Collaborative Research: Testing the Timescale and Geometry of Incremental Pluton Assembly Through 3-D Modeling and Thermochronology

这项研究旨在检验一种假设，即深成岩记录了用于增量组装的地质年代学、热年代学和野外证据。尽管有理论上的考虑，但支持增量增长(特别是数百万年到数千万年)的地质年代学和现场数据仍然存在激烈的争论。内华达山脉岩基岩石的角闪石、黑云母和钾长石氩的热年代学正在被用来解决几个广泛的问题。首先，缓慢增长的深成岩体组合在很大程度上是从铀-铅锆石年龄推断出来的，而来自相同样品的Ar-Ar数据为铀-铅结果的可靠性提供了强有力的测试。其次，如果大型“同质”深成岩块是以增量方式组装的，那么增量之间的接触在野外就被忽略了，而使用块状岩石磁化率的新作图正被用来识别隐秘的接触。最后，对岩体和围岩温度历史的模拟表明，冷却路径对增量岩体组装的速率和几何形状都很敏感。因此，正在将基于锆石和钛铁矿铀铅系统以及角闪石、黑云母和钾长石氩系统的冷却历史与模拟的冷却历史进行比较，以确定侵入增量的空间安排和它们的添加速度。这项研究致力于岩浆房的物理和化学演化，包括侵入机制、岩体组构的发展和允许的岩浆分异过程。我们所模拟的深成岩体及其围岩的复杂热历史，涉及到来自深成岩体的角闪石Ar-Ar年龄的解释；接触变质作用的最高温度和持续时间；早期侵入体成为后来侵入体的围岩时的热、构造和岩石学演化；从深成岩中收集的古地磁数据的解释；以及深成岩体记录了大体积可喷发岩浆体的形成程度。这项研究的重点是为地球表面的火山提供燃料的岩浆室的组装速度。它采用了各种测年技术，相互制衡，努力了解岩浆体是如何形成的，速度有多快，以及它们可能发生灾难性喷发。增量组装假说预测，“超级火山”岩浆室的增长将与为其他火山提供燃料的岩浆室的构造和热历史截然不同。我们应该能够利用这种理解来评估黄石公园等巨大火山复合体灾难性喷发的可能性。这项研究支持了北卡罗来纳大学一名学生的博士研究，以及其他理科硕士的教育活动。以及北卡罗来纳大学和犹他大学的本科生。该项目包括在洛斯阿拉莫斯国家实验室、新墨西哥理工学院、北卡罗来纳大学和犹他大学之间发展新的合作关系。这项研究也是我们对国家公园的支持的一部分。它有助于我们更新约塞米蒂国家公园的地质展品，并在公园的护林员培训中发挥作用。

This research is designed to test the hypothesis that plutons record geochronologic, thermochronologic and field evidence for incremental assembly. Although suggested by theoretical considerations, geochronologic and field data in support of incremental growth (particularly over millions to tens of millions of years) are hotly debated. Hornblende, biotite and potassium-feldspar argon thermochronology of rocks in the Sierra Nevada batholith are being used to address several broad questions. First, slow incremental pluton assembly has largely been inferred from uranium-lead zircon ages, and argon-argon dates from the same samples are providing a robust test of the reliability of the uranium-lead results. Second, if large "homogeneous" plutons were assembled incrementally, then contacts between increments have been overlooked in the field, and new mapping using bulk rock magnetic susceptibility is being used to identify cryptic contacts. Finally, modeling pluton and wall rock temperature histories indicates that cooling paths are sensitive to both the rate and the geometry of incremental pluton assembly. Therefore, cooling histories based on the zircon and titanite uranium-lead systems, and hornblende, biotite and potassium-feldspar argon systems, are being compared to modeled cooling histories in order to resolve spatial arrangements of intrusive increments and the rates at which they are added. This research is addressing the physical and chemical evolution of magma chambers, including mechanisms of intrusion, development of pluton fabrics, and permissible magmatic differentiation processes. The complex thermal histories of plutons and their wall rocks suggested by our modeling bear on interpretation of hornblende argon-argon dates from plutons; the maximum temperatures and durations of contact metamorphism; the thermal, structural and petrologic evolution of early intrusions as they become the wall rocks for later intrusions; the interpretation of paleomagnetic data collected from plutons; and the extent to which formation of large-volume eruptible magma bodies is recorded by plutons. This research focuses on the rates of assembly of magma chambers that feed volcanoes at the surface of the Earth. It employs a variety of dating techniques that act as checks and balances on each other in an effort to understand how, and how fast, the magma bodies are constructed, and their potential for catastrophic eruption. The incremental assembly hypothesis predicts that growth of "super volcano" magma chambers will be profoundly different than the construction and thermal histories of magma chambers that feed other volcanoes. We should be able to use this understanding to assess the potential for catastrophic eruption of huge volcanic complexes such as Yellowstone. The research is supporting the Ph.D. research of a student from the University of North Carolina, as well as the educational activities of other M.Sc. and undergraduate students at the University of North Carolina and the University of Utah. The project includes the development of new collaborative ties between Los Alamos National Laboratory, New Mexico Tech, University of North Carolina, and the University of Utah. The research is also an ongoing part of our support of the National Parks. It is contributing to our efforts to update the geology exhibits in Yosemite National Park, and play a role in Ranger training for the Park.