application of the fission track method in geology
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Part - II. Application of the fission track method in Geology. 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. - PowerPoint PPT PresentationTRANSCRIPT
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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 fromGerman 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
Titanite0.306 ± 0.056 Ma
Titanite0.462 ± 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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Part 2 - The application
Nanga Parbat - I100 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 componentyounging 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 !