The Phanerozoic thermo-tectonic evolution of northern Mozambique constrained by _1hn4_1hn0Ar-_1hn3_1hn9Ar, fission track and (U-Th)-He analyses [Elektronische Ressource] / vorgelegt von Matthias Ch. Daßinnies

THE PHANEROZOIC THERMO-TECTONIC
EVOLUTION OF NORTHERN MOZAMBIQUE
40 39
CONSTRAINED BY AR/ AR, FISSION TRACK
AND (U-TH)/HE ANALYSES

















Dissertation zur Erlangung des Doktorgrades der
Naturwissenschaften am Fachbereich Geowissenschaften
der Universität Bremen


Vorgelegt von
Matthias Ch. Daßinnies
Bremen, 2006





















Tag des Kolloquiums: 22.12.2006
Gutachter: Prof. Dr. J. Jacobs
Prof. Dr. W. Bach
Prüfer: Prof. Dr. T. Mörz
Prof. A. Kopf
Contents
CONTENTS
ACKNOWLEDGEMENTS ...................................................................................................... v
SUMMARY........................................................................................................................ vii
ZUSAMMENFASSUNG ......................................................................................................... x
CHAPTER 1
INTRODUCTION..................................................................................................................1
1.1 Scope of thesis.................................................................................................. 1
1.2 Research objectives and methods..................................................................... 3
1.3 Outline of thesis ............................................................................................... 4
CHAPTER 2
THERMOCHRONOLOGICAL METHODS AND ANALYTICS ...................................................... 6
40 39 2.1 Ar/ Ar dating method................................................................................... 6
2.1.1 Argon isotope measurements and age calculation.............................. 7
2.1.2 Theoretical considerations and definitions......................................... 9
2.1.3 Analytical procedures.......................................................................14
2.2 Fission track dating method ........................................................................... 17
2.2.1 Fission track age and error calculations ........................................... 18
2.2.2 External detector method.................................................................. 22
2.2.3 Fission track length and track annealing .......................................... 24
2.2.4 Modelling of t-T paths from apatite fission track data ..................... 31 2.2.5 Analytical procedures33
2.2.6 Fission track data presentation ......................................................... 38
2.3 (U-Th)/He dating of apatite............................................................................ 40
2.3.1 Helium isotope measurements and age calculation.......................... 41
2.3.2 α-emission balance and helium age correction................................. 44
2.3.3 Age error estimation ......................................................................... 47
2.3.4 Helium diffusion in apatite............................................................... 48
2.3.5 Analytical procedures.......................................................................51
4 2.3.6 Forward modelling of He ages........................................................ 54
4 2.3.7 Remarks on the sample pre-screening and on excess He................ 56
2.4 Estimates on denudation................................................................................. 57

i
Contents
CHAPTER 3
POST PAN-AFRICAN THERMO-TECTONIC EVOLUTION OF THE NORTH MOZAMBICAN
BASEMENT AND ITS IMPLICATION FOR THE GONDWANA RIFTING: INFERENCES FROM
40 39AR/ AR HORNBLENDE, BIOTITE AND TITANITE FISSION TRACK DATING........................59
3.1 Introduction.....................................................................................................60
3.2 Geological setting and previous geochronology.............................................62
3.2.1 Axial Granulite Complex (Unango Group) ......................................62
3.2.2 The eastern domain and the Lurio Belt foreland...............................64
3.2.3 Late Palaeozoic to Early Mesozoic intracontinental rift basin .........66
3.2.4 Marginal rift basins ...........................................................................68
3.3 Analytical procedures.....................................................................................68
40 39 3.3.1 Ar/ Ar analysis..............................................................................68
3.3.2 Titanite fission track analysis............................................................70
3.4 Results ..........................................................................................................71
40 39 3.4.1 Ar/ Ar hornblende analysis...........................................................71
40 393.4.2 Ar/ Ar biotite analysis...................................................................72
3.4.3 78
3.5 Interpretation...................................................................................................83
40 39 3.5.1 Ar/ Ar hornblende data .................................................................83
40 393.5.2 Ar/ Ar biotite data.........................................................................84
40 39 3.5.3 Cooling rates for Ar/ Ar hornblende and biotite results ...............85
3.5.4 Titanite fission track data..................................................................86
3.6 Discussion.......................................................................................................89
3.6.1 Proterozoic to Early Palaeozoic cooling in the south western Axial
Granulite Complex............................................................................89
3.6.2 Early Palaeozoic cooling in the southern basement..........................89
3.6.3 Late Palaeozoic cooling and denudation history...............................92
3.7 Conclusions...................................................................................................100
CHAPTER 4
CENTRAL EASTERN AFRICA DURING GONDWANAS RIFT, BREAK-UP AND DRIFT EVOLUTION
SINCE THE MESOZOIC .....................................................................................................111
CHAPTER 5
PREVIOUS APATITE FISSION TRACK STUDIES IN CENTRAL EAST AFRICA AND EAST
ANTARCTICA..................................................................................................................121
ii
Contents
CHAPTER 6
APATITE FISSION TRACK ANALYSIS – RESULTS AND INTERPRETATION ........................... 125
6.1 Axial Granulite Complex.....................................................................130
6.1.1 Results............................................................................................130 6.1.2 Interpretation..................................................................................
6.2 Mount Tumbine137
6.2.1 Results6.2.2 Interpretation137
6.3 Southern basement.......................................................................................142
6.3.1 Results............................................................................................6.3.2 Interpretation142
6.3.3 Remarks on the D values of the southern basement samples...... 155 par
CHAPTER 7
APATITE (U-TH)/HE ANALYSIS – RESULTS AND INTERPRETATION ................................. 157
4 7.1 Apparently reliable He ages (I)................................................................... 158
4 7.2 Ambiguous He ages (II).............................................................................. 162
4 7.3 Rejected He ages (III) ................................................................................. 162
7.4 Comments on apatite (U-Th)/He dating....................................................... 165
7.5 Results of forward t-T path modelling of (U-Th)He ages............................ 165
7.5.1 Slow and protracted cooling path models....................................... 166
7.5.2 Cooling path models involving reheating events ........................... 168
CHAPTER 8
DISCUSSION – MESOZOIC-CENOZOIC COOLING AND DENUDATION HISTORY
OF THE NORTH MOZAMBICAN BASEMENT ...................................................................... 173
8.1 Axial Granulite Complex ............................................................................. 173
8.2 Mount Tumbine............................................................................................180
8.3 Southern basement.......................................................................................182
8.3.1 The eastern margin.........................................................................
8.3.2 The central southern basement and the Lurio Belt......................... 189
8.4 Denudation estimates for the Permo-Jurassic period ................................... 194
8.5 Inferences on the Mesozoic Gondwana break-up ........................................ 195
CHAPTER 9
THE NORTH MOZAMBICAN – SOUTH CENTRAL MALAGASY RELATIONS: INFERENCES FROM