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Application of the fission track method in Geology Part - II
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3 key questions What geologic questions can be answered? What sampling strategy is required? How can we interpret our fission track data? Part 2 - The application
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What are the processes that we can "date" with fission track data? Very fast processes with rock cooling: volcanic eruptions, intrusions with fast cooling, hydrothermal event, shear heating along fault plane Fast processes with rock cooling: fast exhumation or erosion in an active orogen, fast movements along faults (e.g. tectonic unroofing) Moderately fast processes with rock cooling: moderate exhumation or erosion, moderately cooling in and around intrusive body, Slow processes with rock cooling: slow erosion or exhumation in a decaying orogen Part 2 - The application
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Real "dating" with the FT method Part 2 - The application Only with fast to very fast cooling, the fission track method is able to "date an event" Potential events: volcanic eruption fast cooling intrusion impact event hydrothermal event shear heating along thrust plane
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Process rate estimation with the FT method Part 2 - The application With moderate and slow cooling, the fission track method only estimates cooling rates. It does NOT necessarily mean an "event". Possible processes: erosive denudation tectonic denudation topography formation thermal relaxation
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Fission track dating of a single event - I Australian tektite Glass drops ejected from German impact crater Part 2 - The application
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Fission track dating of a single event - II Bohemian Glass from 1849 with 1% of U can be dated with FT check of the fission decay constant Part 2 - The application
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Comparison between dating methods - I Part 2 - The application Example from German volcano (Kraml et al., in prep.): apatite FT data
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Comparison between dating methods - II Part 2 - The application Example from German volcano (Kraml et al., in prep.):
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Comparison between dating methods - II Part 2 - The application
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FT dating and anthropology Part 2 - The application Titanite 0.306 ± 0.056 Ma Titanite 0.462 ± 0.045 Ma Thermoluminescence 0.292 ± 0.026 Ma 0.312 ± 0.028 Ma U-series dating 0.300 ± 0.040 Ma (Guo et al. 1991)
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How do we know that the FT age represents a single event ? Track length distribution: All tracks are long (mean length > 14.5 m) and the track length distribution is very narrow. Radial plot: All single grain ages plot in a narrow cluster (except for very young ages or grains with low U content). Statistical tests: The calculated central age passes Poissonian 2 tests. Isochrons: The FT age is in agreement with ages from other dating techniques (e.g. U/Pb, Ar/Ar, (U-Th)/He). Absence of regional variation: The FT age is identical within the same material, also if sampled at other localities. Part 2 - The application
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Nanga Parbat - I 100 km
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Fast exhumation processes: example Nanga Parbat - II Part 2 - The application 25 km
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Fast exhumation processes: example Nanga Parbat - III Part 2 - The application
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Fast exhumation processes: example Nanga Parbat - IV Part 2 - The application
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Fast exhumation processes: example Nanga Parbat - V Part 2 - The application From: Brozovic et al. (1997) apatite FT ages: A: 0-1 Ma B: 1-6 Ma C: 6-15 Ma
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Fast exhumation processes: example Taiwan - I Part 2 - The application from Dadson et al. (2003): Exhumation rates (mm yr -1 ) based on apatite FT ages: red: reset FT age orange: partially reset blue: not reset
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Fast exhumation processes: example Taiwan - II Part 2 - The application from Dadson et al. (2003): Bedrock incision rates (mm yr -1 ) as derived from age dating of fluvial terraces much larger than exhumation rates !
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Chicken or egg? How can we know ? regional plate tectonic context very fast cooling points to tectonics climatic evidence accompagnying processes topography analysis Part 2 - The application The main question in research today: Who was first, erosion or tectonics ?
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Uplift - Exhumation - Denudation Part 2 - The application (England & Molnar 1990)
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The effect of topography Part 2 - The application
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Convex and concave T-t paths Assumption: topography evolves in a vertical direction only, no lateral valley shift Part 2 - The application
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The effect of fluid flow Part 2 - The application (from Kohl & Rybach, www.gtr. geophys.ethz.ch/ neatpiora.html)
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Fault planes and ages Part 2 - The application
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Fault movements in the Central Alps Part 2 - The application
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Exhumation in a cratonic continent - I Part 2 - The application (Gleadow et al. 2002)
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Exhumation in a cratonic continent - II Part 2 - The application (Gleadow et al. 2002) 2750 apatite FT ages
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Exhumation in a cratonic continent - III Part 2 - The application (Gleadow et al. 2002)
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Exhumation in a cratonic continent - IV Part 2 - The application (Gleadow et al. 2002)
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The principles of fission track data modelling Part 2 - The application
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The modelling of FT data: age and track length Part 2 - The application
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Genetic algorithm and shrinking of T-t-boxes Part 2 - The application
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Why are detrital zircons better than apatites? Part 2 - The application
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The lag time concept Part 2 - The application
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orogenic cycle Part 2 - The application
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Uplift - erosion - topography Part 2 - The application Hack (1975): uplift and topography form steady-state Penck (1953): uplift is waxing- waning Davis (1899): uplift is short-term process
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Detrital age spectra: static and younging age components Part 2 - The application steady age component younging age component
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Probability density plots of FT ages Part 2 - The application fitted age populations statistical fit to density plot raw data with error envelope (from Garver et al. 1999)
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Decrease and increase of lag time (from Bernet et al. 2001) Part 2 - The application
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Example: European Alps Part 2 - The application pro-wedge retro-wedge
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Example for a decrease of lag time Part 2 - The application (from Bernet et al. 2004)
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Example for a steady lag time Part 2 - The application (from Bernet et al. 2004)
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FT ages along vertical bore hole Part 2 - The application
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FT age evolution along vertical bore hole Part 2 - The application
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FT age evolution along vertical bore hole Part 2 - The application
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FT age evolution along vertical bore hole Part 2 - The application
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example I: bore hole @ Hünenberg Part 2 - The application (from Cederbom et al., in press)
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example II: Rigi Mountain and bore hole @ Weggis Part 2 - The application (from Cederbom et al., in press)
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Exhumed PAZ at Denali, Alaska Part 2 - The application (Fitzgerald et al. 1995)
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Thank you for your attention !
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