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，人们对海脊形态、火山作用和岩浆过程有了大量的了解，但基本的更细尺度的地壳增生过程及其速率在很大程度上仍然未知。该建议利用最近的技术和方法的发展，以量化的空间，形态和地球化学的变化内的新火山区的三段中间扩展的南胡安德富卡海脊（JdFR），以评估有关地壳增生和熔体供应的五个假设：假设1：地壳增生在中间扩展的海脊是情节上的几十年到几百年的时间尺度。假设2：地壳增生分布在JdFR新火山带的8公里宽。假设三：在中间扩张脊的地壳加积主要是在不常见的大体积，大渗出率喷发，而不是更常见的小体积小渗出率喷发。假设4：岩浆库补给发生在~十年的时间尺度上在正常的山脊段，但~千年的时间尺度上在膨胀的segment.Hypothesis 5：源成分比融化过程在中速ridge.To评估这些假设，我们提出了我们的时间约束的地质和火山学数据的合成，为每个部分，以评估他们的结构和岩浆演化如何波动了数千年。我们提出了高精度的微量元素和放射性同位素分析，整合地球化学和形态的变化与地震观测，以评估地壳水平的岩浆补给率和分化。我们提出铀系列分析的双重目的，补充喷发年龄的限制和评估如何地幔熔融过程比较相邻？膨胀的？然后呢？正常吗？脊段。我们还建议使用有针对性的磁古强度测量来测量年龄时，既没有放射性碳，也没有U系列将工作。这一建议使两位早期职业研究人员布赖恩德雷尔和朱莉鲍尔斯进一步进入大洋中脊科学的指导下，两位资深科学家，克莱格和吉尔。本科生将参与实验室培训，数据分析和解释，并介绍结果。结果和公共宣传项目将张贴在海底火山项目网页www.example.com上。我们的研究结果对轴海山特别重要，因为它是海洋观测站倡议区域电缆海洋观测站的终点站，该倡议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，因为它发展了对岩浆系统如何在过去几十年到几千年中达到目前配置的火山学和地质学理解。这项建议支持海洋地质学和地球物理学方案以及海脊2000方案的主要目标。传播高分辨率（1米）测深图和地质图、火山史以及同轴段、轴海山和北方裂缝段的地球化学和地磁数据，将使人们对形成大洋中脊系统的过程有一个无与伦比的了解，提供背景资料，并发展海脊科学界之间的协同互动。

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.