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High pressure evolution in the internal Western Alps

English title High pressure evolution in the internal Western Alps
Applicant Engi Martin
Number 146175
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geology
Start/End 01.04.2013 - 31.03.2016
Approved amount 586'628.00
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Keywords (11)

metamorphic petrology; geochronology; ocean-continent transition; polycyclic orogen; rifting; continental subduction; thermal evolution; high pressure; PTt-paths; Western Alps; Sesia Zone

Lay Summary (German)

Lead
Gebirgsgürtel entstehen durch Konvergenz tektonischer Platten, die oft mit Subduktion ozeanischer Lithosphäre beginnt und mit dem Stapeln von Decken zu einem Kollisionsgebirge enden kann. Prozesse im Subduktionskanal (SK) sind ungenügend erforscht, auch weil Kontinentalränder oft kompliziert aufgebaut sind: sie zeigen eine OCT (Ocean-Continent Transition). Die Analyse von Hochdruckgesteinen erlaubt es Entwicklungen in einem SK detailliert zu rekonstruieren und so die Prozesse zu verstehen.
Lay summary

In den internen Westalpen wird um die räumlich-zeitliche Entwicklung bei der Bildung von Gesteinen unter hohem Druck (HP) quantifiziert. Dazu werden geeignete Gesteinproben aus mehreren Einheiten (u.a. Sesia-Zone, externe Klippen, Piemonte-Liguria Ozean) genau analysiert, um: (a) die Sequenz metamorpher Mineralreaktionen bei der Entwicklung der HP-Gesteine abzuleiten, (b) die Druck-Temperatur Bedingungen zu bestimmen; (c) absolute Alter bei der Entstehung von HP-Mineralen (mit Th-U-Pb Isotopie) zu messen; sowie (d) die zeitliche Anfolge der mehrphasigen Gesteinsdeformation und den räumlichen Bezug der Einheiten zu etablieren.

Das Vorläuferprojekt ergab, dass das bisher akzeptierte "Alter der Sesia-Zone" (~65 Mio Jahre) die gesamte Frühgeschichte dieser Einheit (~85-67 Ma) ignoriert hatte; es war die Exhumation, nicht aber die initiale Subduktion datiert worden. Es gelang uns erstmals die interne Mobilität im Subduktionskanal nachzuweisen. Durch sog. YoYo-Tektonik waren km-Fragmente früh 50-70 km tief versenkt worden. Die Dynamik dauerte länger und war viel komplexer als bisher vermutet; sie wird im jetzigen Projekts genau untersucht. Insbesondere wird der Einfluss der OCT-Strukturen und alternativ postulierter Prozesse (z.B. ablative Erosion im Subduktionskanal) geprüft. Die paläozoische Beckenentwicklung der grössten Sesia-Einheit ("micaschisti eclogitici") und deren permische Metamorphose werden untersucht. Geklärt wird die Beziehung der Ivrea-Zone zu den externen Klippen, um zu prüfen, ob diese bzw. welche von ihnen in einer kontinentalen Rift-Sequenz wann vom NW-Rand des adriatischen Kontinents getrennt wurden. Die Beziehung dieser Klippen (Mont Emilius, Glacier-Rafray, Pillonet etc.) zu den Einheiten der Sesia und Dent Blanche und 2DK und die zeitliche Beziehung zur Entwicklung ihres jetzigen Piemonte-Liguria-Substrats wird geklärt.

Das Projekt erlaubt es, die z.T. widersprüchlichen Resultate numerischer Simulationen im natürlichen Laboratorium Westalpen zu prüfen und die Prozesse an Plattenrändern besser zu verstehen.

Direct link to Lay Summary Last update: 15.04.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Deeply subducted continental fragments: I. Fracturing, dissolution-precipitation and diffusion processes recorded by garnet textures of the central Sesia Zone (Western Italian Alps)
Giuntoli Francesco, Lanari Pierre, Engi Martin (2018), Deeply subducted continental fragments: I. Fracturing, dissolution-precipitation and diffusion processes recorded by garnet textures of the central Sesia Zone (Western Italian Alps), in Solid Earth, 9, 167-189.
Deeply subducted continental fragments–Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps)
Giuntoli Francesco, Lanari Pierre, Burn Marco, Kunz Barbara, Engi Martin (2018), Deeply subducted continental fragments–Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps), in Solid Earth, 9, 191-222.
Non-matrix-matched standardisation in LA-ICP-MS analysis: General approach and application to allanite Th-U-Pb age-dating
Burn M., Lanari P., Pettke T., Engi M. (2017), Non-matrix-matched standardisation in LA-ICP-MS analysis: General approach and application to allanite Th-U-Pb age-dating, in Journal of Analytical Atomic Spectrometry, 1-19.
Permian high-temperature metamorphism in the Western Alps (NW Italy)
Kunz B., Manzotti P., von Niederhäusern B., Engi M., Darling J., Giuntoli F., Lanari P. (2017), Permian high-temperature metamorphism in the Western Alps (NW Italy), in International Journal of Earth Sciences, 1-27.
Petrochronology based on REE-minerals: monazite, allanite, xenotime, apatite
Engi Martin (2017), Petrochronology based on REE-minerals: monazite, allanite, xenotime, apatite, in Reviews in Mineralogy and Geochemistry, 83, 365-418.
An inverse modeling approach to obtain P–T conditions of metamorphic stages involving garnet growth and resorption
Lanari P., Giuntoli F., Loury C., Burn M., Engi . (2017), An inverse modeling approach to obtain P–T conditions of metamorphic stages involving garnet growth and resorption, in European Journal of Mineralogy, 29(2), 181-199.
Local bulk composition effects on metamorphic mineral assemblages
Lanari P., Engi M. (2017), Local bulk composition effects on metamorphic mineral assemblages, in Reviews in Mineralogy and Geochemistry, 83, 55-102.
Significant ages – an introduction to petrochronology
Engi M., Lanari P., Kohn M.J. (2017), Significant ages – an introduction to petrochronology, in Reviews in Mineralogy and Geochemistry, 83, 1-12.
Geology of the Scalaro valley–Sesia Zone (Italian Western Alps)
Regis D., Venturini G., Engi M. (2016), Geology of the Scalaro valley–Sesia Zone (Italian Western Alps), in Journal of Maps, 12(4), 621-629.
Geometry and kinematics of the Roisan-Cignana Shear Zone, and the orogenic evolution of the Dent Blanche Tectonic System (Western Alps)
Manzotti P., Zucali M., Ballèvre M., Robyr M., Engi M. (2014), Geometry and kinematics of the Roisan-Cignana Shear Zone, and the orogenic evolution of the Dent Blanche Tectonic System (Western Alps), in Swiss Journal of Geosciences, 107(1), 23-48.
Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology
Regis D., Rubatto D., Darling J., Cenki-Tok B., Zucali M., Engi M. (2014), Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology, in Journal of Petrology, 55(7), 1429-1456.
Valle d’Aosta section of the Sesia Zone: multi-stage HP metamorphism and assembly of a rifted continental margin
Compagnoni R., Engi M., Regis D. (2014), Valle d’Aosta section of the Sesia Zone: multi-stage HP metamorphism and assembly of a rifted continental margin, in ISPRA, Soc. Geol. Italiana, Geol. Field Trips, 6(1-2), 1-44.
Geochronology of accessory allanite, monazite and rutile in the Barrovian metamorphic sequence of the Central Alps, Switzerland
Boston K., Rubatto D., Hermann J., Engi M., Amelin Y., Geochronology of accessory allanite, monazite and rutile in the Barrovian metamorphic sequence of the Central Alps, Switzerland, in Lithos.
Pervasive eclogitization due to brittle deformation and rehydration of subducted basement. Effects on continental recycling?
Engi Martin, Giuntoli Francesco, Lanari Pierre, Burn Marco, Kunz Barbara, Bouvier Anne-Sophie, Pervasive eclogitization due to brittle deformation and rehydration of subducted basement. Effects on continental recycling?, in Geochemistry, Geophysics, Geosystems.

Collaboration

Group / person Country
Types of collaboration
Univ. Basel: Prof. Ch. de Capitani Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Università di Torino: Prof. R. Compagnoni Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Univ. Bern: Prof. K. Mezger, Prof. Th. Pettke Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Freie Universität Berlin: Prof. Mark Handy Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Univ. Portsmouth: Prof. C.D. Storey Great Britain and Northern Ireland (Europe)
- Publication
SwissSIMS Lausanne: Dr. A.-S. Bouvier, Prof. L. Baumgartner Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Boise State University: Prof. Matthew J. Kohn United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
ANU Canberra: Dr. D. Rubatto Australia (Oceania)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Michel Ballèvre, Rennes France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events



Self-organised

Title Date Place

Awards

Title Year
Honorary Fellowship of SIMP (Società Italiana di Mineralogia e Petrologia) 2017
Outstanding Early Career Scientist Award (European Geoscience Union) 2017
Socio Corrispondente: Accademia delle Scienze di Torino 2016

Associated projects

Number Title Start Funding scheme
126946 High pressure evolution in the internal Western Alps 01.10.2009 Project funding (Div. I-III)

Abstract

The main continental segments of the internal Western Alps (Italy) shall be investigated to quantify their tectono-metamorphic evolution and their interaction leading to the present orogenic setup. The analysis aims at establishing (a) the pre-Alpine regional relations among these units since the Permian, probably as part of an evolving ocean-continent transition zone, as well as (b) the juxtaposition of these tectonic units against one another during Alpine convergence, i.e. since the upper Cretaceous. Field work in the Sesia Zone (comprising three major tectonic units) and in several smaller klippen units now situated on top of Piemonte-Ligurian units, will be conducted primarily by four PhD students (mostly during two summer seasons), aided by a postdoc and the PI. Structurally controlled sampling of suitable rock units, notably the (sparse) monometamorphic cover sequences, and detailed documentation of polyphase deformation features at mesoscopic scale will be essential goals of these field campains.Petrographic characterization of phase relations in samples from each unit, and microstructural analysis in suitable samples will be used to infer the sequence of the evolutionary stages stored. Petrologically useful assemblages will be analyzed for phase compositions (by EMPA) and trace element distributions (by LA-ICP-MS), especially for REE- and U-Th-bearing phases with a potential for dating. Thermobarometry on local phase assemblages, notably those useful for in situ petrochronometry, will be combined with the recognized deformational fabrics, aiming to relate the P-T data to individual deformation phases. Both TWQ and trace-element thermobarometry will be applied, and the sequence of metamorphic reactions will be analyzed using DOMINO. Individual growth zones of datable minerals (allanite, titanite, zircon, monazite, rutile) will be analyzed for their trace element contents and characteristic inclusions, in order to relate datable zones to specific metamorphic stages. Isotopic in situ dating will be done using LA-ICP-MS and ion probe (Cameca 1280 at SwissSIMS). For sample suites from each main unit, as complete a P-T-D-t path as possible will be derived; in favorable cases these data will yield information on the duration of the Alpine burial and exhumation processes, as well as rates of heating and cooling during the orogeny, under blueschist and eclogite facies conditions. On the other hand, in polymetamorphic samples the same analytical approach should allow us characterize (the commonly well preserved) relics of the pre-Alpine high-temperature history. We expect to quantify the pressure conditions and precise age of the probably Permian regional HT-stage, and one goal is to determine the metamorphic field gradient in at least the larger tectonic units. This may allow us to recognize major discontinuities (e.g. from extensional faults) or, conversely, large-scale continuity in rock types, metamorphic and older structural features. These results should allow us to identify the importance of early, rift-related OCT zone elements and their role during convergence.The data for the Cretaceous and Tertiary cycle shall be used to characterize the quantitative burial and exhumation history for each tectonic unit and thus to constrain their regional evolution in relation to one another. The thermal regime, and the depth and time of juxtaposition will allow us to infer the type of mechanism(s) during subduction and those in the evolving collisional orogen, including the processes of unroofing. Given the present state of knowledge and understanding (from the predecessor project), the progress expected from this integrated effort should make the internal Western Alps an excellent test case for several current debates and for modelers keen to test their dynamic simulations. Existing methods of in situ isotopic analysis by SIMS and LA-ICP-MS will be improved, notably to allow small growth zones in allanite, titanite, and zircon to be dated. Thermodynamic data for REE-minerals, notably solution models, will be extended and optimized using well constrained natural assemblages from the samples analyzed in this study. This will result in improved petrochronometers, as thermobarometric data can be obtained directly from the mineral phases used in age dating.
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