Collaborative Research: Linking climate-driven changes in erosion to tectonic processes along the southern Alaska Margin

在活跃的造山运动中，最具挑战性的问题之一是气候如何以质量再分配的形式驱动构造过程。换句话说，气候驱动的侵蚀变化是否会导致山区带暴露的增加，并可能影响构造过程，如隆起和断层，正如数值模型所预测的那样？通过观测和分析数据对这个问题进行研究是具有挑战性的，因为大多数活跃的造山运动发生的地区都被新第三纪末期的残留冰川和冰川景观所覆盖（23？2.5百万年前）。位于阿拉斯加东南部的圣埃利亚斯山带由于其广泛的冰川作用而成为解决这一问题的主要地点。这座活跃山脉最近的侵蚀记录储存在阿拉斯加湾，并在综合大洋钻探计划（IODP）341远征期间恢复。综合分析从大陆架、陆坡和深海勘测者扇钻探获得的深海岩心材料，将提供量化全球和地方气候变化对山脉侵蚀和结构演变影响的手段。年轻的圣伊莱亚斯带，沿着与高速率的构造和侵蚀过程，其靠近阿拉斯加湾提供了一个理想的自然环境，研究气候-构造的相互作用。在地球科学中存在着长期的争论，即新第三纪气候变化是否会影响地表过程（如侵蚀）的速率，从而通过质量的重新分配影响构造过程（如断层）。拟议的研究将检验一种假设，即冰川侵蚀的增加导致了圣埃利亚斯山脉核心的集中挖掘，正如数值和分析数据所提出的那样。两个可能的目标区域已被提出，其中构造-气候反馈可能已经发展：在褶皱冲断带和在锯齿状雅库特板块角落。现有的丰富的陆上地质和热年代学数据提供了一个全面的画面，目前的空间模式的挖掘率，但量化的变化率和模式随着时间的推移一直是一个挑战。研究团队？的方法是调查阿拉斯加湾沉积的圣伊莱亚斯奥陶系的近海沉积记录。该造山带是在全球气候显著变化的时期形成的，包括北方半球冰川作用（iNHG）在上新世-更新第三纪过渡期（PPT）（~2.6 Ma）和中更新世过渡期（MPT）（1.2 - 0.7 Ma）的加剧，以及局部气候变化导致的高山冰川，可能早在晚中新世/上新世（6.5 Ma）。来自IODP Expedition 341岩心的高分辨率磁性地层和生物地层年龄控制允许将沉积岩相和纹理、物源、剥露以及沉积物路线和分布的变化紧密联系起来，以测试沿沿着阿拉斯加南部边缘的气候-构造相互作用的记录。阿拉斯加湾地震反射数据与来自341个岩心的年龄和物源控制相结合，可以从3-D角度检查区域近海沉积系统（测量扇）中的沉积物质量通量。

One of the most challenging questions in active mountain building is how climate might drive tectonic processes, in the form of mass redistribution. In other words, do climate-driven changes in erosion lead to increased exposure of mountainous belts, and perhaps influence tectonic processes, like uplift and faulting, as predicted by numerical models? The study of this question, by means of observational and analytical data is challenging because most areas where active mountain building is occurring are covered by remnant glaciers and glaciated landscapes from the end of the Neogene period (23 ? 2.5 million years ago). The St. Elias mountain belt, in southeast Alaska, is a prime location to address this question due to its extensive glaciation. The recent erosional record of this active mountain range is stored in the Gulf of Alaska and was recovered during Integrated Ocean Drilling Program (IODP) Expedition 341. Integrated analysis of deep-sea core material obtained from drilling at the continental shelf, slope, and the deep-sea Surveyor Fan will provide means to quantify the effect of global and local climate changes on the erosional and structural evolution of a mountain range. The youthfulness of the St. Elias belt, along with high rates of tectonic and erosional processes, and its close proximity of the Gulf of Alaska provide an ideal natural setting to study climate-tectonic interactions. Long-standing debates exist in the Earth sciences on whether Neogene climate change affects rates of surface processes, such as erosion, and consequently influences tectonic processes, such as faulting, through redistribution of mass. The proposed study will test the hypothesis that an increase in glacial erosion has led to focused exhumation in the core of the St. Elias orogeny as proposed by numerical and analytical data. Two possible target regions have been suggested where a tectonic-climate feedback may have developed: in the fold-thrust belt and at the indenting Yakutat plate corner. The wealth of existing onshore geo- and thermochronological data provide a comprehensive picture of the current spatial pattern of exhumation rates, but the quantification of changes in rates and patterns through time has been challenging. The research team?s approach is to investigate the offshore sedimentary record of the St. Elias orogeny deposited in the Gulf of Alaska. This orogeny developed during a period of significant global climate change, including the intensification of Northern Hemisphere glaciation (iNHG) at the Plio-Pleistogene transition (PPT), ~2.6 Ma, and the mid-Pleistocene transition (MPT) from 1.2 to 0.7 Ma, but also a change of local climate resulting in alpine glaciers, perhaps as early as the Late Miocene/Pliocene (6.5 Ma). The high-resolution magnetostratigraphic and biostratigraphic age control from the IODP Expedition 341 cores allow close linking of changes in sedimentary lithofacies and textures, provenanace, exhumation, and sediment routing and distribution, to test the record of climate-tectonic interactions along the southern Alaska margin. The integration of Gulf of Alaska seismic reflection data with the age and provenance control from the 341 cores allow examination of sediment mass flux in the regional offshore depositional system, the Surveyor Fan, from a 3-D perspective through time.