Collaborative Research: Quantifying the Sensitivity of Rifting Processes to Erosion and Sedimentation

裂谷作用是大陆被拉伸并最终分裂的过程，有可能导致新的洋盆的形成。目前，活跃的裂谷作用正在北美大片地区进行，例如在盆地和山脉省、新墨西哥州格兰德河沿岸和加利福尼亚州海湾。裂谷地区往往集中于自然资源(如碳氢化合物、金属、地热)，并可能与重大地震灾害有关。因此，了解形成裂谷建筑和景观的过程在基本和社会层面上都是至关重要的。该项目具体调查了两个关键的裂谷过程：断层生长和岩浆活动对地形应力的敏感性，地形应力是地壳中由于地形起伏而形成的力。众所周知，这种应力会影响构造板块碰撞的大陆变形(例如台湾、喜马拉雅山脉)，但对它们对大陆裂谷的影响却知之甚少。这些应力受到河流和冰川的侵蚀作用以及盆地和低地堆积的沉积物重量的强烈调制。这项研究将结合数值模型和现场观测来评估这种活跃的地表过程如何影响断裂的发展和裂谷期间火山活动的空间范围。它将支持一名职业生涯早期的科学家和一名少数族裔研究生。作为科学推广活动的一部分，这项研究的成果将被广泛分发，并为教育工作者和荒野保护区提供材料。大量的现场和理论研究已经在整个造山带(100？1000公里)的尺度上解决了表面过程和应变在收敛边缘的定位之间的反馈问题。然而，在伸展环境中所做的工作很少，在伸展环境中，岩浆作用是板块边界演化的组成部分，而相当大的地形在单个正常断层范围(10？100公里)的尺度上增长。这项研究的目的是将现有的裂谷模型与地貌演化的真实参数化相结合，以揭示深部地形生长和构造-岩浆变形之间的反馈关系。具体地说，该项目将首先利用景观演变模型记录世界各地裂谷的全部质量再分布效率，该模型允许与可观测数据进行直接比较，例如正常断层底板的总起伏、其主要集水区盆地的形态以及上盘岩块的沉积填充。然后，我们将实施这些校准的景观模型作为长期构造模型中的上边界条件，在该模型中，断层可以自发形成，岩浆侵入体对周围应力场做出反应。一大套数值模拟将使检验下列假设成为可能：(1)下盘的剥蚀和上盘的沉积对于允许半地块适应与断裂的上地壳厚度相称的偏移量是必不可少的；(2)地垒的形成是由低效的地表过程推动的，这种过程保存了地形起伏，并有利于断层附近地形应力的积累；以及(3)地表质量的有效重新分配，焦点是岩浆活动到裂谷轴。模型产出将与断层生长和火山侵位的实地观测进行系统比较，以确定地表过程对大陆裂谷构造-岩浆演化的贡献。

Rifting is the process by which continents get stretched and ultimately break apart, potentially leading to the formation of a new ocean basin. Active rifting is currently underway throughout large extents of North America, for example within the Basin and Range Province, along the Rio Grande River in New Mexico, and in the Gulf of California. Rifting areas often focus natural resources (e.g., hydrocarbons, metals, geothermal heat) and can be associated with significant seismic hazards. Understanding the processes that shape rift architecture and landscapes is therefore essential on both a fundamental and societal level. This project specifically investigates the sensitivity of two key rifting processes: fault growth and magmatic activity to topographic stresses, which are forces in Earth's crust due to the build-up of topographic relief. Such stresses are known to affect continental deformation where tectonic plates collide (e.g., Taiwan, the Himalayas), but little is known regarding their influence on continental rifting. These stresses are strongly modulated by the erosive action or rivers and glaciers, and the weight of sediments accumulating in basins and lowlands. This study will combine numerical models and field observations to assess how such active surface processes influence fault development and the spatial extent of volcanic activity during rifting. It will support an early-career scientist as well as a minority graduate student. The products of this study will be widely distributed as part of scientific outreach initiatives, and provide material for educators and wilderness conservation areas.Numerous field and theoretical studies have addressed the feedbacks between surface processes and strain localization in convergent margins at the scale of entire orogens (100?1000 km). However, very little work has been done in extensional settings, where magmatic processes are an integral part of plate boundary evolution, and sizeable topography grows at the scale of individual normal fault-bounded ranges (10?100 km). The goal of this study is to couple existing rifting models with a realistic parameterization of landscape evolution in order to uncover feedbacks between topography growth and tectono-magmatic deformation at depth. Specifically, the project will first document the full range of mass redistribution efficiency in rifts worldwide using a landscape evolution model that allows direct comparison with observables, e.g., the total relief of normal fault footwalls, the morphology of their major catchment basins, and the sedimentary infill of the hanging wall block. We will then implement these calibrated landscape models as an upper boundary condition in a long-term tectonic model where faults can form spontaneously and magmatic intrusions respond to the ambient stress field. A large suite of numerical simulations will enable tests of the following hypotheses: (1) Denudation of the footwall and deposition on the hanging wall are essential in allowing half-grabens to accommodate offsets commensurate with the thickness of the faulted upper crust; (2) Horst formation is promoted by inefficient surface processes, which preserve relief and favor the build up of topographic stresses near the fault; and (3) Efficient redistribution of surficial masses focuses magmatic activity to the rift axis. Model outputs will be systematically compared with field observations of fault growth and volcanic emplacement to identify the contribution of surface processes to the tectono-magmatic evolution of continental rifts.