Collaborative Research: Fine-scale crustal accretion processes and rates of magma supply and replenishment at the southern Juan de Fuca Ridge neovolcanic zone

自从海底观测出现以来，关于海脊形态、火山作用和岩浆过程已经了解了很多，但基本的更精细的地壳吸积过程及其速率在很大程度上仍然是未知的。这一建议利用最新的技术和方法发展来量化中间扩张的Juan de Fuca Ridge(JdFR)南部三段新火山带内的空间、形态和地球化学变化，以评估关于地壳增生和熔体供应的五个假说：假设1：中间扩张脊处的地壳增生在几十年到数百年的时间尺度上是间歇性的。假设2：地壳隆起分布在JdFR新火山带8公里宽的范围内。假设3：中等扩张海脊的地壳沉积主要是在罕见的大体积、大渗漏率喷发期间完成的，而不是更常见的小体积、小渗漏率喷发。假设4：在正常的山脊段，岩浆储集层的补给发生在~十年的时间尺度上，而在膨胀的山脊段，则在~千年的时间尺度上。假设5：在中速山脊，源岩成分比熔融过程更可变。为了评估这些假说，我们提出了每一段受时间限制的地质和火山数据的综合，以评估它们的构造和岩浆演化在数千年来是如何波动的。我们建议进行高精度的微量元素和放射性同位素分析，将地球化学和形态的可变性与地震学观测结合起来，以评估地壳级别的岩浆补给率和分异。我们提出铀系分析的双重目的是为了补充喷发年龄限制和评估相邻的、充气的、不同的地幔熔融过程的比较。然后呢？正常吗？山脊线段。我们还建议使用有针对性的磁性古强度测量来测量放射性碳和U系列都不起作用的年龄。这一提议使两名早期职业研究人员布莱恩·德雷尔和朱莉·鲍尔斯在两名资深科学家克莱格和吉尔的指导下，进一步深入大洋中脊科学。本科生将参与实验室培训、数据分析和解释以及结果展示。结果和公众推广项目将张贴在海底火山项目网页上，网址为：http://www.mbari.org/volcanism.我们的结果对轴海山特别重要，因为它是海洋观测站倡议(OOI)区域电缆海洋观测站的终点站，旨在解决对了解未来25-30年海洋和海底火山演变至关重要的基本问题。我们的建议补充了这一目标，因为它发展了对过去几十年到几千年来岩浆系统如何形成目前形态的火山学和地质学方面的理解。该提案支持海洋地质学和地球物理学以及Ridge2000计划的主要目标。高分辨率(1-m)水深和地质图、火山历史以及同轴线段、轴向海山段和北部裂隙段的地球化学和地磁数据的传播将提供一个无与伦比的视角，了解塑造大洋中脊系统的过程，为海脊科学界提供背景和发展协同作用。

A great deal has been learned about ridge morphology, volcanism, and magmatic processes since the advent of seafloor observation, yet fundamental finer-scale crustal accretion processes and their rates remain largely unknown. This proposal leverages recent technological and methodological developments to quantify the spatial, morphological, and geochemical variance within the neovolcanic zone of three segments of the intermediate-spreading southern Juan de Fuca Ridge (JdFR) to evaluate five hypotheses about crustal accretion and melt supply: Hypothesis 1: Crustal accretion at intermediate-spreading ridges is episodic on timescales of decades to hundreds of years. Hypothesis 2: Crustal accretion is distributed across the 8km width of the JdFR neovolcanic zone. Hypothesis 3: Crustal accretion at intermediate-spreading ridges is mainly accomplished during infrequent large-volume, large-effusion-rate eruptions rather than the more common small-volume small-effusion-rate eruptions. Hypothesis 4: Magma reservoir replenishment occurs on ~decadal time scales at normal ridge segments, but ~millennial timescales at inflated segments.Hypothesis 5: Source compositions are more variable than melting processes at intermediate rate ridges.To evaluate these hypotheses, we propose a synthesis of our time-constrained geologic and volcanologic data for each segment to assess how their structural and magmatic evolution has fluctuated over thousands of years. We propose high-precision trace element and radiogenic isotope analyses to integrate geochemical and morphological variability with seismological observables to assess crustal-level magma replenishment rates and differentiation. We propose uranium-series analyses for the dual purpose of supplementing eruption age constraints and evaluating how mantle-melting processes compare between adjacent ?inflated? and ?normal? ridge segments. We also propose to use targeted magnetic paleointensity measurements to measure ages when neither radiocarbon nor U-series will work. This proposal brings two early career researchers Brian Dreyer and Julie Bowles further into mid- ocean ridge science with the guidance of two senior scientists, Clague and Gill. Undergraduate student will be involved in laboratory training, data analysis and interpretation, and presentation of results. Results and public outreach items will be posted on the Submarine Volcanism Project webpage at http://www.mbari.org/volcanism. Our results are particularly significant for Axial Seamount as it is a terminus for the regional cabled ocean observatory of the Ocean Observatories Initiative (OOI) designed to address fundamental questions key to understanding the evolution of oceans and submarine volcanoes over the next 25-30 years. Our proposal complements that objective because it develops the volcanological and geological understanding of how the magmatic system arrived at its present configuration over the last several decades to millennia. This proposal supports the major objectives of both the Marine Geology and Geophysics and Ridge2000 Programs. Dissemination of high-resolution (1-m) bathymetric and geologic maps, volcanologic histories, and geochemical and geomagnetic data for CoAxial segment, Axial Seamount, and northern Cleft segments will offer an unparalleled view of the processes that shape the mid-ocean ridge system, providing context and developing synergic interaction among the ridge science community.