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Petrology and kinetics of igneous systems

English title Petrology and kinetics of igneous systems
Applicant Ulmer Peter
Number 184867
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geology
Start/End 01.10.2019 - 30.09.2023
Approved amount 572'928.00
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All Disciplines (3)

Discipline
Geology
Geochemistry
Mineralogy

Keywords (8)

Adamello batholith; Li-partitioning; LI-diffusion; Cumulate cannibalization; magma differentiation; High-An plagioclase; Rhyolitic magmas; magmatic-hydrothermal systems

Lay Summary (German)

Lead
Magmatisch-hydrothermal Prozesse kontrollieren Gestalt und Entwicklung unseres einzigartigen Planeten und sind verantwortlich für die Bildung vieler Erzlagerstätten aber auch für verheerende Vulkanausbrüche, wenn das Magma durch die Erdkruste an die Oberfläche aufsteigt und dort austritt. Dieses Forschungsprojekt untersucht zwei dieser Prozesse im Rahmen von zwei Doktorarbeiten: (A) Elementare und Isotopenfraktionierung von Lithium (Li) sowie Diffusion von Li zwischen Kristallen, Schmelzen und wässrigen Fluiden/Gasen in SiO2-reichen magmatischen Systemen; und (B) - Die Interaktion von aufsteigendem, wasserführendem Magma mit den «plutonischen Wurzeln» flachliegender Magmakammern, die die Zusammensetzung des resultierenden Magmas verändert. Ziel ist die Rolle dieses Prozesses im generellen Rahmen von Magmagenese und Differentiation wasserhaltiger, calk-alkalischer Magmen an konvergenten Plattengrenzen zu verstehen und zu quantifizieren.
Lay summary

Projekt A: Die Quantifizierung des Materialtransfers zwischen unterschiedlichen Reservoiren der Erde ist fundamental zum Verständnis des Erdsystems. Lithium wird zunehmend als Indikator dafür verwendet, da sowohl seine Element- wie Isotopenhäufigkeit in unterschiedlichen Reservoiren stark variiert. Während das Tieftemperaturverhalten von Li in geologischen Systemen gut bekannt ist, gilt dies nicht für Hochtemperatur- Magmasysteme. Diese experimentelle Studie unter hydrothermalen Bedingungen (20-200 MPa, 700-900°C) bestimmt Li- und Li-Isotopenfraktionierung zwischen (1) wässrigen, Cl-haltigen Fluiden/Gasen und rhyolitischer Schmelze und (2) Na-K-Ca-Feldspäten und Quarz und Fluiden/Gasen sowie Schmelze. Die Experimente ermitteln zudem die Li-Diffusivität in Kristallen und Schmelze, die den Modus der Li-Fraktionierung kontrolliert. The experimentellen Resultate erlauben erstmalig den Effekt von Fluid/Gas-Entmischung aus einer silikatischen Schmelze auf die Li-Konzentration und Li-Isotopenverhältnisse zu quantifizieren, was kritische Information zum Verständnis der Bildung von Li-Lagerstätten liefert.

Projekt B: The Entstehung intermediärer bis sauren (SiO2-reicher) magmatischen Gesteinen, die die (obere) Erdkruste bilden ist kontrovers und eine grosse Anzahl möglicher Prozesse werden dafür verantwortlich gemacht. In dieser Studie untersuchen wir die Interaktion aufsteigendem Magmas mit den «Wurzeln» flachliegender Magmakammern durch Assimilation und Teilaufschmelzung. Wir kombinieren dazu detaillierte Feld- und analytische Arbeiten mit experimentellen Studien. In den einzigartigen Aufschlüssen im südlichen Adamello-Massif (N-Italien) kann der Prozess der «Kannibalisierung der plutonischen Wurzeln» direkt beobachtet und dokumentiert werden. Die experimentelle Studie umfasst zwei Serien: (i) Teilaufschmelz- und Assimilationsexperimente unter Fluid-(H2O-)gesättigten Bedingungen um Zusammensetzungen der Schmelzen und residualen Kristallen zu bestimmen und (ii) Zeitserien mit variablen Verhältnissen von Schmelze und (Kumulat-)Kristallen um die Kinetik des Systems zu erfassen, die Raten und Zeitdauer der Prozesse kontrollieren. Petrologie und Geophysik implizieren, dass die Entstehung der intermediären (tonalitischen) Schmelzen vorwiegend in der Unterkruste ablaufen, was jedoch nicht konsistent ist mit experimentellen Resultaten die unter solchen Bedingungen (hoher Druck) die Zusammensetzung der typischen krustenbildenden Tiefengesteine und Vulkanite nicht nachvollziehen können. Die «Kannibalisierung der plutonischen Wurzeln» ist ein möglicher Prozess der diese scheinbare Inkonsistenz auflösen könnte. Diese Studie erstellt die notwendigen Datensets um die potentielle Rolle dieses Prozesses im generellen Rahmen der Magmagenese und Differentiation an konvergenten Plattengrenzen und plutonisch-vulkanischer Systeme im Allgemeinen zu evaluieren.

Direct link to Lay Summary Last update: 01.04.2019

Lay Summary (English)

Lead
Magmatic-hydrothermal processes control the shape and evolution of our unique planet and are responsible for the formation of many economic ore deposits but also for devastating volcanic eruption if these magmas ascend through the crust and extrude at the Earth surface. This project investigates two specific processes with two different PhD studies: (A) - Lithium (Li) elemental and isotope partitioning and diffusion between solid, liquid and hydrous fluid/gas in silicic magmatic systems; and (B) - The interaction of ascending intermediate composition, hydrous melts with the plutonic roots of shallow magma reservoirs modifying the compositions of derivative magmas to assess its role in the overall framework of magma genesis and differentiation of hydrous, calc-alkaline magmas at convergent plate margins held responsible for the formation of continental crust distinguishing our planet from other terrestrial planets.
Lay summary

Project A: Tracing material between different Earth reservoirs is essential to understand the Earth system. Lithium is increasingly used as a tracer as abundance and isotopic composition (6Li and 7Li) reveal large variability. While the low temperature behavior of Li in geologic systems is well understood, its behavior in high-temperature magmas that transit the crust is much less well constrained. This experimental study conducted under hydrothermal conditions (20-200 MPa. 700-900^°C) determines Li and Li isotope partitioning between (1) hydrous, chlorine-bearing fluid/gas and rhyolite melt and (2) Na-Ca-, Na-K-feldspar and quartz and fluid/gas and melt. The experiments will further serve to determine Li-diffusivity in crystals and melt as diffusivity largely controls the mode of Li-isotope fractionation. The experimental results will be the first to provide a framework with which to assess the effects of degassing on lithium and lithium isotopes. Understanding the controls on Li partitioning between melts, co-existing fluids, and solids will provide crucial information for greater understanding of the formation of economic lithium deposits. Currently, extraction of lithium is occurring without a coherent deposit model and thus the amount of environmental damage is significantly greater than the same resulting amount of Li would produce with a more targeted approach.
Project B: The genesis of the intermediate to felsic igneous rocks building the upper crust is controversial and a large number of processes are proposed. Here, we investigate the interaction of ascending magmas with the plutonic roots of shallow level (4-10 km depths) magma reservoirs by assimilation and partial melting. We combine detailed field and analytical work in unique outcrops in the Adamello Batholith (N-Italy) were the process of cannibalization of the plutonic roots of a fossil sub-volcanic magma reservoir is “caught in the very act” with an experimental study simulating the process in the laboratory. The experimental study consists of two different series (i) partial melting and assimilation experiments under fluid-saturated conditions to constrain liquid and residual mineral compositions; and (ii) time-series experiments with variable melt / cumulate proportions to assess the kinetics and, therefore, duration and rates of the process(es). Petrology and geophysics infer that major processes controlling intermediate composition magma evolution occur in the lower crust. However, experiments fail to reconstruct the compositions of shallow level plutonic and volcanic rocks under lower crustal conditions. The cannibalization of the plutonic roots of the shallow magmatic system is a candidate process solving this apparent contradiction. This study provides necessary data sets to evaluate the potential role of this process in the overall framework of magma genesis and differentiation at convergent plate margin and the evolution of plutonic and volcanic systems in general.

Direct link to Lay Summary Last update: 01.04.2019

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
156408 Petrology and kinetics of igneous systems 01.10.2014 Project funding (Div. I-III)

Abstract

This research comprises two PhD student projects addressing 2 different goals: Project A is an experimental study addressing Li elemental and isotope partitioning and diffusion between solid, liquid and fluid/gases in silicic magmatic systems; and Project B is a combined field and experimental study on cannibalization of gabbroic cumulates by intermediate composition melts in arc magmas.Project A - Li abundances and isotopic fractionation are powerful tools to trace the fate and contributions of various reservoirs involved in mass transfer processes, such as subduction components through the entire cycle from ocean floor hydration to volcanic degassing. Most studies rely on the assumption that Li isotopes are not significantly fractionated during high-temperature igneous processes: However, the large mass difference combined with its extremely fast diffusion in silicate melts and solids seriously questions this as recent studies infer that Li abundances and isotopes are significantly affected by post-eruptive processes in rapidly quenched felsic volcanics. Thus, the use of Li to study late-stage magmatic processes requires a fundamental understanding of its behavior during late-stage degassing of melts in shallow magma reservoirs. Here, we propose an experimental study under hydrothermal conditions (20 - 200 MPa, 700-900°C) to determine (1) the hydrous, chlorine bearing fluid/gas - rhyolite melt Li and Li isotope partitioning, and (2) the partitioning between Na-Ca-plagioclase, Na-K sanidine, quartz and biotite and fluid/vapor and melt. An auxiliary target of the experimental study is the determination of Li-diffusivity in crystals and melt as the diffusivity will largely control the mode of Li(isotope) fractionation. The experimental results will be the first to provide a framework with which to assess the effects of degassing on lithium and lithium isotopes.Project B - Magmatism at convergent plate margins is recognized as the principal process responsible for the formation of continental crust distinguishing our planet from the other terrestrial planets. A large number of different processes to generate the dominantly intermediate to felsic compositions constituting the middle and upper crust have been proposed. This project addresses a potentially important, but not well constrained, process: the chemical and physical interaction of ascending hydrous andesitic/dacitic melts from lower/middle crustal magma reservoirs with the gabbroic (plutonic) roots of shallow magmatic (subvolcanic) reservoirs. We propose combining (1) a case study in an exemplary igneous complex in the S-Adamello batholith (N-Italy) where the direct interaction can be documented in detail with (2) an experimental study simulating potential processes operating during this “cannibalization” process. Experiments are conducted at 200 MPa and temperatures of 850-1050°C and consist of 2 series: (i) partial melting experiments under fluid-saturated conditions to access liquid and restite mineral compositions produced during fluid-fluxed melting of gabbroic cumulates; and (2) assimilation of variably fertile gabbroic cumulates by andesitic liquids simulating the incorporation and disintegration processes. Series (ii) experiments are conducted as time-series to additionally access the kinetics of the process(es). The study will provide fundamental data to evaluate the potential role of this process in the overall framework of magma genesis and differentiation of hydrous, calk-alkaline magmas at convergent plate margin.
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