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

海底的含碳沉积物俯冲到地球深处。然而，目前尚不清楚有多少碳以火山气体和喷发的形式重新出现在地表，有多少碳继续进入地幔深处。许多基本的地球过程在这个深层碳循环的平衡中挂着，例如地球的大气演化和钻石的形成，然而这个循环的效率非常不确定。这个项目将研究汤加群岛，这个地方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刘盆地是研究挥发性再循环的理想地点，因为它对100至300公里的深度进行了采样。这一点很重要，因为碳可能会在比水更深的地方释放。结果将检验模型、计算和实验室实验的最新预测，并将适用于其他俯冲带系统的一般碳循环模型。该项目旨在利用熔体包裹体测量再循环到汤加弧和刘盆地岩浆中的俯冲碳和水。最近的研究表明，熔体包裹体中高达90%的二氧化碳可能被其微小的收缩气泡所控制，这种气泡很少被测量到，而且从来没有被测量到过。对于整个刘盆地，只有一项已发表的熔融包裹体分析，没有二氧化碳测量。因此，该项目的主要工作是使用活塞缸装置和Lamont开发的一项技术，对汤加弧和刘弧后的熔融夹杂物和气泡进行再均质实验。所有样品都可以从现有的收藏中获得。假设汤加群岛输出的碳是所有俯冲带中最少的，因为俯冲沉积物输入中缺乏碳，全球寒冷的俯冲板块可能不会在火山弧下释放大量碳，以及高度枯竭的地幔来源。初步数据和计算表明，很少有碳再循环到汤加弧，但可能会有一些出现在弧后。该项目将首次为成对的弧后系统提供二氧化碳(和水)的全面估计。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。熔融包裹体的研究正在经历一场革命，因为人们认识到，已公布的1000‘S二氧化碳丰度中的大多数都被大大低估了。为了量化收缩气泡中的二氧化碳浓度，现在几乎所有的熔融包裹体研究都需要重新审视。为了迎接这一挑战，研究人员将被邀请提交熔融包裹体在拉蒙特进行试验性再均一化，之后样品将被送回分析和发表。其目标是用恢复的二氧化碳生成15-20个新的数据集，优先考虑那些耦合了二氧化碳/S火山气体记录的数据集。该项目还将支持一名博士生。这一奖项反映了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。

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.