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

众所周知，气候条件和构造变形都会影响侵蚀速率，尽管侵蚀速率对这些控制机制随时间的变化的反应仍然知之甚少。这个问题一直很难解决，因为缺乏可靠的替代数据来定义过去的侵蚀率，这些数据记录了可与气候和构造的重大变化相媲美的时间尺度上的速率变化。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侵蚀速率时，这些速率通常反映千年时间尺度上的侵蚀，而山区侵蚀速率通常是以百万年时间尺度来评估的，而许多气候周期的平均时间尺度。通过建立阿根廷东安第斯山脉长达1000万年的古侵蚀速率记录，我们将探索气候和变形之间的权衡，因为它们调节侵蚀。我们将在安第斯山脚沉积的古代河流沉积物中测量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在1900年左右无意中造成的一次独特的暴露，人类将一条河流的部分改道进入灌溉沟渠，并引发了一场大规模的侵蚀事件，在过去的100年里切割了一条超过100米深、10公里长的河道。在丛林中，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暴露。重要的是，这种曝光是过去侵蚀速率的宇宙研究的理想选择，它通过已经建立的地球逆转记录--S磁场和火山灰--提供了极好的年龄控制，可以精确地测定年代。使用三种半衰期和宇宙生成速率不同的同位素，将大大减少与沉积物储存、再循环和同沉积暴露相关的不确定性，并将为更强劲的侵蚀速率历史奠定基础。多同位素方法与碎屑锆石分析相结合，也可能提供建立流域内沉积物埋藏和再动员的地层记录的机会。当与气候和构造抬升的区域记录相结合时，由此产生的侵蚀和泥沙输送记录应该为景观演变的数字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，并探索其可靠地记录超过10Bes自然衰变所造成的极限的侵蚀速率的能力。山区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为社会准备应对全球气候变化的影响提供信息。同样，研究气候和侵蚀之间的长期联系可以帮助地质学家了解古代山脉的命运及其在地球历史上的作用。该项目将代表宇宙成因同位素测年的一种新应用：一种通过测量宇宙射线与地球S表面的岩石和矿物碰撞时产生的稀有同位素来计算岩石在S表面附近的停留时间的技术。成功地解决了将这种测年方法应用于古代沉积物所带来的诸多挑战，这将有助于为在更古老的沉积物中提出类似问题奠定基础，因为更古老的沉积物记录了人们很少了解的地球时期？S更古老的历史。该项目将帮助培训下一代科学家，让他们接触尖端的同位素地球化学技术，并开发解释地球-S沉积记录所需的技能。通过将高级PI与初级调查人员配对，以及将研究生与国际环境中的本科生配对，该项目将促进各种技能和经验水平的连续培训。

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.