Thermal constraints on the role of hydrated oceanic mantle lithosphere in the genesis of intermediate-depth seismicity

水合大洋地幔岩石圈在中深度地震活动成因中作用的热约束

• 批准号: 2021027
• 负责人: Peter van Keken
• 金额: $ 29.81万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-06-15 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2021027&HistoricalAwards=false
• 关键词: Thermal; constraints; role; hydrated; oceanic

While most of the Earth’s earthquakes happen near the surface, a significant subset occurs at greater depths. These earthquakes are generated within tectonic plates that are sinking into the Earth’s mantle through a process called subduction. Subduction plays an important role in the evolution of our planet by cycling volatile materials like water and carbon back into the planet’s interior. Some of these volatiles are released from the slab in time to be returned to the surface through volcanoes, but some fraction are subducted to much greater depths. What we don’t know is what those relative fractions are. Part of the difficulty is in tracing where volatiles are released. The investigators hypothesize that earthquakes that happen in downgoing plates at “intermediate depths” (or between about 70 and 300 km below the Earth’s surface) are caused by the release of water from deep within the subducting plates. Water brought down in the crust of the downgoing plate is probably released at shallower depths, but the water the team is studying, located below the crust of the downgoing plate (known as the “mantle lithosphere”) has the potential to be subducted to much greater depths given the correct conditions. The investigators have found a geological location where they can test whether or not water in the mantle lithosphere is being released during intermediate depth earthquakes. In this project, they will develop thermal models for the complex subduction zones that exist in the selected test areas in order to examine whether the conditions are right for the release of water at the locations where earthquakes are seen. If so, then it will show that these volatiles do not get subducted to greater depths in the Earth, but rather are likely to eventually be returned to the Earth’s surface. This is important for our understanding of the chemical evolution of our planet and its ability to maintain a volatile-rich atmosphere over geologic time. The thermal modeling approach the team develops will be made public to the scientific community. Other scientists can use it to study the thermal properties of complex slabs elsewhere to further our understanding on a broader scale. This project will support an early-career scientist, and will also engage undergraduate summer interns in research visualization efforts. The occurrence of intermediate-depth seismicity in subduction zones is commonly attributed to the metamorphic dehydration of mineral phases within the downgoing oceanic plate. Water is introduced to the plate upon its formation at the ridge and by outer-rise faulting just before subduction, yet the amount of water introduced and its role in intermediate-depth seismicity remains uncertain. Two flat segments in the South American subduction zone are characterized by strong variations in slab geometry and convergence both in space and in time. The investigators hypothesize that these variations lead to temperature variations at depth that control the variable seismicity at intermediate depths. They will test this hypothesis by predicting the thermal structure of the subducted lithosphere through high-resolution 3D and time-dependent finite element models from which they can predict the metamorphic conditions and where dehydration takes place. The full thermal models and open-source modeling capability will be made available in multiple forms so that they can be used by a wide range of researchers ranging from graduate students in petrology and geochemistry to specialists in geodynamical modeling. This project will therefore contribute to software infrastructure and leverage significant investments by the National Science Foundation in subduction zone research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

虽然地球上的大多数地震发生在地表附近，但也有相当一部分地震发生在地壳深处，这些地震通过俯冲作用沉入地幔，在地球的演化过程中发挥着重要作用。通过将水和碳等挥发性物质循环回地球内部，其中一些挥发物及时从板块中释放出来，通过火山返回到地表，但有些部分会潜入更深的地方。我们不知道这些相对分数是什么，部分困难在于追踪挥发物的释放位置。研究人员追踪发生在“中等深度”（或地球以下约 70 至 300 公里）的下降板块中的地震。表面）是由俯冲板块深处的水释放引起的，下降到下降板块地壳中的水可能是在较浅的深度释放的，但该团队正在研究的水位于下降板块地壳下方。在适当的条件下，板块（称为“地幔岩石圈”）有可能俯冲到更大的深度，研究人员已经找到了一个地质位置，可以测试地幔岩石圈中的水是否在中间深度被释放。在这个项目中，他们将为选定的测试区域中存在的复杂俯冲带开发热模型，以检查地震发生地点是否适合释放水。将表明这些挥发物不会潜入地球更深处，而是可能最终返回地球表面，这对于我们了解地球的化学演化及其在地质上维持富含挥发物的大气的能力非常重要。该团队开发的热建模方法将向科学界公开，其他科学家可以使用它来研究其他地方的复杂板的热特性，以进一步加深我们对早期职业科学家的了解。 ，并且还将参与本科生暑期俯冲带中深度地震活动的发生通常归因于下降海洋板块内矿物相的变质脱水，水在板块形成时被引入到洋脊和外隆断层中。就在俯冲之前，但引入的水量及其在中深度地震活动中的作用仍然不确定。南美俯冲带的两个平坦部分的特点是板片几何形状和空间和收敛性的强烈变化。研究人员寻求这些变化导致深度的温度变化，从而控制中间深度的可变地震活动，他们将通过高分辨率 3D 和时间相关的有限元模型预测俯冲岩石圈的热结构来检验这一假设。他们可以预测变质条件以及脱水发生的位置。完整的热模型和开源建模功能将以多种形式提供，以便广泛的研究人员（包括岩石学研究生和研究生）使用。因此，该项目将为软件基础设施做出贡献，并利用美国国家科学基金会在俯冲带研究方面的重大投资。该奖项是美国国家科学基金会的法定使命，并通过利用基金会的智力优势和更广泛的评估，被认为值得支持。影响审查标准。