Collaborative Research: Reconstructing the geometry of magmatic plumbing systems using fluid inclusions

限制供给火山爆发的岩浆在地壳中储存的深度对于火山监测机构解释火山危机期间的动荡信号以及我们对能源关键金属矿床的形成和地壳演化的理解都至关重要。然而，利用地震和地面变形来获得储存深度的流行技术不能用于许多目前活动很少或监测网络有限的潜在危险火山。更广泛适用的测量喷发晶体化学性质的方法具有很大的不确定性。该团队将研究火山学中一种强大但未被充分利用的方法，通过测量被困在生长晶体中的富含气体的流体的密度，称为流体包裹体（FI）。这种方法有可能更加精确和准确，对岩浆在地壳中的储存位置施加非常严格的限制。在研究了以夏威夷和加那利群岛的火山喷发为例的FI深度的优势和劣势后（其中储存深度已通过其他方法确定），将在几个世纪前发生的一系列爆炸性喷发中研究岩浆储存深度，这两个地点未来的这种类型的喷发将带来重大危险。将与夏威夷火山观测站（HVO）合作进行快速响应模拟，以确定在下一次大规模爆发危机期间可以多快获得岩浆储存深度的估计，以及如何使用这些信息为决策提供信息，以减轻社会风险。该提案将促进三个专业人员之间的密切合作，在不同的职业水平上提供免费的科学专业知识，并在跨越三个机构的多层指导结构中支持几名学生和一名博士后。该团队将开发和分发用作校准标准的合成和天然流体包裹体，并举办研讨会，促进使用拉曼光谱的不同研究小组之间的合作和协同作用。该奖项将利用共焦拉曼光谱的光谱和空间分辨率的最新进展，允许高度精确和准确地测量捕获在流体包裹体中的富含CO2的流体的密度，其尺寸可低至约1 µm。富CO2流体的密度和压力之间的简单物理关系意味着FI密度分布可以以非常小的误差（~5-10%）转换为岩浆储存压力，然后使用已知的地壳密度剖面转换为岩浆储存深度。首先，详细的比较从金融机构获得的深度将比较已发表的工作调查熔体包裹体饱和压力的样品从Kallauea火山，夏威夷，和Timanfaya，加那利群岛。这将允许使用高分辨率电子背散射衍射（HR-EBSD）评估影响FI气压的不确定性来源，例如爆裂（当夹杂物爆炸时），以及其他挥发性物质（例如，S，Cl，H）的混合物。在确定了流体包裹体压力测量的优点和缺点之后，将对Kasslauea火山（一个重大的社会危害）从爆发到喷发的转变过程中岩浆管道的变化、加拉帕戈斯从盾牌到后盾牌的演变以及与HVO合作进行的喷发模拟过程中未知样品的变化进行新的限制。将合成具有不同CO2浓度的合成FI，并使用实验校准的拉曼系统进行表征，以分发给世界各地的实验室，用作校准拉曼光谱仪的标准参考材料。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Constraining the depth at which magma feeding volcanic eruptions is stored in the crust is critical both for volcano monitoring agencies to interpret unrest signals during volcanic crises, and for our understanding of the formation of energy-critical metal deposits and the evolution of the Earth’s crust. However, popular techniques using earthquakes and ground deformation to obtain storage depths cannot be used at many potentially hazardous volcanoes which show little activity at present, or have limited monitoring networks. More widely applicable methods which measure the chemistry of erupted crystals are associated with large uncertainty. This team will investigate a powerful but under-used approach in volcanology, by measuring the densities of pockets of gas-rich fluids trapped within growing crystals, known as fluid inclusions (FI). This method has the potential to be significantly more precise and accurate, placing very tight constraints on where magma is stored in the crust. After investigating the strengths and weaknesses of depths from FIs using eruptions from Hawai’i and Canary Islands as a case study (where storage depths have been determined by other methods), magma storage depths will be investigated in a series of explosive eruptions that occurred several centuries ago at both locations where future eruptions of this type present a significant hazard. A rapid response simulation will be carried out in collaboration with Hawaiian Volcano Observatory (HVO) to determine just how quickly estimates of magma storage depths can be obtained during the next large eruptive crisis, and how this information can be used to inform decision making to mitigate societal risk. This proposal will foster close collaborations between three PIs with complimentary scientific expertise at different career levels, and support several students and a postdoc in a multi-tiered mentoring structure spanning three institutions. The team will develop and distribute synthetic and natural fluid inclusions to be used as calibration standards, and a workshop will promote collaboration and synergy between different research groups using Raman spectroscopy.This award will capitalize on recent advances in the spectral and spatial resolution of confocal Raman spectroscopy, allowing highly precise and accurate measurements of the densities of CO2-rich fluids trapped within fluid inclusions down to ~ 1 µm in size. The simple physical relationship between the density and pressure of a CO2-rich fluid means that distributions of FI densities can be converted into magma storage pressures with very small errors (~5-10%), and then magma storage depths using known crustal density profiles. First, detailed comparisons of depths obtained from FIs will be compared to published work investigating melt inclusion saturation pressures in samples from Kīlauea Volcano, Hawai’i, and Timanfaya, Canary Islands. This will permit assessment of sources of uncertainty affecting FI barometry such as decrepitation (when the inclusion explodes) using high-resolution electron backscatter diffraction (HR-EBSD), and the presence of additional volatile species (e.g., S, Cl, H) using synthetic FIs equilibrated with different fluid compositions. After determining the strengths and weaknesses of fluid inclusion barometry, new constraints will be placed on changes in magmatic plumbing during explosive to effusive transitions at Kīlauea Volcano (a significant societal hazard), evolution from shield to post-shield in the Galápagos, and from unknown samples during an eruption simulation in collaboration with HVO. Synthetic FIs with different concentrations of CO2 will be synthesized and characterized with an experimentally calibrated Raman system to distribute to laboratories around the world to use as standard reference materials for calibration of Raman Spectrometers. This will eliminate systematic offsets between densities determined in different laboratories.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.