The thermal regime of the Eastern Alps along the TRANSALP profile [Elektronische Ressource] / vorgelegt von Hans-Dieter Vosteen

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2003
• Nombre de lectures: 17
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

The thermal regime of the Eastern Alps
along the TRANSALP pro le
Von der Fakult at fur Bergbau, Hutten wesen und Geowissenschaften
der Rheinisch-Westf alischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
genehmigte Dissertation
vorgelegt von Diplom-Geologe
Hans-Dieter Vosteen
aus Hannover
Berichter: Univ.-Prof. Dr. rer. nat. Christoph Clauser
Prof. Dr. rer. nat. habil. Bernd Lammerer
Tag der mundlic hen Prufung: 19. Dezember 2003
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek
online verfugbarAbstract
The results of petrophysical laboratory measurements and inverse model-
ling were utilized to estimate the 2-D, steady-state conductive thermal
regime in the Eastern Alpine crust and heat o w at the Moho along the
TRANSALP pro le. Temperature dependence of thermal conductivity
and speci c heat capacity c as well as of heat production rate and densityp
were measured on a set of magmatic, metamorphic and sedimentary rocks,
representing di eren t depth levels of the Eastern Alpine crust. The results
show that in the temperature range from 25 { 300 C thermal di usivit y
relates linearly to thermal conductivity . Based on the approach that
thermal resistivity 1= is a linear function of temperature whose slope
increases with (0), the thermal conductivity at a temperature of 0 C,
two general equations for the temperature dependence of for Eastern
Alpine rocks were formulated. The inversion studies show that while the
large a priori standard deviation of particularly the heat production rate
in the upper crust can be signi can tly reduced a posteriori, the variance of
the middle crust heat production rate remains comparatively large. Using
two extreme models with maximum and minimum heat production rates
in the middle crust the range of Moho temperatures and heat o w can be
estimated. Depending on di eren t assumptions about the composition of
the middle crust we obtain maximum temperatures of around 900 C
30% in the lowermost parts of the European crust. In the Alpine root and
in the Southern Alps, maximum temperatures are 700 { 800 C 10% and
2600 C 10%, respectively. Moho heat o w varies from 5 { 25 mW m
and is largest underneath the European plate and lowest underneath the
Alpine root. The e ect of paleoclimate and exhumation was estimated,
performing 1-D transient forward simulation and an analytical approach.
The main paleoclimatic signal of 6:5 K was detected in a depth of 2 km.
As exhumation leads to an elevation of temperature that increases with
depth, the resulting transient signal in the uppermost 2 km amounts to
zero. The utilized "worst case scenario" leads to a maximum exhumation
signal of around 80 K at a depth of 50 km.Contents
List of Figures iii
List of Tables v
1 Introduction 1
2 Geological setting 4
2.1 Sampling strategy . . . . . . . . . . . . . . . . . . . . . . . 6
3 Rock physics 9
3.1 Density and porosity . . . . . . . . . . . . . . . . . . . . . 9
3.2 Radiogenic heat production rate . . . . . . . . . . . . . . . 11
3.3 Temperature dependence of speci c heat capacity . . . . . 12
3.4 Temp dep of thermal capacity . . . . . . . . 14
3.5 Thermal conductivity at ambient conditions . . . . . . . . 15
3.6 Temperature dependence of thermal conductivity . . . . . 18
3.7 Temp dep of di usivit y . . . . . . . 20
3.8 Developing a general equation for (T) . . . . . . . . . . . 21
3.9 Comparison with other expressions for (T) . . . . . . . . 25
3.10 Thermal di usivit y as a function of thermal conductivity . 30
4 Numerical simulation of the thermal regime of the Eastern
Alps 34
4.1 Basic equations of heat transfer . . . . . . . . . . . . . . . 34
4.2 Simulation techniques . . . . . . . . . . . . . . . . . . . . . 35
4.3 Bootstrapping . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.4 Forward simulation . . . . . . . . . . . . . . . . . . . . . . 40
4.5 Inverse parameter estimation . . . . . . . . . . . . . . . . . 43
5 Transient e ects 53
5.1 E ect of paleoclimate . . . . . . . . . . . . . . . . . . . . . 53
iii CONTENTS
5.2 E ect of exhumation . . . . . . . . . . . . . . . . . . . . . 56
6 Conclusions and discussion 62
References 65
Appendix 73
A Petrographical description of sampled rocks 73
B Results of X-ray uorescence 75
C Earthquake focus depth in Tyrol 80List of Figures
2.1 Geological map of the Eastern Alps . . . . . . . . . . . . . 5
2.2 TRANSALP Pro le and sampling locations . . . . . . . . 8
3.1 Mean values and min{max variation of laboratory measure-
ments of porosity, rock density and bulk density. . . . . . . 10
3.2 Mean values and min{max variation of laboratory measure-
ments of the radiogenic heat production rate. . . . . . . . 12
3.3 Mean values and min{max variation of speci c heat capacity 13
3.4 Mean values and v of thermal capacity . 14
3.5 Min{max variation of laboratory measurements of the ther-
mal conductivity, mean values and anisotropy factors . . . 17
3.6 Min{max variation of thermal conductivity with tempera-
ture for di eren t types of rock . . . . . . . . . . . . . . . . 19
3.7 Min{max variation of thermal di usivit y with temperature
for di eren t types of rock . . . . . . . . . . . . . . . . . . . 21
3.8 Linear regressions of thermal resistivity 1= (T) for di eren t
crystalline rocks of the Eastern Alps . . . . . . . . . . . . 22
3.9 Deviation = (meas.) (calc.) vs. temperature ac-
cording to coe cien ts of this study or to Sass et al. (1992),
respectively . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.10 Comparison of equations for crystalline and sedimentary
rocks of this study with (T) according to Zoth and Haenel
(1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.11 Comparison of the equation for crystalline rocks of this study
with (T) according to Sass et al. (1992) . . . . . . . . . . 28
3.12 of the equation for crystalline rocks of this study
with (T) according to Seipold (1998) . . . . . . . . . . . 29
3.13 Variation of thermal di usivit y at ambient conditions as
a function of conductivity at ambient 31
3.14 Variation of as a function of at temperatures of 100 C
and 200 C . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
iiiiv LIST OF FIGURES
3.15 Variation of as a function of at a temperature of 300 C 33
3.16 Linear and logarithmic regressions of slopes of Fig. 3.13,
Fig. 3.14 and Fig. 3.15 vs. temperature . . . . . . . . . . . 33
4.1 Finite element model with 2015 elements . . . . . . . . . . 41
4.2t model with 936ts . . . . . . . . . . . 42
4.3 A priori and a posteriori thermal conductivity and heat pro-
duction rates . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4 Borehole temperatures vs. a posteriori temperatures . . . . 46
4.5 A posteriori heat o w and thermal conductivity distribution 47
4.6 A p temperature distribution . . . . . . . . . . . . 48
4.7 Pro les of basal heat o w assuming a granodioritic middle
crust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.8 Pro les of basal heat o w assuming a poorly di eren tiated
middle crust . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.1 Paleoclimatic signal calculated from di eren t scenarios . . 54
5.2 E ect of paleoclimate on temperature gradient and heat o w
density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
5.3 Exhumation signal depth dependent from 0 { 100 km . . . 58
5.4 Exh signal in the top 5 km . . . . . . . . . . . . . 59
5.5 Exhumation signal in the Eastern Alpine crust . . . . . . . 59
5.6 Comparison of transient e ects in the Eastern Alpine crust 60
5.7 Error in temperature and heat o w due to transient e ects 61
Appendix 73
C.1 Earthquake focus depth in Tyrol . . . . . . . . . . . . . . . 80List of Tables
2.1 Rock types and associated geological units . . . . . . . . . 6
4.1 Bootstrapping results for thermal conductivity . . . . . . . 39
4.2 Parameter zones and corresponding sampling locations . . 44
Appendix 73
B.1 Results of X-ray uorescence (a) . . . . . . . . . . . . . . . 75
B.2 of X-ray (b) . . . . . . . . . . . . . . . 76
B.3 Results of X-ray uorescence (c) . . . . . . . . . . . . . . . 77
B.4 of X-ray (d) . . . . . . . . . . . . . . . 78
B.5 Results of X-ray uorescence (e) . . . . . . . . . . . . . . . 79
v