Research Frontiers in Appalachian Geology: A Pre-EARTHSCOPE (USArray) Workshop Proposal

EarthScope是迄今为止最大的地球科学计划，旨在为我们对北美大陆4d演化的理解做出新的和根本性的贡献。这项计划的美国阵列组成部分“将极大地改善大陆岩石圈和更深地幔的地震成像，并将这些图像整合到大陆结构、演化和动力学的未解决问题中”（www.Earthscope.org）。为了实现这一愿景，地球科学研究人员有必要开始批判性地评估我们目前关于大陆形成的4d进化记录的知识状况，并提出新的问题，为《地球视野》提供智力挑战。美国大陆内的阿巴拉契亚造山带为探索有关大陆演化的一些关键问题提供了一个地质模板。例如：地形是如何形成的？在三维空间中，陆块及其大陆基础设施的结构是什么？识别深度侵蚀地体和相关缝合带的三维结构特征，将有助于对现代增生过程进行更严格的解释，并有助于区分美国中部常见的埋藏缝合带。岩石圈结构及其变形史对现今东部沿海被动边缘内火山裂谷边缘发育的影响是什么？地震资料能否有效地用于隐伏被动边缘、前陆盆地成像和推断盆地几何形状？陆块增生机制或逆冲构造的新知识是否与古生代沉积中心的存在或缺失有关？什么样的岩石圈结构与阿巴拉契亚山脉的新构造活动有关？该地区发生了许多破坏性的中板块地震，岩石圈的详细成像有可能回答有关中板块地震活动的基本问题。高分辨率地震资料能否成为区分中大陆1500Ma花岗岩流纹岩省与1000 Ma Grenville省（假定位于古生代阿巴拉契亚山脉之下）的最关键判别标准？它可能为解释阿巴拉契亚造山带许多火成岩/火山岩的起源提供了缺失的一环。整个大陆变形的时空尺度是什么？阿巴拉契亚造山带在其历史上大部分时间处于板块边界，其变形历史/机制的记录可以在北美内部得到识别。在整个大陆发展这样的地质关系是EarthScope的愿景。研讨会将为所有地球科学家提供一个开放的论坛，让他们在“地球范围”项目中合作制定新的研究机会，特别是那些涉及阿巴拉契亚山脉自然实验室的研究机会。讲习班的另一项重要目标，与地球范围的更广泛目标保持一致，将是开始发展确定阿巴拉契亚造山带目前知识状况的天气数据库的进程。将邀请数据库科学家协助理解利用信息技术分析多学科数据的研究效益。讲习班将广泛宣传并向所有人开放，但计划将出席人数限制在约50人，包括研究生和机构代表。这将能够及时和明确地制定科学主题，这些主题可以利用EarthScope设施，特别是美国阵列组件。研讨会指导委员会包括A.K.Sinha（首席研究员，弗吉尼亚理工大学，pitlab@vt.edu）、J.F.Read（弗吉尼亚理工大学）、Art Goldstein（科尔盖特大学）和Larry Brown（康奈尔大学），他们将监督研讨会议程的制定。他们还将准备最后的研讨会报告，以便在国家地球科学学会杂志上发表，并提交给美国国家科学基金会。讲习班的形式将包括分组讨论和全体会议。全体会议将提出当前的和大胆的新想法，随后将有一轮突破。分组会议的报告将形成一套共识性建议，以促进阿巴拉契亚地区的研究机会。这些建议将构成讲习班的最后报告。

EarthScope is the largest earth science initiative to date, designed to make new and fundamental contributions to our understanding of the 4-D evolution of continental North America. The U.S.Array component of this initiative "will dramatically improve the seismic imaging of the continental lithosphere and deeper mantle, and integrate these images to unresolved issues of continental structure, evolution and dynamics" (www.Earthscope.org). Towards this vision, it is necessary that earth science researchers begin the process of critically evaluating both the status of our current knowledge regarding the 4-D evolutionary record of continent formation, as well as formulating new questions that will provide the intellectual challenge for EarthScope. The Appalachian orogen within the continental United States provides a geologic template to explore some of the key questions concerning continental evolution .For example:How do terranes accrete? What is the structure in three dimensions of the accreting terrane and its continental infrastructure? Recognizing structural features in 3-D of deeply eroded terranes and associated suture zones will allow for a more rigorous interpretation of both modern accretionary processes, as well as helping discriminate buried suture zones common in the central United States.What is the effect of lithospheric structure and its deformation history on the development of volcanic rifted margins within the present passive margin along the eastern seaboard? Can seismic data be used effectively to image buried passive margins, foreland basins and infer basin geometry? Can new knowledge of terrane accretionary mechanisms or thrust tectonics be related to presence/absence of long lived Paleozoic depocenters? What lithospheric structure is associated with neotectonic activity in the Appalachians? A number of destructive mid-plate earthquakes have occurred in the region, and detailed imaging of the lithosphere holds the potential to answer fundamental questions about mid-plate seismicity.Can high resolution seismic data become the most critical discriminant for distinguishing the 1500Ma granite-rhyolite province of the mid-continent from the 1000 Ma Grenville province assumed to underlie the Paleozoic Appalachians? It may provide the missing link in interpreting the origin of many of the igneous/volcanic rocks of the Appalachian orogen.What are spatial and temporal scales of deformation across the continent? The Appalachian orogen has been at a plate boundary for most of its history, and the record of its deformation history/mechanisms can be recognized into the interior of North America . Developing such geologic relationships across the continent is an EarthScope vision.The workshop will provide an open forum for all earth scientists to collaboratively formulate new research opportunities within the EarthScope program, particularly those involving the natural laboratory provided by the Appalachian Mountains. Another significant objective of the workshop, in keeping with the broader goals of EarthScope, will be to initiate the process of developing synoptic databases that identify the current state of knowledge in the Appalachian orogen. Database scientists will be invited to facilitate the understanding of the research benefits of analyzing multidisciplinary data through use of information technology. The workshop will be widely advertised and open to all, but it is planned that the attendance be limited to approximately 50 individuals, including graduate students and agency representatives. This will enable timely and explicit formulation of science themes that can take advantage of EarthScope facilities, especially the US Array component. The workshop steering committee includes A.K.Sinha (Principal Investigator, Virginia Tech, pitlab@vt.edu), J.F.Read, (Virginia Tech), Art Goldstein (Colgate University) and Larry Brown (Cornell University), and will oversee the development of the workshop agenda. They will also prepare the final workshop report for publication in a national earth science society magazine, as well as for submission to NSF.The workshop format will consist of breakouts coupled with plenary sessions. Plenary sessions will present both current and bold new ideas, and will be followed by a round of breakouts. The reports from the breakout sessions will lead to a consensus set of recommendations for advancing research opportunities in the Appalachian region. These recommendations will constitute the final workshop report.