Collaborative Research: U-series constraints on the ages and petrogenesis of Lau Basin Lavas

合作研究：U系列对Lau盆地熔岩年龄和岩石成因的约束

• 批准号: 0732449
• 负责人: Charles Langmuir
• 金额: $ 21.77万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0732449&HistoricalAwards=false
• 关键词: Collaborative; Research; series; constraints; ages

AbstractLangmuir/ Sims, 0732448; 0732480The investigators will measure U, Th and Ra isotopes on samples from throughout the length of the East Lau Spreading Center, a Ridge 2000 Integrated Study Site, with an emphasis on the ABE vent field, which is the designated "bulls-eye" for this region. These data will be obtained on samples with existing Pb, Sr, Nd and He isotopes, major elements, trace elements and water contents. The resulting data set will be a benchmark for backarc basin studies, will address major problems of ocean ridge and convergent margin science, and provide essential age constraints for the Lau ISS. U-series measurements have the potential to address three important scientific problems in this region:(1) Subduction fluids have high U contents, causing 238U excesses in convergent margin lavas. These excesses decay with time, and reflect the time scale of fluid transport through the mantle wedge at varying distances from the volcanic front. We will test the hypothesis ofdecreasing 238U excess (i.e. greater transport time) with increasing distance from the trench.(2) Back-arc basin and open ocean spreading centers have very different responses to water in the source, with back-arc spreading centers showing no apparent garnet influence, or evidence of effects of deep low degree melts. Langmuir et al. (2006) attribute these differences to the effects of active corner flow and a deep cold slab in the back-arc. Since garnet controls U-Th disequilibria at open ocean ridges, we predict smaller 230Th excesses at back-arcs compared to open ocean ridges. The northern ELSC samples have little or no subduction signature. These samples in particular permit a test of this hypothesis.(3) A host of problems related to ocean ridge formation require knowledge of time scales. Age constraints are essential to relate volcanic activity to tectonics, variations in the underlying magma chamber reflector, and temporal changes in lava compositions. They are an essential link between the volcanic system and the hydrothermal and biological activities that are supported and impacted by temporal and spatial fluctuations in volcanism. U-series are the sole means to quantify time constraints for young ridge volcanism. Our proposed work will add the dimension of time to the study of ridge processes in this region.Broader Impacts: The proposed work is part of a multi-disciplinary effort to understand the ocean ridge system from melt generation in the mantle to volcanism and life on the seafloor. The constraints on fluid fluxes at convergent margins will be pertinent for the large community interested in subduction processes, and to the NSF MARGINS program. Harvard undergraduate students work routinely in Langmuir's lab, and will be exposed to U-series analysis through this project. Langmuir and Sims will also prepare a set of U-series teaching modules. These modules will be part of Langmuir's 'Introduction to Petrology' and Sims' 'Introduction to Isotope Chemistry'. The web-based module will be hosted on their personal web sites, and integrated into the MIT OpenCourseWare as part of Sims' Isotope Chemistry course.

AbstractLangmuir/ Sims，0732448; 0732480研究人员将在整个East Lau扩展中心的长度上测量U，TH和RA同位素，这是一个山脊2000综合研究地点，重点是ABE通风口场，这是该地区指定的“ Bulls-Eye”。这些数据将在具有现有PB，SR，ND的样品和HE同位素，主要元素，微量元素和水含量的样品上获得。由此产生的数据集将是后退流域研究的基准，将解决海洋岭和融合利润科学的重大问题，并为LAU ISS提供基本的年龄限制。 U系列测量值有可能解决该区域的三个重要科学问题：（1）俯冲液具有较高的U含量，导致238U的收敛边缘熔岩过剩。这些过剩的时间会随着时间的推移而衰减，并反映出距火山阵线距离不同的流体传输的时间尺度。我们将测试降低238U过量（即更大的运输时间）的假设，并且与沟槽的距离增加。（2）后弧盆地和开放海洋扩散中心对源水中的水反应截然不同，而后ARC扩散中心没有表现出明显的石榴石影响力或深度低度融化的影响的证据。 Langmuir等。 （2006年）将这些差异归因于主动角流动的影响和后弧中深层冷板的影响。由于石榴石控制着公开海脊中的第三次不平衡，因此与开海脊相比，背弧的第230次过量较小。北部ELSC样品几乎没有俯冲签名。这些样本特别允许对该假设进行检验。（3）与海岭形成有关的许多问题需要了解时间尺度。年龄限制对于将火山活性与构造活动，基础岩浆腔室反射器的变化以及熔岩组成的时间变化联系起来至关重要。它们是火山系统与热水和生物学活动之间的重要联系，这些联系受到火山主义的时间和空间波动的支持和影响。 U系列是量化年轻山脊火山的时间限制的唯一手段。我们提出的工作将增加该地区山脊过程的时间的维度。Broader的影响：拟议的工作是了解从地幔中的熔融产生到火山和海底生活的多学科工作的一部分。收敛利润率的流体通量的限制与对俯冲过程感兴趣的大型社区以及NSF利润率计划有关。哈佛本科生定期在Langmuir的实验室工作，并将通过该项目接触U系列分析。 Langmuir和Sims还将准备一套U系列教学模块。这些模块将是Langmuir的“岩石学入门”和模拟人生的一部分，“同位素化学简介”。基于Web的模块将托管在其个人网站上，并将其集成到MIT OpenCourse软件中，作为SIMS同位素化学课程的一部分。