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、火山作用和岩浆作用已经有了大量的了解，但基本的精细地壳增生过程及其速率在很大程度上仍然是未知的。本研究利用最近的技术和方法发展，量化了中扩张的南胡安·德富卡脊（JdFR）三段新火山带的空间、形态和地球化学差异，以评估关于地壳增生和熔体供应的五种假设：假设1：中扩张脊的地壳增生在几十年到几百年的时间尺度上是间歇性的。假设2：地壳增生分布在JdFR新火山带8km宽的范围内。假设3：中扩张脊的地壳吸积主要发生在不常见的大体积、大渗出率喷发期间，而不是更常见的小体积、小渗出率喷发期间。假设4：岩浆库补给在正常脊段发生在~年代际尺度上，而在膨胀段发生在~千年尺度上。假设5：源成分比中速率脊的熔化过程变化更大。为了评估这些假设，我们提出了对每个区段的时间限制的地质和火山学数据的综合，以评估它们的结构和岩浆演化如何在数千年中波动。我们提出了高精度的微量元素和放射性成因同位素分析，将地球化学和形态变化与地震观测相结合，以评估地壳级岩浆补充速率和分化。我们建议进行铀系列分析，目的有二：补充喷发年龄的限制，并评估相邻的膨胀期和膨胀期地幔熔融过程的比较。和正常的?岭段。我们还建议使用有针对性的古磁强度测量来测量放射性碳和u系列都不起作用的年龄。在两位资深科学家克拉格和吉尔的指导下，这一提议使两位早期职业研究人员布莱恩·德雷尔和朱莉·鲍尔斯进一步深入了洋中脊科学。本科学生将参与实验室培训，数据分析和解释，以及结果的展示。结果和公众宣传项目将公布在海底火山活动项目的网页http://www.mbari.org/volcanism上。我们的研究结果对轴向海山特别重要，因为它是海洋观测站倡议（OOI）的区域电缆海洋观测站的终点，旨在解决了解未来25-30年海洋和海底火山演变的关键基本问题。我们的建议补充了这一目标，因为它发展了火山学和地质学对岩浆系统如何在过去几十年到几千年里形成目前形态的理解。该提案支持海洋地质和地球物理以及Ridge2000计划的主要目标。高分辨率（1米）水深和地质图、火山史、地球化学和地磁数据的传播将为同轴段、轴向海山和北部裂谷段的形成过程提供一个无与伦比的视角，提供背景和发展山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.