Lau Basin Vent Deposit Morphology and Composition: Links to Geologic Setting and Vent Fluid Chemistry

知识价值-热液喷口沉积物与从地幔和地壳到海洋的能量和物质运输路径密切相关，并为生物群提供生境。存款的组成和形态与喷口流体的组成和温度有关，并与控制流体向海底输送的地质环境的结构方面有关。在某些矿床中，生物和/或其产物的结合影响了存款的演化。通过其矿物成分和结构，这些沉积物的年龄从几天到几百年不等，可以记录过去的地质，热液和生物活动。本提案的目标是利用详细的矿物学数据和结构观察，结合地球化学数据（来自矿床和流体）以及迁移和反应的地球化学建模，确定沿着东Lau扩张中心/Valu Fa海岭的6个喷口区矿床的形成和演化。它建立在最近发表的劳综合研究站（ISS）的工作基础上，包括关于火成岩基底成分、喷口流体化学以及构造、火山作用和热液活动之间关系的沿轴趋势的信息（Ferrini等人，2008; Bezos等人，2009; Escrig等人，2009; Mottl等人，接受）。已对2005年回收的矿床进行了初步定性，Ferrini等人（2008年）提供了相对于地质特征的存款描述和位置，并通过海洋地球科学数据系统发布和提供了地球化学和X射线衍射分析。2009年，又回收了更多的样本（包括最近发现的Tahi Moana喷口区的样本），填补了2005年收集的样本集的空白，从而从每个喷口区收集到了一整套出色的、有代表性的喷口存款样本。对这一样本集进行研究，并将所得数据与关于地质背景和喷口流体化学性质的信息结合起来，将有助于检验多年来形成的关于海底喷口存款形成的若干假设。火山基质和喷口流体化学成分从北到南的梯度，结合最南端水手喷口区喷口流体化学成分的显著差异，允许测试关于存款成分、形态和演变受1）火山基质成分和2）岩浆挥发物输入（可能导致pH值非常低的喷口流体）影响程度的假设。将把由此产生的Lau喷口区喷口存款形成模型与为其他描述良好的海底喷口存款开发的模型进行比较。特别令人感兴趣的是，对沿着Lau国际空间站的喷口沉积物的研究，考虑到地质背景和喷口流体化学性质的范围，将允许在全球范围内对表现出许多相似性的喷口区进行比较，而不同之处主要在于单一参数（例如，深度或火山基底成分或流体pH值或动物群）。除了检验具体的假设外，本提案的结果将提供关于矿床内部和表面条件、低温与高温流动的相对通量、生物活动影响存款生长的程度以及矿床中记录的生物活动的程度的重要信息。更广泛的影响-这个项目将提供培训和支持的研究生，并通过WHOI暑期学生研究员计划为本科生的机会。PI将继续她过去所做的推广活动，包括为普通观众撰写论文和演讲。该项目的结果将通过会议、讲习班和出版物向社区公布，并向MGDS/Ridge 2000数据门户提交数据和模型结果。

Intellectual merit - Vent deposits are intimately linked within paths of energy and mass transport from the mantle and crust to the oceans and provide habitats for biota. Deposit composition and morphology are linked to the composition and temperature of vent fluids, and to structural aspects of the geologic setting that control the delivery of fluids to the seafloor. In some deposits, incorporation of organisms and/or their products affects deposit evolution. Through their mineral compositions and textures the deposits, which range in age from days to hundreds of years, serve as recorders of past geologic, hydrothermal and biological activity. The goal of this proposal is to use detailed mineralogical data and textural observations combined with geochemical data (from both deposits and fluids) and geochemical modeling of transport and reaction, to determine the formation and evolution of deposits at 6 vent fields along the East Lau Spreading Center/Valu Fa Ridge. It builds on recent published work for the Lau Integrated Study Site (ISS), including information about along-axis trends in composition of the igneous substrate, vent fluid chemistry, and relationships between tectonics, volcanism and hydrothermal activity (Ferrini et al., 2008; Bezos et al., 2009; Escrig et al., 2009; Mottl et al., accepted). Initial characterization of deposits recovered in 2005 has been done, with deposit descriptions and locations relative to geologic features in Ferrini et al. (2008), and with geochemical and XRD analyses released and available through the Marine Geosciences Data System (MGDS). In 2009, additional samples were recovered (including from the recently discovered Tahi Moana vent field), filling gaps in the sample set collected in 2005, resulting in an excellent full suite of representative vent deposit samples from each vent field. Study of this sample set, and integration and synthesis of resultant data with information on geologic settings and vent fluid chemistry, will allow testing of a number of hypotheses that have been developed over the years about seafloor vent deposit formation. The gradient in the composition of the volcanic substrate and vent fluid chemistry from north to south, combined with the pronounced differences in vent fluid chemistry at the southernmost Mariner vent field, allows testing of hypotheses about extents to which deposit composition, morphology, and evolution are affected by 1) volcanic substrate composition, and 2) input of magmatic volatiles (which can result in very low pH vent fluids). Resulting models of vent deposit formation at Lau vent fields will be compared to models developed for other well-described seafloor vent deposits. Of particular interest is that the study of the vent deposits along the Lau ISS, given the range in geologic settings and vent fluid chemistry, will allow comparisons to be made globally between vent fields that exhibit many similarities, and that differ mainly with respect to a single parameter (e.g., depth or volcanic substrate composition or fluid pH or fauna). In addition to testing specific hypotheses, results of this proposal will provide important information on conditions within and on surfaces of deposits, relative fluxes of low temperature vs high temperature flow, extents to which biological activity affects deposit growth, and extents to which biological activity is recorded in the deposits. Broader Impact -This project will provide training and support for a graduate student, and opportunities for undergraduate students through the WHOI summer student fellow program. The PI will continue the types of outreach she has done in the past, including writing papers for and giving lectures to general audiences. The results of the project will be made available to the community through conferences, workshops and publications, and by submitting data and model results to the MGDS/Ridge2000 Data Portal.