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.

山带的形成是地球上最重要的过程之一。山带影响着地球关键资源的分布，包括具有重要经济意义的矿产、石油和水。它们是板块构造的结果，沿着汇聚的板块之间的边界形成。当山脉变得太高而不稳定时，山带可能会横向膨胀，或者由于重力的作用，物质可能会从山带“逸出”。这种逃逸可能发生在地表暴露的断层上，在那里物质被从山带的侧面推离，或者仅仅是物质从较高的海拔向较低的海拔坍塌。在地壳中至深处（地球表面以下十多公里），岩石以流体般的方式流动。在今天的山脉带，如喜马拉雅山脉，这些流体状的岩石可以从山脉带喷出，要么向地表喷出，要么沿着板状通道完全在地表以下。这些都是促成山带形成和改造的重要过程，但人们对它们的了解还不完全透彻。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研究。这个项目的目的是调查马萨诸塞州东部的一个古老的流区，该流区形成于4.2亿到3.6亿年前，今天部分暴露在地表。地质技术将用于在地表调查该区域，地球物理成像技术将用于阐明地下几何结构。更好地了解这些流动带的形成将有助于我们更详细地了解古代和现代的造山过程，这对我们理解地球资源的分布方式具有重要意义。该项目将涉及多学科研究，将在阿巴拉契亚山脉工作的地质学家和地球物理学家聚集在一起，并与正在进行的国家和国际合作产生协同作用。该项目将有助于培养本科生和研究生，重点是通过科罗拉多矿业学院和耶鲁大学的各种项目培养历史上未开发群体的学生。综合地球物理和地质方法将用于测试新英格兰东南部阿巴拉契亚地体之一纳肖巴地体的河道流动和韧性挤压模型。水道流是由于地壳增厚和压力梯度的作用，弱的、部分熔融的中下地壳层在较强的上、下地壳之间流动。表面的局部剥蚀可能导致向表面的延性挤压。该项目的目的不仅是进一步验证基于野外和地质年代学数据的Nashoba地块演化假设，而且还利用地球物理数据可视化地表以下地质历史时期岩石的韧性流动。为了做到这一点，将在马萨诸塞州东部的Nashoba地块上部署六个紧密间隔的宽带地震站，以补充该地区目前可用的数据。此外，将使用由SEISConn阵列采样的康涅狄格州东部Putnam地层的现有数据。虽然解释韧性挤压带的顶部沿纳肖巴地体的北西边界受到很好的约束，但该韧性挤压带的东南部分可能合并了纳肖巴地体东南的阿瓦隆地体的一部分。为了更好地约束韧性挤压带的边界，将在阿瓦隆地体的这一部分进行新的构造填图和地质年代学。结合新的和现有的构造、地质年代学和地震成像限制，将用于测试水道流动假说和其他假说，包括逆冲和正断层、正花结构或变质核复合体。纳肖巴和普特南地体的演化将被置于新英格兰东南部阿巴拉契亚山脉构造史的整体背景中。所使用的方法和潜在的结果可能为造山带演化背后的基本过程提供新的证据，使其能够与现代造山带（喜马拉雅山脉）以及其他古老造山带（如加拿大科迪勒拉山脉）进行比较，这些造山带已经提出了河道流动和韧性挤压。本项目资金由NSF EAR构造和地球物理项目提供。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。