Testing the Processes of Melt Differentiation in the Mexican Volcanic Belt

测试墨西哥火山带熔体分异过程

• 批准号: 0738707
• 负责人: Susanne Straub
• 金额: $ 23.42万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-15 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738707&HistoricalAwards=false
• 关键词: Testing; Processes; Melt; Differentiation; Mexican

This project was co-supported by the Petrology and Geochemistry with the Office of International Science and Engineering. It aims to study processes leading to magma formation ('differentiation') in subduction zones using the Mexican arc as an example. On the Earth's surface, subduction zones form conspicuous chains of volcanoes ('volcanic arcs') parallel to the deep-sea trenches (e.g. the Cascades, Aleutians, Mexico). The formation of arc magmas has intrigued earth scientists ever since the role of subduction zones was recognized, and yet it remains poorly understood. Understanding the process of arc magma formation, however, is essential to quantitatively assess the impact of the arc out flux (including the out flux of volatiles) on the evolution and maintenance of a habitable Earth. This project will test whether recently discovered unusual Ni-rich olivines (up to 0.35-0.53 wt% Ni) that are ubiquitous in primitive alkaline and calc-alkaline magmas of the central Mexican Volcanic Belt may provide a vital clue. These Ni-rich olivines are so unusual since they rule out that arc magmas are simply melts, or mixtures of melts, that either originate from (i) the subducting oceanic crust ('slab'), located approximately ~110-120 km below the volcanic arc, (ii) the Earth peridotite mantle, at 45-110 km depth, or (iii) the pre-existing crust (0-45 km depth) on which the Mexican volcanoes are constructed. Thus, other processes must apply. A possible process may be the formation of a new 'pyroxenite lithology' in the source region of arc magmas. This lithology may form by reaction of silica-rich melts from the slab and the subarc peridotite mantle and generate arc magmas by melting. The research plan involves a detailed study of olivine phenocrysts from Mexican arc volcanic rocks that include: (a) petrographic textures, (b) trace elements in olivines (Co, Mn, Ca, Sc, V, Ni, Ti, Al, B and Li) by laser-ablation methods, (c) volatiles (H2O, CO2, S, F, Cl) and B and B isotopes in their primary melt inclusions by SIMS methods, and (d) He-isotope ratios of olivine separates. Since similar Ni-rich olivines have been recently been found in other arcs, e.g. the Cascades, Japan, Aleutians and Kamchatka, the outcome of this project has broader implications for global arc volcanism. The project promotes scientific partnership between three institutions in the U.S., as well as between the U.S., Mexico and Scotland. It also supports a female career scientist with a disability.

该项目由岩石学和地球化学与国际科学与工程办公室共同支持。 它旨在研究以墨西哥弧为例，导致俯冲区域中岩浆形成（“分化”）的过程。在地球表面，俯冲带形成了与深海沟渠平行的火山（“火山弧”）的明显链（例如，喀斯喀特式，阿留申，墨西哥）。自从认识到俯冲带的作用以来，弧岩的形成就引起了地球科学家的兴趣，但仍然很了解。然而，了解弧岩浆形成的过程对于定量评估弧外通量（包括挥发物的外向）对宜居地球的演变和维护至关重要。该项目将测试最近在墨西哥火山带原始碱性和钙碱性岩浆中无处不在的不寻常Ni富含Ni的橄榄石（高达0.35-0.53 wt％Ni）可能会提供重要的线索。这些富含Ni的橄榄石是如此不寻常建造墨西哥火山的（0-45公里深度）。因此，必须适用其他过程。可能的过程可能是在弧岩浆源区域中形成新的“辉石岩石岩石学”。这种岩性可能是通过硅胶熔体和超级牛皮岩地幔的反应形成的，并通过熔化产生弧岩浆。 The research plan involves a detailed study of olivine phenocrysts from Mexican arc volcanic rocks that include: (a) petrographic textures, (b) trace elements in olivines (Co, Mn, Ca, Sc, V, Ni, Ti, Al, B and Li) by laser-ablation methods, (c) volatiles (H2O, CO2, S, F, Cl) and B and B isotopes in their primary melt通过SIMS方法和（D）橄榄石分离的HE-同位素比。由于最近在其他弧线中发现了类似的富含Ni的橄榄石，例如级联，日本，阿留申派和坎奇特卡，该项目的结果对全球弧火山主义具有更广泛的影响。该项目促进了美国三个机构以及美国，墨西哥和苏格兰之间的科学伙伴关系。它还支持残疾的女性职业科学家。