Evaluating links between primordial mantle domains and deep mantle structures using 182W and 3He/4He

许多地幔柱衍生的洋岛玄武岩夹带多种地幔成分，代表回收，环境和原始同位素域。这些成分的混合物，板内火山采样，定义同位素混合阵列独特的每个羽。其中一个组成部分，FOZO（“焦点区”），是不寻常的，因为它是共同的许多地幔柱。FOZO组分的特征是铅、钕、锶和氦同位素的特定和相对狭窄的组成范围，其中大多数羽流的同位素组成重叠。值得注意的是，FOZO型储层保留了原始氦同位素组成，与地幔的其他部分相比，这些组成没有被随后的过程显着改变。虽然FOZO的锶-铅-钕成分定义自首次发现以来经历了几次修订，但原始氦同位素仍然是这种油藏类型的重要定义特征。原始氦比最近被链接到地震可检测的结构在深地幔以及参数在羽系统，如材料浮力和温度，这表明水库与升高的原始氦是地震，热，和化学不同的“典型”下地幔材料。这项研究的结果将有助于我们更好地了解早期地球的地球化学演化。与地球化学家和地球动力学家合作，这项研究将提供对原始地幔域的大小，形状和发展的限制，这些域经常有助于深源火山活动。此外，该项目将为PI提供两年的支持，并扩大她在同位素地球化学方面的专业知识，包括短寿命同位素系统学。最近，在羽流衍生火山活动中发现了钨同位素的变化，这是由铪的一种熄灭同位素的衰变驱动的。在羽流中，发现异常钨与原始氦的样品，这意味着第二个原始同位素约束可能存在FOZO型熔体。然而，携带异常钨和氦的FOZO型物质与核幔边界附近检测到的超低速带有关。其他成分被认为是在地幔柱中发现的环境地幔域的样本，缺乏明显的氦和钨异常，但需要更多的数据来充分测试地震结构和同位素成分之间的联系。为了测试这种情况，将对缺乏任何回收地壳物质（一种可能的污染物）证据的羽流进行氦和钨同位素分析。路易斯维尔、胡安费尔南德斯、鲍伊、科布和卡罗琳羽流因其缺乏再循环成分和可变氦同位素组成而被选中。新数据将与地震分辨下地幔结构的空间相关性（或缺乏相关性）联系起来，以确定FOZO型熔体、环境下地幔成分和深部地幔结构之间的关系。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。

Many mantle plume-derived ocean island basalts entrain multiple mantle components, representing recycled, ambient, and primordial isotopic domains. The mixtures of these components, sampled by intraplate volcanoes, define isotopic mixing arrays unique to each plume. One of these components, FOZO (“Focal Zone”), is unusual in that it is common to many mantle plumes. The FOZO component is characterized by a specific and relatively narrow compositional range in lead, neodymium, strontium, and helium isotopes, where isotopic compositions of most plumes overlap. Notably, FOZO-type reservoirs retain primordial helium isotopic compositions that have not been as significantly modified by subsequent processes compared to other parts of the mantle. While the strontium-lead-neodymium compositional definition of FOZO has undergone several revisions since it was first identified, primordial helium isotopes have remained an important defining characteristic of this reservoir type. Primordial helium ratios have recently been linked to seismically-detectable structures in the deep mantle as well as parameters in plume systems such as material buoyancy and temperature, suggesting that reservoirs with elevated primordial helium are seismically, thermally, and chemically distinct from “typical” lower mantle material. The findings from this study will improve our understanding of the geochemical evolution of the early Earth. In collaboration with geophysicists and geodynamicists, this study will provide constraints on the size, shape, and development of primordial mantle domains that frequently contribute to deeply-sourced volcanism. In addition, this project will provide two years of support for the PI and broaden her expertise in isotope geochemistry to include short-lived isotope systematics.Recently, variations in tungsten isotopes, driven by the decay of an extinct isotope of hafnium, were discovered in plume-derived volcanism. In plumes, anomalous tungsten is found in samples with primordial helium, implying that a second primordial isotopic constraint may exist for FOZO-type melts. Tentatively, FOZO-type material carrying anomalous tungsten and helium have been linked to ultra-low velocity zones detected near the core-mantle boundary. Other compositions thought to sample ambient mantle domains found in plumes lack distinct helium and tungsten anomalies, but additional data are needed to fully test the links between seismic structures and isotopic composition. To test this scenario, plumes that lack evidence of any recycled crustal material, a possible contaminant, will be analyzed for helium and tungsten isotopes. The Louisville, Juan Fernandez, Bowie, Cobb, and Caroline plumes have been selected for their lack of recycled componentry and variable helium isotopic compositions. The new data will then be linked to spatial correlations (or lack thereof) with seismically-resolved lower mantle structures to determine the relationship of FOZO-type melts, ambient lower mantle compositions, and the structure of the deep mantle.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.