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

合作研究：了解构造环境对大洋中脊系统岩浆作用深度的影响铺设海底的岩石覆盖地球表面约70%，由大洋中脊系统(MOR)系统的火山产生。这些火山可以说是地壳中最大的地质系统。通过分析莫尔火山喷发的熔岩，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是如何发生化学变化的。然而，关于地层的深度以及这种情况在MOR系统的不同部分可能会发生什么变化，人们了解得较少。根据晶体(熔体包裹体)中捕获的岩浆液滴中的二氧化碳，关于莫尔熔岩中晶体形成深度的新数据表明，晶体在很大的深度范围内产生。因此，这些晶体记录了从深处输送过程中遇到的岩浆成分以及控制洋壳形成的过程。这项研究将对微观熔体包裹体和晶体进行化学分析，以了解全球岩浆形成的深度是如何变化的。这一新数据将提供有关不同MOR环境下结晶深度和地幔碳收支的信息。这项提议的一个核心方面涉及到与南达科他州部落学院的学生进行接触，这将包括三个部分，包括南达科他州矿场的当前项目，指导奥格拉拉拉科塔学院(OLC)的学生，以及就奥拉拉拉科塔学院分析设施的发展提供建议。目前对洋壳演化的了解在很大程度上依赖于海底火山玻璃和最近的熔融包裹体(MI)成分。这些数据最能说明上地幔和地壳中活跃的一系列复杂的混合和分异过程--本质上是正在发生什么。难以限制的是，就深度而言，特定过程在哪里活跃，这使得解决发生在熔化制度中的过程与发生在向地表输送过程中的过程的影响之间的影响具有挑战性。有关熔体包裹体捕获深度的新数据(基于CO2饱和度/浓度)表明，海底玄武岩中的许多结晶货物，特别是斜长超长玄武岩(PUB)中的结晶货物，是在广泛压力范围内结晶的产物。因此，它们为研究一系列岩浆成分在运输过程中如何演变以及控制洋壳形成的过程的能量和质量分布在不同的构造环境(不同的扩张率、岩浆供应、熔融程度等)之间有何不同提供了机会。本研究将采用电子探针(主要元素组成)、激光电感耦合等离子体质谱(痕量元素组成)、二次离子质谱仪(玻璃CO_2、H_2O、S)和拉曼光谱(MI气泡密度/组成)进行联合分析。所选择的样品代表了一系列酒吧熔岩，这些熔岩来自不同的环境，在轴线上，拉开盆地，超慢到中等的扩张速度，以及来自具有不同地壳厚度特征的山脊。这些新信息将促进对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环境下的相对结晶深度(晶体分选如何影响所采集的样品)，2)导致MOR分异的过程的深度相关性，3)可以在多大程度上利用CO2/微量元素比值来估计地幔C预算。这项提议的一个核心方面涉及向南达科他州部落学院的学生进行外联，这将由三部分组成，包括南达科他州矿场当前的项目，指导奥格拉拉·拉科塔学院(Oglala Lakota College，OLC)的学生，以及就Oglala Lakota College(OLC)的分析设施的发展提供建议。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.