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

智力上的优点——从地幔和地壳到海洋的能量和物质运输路径与喷口沉积物密切相关，并为生物群提供栖息地。沉积物的组成和形态与喷口流体的组成和温度有关，也与控制流体向海底输送的地质环境的结构有关。在一些沉积物中，生物和/或其产物的结合影响了沉积物的演化。这些沉积物的年龄从几天到几百年不等，通过它们的矿物成分和质地，它们记录了过去的地质、热液和生物活动。本课题的目标是利用详细的矿物学数据和结构观测资料，结合地球化学数据（包括沉积物和流体）和地球化学模拟的运输和反应，确定东劳扩张中心/Valu Fa Ridge沿线6个喷口田沉积物的形成和演化。它建立在Lau综合研究站点（ISS）最近发表的工作基础上，包括火成岩基底组成的沿轴趋势、喷口流体化学以及构造、火山作用和热液活动之间的关系（Ferrini等人，2008年；Bezos等人，2009年；Escrig等人，2009年；Mottl等人，已接受）。对2005年回收的矿床进行了初步表征，并根据ferferrini等人（2008年）的地质特征对矿床进行了描述和定位，并通过海洋地球科学数据系统（MGDS）发布了地球化学和XRD分析。2009年，又回收了更多的样品（包括最近发现的Tahi Moana喷口田），填补了2005年收集的样品集的空白，从而从每个喷口田获得了一整套极具代表性的喷口沉积物样品。对这组样本进行研究，并将所得数据与地质环境和喷口流体化学信息进行整合和综合，将能够检验多年来关于海底喷口沉积物形成的一些假设。火山底物组成和喷口流体化学从北向南的梯度，结合Mariner喷口最南端喷口流体化学的显著差异，可以测试沉积物组成、形态和演化在多大程度上受到以下因素的影响：1)火山底物组成，2)岩浆挥发物的输入（这可能导致非常低的pH值喷口流体）。所得的Lau喷口沉积形成模型将与其他描述良好的海底喷口沉积模型进行比较。特别令人感兴趣的是，考虑到地质环境和喷口流体化学的范围，对Lau国际空间站沿线喷口沉积物的研究将允许在全球范围内比较表现出许多相似之处的喷口场，以及主要在单一参数（例如，深度或火山底物组成或流体pH值或动物）方面的差异。除了测试特定的假设外，本提案的结果将提供关于沉积物内部和表面条件、低温与高温流动的相对通量、生物活动影响沉积物生长的程度以及沉积物中记录生物活动的程度的重要信息。更广泛的影响-该项目将为研究生提供培训和支持，并通过WHOI暑期学生研究员计划为本科生提供机会。PI将继续她过去所做的外展活动，包括为普通观众撰写论文和演讲。该项目的成果将通过会议、研讨会和出版物，以及向MGDS/Ridge2000数据门户网站提交数据和模型结果，向社会提供。

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.