Collaborative Research: Testing for Channel Flow and Ductile Extrusion In The Southeastern New England Appalachians Using An Integrated Geophysical and Geological Approach

合作研究：使用综合地球物理和地质方法测试新英格兰东南部阿巴拉契亚山脉的河道流动和延性挤压

• 批准号: 2220234
• 负责人: Maureen Long
• 金额: $ 16.54万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-15 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2220234&HistoricalAwards=false
• 关键词: Collaborative; Research; Testing; Channel; Flow

The formation of mountain belts is one of the most important processes that takes place on Earth. Mountain belts affect the distribution of key Earth resources, including economically important minerals, petroleum, and water. They form as a result of plate tectonics, along boundaries between converging plates. When mountain ranges become too high to be stable, the mountain belt may expand laterally, or material may ‘escape’ from the belt, due to the force of gravity. This escape may occur along faults that are exposed at the surface, where material is pushed away sideways from the mountain belt, or simply by collapse of material from higher to lower elevation. At mid-to deep-crustal levels (more than ten kilometers below the Earth’s surface) rocks flow in a fluid-like manner. In present-day mountain belts such as the Himalaya, these fluid-like rocks can be squirted away from the mountain belt, either toward the surface or entirely below the surface along tabular channels. These are important processes that contribute to the formation and modification of mountain belts, but they remain imperfectly understood. Specifically, because these rock flow zones are often below the surface, they are difficult to investigate in present-day mountain belt systems. The purpose of this project is to investigate an ancient flow zone in eastern Massachusetts that formed about 420 to 360 million years ago and today is partially exposed at the surface. Geological techniques will be used to investigate the zone at the surface and geophysical imaging techniques to elucidate the subsurface geometry. A better understanding of the formation of these flow zones will help us understand both ancient and modern mountain building processes in more detail, with important implications for our understanding of how Earth resources are distributed. This project will involve multi-disciplinary research that brings together geologists and geophysicists working in the Appalachians, and is synergistic with ongoing national and international collaborations. This project will contribute to the training of undergraduate and graduate students, with a focus on training students from historically untapped groups through various programs at the Colorado School of Mines and Yale University.An integrated geophysical and geological approach will be used to test a model of channel flow and ductile extrusion for one of the Appalachian terranes, the Nashoba terrane, in SE New England. Channel flow is flow of a weak, partially molten mid- to lower crustal layer between more competent overlying and underlying crust as a result of crustal thickening and pressure gradients. Localized denudation at the surface may cause ductile extrusion towards the surface. The purpose of this project is not only to further test a hypothesis for the evolution of the Nashoba terrane based on field and geochronology data, but also to visualize ductile flow of rocks during the geologic past below the surface using geophysical data. To do this, a tightly spaced array of six broadband seismic stations will be deployed across the Nashoba terrane in eastern Massachusetts, complementing currently available data in the area. Additionally, existing data from the Putnam terrane in eastern Connecticut, as sampled by the SEISConn array, will be used. While the top of the interpreted ductile extrusion zone is well constrained along the NW boundary of the Nashoba terrane, the SE part of the zone may have incorporated part of the Avalon terrane SE of the Nashoba terrane. New structural mapping and geochronology will be carried out in this part of the Avalon terrane to constrain the boundary of the ductile extrusion zone better. Combined new and existing structural, geochronological, and seismic imaging constraints will be used to test the channel flow hypothesis against alternative hypotheses, including thrust and normal faults, a positive flower structure, or a metamorphic core complex. The evolution of the Nashoba and Putnam terranes will then be placed in the overall context of the tectonic history of the SE New England Appalachians. Methods used and potential outcomes may provide new evidence for fundamental processes behind evolution of orogenic systems, enabling comparisons with modern systems (the Himalayas) as well as other ancient orogens (e.g., Canadian Cordillera) where channel flow and ductile extrusion have been proposed.Funding for this project is provided by NSF EAR Tectonics and Geophysics Programs.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.

山脉带的形成是地球上发生的最重要的过程之一，山脉带影响着地球上重要资源的分布，包括经济上重要的矿物、石油和水。它们是板块构造沿边界形成的。当山脉变得太高而不稳定时，山脉带可能会横向扩展，或者由于重力的作用，物质可能会从山脉中“逸出”，这种逸出可能会沿着暴露在地表的断层发生。材料在哪里从山带向侧面推开，或者简单地通过物质从较高海拔向较低海拔的塌陷，在地壳中层到深层（距地球表面十多公里），岩石以类似流体的方式流动。在像喜马拉雅山这样的白天山脉中，这些流体状岩石可以从山脉中喷出，要么沿着板状通道喷向地表，要么完全在地表以下，这些都是有助于山脉形成和改造的重要过程。但它们仍然不完美具体来说，由于这些岩石流动带通常位于地表以下，因此很难在当今的山带系统中进行调查。该项目的目的是调查马萨诸塞州东部形成的约 420 至 3.6 亿个古老的流动带。几年前和今天部分暴露在地表的地质技术将用于研究该区域的地表，而地球物理成像技术将用于阐明地下流动区域的几何形状，这将有助于我们了解古代和现在的流动区域。现代造山工艺更多该项目将涉及阿巴拉契亚地区地质学家和地球物理学家的多学科研究，并与正在进行的国家和国际合作产生协同作用。培训本科生和研究生，重点是通过科罗拉多矿业学院和耶鲁大学的各种项目培训来自历史上未开发群体的学生。将使用综合地球物理和地质方法来测试河道流动和延性模型位于新英格兰东南部的阿巴拉契亚地体之一纳肖巴地体的挤压作用是由于地壳增厚和压力梯度而在较充沛的上覆地壳和下伏地壳之间形成的弱的、部分熔融的中下地壳层的流动。地表的局部剥蚀可能会导致向地表的延性挤压，该项目的目的不仅是进一步检验基于 Nashoba 地体演化的假设。现场和地质年代学数据，还可以使用地球物理数据可视化地表以下地质历史期间岩石的延性流。为此，将在马萨诸塞州东部的纳肖巴地体上部署一个紧密排列的六个宽带地震台，以补充目前的情况。此外，将使用由 SEISConn 阵列采样的康涅狄格州东部普特南地体的现有数据，而解释的延性挤压区域的顶部受到很好的约束。沿着 Nashoba 地体的西北边界，该区域的 SE 部分可能合并了 Nashoba 地体 SE 的一部分。将在 Avalon 地体的这一部分进行新的构造测绘和地质年代学，以限制该区域的边界。结合新的和现有的结构、地质年代学和地震成像约束，将可以更好地检验河道流假说与替代假说，包括逆冲断层和正断层，这是一个积极的结果。纳肖巴地体和普特南地体的演化将被置于新英格兰阿巴拉契亚山脉东南部构造历史的整体背景中，所使用的方法和潜在的结果可能为演化背后的基本过程提供新的证据。造山系统，可以与现代系统（喜马拉雅山）以及其他古代造山带（例如加拿大科迪勒拉山脉）进行比较，其中河道流和延性挤压已被研究该项目的资金由 NSF EAR 构造和地球物理学计划提供。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。