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Geomagnetic Response from Meteorite Impacts

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Geomagnetic Response from Meteorite Impacts Ludwig-Maximilians-Universität München Geomagnetic response from meteorite impacts Dissertation zur Erlangung des Doktorgrades an der Fakultät für Geowissenschaften der Ludwig-Maximilians-Universität München vorgelegt von Michael Eitel München, den 18.12.2018 1. Gutachter: Prof. Dr. Stuart Gilder 2. Gutachter: Prof. Dr. Kai Wünnemann Tag der mündlichen Prüfung: 06.05.2019 CONTENTS Contents List of figures................................................................................................................1 List of tables..................................................................................................................3 Summary.......................................................................................................................4 1 Introduction...............................................................................................................6 1.1 Crater Formation.............................................................................................10 1.2 Magnetic field recording in impact structures.................................................12 1.3 Original contributions from this thesis............................................................14 2 Rochechouart impact crater melt breccias record no geomagnetic field reversal...17 2.1 Abstract............................................................................................................17 2.2 Introduction.....................................................................................................18 2.3 Geological setting and sampling.....................................................................21 2.4 Experimental results........................................................................................23 2.4.1 Stepwise demagnetization........................................................................23 2.4.2 Curie point experiments...........................................................................26 2.4.3 Optical microscopy, Raman spectroscopy and electron microprobe analyses....................................................................................................28 2.4.4 Paleointensity...........................................................................................30 2.4.5 Anisotropy of TRM..................................................................................33 2.5 Interpretation and conclusions.........................................................................35 2.6 Acknowledgments...........................................................................................39 3 A paleomagnetic and rock magnetic study of the Manicouagan impact structure: Implications for crater formation and geodynamo effects.....................................40 3.1 Abstract............................................................................................................40 3.2 Introduction.....................................................................................................41 3.3 Geological setting and sampling.....................................................................43 3.4 Experimental results........................................................................................45 3.4.1 Curie temperature....................................................................................45 3.4.2 Reflective light microscopy and electron microprobe analyses..............47 CONTENTS 3.4.3 Bulk susceptibility, magnetic hysteresis, and low-temperature characteristics..........................................................................................48 3.4.4 Stepwise demagnetization and paleomagnetic directions........................54 3.4.5 Paleointensity...........................................................................................59 3.4.6 Anisotropy of magnetic remanence.........................................................60 3.5 Interpretations..................................................................................................62 3.5.1 Crater formation processes......................................................................62 3.5.2 The central magnetic anomaly.................................................................63 3.5.3 Effect of impact on the geodynamo.........................................................64 3.6 Conclusions.....................................................................................................67 3.7 Acknowledgments...........................................................................................68 4 Magnetic signatures of terrestrial meteorite impact craters: A summary...............69 4.1 Abstract............................................................................................................69 4.2 Brief description of an impact event with relevance to magnetism................70 4.3 Link between crater structure and local aeromagnetic signatures...................72 4.4 Magnetic mineralogy.......................................................................................78 4.4.1 Melt rocks................................................................................................78 4.4.2 Target rocks..............................................................................................81 4.4.3 Shock remanent magnetization................................................................83 4.5 Paleomagnetism...............................................................................................87 4.5.1 Crater Formation Processes.....................................................................87 4.5.2 Do Meteorite Impacts Influence the Geodynamo?..................................89 4.6 Conclusions.....................................................................................................93 4.7 Acknowledgments...........................................................................................94 5 AF demagnetization and ARM acquisition at elevated temperatures in natural titanomagnetite bearing rocks................................................................................95 5.1 Abstract...........................................................................................................95 5.2 Introduction.....................................................................................................96 5.3 Sample description..........................................................................................97 5.4 Results.............................................................................................................98 5.4.1 Rock-magnetic properties........................................................................98 5.4.2 AF-demagnetization...............................................................................100 CONTENTS 5.4.3 TRM, ARM and tARM acquisition.......................................................102 5.5 Discussion.....................................................................................................103 5.5.1 Coercivity spectra..................................................................................103 5.5.2 Additivity...............................................................................................105 5.5.3 Thermal Fluctuations.............................................................................106 5.6 Conclusion.....................................................................................................108 5.7 Acknowledgments.........................................................................................108 6 Conclusions and outlook.......................................................................................110 Appendix...................................................................................................................114 References.................................................................................................................117 Acknowledgments.....................................................................................................150 LIST OF FIGURES List of figures 1.1 Model of impact induced shock waves traveling through Earth.......................9 1.2 Stages of the formation of a meteorite impact crater.......................................11 1.3 Cooling time of impact melt as a function of distance from the surface.........13 1.4 Magnetically shielded AF/ARM coil...............................................................16 2.1 Locality and geologic map of the Rochechouart crater region........................21 2.2 Orthogonal demagnetization diagrams from Rochechouart............................24 2.3 Thermomagnetic curves and Curie temperatures from Rochechouart............26 2.4 Microscope images and Raman spectra from Rochechouart...........................28 2.5 Electron microprobe concentration maps from Rochechouart........................29 2.6 Arai plots and orthogonal demagnetization diagrams.....................................31 2.7 Paleointensity results from the Rochechouart impact crater...........................32 2.8 Rochechouart pole and virtual dipole moment................................................37 3.1 Geologic and magnetic anomaly map of the Manicouagan impact crater......42 3.2 Thermomagnetic curves of samples from Manicouagan.................................45 3.3 Microscopy images and microprobe maps from Manicouagan.......................47 3.4 Rock magnetism of the Manicouagan drill cores............................................49 3.5 Orthogonal
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