
• 金额: $ 15.75万
• 依托单位: Middlebury College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-05-15 至 2016-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1148233&HistoricalAwards=false
• 关键词: RUI; Collaborative; Research; Reconstructing; Mid

Both climatic conditions and tectonic deformation are known to influence rates of erosion, although the response of erosion rates to changes in these controling mechanisms over time is still poorly understood. This question has been difficult to address due to a lack of reliable proxy data that can define past erosion rates that record rate changes over timescales comparable to significant changes in climate and tectonics. For example, when modern rates are assessed using the concentrations of cosmogenic nuclides in eroded sediments, those rates typically reflect erosion on millennial timescales, whereas erosion of mountain belts rates is typically assessed at million-year time scales that average across many climate cycles. By developing a ~10-million-year-long record of paleo-erosion rates in the Eastern Andes of Argentina, we will explore the trade-offs between climate and deformation as they modulate erosion. We will measure three different cosmogenic isotopes (10Be, 21Ne, and 26Al) in ancient river sediments that were deposited in the Andean foothills. This study will capitalize on a unique exposure that was inadvertently created by humans who, in about 1900, diverted part of a river into an irrigation ditch and triggered a massive erosional event that has cut a channel over 100 m deep and 10 km long in the past 100 years. In the midst of the jungle, this incision has revealed a pristine exposure of a ~7-km thickness sediments eroded from the Andes over the past 10 million years. Importantly, this exposure is ideal for cosmogenic studies of past erosion rates, and it offers superb age control via its already establish record of reversals of Earth?s magnetic field and volcanic ashes that can be precisely dated. Using three isotopes with different half-lives and cosmogenic production rates will allow significant reduction of uncertainties associated with sediment storage, recycling, and syn-depositional exposure, and will underpin a more robust history of erosion rates. The multi-isotope approach, paired with detrital zircon analyses, may also provide an opportunity to establish a stratigraphic record of sediment burial and remobilization within the catchment. When paired with regional records of climate and tectonic uplift, the resulting erosion and sediment transport records should provide valuable constraints for numerical models of landscape evolution. The project will also broaden the scope of applications for stable 21Ne and serve as an exploration of its ability to reliably record erosion rates beyond the limits imposed by natural decay of 10Be.The relationship between rates erosion in mountain belts and the external factors that drive this erosion is key to our understanding of both modern and ancient geologic systems. For example, predicting climate-induced changes in erosion rates from mountain ranges can inform societal preparedness for the effects of global climate change. Likewise, studies of the long-term linkage between climate and erosion can help geologists understand the fate of ancient mountain belts and their role in Earth history. This project will represent a novel application of cosmogenic isotope dating: a technique that computes the residence time of rocks near the Earth?s surface by measuring rare isotopes produced when cosmic rays collide with rocks and minerals at the Earth?s surface. Success in addressing the many challenges associated with applying this type of dating to ancient sediments will help lay the foundation for asking similar questions in even older sediments, which record poorly understood periods of Earth?s much older history. The project will help to train the next generation of scientists by exposing them to cutting-edge isotope geochemistry techniques and by developing the skills necessary to interpret Earth?s sedimentary record. By pairing a senior PI with junior investigators, as well as graduate students with undergraduates in an international setting, the project will promote a continuum of training across a variety of skill sets and experience levels.

众所周知，气候条件和构造变形都会影响侵蚀速率，但侵蚀速率对这些控制机制随时间变化的响应仍知之甚少。由于缺乏可靠的代理数据来定义过去的侵蚀率，这些数据记录了与气候和构造的重大变化相当的时间尺度上的侵蚀率变化，因此这个问题很难解决。 例如，当使用侵蚀沉积物中宇宙成因核素的浓度来评估现代速率时，这些速率通常反映千年时间尺度的侵蚀，而山地带的侵蚀速率通常是在数百万年时间尺度上评估的，这些时间尺度是许多气候周期的平均值。通过在阿根廷安第斯山脉东部建立约一千万年的古侵蚀率记录，我们将探索气候和变形在调节侵蚀时的权衡。我们将测量安第斯山麓沉积的古代河流沉积物中的三种不同的宇宙成因同位素（10Be、21Ne 和 26Al）。这项研究将利用人类无意中造成的独特暴露，大约在 1900 年，人类将部分河流改道进入灌溉沟渠，并引发了大规模的侵蚀事件，在过去的 100 年里，这条河道被切割成 100 多米深、10 公里长的河道。 在丛林中央，这个切口揭示了过去 1000 万年来安第斯山脉侵蚀的约 7 公里厚的沉积物的原始状态。重要的是，这种暴露对于过去侵蚀率的宇宙成因研究是理想的，并且通过其已经建立的地球磁场反转记录和可以精确测定日期的火山灰提供了极好的年龄控制。 使用具有不同半衰期和宇宙生成速率的三种同位素将显着减少与沉积物储存、回收和同沉积暴露相关的不确定性，并将支持更稳健的侵蚀率历史。 多同位素方法与碎屑锆石分析相结合，还可以提供建立流域内沉积物埋藏和再活动的地层记录的机会。当与气候和构造隆升的区域记录相结合时，由此产生的侵蚀和沉积物输送记录应该为景观演化的数值模型提供有价值的约束。 该项目还将扩大稳定 21Ne 的应用范围，并探索其可靠记录超出 10Be 自然衰变限制的侵蚀速率的能力。山地侵蚀速率与驱动这种侵蚀的外部因素之间的关系是我们理解现代和古代地质系统的关键。 例如，预测气候引起的山脉侵蚀率变化可以帮助社会做好应对全球气候变化影响的准备。 同样，对气候与侵蚀之间长期联系的研究可以帮助地质学家了解古代山脉的命运及其在地球历史中的作用。 该项目将代表宇宙成因同位素测年的新颖应用：一种通过测量宇宙射线与地球表面岩石和矿物碰撞时产生的稀有同位素来计算地球表面附近岩石停留时间的技术。成功解决与将这种类型的年代测定应用于古代沉积物相关的许多挑战，将有助于为在更古老的沉积物中提出类似问题奠定基础，这些沉积物记录了人们对地球更古老的历史时期知之甚少的时期。 该项目将帮助培养下一代科学家，让他们接触最先进的同位素地球化学技术，并培养解释地球沉积记录所需的技能。 通过在国际环境中将高级 PI 与初级研究员、研究生与本科生配对，该项目将促进跨各种技能和经验水平的连续培训。