Collaborative Research: Elucidating Physical Processes in Upper Crustal Magma Systems - Evidence from Miocene Intrusive and Extrusive Sequences in Southern Nevada

物理运输过程决定了岩浆穿越上地壳的方式，它们是如何被改造的，它们在哪里沉积，它们是否以及如何喷发，以及它们的最终产物是什么。该项目将利用一个极好的自然实验室来研究运输和分布岩浆物质的物理机制：拉斯维加斯以南的科罗拉多河地区，在那里，相对年轻（约1500万年）的岩浆系统通过与裂谷有关的断裂、高起伏和稀疏植被的陡峭倾斜组合而引人注目地暴露出来。大量的岩体、广泛的岩脉群和厚厚的火山层序记录了一个相对短暂但高产的岩浆流入时期。该项目的一个关键部分将致力于了解岩体（大型侵入岩体，在地表下凝固）以及它们对岩浆房的性质和历史的说明（岩浆房是在深处临时的富含熔体的区域，凝固形成岩体，并可能在地表喷出岩浆）。岩体、形成它们的岩浆房、为岩浆房提供补给的岩脉、为地表火山喷发提供补给的岩脉都必须具有动态历史，但是在这些系统中移动晶体、熔体和固体或近固体岩石碎片的物理过程还没有得到很好的理解。研究区火山岩和侵入岩的总体分布及其内部结构的细节表明，流体动力学模型类似于地表环境中的流体和颗粒输运，特别是沉积和物质消耗过程。该项目将解决这个基本的、普遍的问题：上地壳的物理运输过程如何决定岩浆系统产物的最终分布、物理和成分特征？为了评价这个广泛的问题，重点将放在以下更具体的问题上：(1)沉积过程如何决定了岩体的构造和最终结构？(2)外部因素（充注、顶板坍塌、喷发、构造运动）如何影响岩浆房内部的物理过程？(3)熔融分数和体积在岩体（~岩浆库）的生命周期中变化多少，为什么变化？(4)是什么决定了深部岩浆在岩浆房中停留时是未经修饰地穿越上地壳还是经过修饰？岩浆房是否起到了有效的过滤作用，选择性地抑制了某些岩浆或岩浆物质的进一步上升？(5)是什么决定了岩浆池是形成深岩体，还是局限于岩脉，还是会喷发？对关键地区的实地研究将描绘关键结构的特征和地图模式，为机械运输和沉积过程提供证据，并为进一步分析提供样本。这些样品将用于矿物中示踪元素和同位素的详细放射性测年和微量分析。岩浆的液体+颗粒类似物的补充实验室实验将评估岩浆系统中可能的流体动力学过程。样品地球化学和地质年代学以及实验室实验将共同验证基于现场的岩浆运输假设。本项目将为7名硕士生和12名本科生提供理想的科研训练和论文基础。学生们将展示和发表他们的成果，并获得将仔细的实地观察与先进的分析工作相结合的经验，在合作研究中，以及将当地的努力整合到全球框架中。这项工作不仅为他们在岩石学、地球化学和构造学方面的进一步研究做准备，而且为他们解决广泛的地球科学问题和教学做准备。根据过去的经验，这些学生中很大一部分将是女性，少数民族学生也可能参加。这项研究将促进PI和他们的学生以及一些非正式合作者之间的思想交流，这些合作者将增加他们自己的观点和专业知识，在某些情况下还将增加分析方法。这些合作、正式和非正式的实地考察、专家和普通观众的演讲以及出版的作品将传播发展中的思想，促进各种论坛的讨论，并展示这一壮观的岩浆过程的例子。大部分研究将在米德湖国家休闲区进行，这将为向公众展示新想法提供一个绝佳的场所。该项目还将为范德比尔特大学一个涉及地质和环境工程的新合作项目做出贡献。虽然主要是一个基础科学项目，但这项工作的结果将有助于了解喷发过程，从而对火山危害产生影响。

Physical transport processes determine the ways in which magmas traverse the upper crust, how they are modified, where they are deposited, whether and how they erupt, and what their final products will be. This project will investigate the physical mechanisms that transport and distribute magmatic materials using a superb natural laboratory: the Colorado River region south of Las Vegas, where relatively young (~15 million years old) magmatic systems are spectacularly exposed through a combination of steep tilting during rift-related faulting, high relief, and sparse vegetation. Numerous plutons, extensive dike swarms, and thick volcanic sequences document a relatively brief but highly productive episode of magma influx. A key part of the project will be devoted to understanding the plutons (large bodies of intrusive rock, solidified beneath the surface) and what they say about the nature and history of magma chambers (temporary melt-rich zones at depth that solidify to form plutons and may expel magma to erupt at the surface). Plutons, the magma chambers that formed them, dikes that fed the chambers, and dikes that fed volcanic eruptions at the surface all must have dynamic histories, but the physical processes that move crystals, melts, and fragments of solid or near-solid rocks within these systems are not well understood. General distributions of volcanic and intrusive rocks in the study area and details of their internal structure suggest fluid dynamic models that are analogous to fluid and particle transport in surface environments - notably sedimentation and mass wasting processes.The project will address this fundamental, general issue:How do physical transport processes in the upper crust determine the eventual distribution and physical and compositional characteristics of the products of a magma system?To evaluate this broad problem, the focus will be on the following more specific questions:(1) How do depositional processes dictate the construction and ultimate architecture of plutons?(2) How do external factors (recharging, roof collapse, eruption, tectonism) influence internal physical processes within magma chambers?(3) How much, and why, do melt fraction and volume vary over the lifetime of a pluton (~magma chamber)? (4) What determines whether deep-level magmas transit the upper crust unmodified or are modified during residence in magma chambers?; Do magma chambers serve as effective filters, selectively inhibiting further ascent of certain magmas or magmatic materials? (5) What determines whether magma pools to form plutons, remains restricted to dikes, or erupts?Field studies of key areas will characterize critical structures and map patterns that provide evidence for mechanical transport and deposition processes and provide samples for further analysis. These samples will be used for detailed radiometric dating and microanalysis of tracer elements and isotopes in minerals. Complementary lab experiments on liquid + particle analogs of magma will evaluate plausible fluid dynamic processes in the magma systems. Together, the sample geochemistry and geochronology and lab experiments will test field-based magma transport hypotheses.This project will provide ideal research training and constitute the basis for theses for 7 Master's and 12 undergraduate students. The students will present and publish their results and gain experience in combining careful field observation with advanced analytical work, in collaborative research, and in integrating their local efforts into a global framework. This work prepares them not only for further research in petrology, geochemistry, and tectonics, but also for a broad range of Earth science problem solving and teaching. Based on past experience a large proportion of these students will be female and participation by minority students is likely. The study will stimulate exchange of ideas between the PI's and their students and several informal collaborators who will add their own perspectives and expertise and in some cases analytical methodologies. These collaborations, formal and informal field trips, and presentations to specialist and general audiences as well as published work will disseminate developing ideas, foster discussion in a variety of forums, and showcase this spectacular example of magmatic processes. Much of the research will take place in Lake Mead National Recreation area, which will provide an excellent venue for presentation of new ideas to the public. The project will also contribute to a new cooperative program at Vanderbilt involving geology and environmental engineering.Although principally a basic science project, the results of this work will contribute to understanding of eruptive processes and thus will bear upon volcanic hazards.