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Isotopic and age constraints on multistage fluid incorporation and release in oceanic lithosphere: a microanalytical study

English title Isotopic and age constraints on multistage fluid incorporation and release in oceanic lithosphere: a microanalytical study
Applicant Rubatto Daniela
Number 191959
Funding scheme Project funding
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geochemistry
Start/End 01.09.2020 - 31.08.2024
Approved amount 931'073.00
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All Disciplines (2)

Discipline
Geochemistry
Geochronology

Keywords (7)

geochronology ; oxygen isotopes ; metasomatism ; serpentinite; oceanic alteration ; subduction ; water-rock interaction

Lay Summary (German)

Lead
Der Kreislauf der Elemente und der Materie in der festen Erde wird von grossräumigen tektonischen Prozessen beherrscht, die die Subduktion der Kruste in den Erdmantel und die Rückführung an die Oberfläche (Kruste) einschliessen. Die Hauptträger im Wasserkreislauf sind die ozeanische Kruste mit dem darunter liegenden Erdmantel. Dieses Material nimmt Wasser am Ozeanboden auf und gibt es in der Tiefe in Subduktionszonen ab. Diese Freisetzung von Wasser in der Tiefe hat Auswirkungen erster Ordnung auf wichtige geologische Prozesse von der Seismizität bis hin zu Vulkanausbrüchen. Die Verfolgung dieses Wasserkreislaufs ist daher von primärer Bedeutung für das Verständnis der Funktionsweise des Planeten.
Lay summary

Ziel dieses Projekts, ist die Rekonstruktion der Isotopensignatur und des zeitlichen Ablaufs der Wasser-Gesteins-Interaktion während der Schritte dieses Zyklus.  Wir werden fortschrittliche analytische Methoden verwenden, mit denen die Sauerstoffisotopenzusammensetzung von Mineralien als Marker der Fluid-Gesteins-Wechselwirkung im Mikromassstab gemessen werden kann. Darüber hinaus werden wir Datierungsmethoden für Mineralien entwickeln, die in dem interessierenden Gestein gefunden werden, um eine Zeitlinie in diesem Wasser-Gestein-Austausch zu erstellen.  

Die Ergebnisse dieses Projekts werden direkt in geodynamische und geochemische Modelle unseres Planeten einfliessen, mit Auswirkungen auf die Interpretation seismischer Daten in Subduktionszonen. Da Fluide in zahllosen geologischen Umgebungen aktiv sind, werden die hier entwickelten Werkzeuge vollständig auf andere Studienbereiche wie Hydrothermalismus, Erzvorkommen und fluidverstärkte Deformation übertragbar sein. 

Direct link to Lay Summary Last update: 16.04.2020

Lay Summary (English)

Lead
The cycle of elements and matter in the solid Earth is dominated by large-scale tectonic processes that include subduction of crust to the mantle and recycling back to the surface (crust). The main carriers in the cycle of water are the oceanic crust with the underlying mantle. This material incorporates water at the oceanic floor and releases it at depth in subduction zones. This release of water at depth has first order consequences on major geological processes from seismicity to volcanic eruptions. Tracking this water cycle is thus of primary importance for understanding the working of the planet.
Lay summary

The aim of this project is to reconstruct the isotopic signature and the timing of water-rock interaction during the steps of this cycle, from oceanic alteration of rocks to release in subduction.  We will use advanced analytical methods that can measure the oxygen isotopic composition of minerals as a marker of fluid-rock interaction at the microscale. Similarly we will develop dating methods for minerals that are found in the rock of interest to put a time line in this water-rock exchange. 

The outcomes from this project will directly feed into large scale geodynamic and geochemical models of our Planet with implications for the interpretation of seismic data at subduction zones. Because fluids are active in countless geological settings, the tools developed here will be fully transferrable to other areas of studies like hydrothermalism, ore deposits and fluid-enhanced deformation.

 
Direct link to Lay Summary Last update: 16.04.2020

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
166280 Tracing the invisible path of fluids in the crust with microscale oxygen isotope measurements in key metamorphic minerals 01.04.2016 Project funding
204491 Exploring lower continental crust: petrology, geochemistry, geophysics and the Ivrea drilling project (DIVE) 01.09.2022 Project funding

Abstract

The proposed research aims to develop methodologies and knowledge to reconstruct the multistage uptake of fluids in oceanic lithosphere and their subsequent release from serpentinites during subduction, along with fluid interaction with associated metasomatic rocks. These fluids have first order control on large-scale geochemical cycles and element recycling, as well as the rheological and seismic behaviour of the lithosphere. The complexity of the material investigated demands a novel microanalytical approach that takes advantage of textural relationships to resolve the multistage nature of the processes. The project will follow the heterogeneity (textural, chemical, isotopic) of serpentinites and associated metasomatic rocks from their oceanic source (PhD student 1) to the subduction where they dehydrate (PhD student 2). A novel effort will specifically target the chronology of serpentinites and metasomatic rocks (PDoc). The approach combines the (i) study of natural samples from diverse tectonic settings by microscale oxygen isotopes and trace elements, (ii) developments of new methods and standards for oxygen analysis and dating minerals in these challenging rock types, and (iii) geochemical modelling to interpret the data in terms of temperature and mineral fractionation, episodic fluid releases rather than bulk signals, time and fluid/rock ratios. The outcome will be to reconstruct the distinct episodes of water incorporation and release in the ultramafic part of the lithosphere, their geochemical signature and timing and to provide constraints for realistic geodynamic and geochemical models of one of the fundamental mass transfer processes in our planet.
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