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
Application of the fission track method in Geology
Part - II
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
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
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
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
Fission track dating of a single event - I
Australian tektite
Glass drops ejected fromGerman impact crater
Part 2 - The application
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
Comparison between dating methods - I
Part 2 - The application
Example from German volcano (Kraml et al., in prep.):apatite FT data
Comparison between dating methods - II
Part 2 - The application
Example from German volcano (Kraml et al., in prep.):
Comparison between dating methods - II
Part 2 - The application
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)
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
Part 2 - The application
Nanga Parbat - I100 km
Fast exhumation processes: example Nanga
Parbat - II
Part 2 - The application
25 km
Fast exhumation processes: example Nanga Parbat - III
Part 2 - The application
Fast exhumation processes: example Nanga
Parbat - IV
Part 2 - The application
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
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
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 !
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 ?
Uplift - Exhumation - Denudation
Part 2 - The application
(England & Molnar 1990)
The effect of topography
Part 2 - The application
Convex and concave T-t paths
Assumption:topography evolves in a vertical direction only, no lateral valley shift
Part 2 - The application
The effect of fluid flow
Part 2 - The application
(from Kohl & Rybach,
www.gtr.geophys.ethz.ch/
neatpiora.html)
Fault planes and ages
Part 2 - The application
Fault movements in the Central Alps
Part 2 - The application
Exhumation in a cratonic continent - I
Part 2 - The application
(Gleadow et al. 2002)
Exhumation in a cratonic continent - II
Part 2 - The application
(Gleadow et al. 2002)
2750 apatite FT ages
Exhumation in a cratonic continent - III
Part 2 - The application
(Gleadow et al. 2002)
Exhumation in a cratonic continent - IV
Part 2 - The application
(Gleadow et al. 2002)
The principles of fission track data modelling
Part 2 - The application
The modelling of FT data: age and track length
Part 2 - The application
Genetic algorithm and shrinking of T-t-boxes
Part 2 - The application
Why are detrital zircons better than apatites?
Part 2 - The application
The lag time concept
Part 2 - The application
orogenic cycle
Part 2 - The application
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
Detrital age spectra: static and younging age components
Part 2 - The application
steady age componentyounging age component
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)
Decrease and increase of lag time
(from Bernet et al. 2001)
Part 2 - The application
Example: European Alps
Part 2 - The application
pro-wedge
retro-wedge
Example for a decrease of lag time
Part 2 - The application
(from Bernet et al. 2004)
Example for a steady lag time
Part 2 - The application
(from Bernet et al. 2004)
FT ages along vertical
bore hole
Part 2 - The application
FT age evolution
along vertical bore hole
Part 2 - The application
FT age evolution
along vertical bore hole
Part 2 - The application
FT age evolution
along vertical bore hole
Part 2 - The application
example I: bore hole @ Hünenberg
Part 2 - The application
(from Cederbom et al., in press)
example II: Rigi Mountain and bore hole
@ Weggis
Part 2 - The application
(from Cederbom et al., in press)
Exhumed PAZ at Denali, Alaska
Part 2 - The application
(Fitzgerald et al. 1995)
Thank you for your attention !