Volatile Recycling at Tonga-Lau: A Global End-Member

海底含碳沉积物俯冲到地球深处。然而，目前尚不清楚有多少碳在火山气体和喷发中重新出现在地表，有多少继续进入地幔深处。许多基本的地球过程都在这个深层碳循环的平衡中徘徊，比如地球大气的演化和钻石的形成，然而这个循环的效率是高度不确定的。这个项目将研究汤加群岛，一个被认为是所有俯冲带中碳排放量最少的地方。位于汤加群岛后面的劳盆地是研究挥发性再循环的理想场所，因为它的采样深度为100至300公里。这一点很重要，因为碳可能在比水更深的地方释放。结果将检验最近从模型、计算和实验室实验中得出的预测，并将应用于其他俯冲带系统的一般碳循环模型。本项目旨在利用熔融包裹体测量再循环到汤加弧和劳盆地岩浆的俯冲碳和水。最近的研究表明，熔体包裹体中高达90%的二氧化碳可能包含在它们的微小收缩气泡中，这些气泡很少被测量，在汤加弧中也从未被测量过。对于整个劳盆地，只有一个已发表的熔体包裹体分析，没有二氧化碳测量。因此，本项目的主要工作是利用在拉蒙特开发的活塞缸装置和技术，对汤加弧和劳弧后的熔体内含物和气泡进行实验再均匀化。所有样品都可以从现有的集合中获得。据推测，汤加群岛是所有俯冲带中碳排放量最少的，原因是俯冲沉积物输入中缺乏碳，全球范围内的冷俯冲板块可能无法释放出火山弧下的大量碳，以及地幔源高度枯竭。初步的数据和计算表明，很少有碳循环到汤加弧，但有些可能会出现在弧后。该项目将首次为成对弧-弧-弧系统提供CO2（和H2O）的综合估算。这个项目的一个主要的更广泛的影响是社区重新同质化的努力。熔体包裹体的研究正在经历一场革命，因为人们认识到，在已公布的二氧化碳丰度中，大多数都被大大低估了。实际上，现在每一个熔体包裹体研究都需要重新审视，以便量化收缩泡中的二氧化碳浓度。为了应对这一挑战，研究人员将被邀请提交熔体包裹体在拉蒙特进行实验再均质，之后样品将返回进行分析和发表。目标是生成15-20个包含恢复CO2的新数据集，优先考虑那些具有CO2/S火山气体记录的数据集。该项目还将资助一名博士生。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。

Carbon-bearing sediments on the seafloor subduct into the deep earth. However, it is unclear how much carbon re-emerges at the surface in volcanic gases and eruptions and how much continues into the deep mantle. Many fundamental earth processes hang in the balance of this deep carbon cycle, such as the earth’s atmospheric evolution and the formation of diamonds, and yet the efficiency of this cycle is highly uncertain. This project will study the Tonga Islands, a location that is thought to output the least amount of carbon of any subduction zone. The Lau Basin, located behind the Tonga Islands is ideal for studying volatile recycling as it samples depths from 100 to 300 km. This is important, as carbon may be released at greater depths than water. Results will test recent predictions from models, calculations, and laboratory experiments and will apply to general carbon cycle models for other subduction zone systems. This project aims to measure the subducted carbon and water recycled to Tonga Arc and Lau Basin magmas using melt inclusions. Recent work has demonstrated how up to 90% of the CO2 in melt inclusions may be contained with their tiny shrinkage bubbles, which are rarely measured, and never have been for the Tonga arc. For the entire Lau Basin, there is a single published melt inclusion analysis with no CO2 measurement. Thus, the primary effort in this project is to experimentally rehomogenize melt inclusions and bubbles from the Tonga Arc and Lau back-arc using the piston cylinder apparatus and a technique developed at Lamont. All samples are available from existing collections. The Tonga islands are hypothesized to output the least amount of carbon of any subduction zone owing to the lack of carbon in subducting sediment input, a globally cold subducting slab that may not liberate substantial carbon beneath the volcanic arc, and a highly depleted mantle source. Preliminary data and calculations suggest that very little carbon recycles to the Tonga arc, but that some may emerge in the back-arc. This project will provide the first comprehensive estimates for CO2 (and H2O) for a paired arc-back-arc system. A major broader impact of this project is a Community Rehomogenization effort. The study of melt inclusions is undergoing a revolution, given the recognition that most of the 1000’s of published CO2 abundances are greatly under-estimated. Virtually every melt inclusion study now needs to be revisited in order to quantify the CO2 concentration in the shrinkage bubble. In order to meet this challenge, researchers will be invited to submit melt inclusions for experimental rehomogenization at Lamont, after which samples will be returned for analysis and publication. The goal is to generate 15-20 new datasets with restored CO2, prioritizing those that have coupled CO2/S volcanic gas records. This project will also support a PhD student.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.