Collaborative Research: Subduction Dynamics, Mantle Structure, and Cenozoic Tectonic Evolution of South America

合作研究：南美洲俯冲动力学、地幔结构和新生代构造演化

• 批准号: 1565475
• 负责人: Susan Beck
• 金额: $ 28.99万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2021-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1565475&HistoricalAwards=false
• 关键词: Collaborative; Research; Subduction; Dynamics; Mantle

The physics behind several fundamental aspects of the South American tectonics remains elusive. For example, various geological records suggest that the Andes Mountains started to shorten significantly since at least 40 million years ago. However, paleo-altimetry proxy data reveal that most of the surface elevation of the Andes remained relatively low until as late as 20 or 15 million years ago, a time frame that is inconsistent with the shortening history. Furthermore, the early Cenozoic arc volcanism along the central Andes suddenly shifted more than 500 km inland around 30 million years ago and formed widespread silicic volcanic activity that continues to the present. Consequently, a clear relationship among these tectonic events is lacking. An important reason is that both the mantle structures beneath South America and their dynamic evolution remain poorly understood. In this proposal, the team plans to carry out a multidisciplinary research project to attempt to improve our knowledge about the observational records of surface tectonics, deep mantle seismic properties, and their geodynamic relationship with the temporal evolution of subduction beneath the continent. By collecting more data related to the tectonic history of South America and to the present-day mantle interior, they will build a sophisticated 4-dimentional geodynamic model using data assimilation, in order to quantitatively reproduce the past subduction history. Ultimately, the team hopes to better understand the Cenozoic evolution of the South American continent. The team plans to achieve this goal through a collaborative research effort that involves seismology (led by PI Beck), geology (led by PI DeCelles), and geodynamics (led by PI Liu). They propose to reproduce the Cenozoic subduction history beneath South America and associated continental deformation using geodynamic models constrained by geophysical and geological observations. This project includes interdisciplinary training of several graduate students at two institutions, and also involves undergraduates at both institutions who will be involved in the research and will all students will participate in a summer field trip to western U.S. Cordillera as an analog for the South American Cordillera. This multi-disciplinary combination will provide a unique opportunity for the students to understand orogenic systems at plate scale.Multiple fundamental questions exist about the Cenozoic tectonic history of South America, including the asynchronous crustal shortening and surface uplift/subsidence history of the Andes, and the enigmatic Central Andean flare-up magmatism occurring during the late Cenozoic. None of the earlier proposed geodynamic models for the Cenozoic evolution of South America could simultaneously explain all these tectonic records and it is unclear whether these different physical processes could co-exist and interact in reality. An important reason for the existence of these alternative models is the uncertain subduction and mantle dynamics due to our imperfect knowledge of deep mantle structures beneath South America. Key observational constraints on the geodynamic and tectonic evolution include an improved present-day mantle seismic structure, especially in the lower mantle, a better identified relationship among structural deformation, surface uplift and magmatic history within western South America, and time-dependent geodynamic models that are consistent with these observational records.

南美构造的几个基本方面背后的物理学仍然难以捉摸。例如，各种地质记录表明，至少4000万年前，安第斯山脉开始显着缩短。但是，古占代理数据表明，直到20或1500万年前，安第斯山脉的大部分表面升高一直保持相对较低，这与缩短历史不一致。此外，在安第斯山脉中部的新生代弧火山发生突然在3000万年前向内陆移动了500公里，并形成了广泛的硅火山活动，一直持续到现在。因此，缺乏这些构造事件之间的明确关系。一个重要的原因是，南美下的地幔结构及其动态进化尚不清楚。在该提案中，该团队计划进行一个多学科研究项目，以试图提高我们对地表构造，深层地震地震属性的观察性记录以及与俯冲下俯冲的时间演变的地球动力学关系。通过收集与南美构造历史以及与当今地幔内饰有关的更多数据，他们将使用数据同化建立一个复杂的4维地球动力学模型，以定量地重现过去的俯冲历史。最终，该团队希望更好地了解南美大陆的新生代发展。 该团队计划通过涉及地震学（由PI Beck的领导），地质学（由PI Decelles领导）和地球动力学（由Pi Liu领导）的合作研究工作实现这一目标。他们建议使用受地球物理和地质观察的约束的地球动力学模型来重现南美下的新生代俯冲历史，并相关的大陆变形。该项目包括对两个机构的几名研究生的跨学科培训，还涉及两家机构的大学生，他们将参与研究，所有学生将参加夏季前往美国西部Cordillera的夏季野外旅行，以此作为南美柯蒂利拉的模拟。 这种多学科的组合将为学生提供一个独特的机会，可以在板尺度上了解造山学系统。关于南美的新生代构造历史存在的多种基本问题，包括安斯特斯的异步壳缩短和表面上升/沉降历史，以及在后期发生的cenozo cenozoikic cenozoikic cente of the Andemate centerem flare magmatism。较早提出的用于南美新生代进化的地球动力学模型不能同时解释所有这些构造记录，而且尚不清楚这些不同的物理过程是否可以共存并在现实中相互作用。存在这些替代模型的一个重要原因是由于我们对南美下深层地幔结构的不了解而导致的不确定的俯冲和地幔动态。对地球动力和构造进化的关键观察限制包括改进的当今地幔地震结构，尤其是在下层壁台上，在南美西部的结构变形，表面隆升和岩浆历史之间具有更好的确定关系，以及时间依赖的地球动力学模型，这些模型与这些观测记录保持一致。