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Element distribution and heavy stable isotope fractionation at the magmatic-hydrothermal transition

English title Element distribution and heavy stable isotope fractionation at the magmatic-hydrothermal transition
Applicant Pettke Thomas
Number 157121
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geochemistry
Start/End 01.05.2015 - 30.04.2019
Approved amount 299'750.00
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All Disciplines (2)

Discipline
Geochemistry
Geology

Keywords (8)

miarolitic cavities; magmatic-hydrothermal transition; analytical geochemistry; Molybdenum isotope fractionation; element distribution coefficients; aqueous fluid inclusions; melt inclusions; LA-ICP-MS

Lay Summary (German)

Lead
Die Elementverteilung zwischen Restschmelze und wässriger, fluider Phase in fortgeschrittenen Stadien der Kristallisation von Magmen in der Erdkruste sind entscheidend für magmatisch-hydrothermale Prozesse und stehen am Anfang der Bildung von grossen Cu-Au-Mo-Sn-W Erzlagerstätten. Dieses Projekt beabsichtigt, diese Verteilung für >25 Elemente zu quantifizieren, basierend auf LA-ICP-MS Analytik von kogenetischen Flüssigkeits- und Schmelzeinschlüssen. Exzellentes Probenmaterial wird bei Feldarbeit im Torres del Paine Intrusionskomplex gesammelt, einer seichten Intrusion, die als Analog zu subvulkanischen Magmenkammern verstanden werden kann, dem Ursprungsort solch erzbildender hydrothermaler Fluide. Zudem ist beabsichtigt, die Isotopenfraktionierung von Mo in diesem Milieu zu quantifizieren, was einen essentiellen Beitrag zum besseren Verständnis des globalen Mo Zyklus geben wird.
Lay summary

Die progressive Kristallisation von Magmen in subvulkanischem Milieu assoziiert mit kollidierenden Plattenrändern führt schliesslich zur Sättigung einer wässrigen, salzhaltigen Phase in der Restschmelze. Dieses so genannte magmatisch-hydrothermale Fluid hat das Potential, im subvulkanischen Milieu grosse Metalllagerstätten zu bilden, vorab Cu, Mo, W, Sn und zum Teil auch Au, Ag. Diese Erzmetalle werden dem kristallisierenden Magma effizient durch die Fluid-Entmischung entzogen, was also als Auslöser dieser Erzlaberstättenbildung verstanden werden kann.

Dieses Projekt beabsichtigt auf Basis von natürlichen Proben aus der Torres del Paine Intrusion (Patagonien), die Verteilungskoeffizienten von <25 Elementen bei dem Stadium der Fluid-Entmischung zu quantifizieren. Dazu werden koexistierende Flüssigkeits- und Schmelzeinschlüsse, welche in Quarzkristallen aus myarolitischen Hohlräumen bei deren Wachstum bei rund 800 °C eingeschlossen wurden, mittels LA-ICP-MS und weiteren Techniken analysiert. Solch quantitative Daten sind bis heute Mangelware. Die Resultate leisten somit einen wertvollen Beitrag zum besseren Verständnis der Bildung von magmatisch-hydrothermalen Erzlagerstätten und können dadurch entscheidend beitragen zur fortwährenden Versorgung mit diesen für die Gesellschaft essentiellen Metallen.

Ein weiterer Aspekt betrifft die Quantifizierung der Mo Isotopenzusammensetzung und deren Fraktionierung während dieser Fluid-Entmischung. Diese neuen Daten dienen der globalen Mo Isotopensystematik, ein wertvolles geochemisches Werkzeug, um die Geschichte der Bildung freien Sauerstoffs in der Atmosphäre vor rund 2500 Millionen Jahren besser zu verstehen. Dies ist schliesslich eine der Grundlagen des meisten Lebens auf unserem Planeten, wie wir es kennen.

Direct link to Lay Summary Last update: 03.04.2015

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Element Partitioning at the Magmatic-Hydrothermal Transition in a Shallow Plutonic System
KaufmannAnne, PettkeThomas, BaumgartnerLukas (2018), Element Partitioning at the Magmatic-Hydrothermal Transition in a Shallow Plutonic System, Goldschmidt Conference 2018, Boston, USA.
Fluid-involved processes at the magmatic-hydrothermal transition in Torres del Paine, Chile, studied through inclusions in miarolitic quartz. Abstract
Kaufmann Anne, Pettke Thomas, Baumgartner Lukas (2017), Fluid-involved processes at the magmatic-hydrothermal transition in Torres del Paine, Chile, studied through inclusions in miarolitic quartz. Abstract, Abstract Volume of the 15th Swiss Geoscience Meeting, Davos, Switzerland, Abstract pp. 83 - 84.
Fluid-involved processes at the magmatic-hydrothermal transition in Torres del Paine, Chile, studied through fluid inclusions in miarolitic quartz. Abstract
Kaufmann Anne, Pettke Thomas, Baumgartner Lukas (2017), Fluid-involved processes at the magmatic-hydrothermal transition in Torres del Paine, Chile, studied through fluid inclusions in miarolitic quartz. Abstract, 14th Biennial SGA Meeting, Quebec City, Canada, 20-23 August 2017, Abstract number: 173-VXAj-53.
The magmatic-hydrothermal transition at the Torres del Paine igneous complex, Chile - documented by silicate melt and aqueous fluid inclusions in miarolitic quartz. Abstract
Kaufmann Anne, Pettke Thomas, Baumgartner Lukas (2017), The magmatic-hydrothermal transition at the Torres del Paine igneous complex, Chile - documented by silicate melt and aqueous fluid inclusions in miarolitic quartz. Abstract, ECROFI 2017 - Nancy, France, 23-29 June 2017, Abstract S3.T13.
The magmatic-hydrothermal transition at the Torres del Paine igneous complex, Chile - first results of an on-going fluid/melt inclusion study. Abstract
Kaufmann Anne, Pettke Thomas, Baumgartner Lukas (2016), The magmatic-hydrothermal transition at the Torres del Paine igneous complex, Chile - first results of an on-going fluid/melt inclusion study. Abstract, 14th Swiss Geoscience Meeting, Geneva, Switzerland, 18-19 November 2016, Abstract P 2.7.
Fluid Inclusion Gold Concentrations: From Analysis to Implications for Hydrothermal Ore Formation
PettkeThomas, DiamondLarryn (2015), Fluid Inclusion Gold Concentrations: From Analysis to Implications for Hydrothermal Ore Formation, ECROFI-XXIII Extended Abstracts Volume, Leeds - UK, 27 - 29 June, 2015.
Characterisation of a Natural Quartz Crystal as a Reference Material for Microanalytical Determination of Ti, Al, Li, Fe, Mn, Ga and Ge
Audétat Andreas, Garbe-Schönberg Dieter, Kronz Andreas, Pettke Thomas, Rusk Brian, Donovan John J., Lowers Heather A. (2015), Characterisation of a Natural Quartz Crystal as a Reference Material for Microanalytical Determination of Ti, Al, Li, Fe, Mn, Ga and Ge, in Geostandards and Geoanalytical Research, 39(2), 171-184.
Molybdenum isotope fractionation between melt, exsolved fluid and hydrothermal minerals at the magmatic-hydrothermal transition
Kaufmann Anne, Pettke Thomas, O'SullivanEdel, WilleMartin, Molybdenum isotope fractionation between melt, exsolved fluid and hydrothermal minerals at the magmatic-hydrothermal transition, GeoMünster 2019, Münster, Germany, 22.9.2019.

Collaboration

Group / person Country
Types of collaboration
Proff L. Baumgartner & O. Müntener, Institute of Earth Sciences, University of Lausanne Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Dr. A. Audetat, Bayerisches Geoinstitut / Universität Bayreuth Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Associated projects

Number Title Start Funding scheme
170722 A new state-of-the-art Laser Ablation ICP-MS facility with emphasis on mapping and technique development 01.01.2017 R'EQUIP
172688 Redox conditions and sulphide-oxide-silicate mineral and fluid geochemistry of subducted hydrous mantle rocks 01.03.2018 Project funding (Div. I-III)
137686 The mineral and fluid chemistry of prograde serpentinite dehydration 01.08.2012 Project funding (Div. I-III)

Abstract

In the evolution of igneous systems the magmatic-hydrothermal transition is the stage where specific elements get mobilized by partitioning into an aqueous fluid exsolving from crystallizing magmas. Knowledge of fluid/melt partition coefficients is thus essential to quantify the mass transfer of elements from magmas into diverse geological environments, including the subvolcanic realm where magmatic-hydrothermal ore deposits may form or into the atmosphere via quiet or violent volcanic degassing.This project proposes to quantify, in the subvolcanic magmatic environment, (i) element distribution coefficients between residual melt, minerals, and aqueous fluids for well over 25 elements, from Li to U, and (ii) Mo isotope fractionation between residual silicate melt, minerals and exsolving aqueous fluids. Focus is on the Torres del Paine igneous system that documents - at excellent outcrop conditions - diverse features of fluid saturation. These include pegmatoid to frothy zones and miarolitic cavities within the intrusive bodies that record hydrothermal processes from ~750 down to ~300 °C that appear not to have communicated with the rocks hosting the intrusions. Coexisting silicate melt and aqueous fluid inclusions, minerals and coexisting liquid-vapour fluid inclusions will be analyzed by detailed microscopy, Raman spectroscopy, LA-ICP-MS, EPMA, SIMS, and by liquid sample MC-ICP-MS techniques. The new partitioning data shall be interpreted in light of intensive parameters, e.g., fO2, fluid chlorinity at exsolution, concentration of other volatiles (F, S), and melt composition (e.g., aluminum saturation index, Cl/H2O concentration ratio) of which some have already been tightly constrained thanks to diverse research initiatives during the past years.Our recent finding of prominent Mo isotope fractionation during igneous differentiation up to and including fluid exsolution awaits confirmation by direct analysis of coexisting fluid and melt fractions (available in fluid and melt inclusions). Because fayalite is stable in the miarolitic cavities, fluid - ferrous silicate mineral d98Mo can also be quantified (note that common cavity minerals like quartz and feldspars do not host Mo).This project and future research initiatives in this direction are considered to be essential for our better understanding of how magmatic volatiles play their central role in the transport of chemical components between active magmatic systems and diverse geologic environments and, more specifically, what the decisive parameters are for the formation of magmatic-hydrothermal ore deposits.
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