Collaborative Research: Understanding the influence of tectonic setting on the depth of magmatic processes in the mid-ocean ridge system

合作研究：了解构造环境对洋中脊系统岩浆过程深度的影响铺铺海底的岩石覆盖了地球表面的70%，是由沿洋中脊（MOR）系统的火山产生的。这些火山可以说代表了地壳中最大的地质系统。通过分析MOR喷发的熔岩，地质学家了解了这些岩浆是如何产生的，以及它们在上升到地表时如何发生化学变化。然而，对于地层深度以及在MOR系统的不同部分地层深度如何变化，人们知之甚少。关于MOR熔岩中晶体形成深度的新数据，基于被困在晶体中的岩浆液滴（熔融包裹体）中的二氧化碳，表明晶体的产生深度范围很广。因此，这些晶体提供了岩浆从深处运输过程中遇到的岩浆成分和控制海洋地壳形成过程的记录。这项研究将化学分析微观熔体包裹体和晶体，以了解岩浆形成的深度如何在全球范围内变化。这些新数据将提供不同MOR环境下的结晶深度和地幔碳收支的信息。该提案的一个核心方面涉及向南达科他州部落学院的学生伸出援手，该计划将由三个部分组成，包括南达科他州矿山的现有项目，指导奥格拉拉拉科塔学院（OLC）的学生，并为OLC的分析设施发展提供建议。目前对海洋地壳演化的理解在很大程度上依赖于海底火山玻璃，以及最近的熔融包裹体（MI）成分。这些数据对上地幔和地壳中活跃的混合和分化过程的复杂排列提供了最丰富的信息——本质上是“什么”正在发生。一直以来难以确定的是具体过程在深度上活跃的“位置”，这使得解决融化过程中发生的过程与向地表运输过程中发生的过程的影响具有挑战性。关于熔体包裹体包裹深度的新数据（基于CO2饱和度/浓度）表明，海底玄武岩中的大部分结晶货物，特别是斜长石超水玄武岩（PUB）中的结晶货物，是在很宽的压力范围内结晶的产物。因此，它们提供了一个机会来研究岩浆组成在运输过程中是如何演变的，以及控制海洋地壳形成过程的能量和质量分布在不同的构造环境（不同的扩张速度、岩浆供应、融化程度等）中是如何不同的。本研究将通过电子探针（主要元素组成）、激光ICP-MS（微量元素组成）、二次离子质谱（玻璃CO2、H2O、S）和拉曼光谱（MI气泡密度/组成）进行联合分析。所选的样品代表了来自一系列背景的PUB熔岩，在轴上，拉离盆地，超慢至中等扩张速率，以及来自不同地壳厚度特征的脊。这一新信息将提高对MORB岩石学中一些基本问题的理解，包括：1)橄榄石和斜长石在不同MOR环境下的结晶比较深度（晶体分选如何影响取样），2)负责MOR分化的过程对深度的依赖，3)二氧化碳/微量元素比率可用于估计地幔C收支的程度。该提案的一个核心方面涉及向南达科他州部落学院的学生伸出援手，该计划将由三个部分组成，包括南达科他州矿山的现有项目，指导奥格拉拉拉科塔学院（OLC）的学生，并为OLC的分析设施发展提供建议。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Collaborative Research: Understanding the influence of tectonic setting on the depth of magmatic processes in the mid-ocean ridge system The rocks that pave the seafloor cover ~70% of the Earth’s surface and are produced by volcanoes along the mid-ocean ridge (MOR) system. These volcanoes arguably represent the largest geologic system in the Earth’s crust. By analyzing the lavas erupted at the MOR, geologists understand how these magmas are produced and how they chemically change as they rise to the surface. However, less is understood about depths of formation and how that may change in different parts of the MOR system. New data on depth of formation of the crystals in MOR lavas, based on CO2 in trapped droplets of magma in crystals (melt inclusions), indicate that the crystals are produced over a wide depth range. Those crystals therefore provide a record of magma compositions encountered during transport from depth and of processes controlling ocean crust formation. This study will chemically analyze microscopic melt inclusions and crystals to understand how the depth of magma formation varies globally. This new data will provide information on the depth of crystallization in different MOR environments and the carbon budget of the mantle. A core aspect of this proposal involves outreach to students at the tribal colleges in South Dakota which will consist of three parts including current programs at South Dakota Mines, mentoring students from Oglala Lakota College (OLC), and providing advice on the development of the analytical facilities at OLC.Current understanding of the evolution of the ocean crust relies heavily on submarine volcanic glasses and, more recently, melt inclusion (MI) compositions. Such data is most informative about the complex array of mixing and differentiation processes active in the upper mantle and crust - in essence “what” is happening. What has been difficult to constrain is “where” specific processes are active in terms of depth, making it challenging to resolve the influences of processes occurring in the melting regime versus those that occur during transport to the surface. New data on depth of entrapment for melt inclusions (based on CO2 saturation/concentration) indicate that much of the crystal cargo in ocean floor basalts, particularly those from plagioclase ultraphyric basalts (PUB) are the products of crystallization at a wide range of pressure. They therefore provide an opportunity to investigate how the array of magma compositions evolves during transport and how the distribution of energy and mass of the processes controlling ocean crust formation differs between tectonic settings (different spreading rates, magma supply, extent of melting, etc.). This study will conduct combined analysis by electron microprobe (for major element composition), Laser ICP-MS (trace element compositions), secondary ion mass spectrometry (glass CO2, H2O, S), and Raman spectroscopy (MI bubble density/composition). The samples selected represent a number of PUB lavas from a range of settings, on axis, pull apart basins, ultra-slow to intermediate spreading rates and from ridges characterized by different crustal thicknesses. This new information will improve understanding of a number of fundamental questions in MORB petrology including: 1) the comparative depth of crystallization in different MOR environments for olivine and plagioclase (how crystal sorting influence what is being sampled), 2) the depth dependence of the processes responsible for MOR differentiation, 3) the extent to which CO2/trace element ratios can be used to estimate the mantle C budget. A core aspect of this proposal involves outreach to students at the tribal colleges in South Dakota which will consist of three parts including current programs at South Dakota Mines, mentoring students from Oglala Lakota College (OLC), and providing advice on the development of the analytical facilities at OLC.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.