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Magnetic survery forward modelling and paleomagnetic reconstruction of the South China Block in the Ediacaran

  • Author / Creator
    Lysak, Benjamin
  • Studying the Earth’s magnetic field and Earth materials response to the magnetic field provides us with a plethora of information of underground features, paleoclimatology, and paleogeographic features. Measuring magnetic intensity is one of the fastest geophysical survey methods used in research and natural resource exploration. Accurate modeling of two-dimensional magnetic anomalies is crucial in resource estimation and exploration plans. Paleomagnetism is the study of Earth’s ancient magnetic field that is recorded in rocks. By determining the primary magnetization stored in a rock along with its age we can compute paleomagnetic poles which in turn give us information about the latitude of where it was deposited and tectonic block rotation, using this information is the only latitudinal constraint that can be used in paleogeographic reconstructions. The very first computational algorithm and most referred in literature is that of Talwani and Heirtzler (1964) for calculating of the magnetic anomaly caused by two-dimensional irregular shape subsurface structure has particular fundamental and educational significance in geophysics theory. We re-derive this algorithm from first principles and discuss previous derivation omissions. Our resulting solution differs from the original publication. Based on our new solution we present the two-dimensional forward magnetic modeling software and associated tutorials which are available for download from the website www.ualberta.ca/~vadim/software.htm. Additionally, we include the computation of the remnant magnetization which can be found using already published apparent polar wonder paths. The paleogeography of the South China Block (SCB) from the breakup of Rodinia to the assemblage of Pangea is widely debated and many alternative models have been produced due to the lack of reliable paleomagnetic poles before the Late Paleozoic. Published Ediacaran poles do not match each other are unreliable based on criteria outlines in Van der Voo (1990) and do not determine primary magnetization. We present a new study from the boundary of Doushantuo and Dengying Formations (551 Ma) of the SCB that passed both polarity and fold tests. We have primary directions at the top of the Doshantuo formation and bottom of the Dengying formation from four sections that are separated by 10 - 120 km located in the South of the Shaanxi Province, China. From these four sampled sections two sections showed results with primary magnetizations. We obtained both low and high temperature components performing thermal demagnetization. The high temperature component can be evaluated from both component directions and demagnetization circles in both normal and reverse polarities. The low temperature component directions are usually scattered with some clustering close to the present field of the Earth. The new paleogeographic position of the SCB is at the equator which differs from many publications. Using our new pole, we re-evaluate the Ediacaran paleogeography of the South China Block and its relationship with Gondwana continents.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-095q-7q07
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.