Collaborative Research: Virginia's Volcanoes: a Window into Eastern North America Mantle Processes

最近在弗吉尼亚州Mineral发生的5.8级地震影响了美国东海岸的主要大都市地区，并引发了更好地了解北美东部边缘（ENAM）地质特征的需求。在弗吉尼亚州和西弗吉尼亚州暴露的一组超过100个火山体大约有4700万至4900万年的历史，是美国东海岸已知最年轻的火山爆发，这些岩浆和岩石碎片是他们在上升和喷发过程中从地壳和地幔收集的，是最近地质时代地壳和地幔的唯一直接样品。这项研究的结果将与目前沿着东海岸部署的EarthScope移动式地震仪阵列以及其他地震研究的数据结合使用，以创建美国东部地壳和地幔状态的全面图片，为未来潜在的地震灾害提供背景。该项目将支持弗吉尼亚理工大学和詹姆斯麦迪逊大学的研究生和本科生研究。实地地点靠近两所大学，因此很容易进行实地定性和取样。除了普通教育教材外，还将为初中和高中学生安排实地考察，并通过终身学习研究所开设推广课程。弗吉尼亚理工大学的地球科学博物馆将举办一个展览。这项研究的数据将与公众、GeoPRISMS和EarthScope社区共享。 目前存在的制约因素很少的组成和结构的软流圈和岩石圈下的ENAM。地球化学和岩石学数据对于解释该区域的地震数据和了解ENAM裂谷向漂移过渡的长期持续演变以及世界各地的裂谷边缘至关重要。在弗吉尼亚州和西弗吉尼亚州暴露的一群始新世火山体是美国东部已知的最年轻的岩浆活动，也是ENAM中地幔和下地壳新生代过程的唯一岩石学窗口。我们推测：1）始新世岩浆是由浅部软流圈（例如，岩石圈脱层、边缘驱动的对流或深俯冲的影响），2）熔融与岩石圈对泛古陆解体和/或Farallon俯冲的响应有关，这些俯冲至少在始新世持续在这一被动边缘之下。我们将用一系列的地球化学、光谱学和岩石学观测和建模来检验这些假设。熔体和基底捕虏体的年代学将评估熔融过程，约束岩石圈的结构和演化，并评估火山活动相对于捕虏体年龄的年龄。EarthScope可移动阵列目前正在沿着东海岸部署到2013年，我们项目的位置位于？里士满断面？建议进行集中地震研究。我们的数据将产生一个垂直剖面深入到ENAM，这将提供重要的限制基底和地幔成分，岩石圈和软流圈结构，挥发性成分的大规模地球动力学和地震研究。

The recent magnitude 5.8 earthquakes in Mineral, VA, impacted major metropolitan areas on the East Coast of the U.S. and sparked a need to better understand the geologic characteristics the of Eastern North America Margin (ENAM). A group of more than 100 volcanic bodies approximately 47-49 million years old exposed in Virginia and West Virginia are the youngest known eruptions on the East Coast of the U.S. These magmas and the fragments of rock they collected from the crust and mantle during their ascent and eruption are the only direct samples of the crust and the mantle in recent geologic times. The results from this study will be used in conjunction with data from the EarthScope Transportable Array of seismometers currently being deployed along the East Coast as well as other seismic studies to create a comprehensive picture of the state of the crust and mantle underneath the Eastern U.S., providing context for the potential of future seismic hazards. This project will support graduate and undergraduate research at Virginia Tech and James Madison University. The proximity of the field site to both universities makes field characterization and sampling highly accessible. A field trip for middle and high school students and an outreach course through the Lifelong Learning Institute will be developed in addition to course materials for general education. An exhibit will be created for the Museum of Geociences at Virginia Tech. Data from this research will be shared with the public, the GeoPRISMS and EarthScope communities. Few constraints currently exist on the composition and structure of the asthenosphere and lithosphere under the ENAM. Geochemical and petrologic data are critical for interpretation of seismic data in the region and understanding the long-term, continued evolution of the rift-to-drift transition for ENAM, as well as for rift margins worldwide. A swarm of Eocene volcanic bodies exposed in Virginia and West Virginia are the youngest known magmatism in the Eastern U.S. and are the only petrologic window into Cenozoic processes in the mantle and lower crust in ENAM. We hypothesize that: 1) The Eocene magmas were generated through adiabatic melting of shallow asthenosphere (e.g., lithospheric delamination, edge-driven convection, or effects from deep subduction), 2) Melting is related to the lithospheric response to the breakup of Pangaea and/or Farallon subduction that continued under this passive margin at least through the Eocene. We will test these hypotheses with an array of geochemical, spectroscopic, and petrologic observations and modeling. Geochronology of the melts and basement xenoliths will evaluate melting processes, constrain the structure and evolution of the lithosphere, and evaluate the age of the volcanic activity relative to the age of the xenoliths. The EarthScope Transportable Array is currently being deployed along the East Coast through 2013 and the location of our project lies within the ?Richmond Transect? proposed for concentrated seismic studies. Our data will produce a vertical cross-section deep into the ENAM that will provide important constraints on basement and mantle composition, lithospheric and asthenospheric structures, and volatile contents for large-scale geodynamic and seismic studies.