1. Detrital thermochronology applied to sedimentary basins Barbara Carrapa
After Painter et al. (2014)

2. Thermochronology applied to sedimentary basins
Timing and patterns of erosion, which informs about processes of basin formation.
Deformation related to regional tectonics.
Past climate change.
Timing and duration of hydrocarbon generation, migration and trapping.
Fluid flow.

3. Mechanisms responsible for heating-cooling are different depending on different sedimentary basins:
Crustal thinning
Crustal loading
Subcrustal loading
Mantle-lithosphere tickening

4. Cooling as a proxy for erosion and tectonics
60oC isotherm
120oC isotherm
TECTONIC EXHUMATION
Deformation leads to formation of relief, orographic barrier, higher slopes….enhancing erosion through surface processes

5. Detrital mineral
Cooling path
Closure T
After Fosdick et al. (2014)

6. Different thermochronological systems
If we know the closure T,
by assuming a paleogeothermal gradient we can calculate the magnitude and rate of erosion
Depth of erosion/burial to be recorded by a given thermochronometer =
(Closure T- Surface T)/geothermal gradient

7. Most common thermochronometers used in detrital studies
If we know the closure T (c),
by assuming a paleogeothermal gradient (e.g. 30oC/km) we can calculate the magnitude and rate of erosion
T (c) = 350oC
T (c) = 250oC
T (c) = 120oC

8. Most common thermochronometers used in detrital studies
Depth of erosion/burial to be recorded by a given thermochronometer =
(Closure T- Surface T)/geothermal gradient
T (c) = 350oC
T (c) = 250oC
T (c) = 120oC

9. Detrital thermochronology and provenance
Assumption: different sources are characterized by different cooling ages
Detrital ages (or populations) are geologically significant

10. 40Ar/39Ar thermochronology
Single grain total fusion ages
Single grain step-heating age
N of grains = 1
N of analyses = 10 (T steps)
N of grains = 100
N of analyses = 100
MSWD<2.5
If the single grain age represents an undisturbed signal even a single 40Ar/39Ar age can be significant

11. Fission Track thermochronology
Example: SP32, Geste Fm. (Eocene), Argentina
Binomfit
(Brandon, 2002)
56.7
N=100
43.7
DensityPlotter
(Vermeesch, 2012)

12. An example from the Alps
35-50
Voltri Group (HP rocks)
(Liguro Piemontese domain)
→oceanic domain
45,70
Sesia Lanzo
(Austroalpine)→ Adria
Ligurian Alps
(Briançonnais-
Penninic cover)→Europe
Western Alps
Po Plain
320
Argentera Massif
(Helvetic)→Europe
35,80,
120
Dora Maira (UHP rocks)
(Penninic basement)→Europe
Tertiary Piedmont Basin
Ligurian Sea
40Ar/39Ar age signals for the Alps from the literature

13. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

14. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

15. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

16. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

17. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

18. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

19. Provenance 45,70 Western Alps Po Plain 35,80, 120 35-50 320 280-380
Tertiary Piedmont Basin
35-50
320
Ligurian Sea

20. Detrital thermochronology as a proxy for sediment source erosion tectonics and climate
Assumptions:
Cooling ages are geologically significant
Cooling ages represent erosion and tectonics and not a magmatic signal
The maximum temperature in the basin was never higher enough to resent the cooling age after deposition

21. Erosion, transport and deposition: the concept of lag time
Garver et al. (1999)
In order to estimate an erosion rate we need to know G and Tc
Example: Ts 20
Tc 120
G= 20oC/km
DT= te-tc = lag time = 5 My
We assume that td = te
Lag time

22. Short lag times (~0) = fast erosion
Copeland and Harrison (1990)

23. Erosion, transport and deposition
Garver et al. (1999)
Example, Sample 1:
Ts 20
Tc 120oC
G= 20oC/km
DT= Te-Tc = lag time
We assume that td = te
td= time of deposition = 10 Ma
tc= 15 Ma
What is the lag time and the
erosion rate?

24. Lag time plot Line of constant 5 lag time 10 Line of
Line of
constant 5 lag time 10
Line of
constant 0 lag time
Depositional age (Ma) 20 10 20
Detrital cooling age (Ma)
For a detrital cooling age of 25, depositional age is 20 for a lag time of 5 Ma
For a detrital cooling age of 15, depositional age is 10 Ma for a lag time of 5 Ma
For a detrital cooling age of 5, depositional age is 0 for a lag time of 5 Ma

25. Detrital thermochronology and the concept of lag time
cooling age – depositional age (after Brandon and Vance, 1992)
Orogenic steady-state = constant lag up-section.
Orogenic construction= decrease lag time up-section.
Orogenic decay = increase lag time up-section.
Depositional age
Detrital cooling age

26. Lag time trends and orogenic evolution
I. Introduction to thermochronology II Thermochronology and thrust belts III Detrital thermochonology
Lag time trends and orogenic evolution
Steady state exhumation = constant lag time upsection
Bernet et al. (2001)

27. Lag time trends and orogenic evolution
I. Introduction to thermochronology II Thermochronology and thrust belts III Detrital thermochonology
Lag time trends and orogenic evolution
Zircon Fission Track ages
Bernet et al. (2001)

28. What is the lag time trend up-section?
Depositional age
Late Miocene
Detrital cooling age
Early-mid Miocene
40Ar/39Ar ages
Late Oligocene
Carrapa et al. (2003)

29. Foreland basin evolution: Detrital thermochronology of the
N America Cordillera
Sevier fold and thrust belt
Sevier and Laramide
foreland
Basin and Range

30. Testing models of foreland basin evolution
Two-phase model vs. classic model
Heller et al. (1988)

31. Predictions:
In case of significant reworking: long lag-times are expected
Short lag times would indicate rapid erosion and active tectonics

32. Depositional ages
Maximum depositional ages by zircon U-Pb geochronology match biostratigraphic ages (ammonite zones) and Ar/Ar ages of intercalated ashes

33. Which thermochronometer will tell us about source exhumation?
Questions:
Which thermochronometer will tell us about source exhumation?
1. We need to check on the magnitude of heating due to burial after deposition.
2. We need to check on the magnitude of source exhumation
ZHe Ages (Ma)
Cobble in syn-orogenic conglomerate
Depositional Ages (Ma)
Basement samples

34. 1. If the apatite are magmatic their U-Pb and AFT ages should match
Questions:
Are detrital cooling ages representative of source exhumation or a magmatic in origin?
1. If the apatite are magmatic their U-Pb and AFT ages should match
AFT population Ages (Ma)
Depositional Ages (Ma)

35. Interpretation of the youngest P

36. After double dating the apatites (P1) we exclude the ones that have the same U-Pb and AFT ages from the lag time plot
0-5 My lag times: >1 mm/yr erosion rates

37. How is the foreland behaving?
Two-phase model vs. classic model
Heller et al. (1991)

38. How do we sustain high erosion rates?

39. Triple dating of apatite: a case study from the Andes

40. The earliest record of syn-orogenic sedimentation in the Puna Plateau
Geste Formation (Eocene) Salar de Pastos Grandes E w
lower member
upper member
middle member

41. U/Pb-FT-(U-Th)/He Apatite triple dating
AFT was applied to 100 apatite grains for each detrital sample. Detrital populations were determined using Binomfit (Brandon, 2002).
After Carrapa and DeCelles, Tectonics (2008)
After Carrapa and DeCelles et al. (2008)

42. U/Pb-FT-(U-Th)/He Apatite triple dating
U-Pb ages (Ma)
2) The same apatite grains were then analyzed by U-Pb at the Arizona laser-chrone center.
Are the young AFT ages (P1) representative of exhumation?
After Carrapa et al. (2009)

43. Constraining the tectono-thermal history of the source to sink system
Post burial basin exhumation after 10 Ma

44. Thermal modeling of AFT ages
Source area exhumation
After Carrapa et al., Geology (2009)

45. Detrital 40Ar/39Ar ages are pre-Cenozoic recording an earlier orogenic signal

46. Thrust belt and foreland combined thermal record
Fosdick et al. (2015)

48. Detrital Apatite (U-Th)/He thermochronology
Fosdick et al. (2015)

49. Relationships between detrital ages, relief and erosion
Stock and Montgomery (1996)
Inverse of erosion

50. Exercise Use an exhumation rate of 0.2mm/yr.
1) Calculate the age gradient (Dt);
2) Using the detrital age range between P1 and P2, for the youngest sample, calculate the paleorelief.
Ca. 2km