Determining the speed of intracontinental subduction – preliminary results of zoned garnet geochronology in micaschists from the Schneeberg Complex, Eastern Alps.

2020 ◽  
Author(s):  
Kathrin Fassmer ◽  
Peter Tropper ◽  
Hannah Pomella ◽  
Thomas Angerer ◽  
Gerald Degenhard ◽  
...  
Keyword(s):  
High Pressure ◽  
Carbonaceous Material ◽  
Eastern Alps ◽  
Garnet Growth ◽  
Prograde Metamorphism ◽  
Fast Process ◽  
Pt Path ◽  
3D Information ◽  
Growth Zoning ◽  
Different Parts

<p>In collisional orogens continental crust is subducted to (ultra-)high-pressure (HP/UHP) conditions as constrained by petrologic, tectonic and geophysical observations. These (U)HP rocks are exhumed by an extremely fast process (few Ma) as numerous rocks still preserve their high-pressure metamorphic assemblages, which would not be the case if they had time to re-equilibrate at lower pressure conditions. Despite a wealth of studies on the subduction and exhumation of UHP rocks, the duration of prograde metamorphism during subduction is still not well constrained.</p><p>We plan to do Lu-Hf and Sm-Nd geochronology on metamorphic rock samples to date the duration of garnet growth, which represents a major part of prograde metamorphism from the greenschist-facies on. Micaschist samples from the Schneeberg and Radenthein Units in the Eoalpine high-pressure belt (Eastern Alps) will be used for dating as they contain cm- to dm-sized garnets, which experienced only one subduction-exhumation cycle with P-T conditions reaching 600 °C and up to 1 GPa. With dating different parts of big garnet grains we test (1) if it is possible to resolve the duration of garnet growth within single crystals, (2) if both systems, Lu-Hf and Sm-Nd, are needed for better age-constraints, and (3) whether both systems date the same events in the PT-path or give differing information. Additionally we will perform U-Pb geochronology on titanite in order to obtain the age of the first stages of exhumation and on rutile inclusions as well as matrix rutiles to confirm the Eoalpine prograde age with this additional method. Therefore, we will be able to compare the duration of subduction and the timing of initial exhumation in a single sample. We then will constrain the PT-path of the samples that will be dated by pseudosection modeling combined with Zr-in-rutile geothermometer, quartz-in-garnet geobarometer, and carbonaceous material geothermometer. In addition EPMA, µ-XRF, LA-ICPMS, and µCT will be used to control if garnets preserved major and trace elemental growth zoning and to provide spatial 3D information on inclusion patterns. With dating different parts of single garnet crystals separately with Lu-Hf and Sm-Nd geochronology, we will add tight time constraints to the PT-path and constrain the duration of garnet growth.</p><p>With this contribution we formulate the working hypothesis that prograde subduction together with  exhumation is a fast process. The basis for testing the idea of fast prograde metamorphism is that many geochronological studies propose a prograde duration of < 10 Ma and studies using geospeedometry sometimes propose an even shorter duration, which is the impetus for this investigation.</p>

Determining the speed of intracontinental subduction – preliminary results of zoned garnet geochronology in micaschists from the Schneeberg and Radenthein Complexes, Eastern Alps

2021 ◽  
Author(s):  
Kathrin Fassmer ◽  
Peter Tropper ◽  
Hannah Pomella ◽  
Thomas Angerer ◽  
Gerald Degenhart ◽  
...  
Keyword(s):  
High Pressure ◽  
Carbonaceous Material ◽  
Eastern Alps ◽  
Garnet Growth ◽  
Published Data ◽  
Prograde Metamorphism ◽  
Preliminary Results ◽  
Pt Path ◽  
Zr In Rutile ◽  
Different Parts

<p>In collisional orogens continental crust is subducted to (ultra-)high-pressure (HP/UHP) conditions as constrained by petrologic, tectonic and geophysical observations. Despite a wealth of studies on the subduction and exhumation of UHP rocks, the duration of prograde metamorphism during subduction is still not well constrained.</p><p>We plan to apply Lu-Hf and Sm-Nd geochronology on metamorphic rock samples to date the duration of garnet growth, which represents a major part of prograde metamorphism from the greenschist-facies onward. Micaschist samples from the Schneeberg and Radenthein Units in the Eoalpine high-pressure belt (Eastern Alps) will be used for dating as they contain cm- to dm-sized garnet blasts, which experienced only one subduction-exhumation cycle. With dating different parts of big garnet grains, we test whether (1) it is possible to resolve the duration of garnet growth within single crystals, and (2) Lu-Hf and Sm-Nd systems date the same events in the PT-path or yield complementary information. Additionally, we will perform U-Pb geochronology on titanite in order to obtain the age of the first stages of exhumation; in addition, dating of rutile inclusions as well as matrix rutiles will be used to test Eoalpine prograde age. We will also apply U-Th-Pb monazite dating (EPMA and LA-ICPMS) to some of the samples. Collectively, these data will allow us to compare the duration of subduction and the timing of initial exhumation in a single sample. We then will constrain the PT-path of the dated samples by pseudosection modeling combined with Zr-in-rutile, quartz-in-garnet, and carbonaceous material geothermo(baro)metry. We already have preliminary results for Zr-in-rutile thermometry of rutile inclusions in garnets and matrix rutiles for samples from both locations. We measured Zr content with an EPMA and used the calibrations of Tomkins et al. (2007) and Kohn (2020). The calibration of Kohn (2020) gives overall slightly lower temperatures, but all obtained temperatures lay in a range of c. 500-600 °C in accordance with previously published data. In addition, EPMA, µ-XRF, LA-ICPMS, and µCT will be used to control if garnets preserved major and trace elemental growth zoning and to provide spatial 3D information on inclusion patterns. µCT analyses were already successfully used to obtain the chemical centre of the garnet grains in order to be able to cut them directly through there center. This is important for all in-situ chemical analyses. With dating different parts of single garnet crystals separately with Lu-Hf and Sm-Nd geochronology, we will add tight time constraints to the PT-path and constrain the duration of garnet growth.</p><p>With this contribution we formulate the working hypothesis that prograde subduction together with exhumation is a fast process. The basis for testing the idea of fast prograde metamorphism is that many geochronological studies propose a prograde duration of < 10 Ma and studies using geospeedometry sometimes propose an even shorter duration, which is the impetus for this investigation.</p><p>References:</p><p>Kohn, M.J. (2020). A refined zirconium-in-rutile thermometer. American Mineralogist(105), 963-971.</p><p>Tomkins, H.S., Powell, R. & Ellis, D.J. (2007). The pressure dependence of the zirconium-in-rutile thermometer. Journal of Metamorphic Geology(25), 703-713.</p>

scholarly journals Prograde and retrograde P–T evolution of a Variscan high-temperature eclogite, French Massif Central, Haut-Allier

2020 ◽  
Vol 191 ◽  
pp. 14
Author(s):  
Luc de Hoÿm de Marien ◽  
Pavel Pitra ◽  
Florence Cagnard ◽  
Benjamin Le Bayon
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Garnet Growth ◽  
French Massif Central ◽  
Temperature Peak ◽  
Massif Central ◽  
Slab Rollback ◽  
High Pressure Granulite ◽  
Garnet Growth Zoning ◽  
Growth Zoning

The P–T evolution of a mafic eclogite sample from the Haut-Allier was studied in order to constrain the dynamic of the Variscan subduction in the eastern French Massif Central. Three successive metamorphic stages M1, M2 and M3, are characterized by assemblages comprising garnet1-omphacite-kyanite, garnet2-plagioclase, and amphibole-plagioclase, respectively, and define a clockwise P–T path. These events occurred at the conditions of eclogite (M1; ∼ 20 kbar, 650 °C to ∼ 22.5 kbar, 850 °C), high-pressure granulite (M2; 19.5 kbar and 875 °C) and high-temperature amphibolite facies (M3; < 9 kbar, 750–850 °C), respectively. Pseudosection modelling of garnet growth zoning and mineralogy of the inclusions reveal a prograde M1 stage, first dominated by burial and then by near isobaric heating. Subsequent garnet1 resorption, prior to a renewed growth of garnet2 is interpreted in terms of a decompression during M2. High-pressure partial melting is predicted for both the M1 temperature peak and M2. M3 testifies to further strong decompression associated with limited cooling. The preservation of garnet growth zoning indicates the short-lived character of the temperature increase, decompression and cooling cycle. We argue that such P–T evolution is compatible with the juxtaposition of the asthenosphere against the subducted crust prior to exhumation driven by slab rollback.

scholarly journals Preservation of Garnet Growth Zoning and the Duration of Prograde Metamorphism

2010 ◽  
Vol 51 (11) ◽  
pp. 2327-2347 ◽  
Author(s):  
Mark J. Caddick ◽  
Jiří Konopásek ◽  
Alan B. Thompson
Keyword(s):  
Garnet Growth ◽  
Prograde Metamorphism ◽  
Garnet Growth Zoning ◽  
Growth Zoning

scholarly journals Sr-bearing high-pressure tourmaline from the Kreuzeck Mountains, Eastern Alps, Austria

2019 ◽  
Vol 31 (4) ◽  
pp. 791-798
Author(s):  
Andreas Ertl ◽  
Dan Topa ◽  
Gerald Giester ◽  
George R. Rossman ◽  
Ekkehart Tillmanns ◽  
...  
Keyword(s):  
High Pressure ◽  
Eastern Alps

Origin and mechanical significance of honeycomb garnet in high-pressure metasedimentary rocks from the Tauern Window, Eastern Alps

2007 ◽  
Vol 25 (5) ◽  
pp. 565-583 ◽  
Author(s):  
A. T. HAWKINS ◽  
J. SELVERSTONE ◽  
A. J. BREARLEY ◽  
R. J. BEANE ◽  
R. A. KETCHAM ◽  
...  
Keyword(s):  
High Pressure ◽  
Eastern Alps ◽  
Tauern Window ◽  
Metasedimentary Rocks

scholarly journals New evidence for the prograde and retrograde PT-path of high-pressure granulites, Moldanubian Zone, Lower Austria, by Zr-in-rutile thermometry and garnet diffusion modelling

Lithos ◽  
2019 ◽  
Vol 342-343 ◽  
pp. 420-439 ◽  
Author(s):  
Philip Schantl ◽  
Christoph Hauzenberger ◽  
Friedrich Finger ◽  
Thomas Müller ◽  
Manfred Linner
Keyword(s):  
High Pressure ◽  
Moldanubian Zone ◽  
Diffusion Modelling ◽  
Pt Path ◽  
New Evidence ◽  
Garnet Diffusion ◽  
Zr In Rutile

Weibull Distributions Applied to Cost and Risk Analysis for Aero Engines

2008 ◽  
Author(s):  
D. S. Pascovici ◽  
K. G. Kyprianidis ◽  
F. Colmenares ◽  
S. O. T. Ogaji ◽  
P. Pilidis
Keyword(s):  
High Pressure ◽  
Risk Analysis ◽  
Economic Model ◽  
Spare Parts ◽  
Weibull Distributions ◽  
High Pressure Turbine ◽  
Aero Engines ◽  
The Cost ◽  
The Impact ◽  
Different Parts

This paper presents the use of Weibull formulation to the life analysis of different parts of the engine in order to estimate the cost of maintenance, the direct operating costs (DOC) and net present cost (NPC) of future type turbofan engines. The Weibull distribution is often used in the field of life data analysis due to its flexibility—it can mimic the behavior of other statistical distributions such as the normal and the exponential. The developed economic model is composed of three modules: a lifing module, an economic module and a risk module. The lifing module estimates the life of the high pressure turbine blades through the analysis of creep and fatigue over a full working cycle of the engine. The value of life calculated by the lifing is then taken as the baseline distribution to calculate the life of other important modules of the engine using the Weibull approach. Then the lower of the values of life of all the distributions is taken as time between overhaul (TBO), and used into the economic module calculations. The economic module uses the TBO together with the cost of labour and the cost of the engine (needed to determine the cost of spare parts) to estimate the cost of maintenance and DOC of the engine. In the present work five Weibull distributions are used for five important sources of interruption of the working life of the engine: Combustor, Life Limited Parts (LLP), High Pressure Compressor (HPC), General breakdowns and High Pressure Turbine (HPT). The risk analysis done in this work shows the impact of the breakdown of different parts of the engine on the NPC and DOC, the importance that each module of the engine has in its life, and how the application of the Weibull theory can help us in the risk assessment of future aero engines. A detailed explanation of the economic model is done in two other works (Pascovici et. al. [6] and Pascovici et. al. [7]), so in this paper only a general overview is done.

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