Conditions of Melt Generation Associated with the Colorado Plateau

技术描述：USArray 数据极大地推进了对美国西南部上地幔结构和物理特性的了解。对于科罗拉多高原（CP），有证据表明，上地幔可能因致密区域的重力失稳（如滴落/分层）和/或与软流圈并置的岩石圈的热再生/熔化侵入而发生重大改变。该项目的重点是通过确定与科罗拉多高原北部和西南部过渡区岩石圈不稳定相关的熔体产生和分离条件来评估这些情景。这项研究的总体目标是 (1) 提供熔融条件的详细参数；(2) 深入了解熔融区域的岩性非均质性。本研究中获得的新数据包括：（1）通过对橄榄石中名义无水单斜辉石和熔体包裹体的分析来估计岩浆水含量； (2)熔融和单斜辉石结晶的压力和温度； (3)源氧逸度的估算； (4)从橄榄石的微量元素特征和整个岩石的微量元素和同位素特征(特别是Hf和Os同位素)对地幔岩性非均质性作用的限制。这些数据与 USArray 的地震各向异性观测一起被考虑，以评估中部地区融化动力学的情景以及科罗拉多高原及其过渡带下方岩石圈的结构和演化。更广泛的影响和意义：正如地震波可以揭示地球内部物理性质的异质性一样，火山岩的成分特征也可以揭示其化学性质的异质性。通过这两种方法，可以深入了解物理和化学性质的相互依赖性和演变。该项目利用与地球外壳的深刻变化相关的熔岩和矿物的化学成分来了解造成神秘火山活动的岩浆源的压力、温度和化学成分（尤其是流体）。这些结果有助于阐明大陆融化的起源，并更好地解释北美板块结构和动力学的地震模型。该项目正在为两名研究生提供收集和解释新颖的高质量地球化学数据的专业培训。它还促进了首席研究员和其他三所大学的科学家之间的合作。这项研究的结果将在国内和国际会议以及同行评审的出版物上专业分享。有关 CP 相关火山活动起源的见解也将传播给日落火山口和埃尔马尔佩斯国家纪念碑的博物学家。

Technical description: USArray data are significantly advancing knowledge of the structure and physical properties of the upper mantle beneath the southwestern US. For the Colorado Plateau (CP), there is evidence that the upper mantle may be substantially modified by gravitational destabilization of dense domains as drips/delaminations and/or by thermal rejuvenation +/- melt invasion of the lithosphere where it is juxtaposed against the asthenosphere. This project is focused on evaluating these scenarios by determining conditions of melt generation and segregation associated with lithosphere destabilization across the north- and southwestern transition zones of the Colorado Plateau. The overarching goals of this study are (1) providing intensive parameters for melting conditions and (2) gaining insights into the lithologic heterogeneity in zones of melting. New data being acquired in this study include: (1) estimates of magmatic water contents from analyses of nominally anhydrous clinopyroxene and melt inclusions in olivine and; (2) pressures and temperatures of melting and clinopyroxene crystallization; (3) estimates of source oxygen fugacity; and (4) limits on the role of lithologic heterogeneities in the mantle from minor element characteristics of olivine and from trace element and isotopic characteristics of whole rocks (especially Hf and Os isotopes). These data are being considered along with seismic anisotropy observations from USArray to evaluate scenarios for the dynamics of melting beneath the CP and for the structure and evolution of lithosphere beneath the Colorado Plateau and its transition zones. Broader impact and significance: Just as seismic waves can reveal heterogeneities in the physical properties of Earth's interior, compositional features of volcanic rocks can reveal heterogeneities in its chemical properties. From these twin approaches, insights into the interdependence and evolution of the physical and chemical properties are possible. This project is using the chemistry of lavas and minerals associated with profound changes in the Earth's outer shell to learn about the pressures, temperatures, and chemical compositions - especially fluids - of magma sources responsible for enigmatic volcanism. The results are helping to elucidate the origin of continental melting and to better interpret seismic models for the structure and dynamics of the North American plate. The project is providing professional training for two graduate students in the collection and interpretation of novel high quality geochemical data. It is also fostering collaborations between the principal investigator and scientists at three other universities. The results of this study will be shared professionally at national and international conferences as well as in peer-reviewed publications. Insights into the origin of CP-related volcanism will also be disseminated to naturalists at Sunset Crater and El Malpais National Monuments.