Simple Models for Trace Element Fractionation During Concurrent Melting, Melt Migration, and Melt-rock Reaction in an Upwelling Heterogeneous Mantle Column

上涌非均质地幔柱中同时熔融、熔体迁移和熔岩反应过程中微量元素分馏的简单模型

• 批准号: 0911501
• 负责人: Yan Liang
• 金额: $ 30.57万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911501&HistoricalAwards=false
• 关键词: Simple; Models; Trace; Element; Fractionation

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit: Several lines of evidence suggest that melt generation and segregation regions in the mantle are heterogeneous and consist of chemically (e.g., enriched vs. depleted) and lithologically (e.g., peridotite vs. pyroxenite) distinct domains of variable size and dimension. Partial melting of such regions give rises to a diverse range of basaltic magma compositions. To preserve geochemical signatures developed at depth, basalts must rise to the surface without extensive re-equilibration with their surrounding mantle wallrocks. This can be accomplished by focused melt flow through high-porosity melt channels. To form high-porosity channels, pyroxenes in the peridotite matrix must dissolve in the percolating melt. The matrix dissolution rate and melt suction rate are important in determining the spatial distribution of the channel and chemical compositions of the melt extracted at the top of the channel and the matrix. During grain-scale porous flow, re-equilibration between crystals and their interstitial melt may be incomplete. Models for trace element fractionation and distribution during melting and melt extraction in the mantle must include these fundamental observations or constraints as part of the formulation. The primary objective of this project is to develop self-consistent models for trace element and isotope fractionation and distribution during concurrent melting, melt migration, and melt-rock interaction in an upwelling, heterogeneous, two-porosity double lithology mantle column. Both steady-state models and time-dependent models will be developed. The steady-state models will be used to constrain the relative melt suction rate using selected incompatible trace element abundances in diopside in abyssal peridotites and peridotites from Oman ophiolite. Laboratory dissolution experiments will be conducted at selected temperatures and pressures to determine the rates of harzburgite and lherzolite dissolution and the depth of high-porosity melt channel initiation along two mantle adiabats: one for melt migration beneath the mid-ocean ridge and the other for melt migration in a mantle plume. Results from these laboratory and geochemical studies will provide critical inputs to the general time-dependent melting models that will allow geochemists to map chemical heterogeneities observed in erupted basalts into their mantle sources, and to infer the processes of melt segregation and melt-rock interaction from trace element abundances in residual peridotites, mid-ocean ridge basalts (MORB) and ocean island basalts (OIB).Broader Impacts: The origin and distribution of mantle heterogeneity are of central importance to a broad range of Earth and planetary scientists. The dynamic parameters obtained using the new melting models will likely stimulate geodynamists to develop more sophisticated 2-D and 3-D models for melt migration beneath mid-ocean ridges and in mantle plumes. The distribution of high-porosity melt channels in the mantle as inferred from this proposed study will motivate structure geologists to conduct more detailed mapping in ophiolites, geophysicists and seismologists to design new experiments to image the mantle beneath mid-ocean ridges. Results from this study will also be disseminated to a broader audience through public lectures, and undergraduate and graduate courses. And finally, the proposed project will provide hands on experience for undergraduates, research opportunities for senior thesis, experimental, computational, and educational experience for graduate students.

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit: Several lines of evidence suggest that melt generation and segregation regions in the mantle are heterogeneous and consist of chemically (e.g., enriched vs. depleted) and lithologically (e.g., peridotite vs. pyroxenite) distinct domains of variable size and dimension.此类区域的部分融化使多种玄武岩岩浆成分的升高。为了保护深度发展的地球化学特征，玄武岩必须升至表面，而不会在其周围的地幔壁架上进行大规模的重新平衡。这可以通过聚焦的熔体流通过高孔隙率熔体通道来实现。为了形成高孔隙率通道，橄榄岩基质中的辉石必须溶于渗透熔体。基质溶解速率和熔体抽吸速率对于确定在通道顶部和基质上提取的熔体的通道和化学成分的空间分布很重要。在晶尺度的多孔流动期间，晶体及其间质熔体之间的重新平衡可能不完整。在地幔中熔化和熔融提取过程中的微量元素分馏和分布的模型必须包括这些基本观测或约束作为公式的一部分。该项目的主要目的是在同时熔化，融化迁移和熔体摇滚相互作用中开发自洽模型，以上升，异构，两孔双孔隙率双层晶体学套柱的相互作用。将开发稳态模型和时间依赖的模型。稳态模型将使用来自阿曼蛇绿岩的深渊橄榄岩和橄榄岩中的Diopside中选定的不兼容的痕量元素丰度来限制相对熔体吸力率。将在选定的温度和压力下进行实验室溶解实验，以确定哈尔兹堡和氯唑群溶解的速率，以及沿两个地幔糖果的高孔隙率融化通道启动的深度：一种用于融化的融化，用于融化的近距离山脊，另一个用于在地幔盘中融化。这些实验室和地球化学研究的结果将为一般时间依赖时间的融化模型提供关键的输入，这些融化模型将使地球化学主义者能够在爆发的玄武岩中观察到的化学异质性映射到其地幔来源中，并推断熔体隔离和融化岩石互动的过程，从残留的甲壳虫中，贝斯（Mid ocealse），贝斯（Mid oceals），贝斯（Mid oceals），海洋中的山海（Mid ocean oceal coreans），沿海地区（Mid ocean oceal sasel），沿海地区（Mid oceal oceal sasel），层质沿海泥土（ 。使用新的熔融模型获得的动态参数可能会刺激地球动力学家，以开发更复杂的2-D和3-D模型，以在中山脊和地幔羽流下方的熔体迁移。从这项提出的研究中推断出的地幔中高孔隙率融化通道的分布将激发结构地质学家在蛇绿岩，地球物理学家和地震学家中进行更详细的映射，以设计新的实验，以形象地幔中近距离山脊。这项研究的结果还将通过公开讲座以及本科和研究生课程传播给更广泛的受众。最后，拟议的项目将为本科生提供经验，研究生的研究机会，实验性，计算和教育经验。