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

山地带的形成是地球上发生的最重要的过程之一。山脉带影响着地球主要资源的分布，包括经济上重要的矿产、石油和水。它们是板块构造的结果，沿着会聚的板块之间的边界形成。当山脉变得太高而不稳定时，山带可能会横向扩张，或者由于重力的作用，物质可能会从山带中“逸出”。这种逃逸可能发生在地表暴露的断层上，那里的物质被推离山脉带的侧面，或者仅仅是由于物质从较高的海拔向较低的海拔坍塌。在地壳中至深层(地球表面下十多公里处)，岩石以类似流体的方式流动。在今天的山脉地带，如喜马拉雅山脉，这些类似流体的岩石可以沿着板状渠道向地表或完全在地表以下喷射。这些都是有助于山脉带形成和改造的重要过程，但人们对它们的理解仍然不完全。具体地说，因为这些岩石流带往往在地表以下，所以在今天的山地带系统中很难进行调查。这个项目的目的是调查马萨诸塞州东部的一个古老的流动带，它形成于大约4.2亿到3.6亿年前，今天部分暴露在地表。将使用地质技术来调查地表的地带，并使用地球物理成像技术来阐明地下几何图形。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，对于我们理解地球资源是如何分布的具有重要意义。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协同工作。该项目将帮助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来培训历史上未开发的群体的学生。将使用综合地球物理和地质方法来测试新英格兰东南部阿巴拉契亚地体之一的纳舒巴地体的沟道流动和韧性挤压模型。沟道流是由于地壳增厚和压力梯度，在更有能力的上、下地壳之间形成的弱的、部分熔融的中下地壳层的流动。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纳舒巴地体演化假说，而且还利用地球物理数据可视化地表下地质过去期间岩石的韧性流动。为了做到这一点，将在马萨诸塞州东部的纳舒巴地体上部署一个由六个宽带地震台组成的紧密间隔的阵列，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普特南地体的现有数据。虽然所解释的韧性挤压带的顶部沿Nashoba地体的NW向边界被很好地约束，但该带的SE部分可能并入了Nashoba地体的部分Avalon地体SE。将在阿瓦隆地体的这一部分进行新的构造填图和年代学研究，以更好地约束韧性挤压带的边界。新的和现有的构造、地质年代学和地震成像约束将被用来检验渠道流假说与其他假说的对比，这些假说包括逆冲和正断层、正花状构造或变质核杂岩。然后，纳舒巴和普特南地体的演化将被置于阿巴拉契亚新英格兰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造山系统演化背后的基本过程提供新的证据，使之能够与现代系统(喜马拉雅山脉)以及其他提出了水道流动和韧性挤压的古老造山带(例如加拿大科迪勒拉)进行比较。该项目的资金由NSF EAR构造和地球物理计划提供。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.