Search for: All records

Subduction transports volatiles between Earth’s mantle, crust, and atmosphere, ultimately creating a habitable Earth. We use isotopes to track carbon from subduction to outgassing along the Aleutian-Alaska Arc. We find substantial along-strike variations in the isotopic composition of volcanic gases, explained by different recycling efficiencies of subducting carbon to the atmosphere via arc volcanism and modulated by subduction character. Fast and cool subduction facilitates recycling of ~43 to 61% sediment-derived organic carbon to the atmosphere through degassing of central Aleutian volcanoes, while slow and warm subduction favors forearc sediment removal, leading to recycling of ~6 to 9% altered oceanic crust carbon to the atmosphere through degassing of western Aleutian volcanoes. These results indicate that less carbon is returned to the deep mantle than previously thought and that subducting organic carbon is not a reliable atmospheric carbon sink over subduction time scales.

 

The degassing of CO₂and S from arc volcanoes is fundamentally important to global climate, eruption forecasting, ore deposits, and the cycling of volatiles through subduction zones. However, all existing thermodynamic/empirical models have difficulties reproducing CO₂‐H₂O‐S trends observed in melt inclusions and provide widely conflicting results regarding the relationships between pressure and CO₂/SO₂in the vapor. In this study, we develop an open‐source degassing model, Sulfur_X, to track the evolution of S, CO₂, H₂O, and redox states in melt and vapor in ascending mafic‐intermediate magma. Sulfur_X describes sulfur degassing by parameterizing experimentally derived sulfur partition coefficients for two equilibria: RxnI. FeS (m) + H₂O (v)  H₂S (v) + FeO (m), and RxnII. CaSO₄(m)  SO₂(v) + O₂(v) + CaO (m), based on the sulfur speciation in the melt (m) and co‐existing vapor (v). Sulfur_X is also the first to track the evolution offO₂and sulfur and iron redox states accurately in the system using electron balance and equilibrium calculations. Our results show that a typical H₂O‐rich (4.5 wt.%) arc magma with high initial S⁶⁺/ΣS ratio (>0.5) will degas much more (∼2/3) of its initial sulfur at high pressures (>200 MPa) than H₂O‐poor ocean island basalts with low initial S⁶⁺/ΣS ratio (<0.1), which will degas very little sulfur until shallow pressures (<50 MPa). The pressure‐S relationship in the melt predicted by Sulfur_X provides new insights into interpreting the CO₂/S_Tratio measured in high‐T volcanic gases in the run‐up to the eruption.

 

The depth at which volcanic arc magma is stored is determined by the amount of water in the magma. 

Inclusions of basaltic melt trapped inside of olivine phenocrysts during igneous crystallization provide a rich, crystal-scale record of magmatic processes ranging from mantle melting to ascent, eruption, and quenching of magma during volcanic eruptions. Melt inclusions are particularly valuable for retaining information on volatiles such as H 2 O and CO 2 that are normally lost by vesiculation and degassing as magma ascends and erupts. However, the record preserved in melt inclusions can be variably obscured by postentrapment processes, and thus melt inclusion research requires careful evaluation of the effects of such processes. Here we review processes by which melt inclusions are trapped and modified after trapping, describe new opportunities for studying the rates of magmatic and volcanic processes over a range of timescales using the kinetics of post-trapping processes, and describe recent developments in the use of volatile contents of melt inclusions to improve our understanding of how volcanoes work. ▪  Inclusions of silicate melt (magma) trapped inside of crystals formed by magma crystallization provide a rich, detailed record of what happens beneath volcanoes. ▪  These inclusions record information ranging from how magma forms deep inside Earth to its final hours as it ascends to the surface and erupts. ▪  The melt inclusion record, however, is complex and hazy because of many processes that modify the inclusions after they become trapped in crystals. ▪  Melt inclusions provide a primary archive of dissolved gases in magma, which are the key ingredients that make volcanoes erupt explosively. 

This bibliography was prepared as a synthesis product following the GeoPRISMS Alaska workshop at Lamont Doherty Earth Observatory in August 5-6, 2019 on Subduction Cycles and Deformation at the Alaska-Aleutian margin. The link to workshop web page, including agenda and participant list, is here: [https://sites.google.com/view/alaska-workshop/home?authuser=0]. With a total of 45 participants (51% early career faculty, postdocs or students), there were representatives from all ~19 GeoPRISMS-AK funded projects (FY12-18). A post-conference survey in December 2019 requested information from attendees as to their relevant publications and proposals, including those in preparation and planned. This document is based on that input as well as some 2020 updates. The products listed here include formal GeoPRISMS project outputs, as well as those laterally related to PI group projects. Terry Plank (the workshop organizer and PI) initiated this project and did the initial document curation. She would be happy to pass the project onto another curator in the future. Publications are annotated so as to provide a short synopsis of the research scope, results and context within Alaska Subduction research. Four research themes, which are similar to those developed at the workshop, provide structure to the paper groupings within the Bibliography: 1) The Alaska-Aleutian Megathrust 2) Magmatic Volatiles at Arcs 3) Arc Formation and Continental Growth 4) Arc Volcano Systems Papers and proposals in press, in revision, in preparation and planned are also included to keep the community informed of upcoming and ongoing work. The intent is to update this document periodically and disseminate it publicly and broadly as a living GeoPRISMS legacy product.