metamorphic petrology; geochronology; ocean-continent transition; polycyclic orogen; rifting; continental subduction; thermal evolution; high pressure; PTt-paths; Western Alps; Sesia Zone
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.
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.
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
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
Engi Martin (2017), Petrochronology based on REE-minerals: monazite, allanite, xenotime, apatite, in Reviews in Mineralogy and Geochemistry
, 83, 365-418.
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.
Lanari P., Engi M. (2017), Local bulk composition effects on metamorphic mineral assemblages, in Reviews in Mineralogy and Geochemistry
, 83, 55-102.
Engi M., Lanari P., Kohn M.J. (2017), Significant ages – an introduction to petrochronology, in Reviews in Mineralogy and Geochemistry
, 83, 1-12.
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.
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.
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.
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.
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
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
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.