Assessing segment-scale compositional control over slow-spreading ridge morphology

洋中脊洋壳的形成是板块构造的重要组成部分，在地球的长期化学循环和能量收支中起着关键作用。在大洋中脊观测到的海底地形是由断裂和火山喷发共同作用形成的，但控制断裂和火山作用的潜在因素仍然只是部分了解。这两个过程的变化会导致地壳和海底特征的显著不同，特别是在缓慢分开的洋中脊。本研究利用缓慢扩张的大西洋中脊喷发的海底熔岩的地球化学来调查和了解地幔层的潜在变化如何影响火山活动的活力，从而影响海底本身的物理特征和海洋地壳的结构。该项目支持博士研究生的培训，描述该项目的公共宣传材料将通过内布拉斯加大学州立博物馆分发。这个项目的目的是研究岩浆流在缓慢扩张的脊轴上的潜在变化的原因，这反过来又驱动了地壳构造风格和在脊轴上存在、不存在或偶然出现的长期分离断层。该项目的基本原理是，对地壳构造机制的限制将最终导致一个强大的、全面的模型，该模型将准确地描述全球地壳在所有扩张速度下的增长。该项目验证的中心假设表明，缓慢扩张的脊形态主要是在段尺度上由下伏地幔的成分非均质性控制的。该研究的具体研究目标是识别和评估地球化学变化，这些地球化学变化反映了在脊段长度尺度上来自富集、肥沃的地幔岩石的部分熔体的贡献。该项目主要使用U-Th-Pa-Ra同位素不平衡，这对地幔熔融力特别敏感。不平衡将通过对比在24-30N之间沿中大西洋脊北部凯恩-亚特兰蒂斯超段表现出不同形态类型的二级脊段来评估。

The formation of oceanic crust at mid-ocean ridges is a major component of plate tectonics, and plays a key role in long-term chemical cycles and energy budgets on Earth. The seafloor topography observed at mid-ocean ridges is generated through a combination of faulting and volcanic eruptions, but the underlying factors that control faulting and volcanism remain only partially understood. Variations in these two processes can result in dramatically different crustal and seafloor characteristics, particularly at mid-ocean ridges that spread apart at slow rates. This study uses the geochemistry of seafloor lavas erupted at the slow-spreading Mid-Atlantic Ridge to investigate and understand how underlying variations in Earth's mantle layer might influence the vigor of volcanic activity and therefore, the physical characteristics of the seafloor itself and the structure of the oceanic crust. The project supports the training of a PhD student, and public outreach materials describing the project will be distributed through the University of Nebraska State Museum.This project aims to investigate the causes of underlying variations in magma flux to slow-spreading ridge axes, which in turn drive crustal construction style and the presence, absence, or episodicity of long-lived detachment faults at the ridge axis. The project rationale is that constraints on crustal construction mechanisms will ultimately lead to a robust, comprehensive model that will accurately characterize global crustal growth at all spreading rates. The central hypothesis tested in the project states that slow-spreading ridge morphology is principally controlled at the segment scale by the compositional heterogeneity of the underlying mantle. The specific research goal for the proposed study is to identify and assess geochemical variations that fingerprint the contributions of partial melts derived from enriched, fertile mantle rocks at the ridge segment length scale. The project principally uses U-Th-Pa-Ra isotope disequilibria, which are particularly sensitive to mantle melt fertility. Disequilibria will be assessed through comparisons between second-order ridge segments that exhibit distinct morphologic types along the Kane-Atlantis supersegment of the northern Mid-Atlantic Ridge between 24-30N.