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Application of the fission track method in Geology Part - II.

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Presentation on theme: "Application of the fission track method in Geology Part - II."— Presentation transcript:

1 Application of the fission track method in Geology Part - II

2 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

3 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

4 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

5 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

6 Fission track dating of a single event - I Australian tektite Glass drops ejected from German impact crater Part 2 - The application

7 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

8 Comparison between dating methods - I Part 2 - The application Example from German volcano (Kraml et al., in prep.): apatite FT data

9 Comparison between dating methods - II Part 2 - The application Example from German volcano (Kraml et al., in prep.):

10 Comparison between dating methods - II Part 2 - The application

11 FT dating and anthropology Part 2 - The application Titanite ± Ma Titanite ± Ma Thermoluminescence ± Ma ± Ma U-series dating ± Ma (Guo et al. 1991)

12 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

13 Nanga Parbat - I 100 km

14 Fast exhumation processes: example Nanga Parbat - II Part 2 - The application 25 km

15 Fast exhumation processes: example Nanga Parbat - III Part 2 - The application

16 Fast exhumation processes: example Nanga Parbat - IV Part 2 - The application

17 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

18 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

19 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 !

20 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 ?

21 Uplift - Exhumation - Denudation Part 2 - The application (England & Molnar 1990)

22 The effect of topography Part 2 - The application

23 Convex and concave T-t paths Assumption: topography evolves in a vertical direction only, no lateral valley shift Part 2 - The application

24 The effect of fluid flow Part 2 - The application (from Kohl & Rybach, geophys.ethz.ch/ neatpiora.html)

25 Fault planes and ages Part 2 - The application

26 Fault movements in the Central Alps Part 2 - The application

27 Exhumation in a cratonic continent - I Part 2 - The application (Gleadow et al. 2002)

28 Exhumation in a cratonic continent - II Part 2 - The application (Gleadow et al. 2002) 2750 apatite FT ages

29 Exhumation in a cratonic continent - III Part 2 - The application (Gleadow et al. 2002)

30 Exhumation in a cratonic continent - IV Part 2 - The application (Gleadow et al. 2002)

31 The principles of fission track data modelling Part 2 - The application

32 The modelling of FT data: age and track length Part 2 - The application

33 Genetic algorithm and shrinking of T-t-boxes Part 2 - The application

34 Why are detrital zircons better than apatites? Part 2 - The application

35 The lag time concept Part 2 - The application

36 orogenic cycle Part 2 - The application

37 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

38 Detrital age spectra: static and younging age components Part 2 - The application steady age component younging age component

39 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)

40 Decrease and increase of lag time (from Bernet et al. 2001) Part 2 - The application

41 Example: European Alps Part 2 - The application pro-wedge retro-wedge

42 Example for a decrease of lag time Part 2 - The application (from Bernet et al. 2004)

43 Example for a steady lag time Part 2 - The application (from Bernet et al. 2004)

44 FT ages along vertical bore hole Part 2 - The application

45 FT age evolution along vertical bore hole Part 2 - The application

46 FT age evolution along vertical bore hole Part 2 - The application

47 FT age evolution along vertical bore hole Part 2 - The application

48 example I: bore Hünenberg Part 2 - The application (from Cederbom et al., in press)

49 example II: Rigi Mountain and bore Weggis Part 2 - The application (from Cederbom et al., in press)

50 Exhumed PAZ at Denali, Alaska Part 2 - The application (Fitzgerald et al. 1995)

51 Thank you for your attention !


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