Collaborative Research: The Asthenosphere and Mantle Dynamics

合作研究：软流圈和地幔动力学

• 批准号: 1522012
• 负责人: Adrian Lenardic
• 金额: $ 8.83万
• 依托单位: William Marsh Rice University
• 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: 2016-02-15 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1522012&HistoricalAwards=false
• 关键词: Collaborative; Research; Asthenosphere; Mantle; Dynamics

The majority of changes that occur on our planet can be tracked back to one of two energy sources: 1) Energy from the sun and 2) Energy from the Earth's interior. How interior energy shapes the Earth's surface links directly to understanding the dynamics of plate tectonics. Plate tectonics stands as one of the three major scientific revolutions of the 20th century, along with quantum mechanics and relativity. As a theory it remains a kinematic one in that it describes the motion of plates at the Earth's surface but does not connect the motions directly to the forces that drive the motion. Extending plate tectonics theory from a kinematic one to a dynamic one has been a something of a grand challenge in the geological and geophysical communities. From the inception of plate tectonics as a kinematic theory, it has been suspected that the dynamics of plate tectonics is connected to the existence of a low viscosity zone below plates - the asthenosphere. Mapping, quantifying, and seeking to bring conceptual understanding to several of the factors that tie into this long suspected connection is the theme of this work. More specifically, over the next one year cycle, the team will: A) Test the hypothesis that changes in asthenosphere structure can drive rapid changes in plate motion of the type recently identified to have occurred on the Earth 50-100 Million years ago and B) Explore the interaction between plate tectonics and the cycling of volatiles between surface reservoirs and the Earth's deep interior (e.g., deep water cycling can effect the nature of the asthenosphere through its role on rock melting).The investigators will explore the effects of a low viscosity asthenosphere on mantle dynamics. Numerical mantle convection experiments will be used to map the combined effects of a low-viscosity asthenosphere and plate boundary failure on maintaining a plate-tectonic mode of mantle convection. A specific goal will be to identify conditions that allow for rapid changes in plate motions, as have recently been inferred for the Earth's Cretaceous. Numerical work will be augmented with theoretical scaling analysis. The analysis will provide insight into energetic balances between the resistance to plate motion associated with dissipation at plate margins, within the asthenosphere, and in the bulk mantle. This will allow the PIs to link dynamic modeling to instantaneous flow studies that isolate the balance of dissipation between plate processes and the bulk mantle. That link will bring added observational constraints to bear on their results and predictions. The analysis will also be extended to model deep volatile cycling (water and carbon) within the Earth and volatile exchange from the surface to the interior of our planet over geologic time. The key feedback this introduces, relative to the role of the asthenosphere on maintaining plate tectonics, comes from the ability of volatiles to effect melting in the upper mantle, which can significantly alter the structure of the asthenosphere.

地球上发生的大部分变化都可以追溯到两种能量来源之一：1）来自太阳的能量和2）来自地球内部的能量。内部能量如何塑造地球表面直接关系到了解板块构造的动力学。板块构造学是20世纪三大科学革命之一，与量子力学和相对论并列。作为一个理论，它仍然是一个运动学的一个，因为它描述了板块在地球表面的运动，但没有将运动直接与驱动运动的力联系起来。 将板块构造理论从运动学扩展到动力学，一直是地质和地球物理学界的一个重大挑战。从板块构造作为运动学理论的开始，人们就怀疑板块构造的动力学与板块下方低粘度区--软流层的存在有关。映射，量化，并寻求带来概念上的理解，以配合到这个长期怀疑连接的几个因素是这项工作的主题。更具体地说，在接下来的一年周期中，该团队将：A）测试软流圈结构的变化可以驱动最近确定的50 - 1亿年前发生在地球上的板块运动类型的快速变化的假设，以及B）探索板块构造与表面储层和地球深部内部之间的挥发物循环之间的相互作用（例如，深水循环可以通过其在岩石融化中的作用影响软流层的性质）。研究人员将探索低粘度软流层对地幔动力学的影响。将利用数值地幔对流实验来绘制低粘度软流圈和板块边界破坏对维持地幔对流的板块构造模式的综合影响。一个具体的目标将是确定允许板块运动快速变化的条件，就像最近对地球白垩纪的推断一样。数值工作将通过理论缩放分析来增强。分析将提供洞察力之间的能量平衡的阻力板块运动与耗散在板块边缘，软流圈内，并在散装地幔。这将允许PI将动态建模与瞬时流动研究联系起来，从而隔离板块过程和大块地幔之间的耗散平衡。这种联系将给他们的结果和预测带来更多的观测约束。该分析还将扩展到模拟地球内部的深层挥发性循环（水和碳）以及地质时期从地球表面到内部的挥发性交换。相对于软流层在维持板块构造中的作用，这引入的关键反馈来自挥发物影响上地幔熔融的能力，这可以显着改变软流层的结构。